Technological Parameters of Electrospinning Technology in the Production of Functional Materials Nanostructures

#### **Chapter 1**

## Active Electrospun Mats: A Promising Material for Active Food Packaging

*Cristian Patiño Vidal, Cristina Muñoz-Shugulí, Marcelo Patiño Vidal, María José Galotto and Carol López de Dicastillo*

#### **Abstract**

Nowadays, polymeric materials are widely used in the development of food packages. However, as food products with a greater safety and longer durability are required, packaging research area has been focused on the production of functional materials able to reach such further protection. The incorporation of natural and synthetics active compounds into the polymeric materials by traditional techniques has been the main used strategy, surging thus the research area of active food packaging. Furthermore, the latest science advances provide promising technologies for developing packaging materials, such as the electrospinning. This technique has allowed obtaining ultrathin electrospun mats based on micro- and/or nanofibers that have been proposed as novel active materials able to be applied as wrapper films, sachets and bags during the food packaging. In this chapter, the description of electrospinning, the effect of their principal parameters during the development of active food packaging materials as well as their current applications on different foodstuffs are presented.

**Keywords:** active compound, food package, food shelf life

#### **1. Introduction**

Packaging is one of the most useful tools used by the food industry to protect several foodstuffs against contamination and spoilage. Traditionally, materials such as plastic, glass, metals, paper and board have been used for developing food packages [1, 2]. However, the interest by polymeric materials have enormously increased because they exhibit several advantages, such as low-cost, low-weight and good mechanical, barrier and optical properties [3, 4]. Therefore, processed and non-processed foods are daily packaged into plastic materials in order to avoid their contamination by odors, dust and microorganisms, as well as their deterioration by temperature, humidity, light, shocks, physical damage, among others [5, 6]. Despite of several benefits that packaging industry offers to food, oxidation and microbial spoilage are the principal mechanisms that entail a great loss of fruits, vegetables,

#### **Figure 1.**

*Articles related to traditional food packaging and active food packaging in the last two decades (data obtained from Web of Science data basis).*

meats, dairy and bakery products during their production, transport, processing, storage, and marketing [5]. In this context, during the last decades, the packaging area has centered its aims to the development of materials able to maintain or improve the properties of food, and therefore, extend its shelf-life. Several studies have developed different functional materials which in turn have allowed the surging of active food packaging in the last years. Thus, **Figure 1** shows a comparison between the number of indexed articles about "Food packaging" and "Active food packaging", published in the Web of Science (WOS) data basis. This figure shows the growing interest in food packaging research area during the last two decades, evidencing that active food packaging has been specifically leading during the last 5 years when compared to traditional food packaging published research.

#### **2. Active food packaging technology**

#### **2.1 Definition**

Active food packaging is considered a system of positive interaction between the food, the packaging material and the environment with the aim of preserving the properties of food and avoiding its deterioration during transport and storage [7]. In this way, compounds or substances with an active function (active compounds) have been incorporated into polymers in order to obtain active materials [6]. Natural and synthetic active compounds, such as plant extracts, essential oils, peptides, enzymes, organic acids, salts, metals ions, metal oxides, nanoparticles, among others, have afford to the packaging materials different functionalities, such as: (i) releasing/emitting of antioxidants, antimicrobial, sulfur dioxide, preservatives, ethanol and flavors; (ii) absorbing/scavenging of carbon dioxide, oxygen ethylene, flavors, moisture, UV light; and (iii) controlling the microbial, temperature and quality of foods [8, 9].

*Active Electrospun Mats: A Promising Material for Active Food Packaging DOI: http://dx.doi.org/10.5772/intechopen.101781*

#### **2.2 Formats and technologies**

The design of active packaging systems has been mainly focused on the characteristics of the active compound and packaged food. **Figure 2** shows the five mechanisms for generating an active packaging system through [7, 10]:

Incorporation external devices (labels, pads or sachets loaded with some active compound) into the package able to release or absorb substances.

Coating of active compound onto inner surface of packaging material. This system is useful for heat-sensitive compounds or incompatible and immiscible with polymeric matrix.

Immobilization of active compound in the inner layer of packaging material through ion or covalent linkages. It is important the presence of functional groups on active compound and polymer to get the immobilization.

Direct addition of the active compound into the packaging material matrix [11].

By using polymers with some active function (e.g., chitosan) to develop composites or multilayer materials.

Most polymeric materials that have been part of above-mentioned active packaging systems have been obtained through traditional techniques, such as melting based processes (melt blending, hot pressing, cast extrusion, injection molding), casting, coating [12]. For example, the extrusion technique was recently used by producing active labels based on low-density polyethylene films loaded with different essential oils and vegetable oils [13]. In this work, fresh beef was packaged into commercial trays with modified atmosphere (70% O2 + 30% CO2), and the active labels were placed on the top of the tray in order to protect the food. Results

**Figure 2.**

*Routes for obtaining an active packaging system.*

demonstrated a great effectivity of active packaging system because the shelf-life of fresh meat was extended by 22%. On the other hand, casting technique has been also a useful tool for producing active food packaging systems. In this context, Sooch and Mann developed an active package from gelatin and copper nanoparticles doped with titanium dioxide. Tomatoes were wrapped with these packaging materials, and the shelf-life of vegetables was extended by 18 days [14]. Likewise, multilayer materials for active packaging of meat products have been also developed through coating technique. Bilayer films composed by poly(lactic) acid (PLA), as substrate, and chitosan or blends of chitosan/caseinate enriched with rosemary essential oil, as coating, were recently used for protecting fresh minced chicken meats. In this case, oxidation process and color changes of food were not shown for 14 days because the food was in direct contact with active materials [15].

On the other hand, non-traditional techniques as carbon dioxide supercritical impregnation and atomic layer deposition (ALD) have been also employed for developing active materials. However, the application of such technologies in food has been not already evaluated. Villegas et al. impregnated cinnamaldehyde through supercritical carbon dioxide into PLA film in order to obtain an antibacterial material. Active film showed a strong and effective antibacterial activity against *Staphylococcus aureus* and *Escherichia coli* [16]. Unlike supercritical impregnation, the combination of electrospinning and ALD process has allowed to produce metallic oxide nanostructures with antimicrobial properties that can be subsequently incorporated into polymers. In this context, nanotubes and spherical particles of titanium dioxide (TiO2) and zinc oxide (ZnO) have been produced by this combination [17–19]. In all studies, metallic oxide nanostructures showed a high antimicrobial property against Gram-positive and Gram-negative bacteria.

As the technology has been progressed, in the last decade, a novel technique known as electrospinning has been used for developing polymeric materials that posteriorly play a fundamental role in the active packaging system.

#### **3. Electrospinning**

Electrospinning is an efficient and novel technique that consists in the application of an electric field to a polymeric solution in order to produce thinner structures known as "fibers" [11]. As **Figure 3** shows, the electrospinning is composed by three main components: (i) a high voltage source composed by two electrodes that are connected to the output of a metal needle and to collector, (ii) an injection pump that impulses the polymeric solution through plastic tube to metal needle, and (iii) a collector. To obtain the fibers, it is necessary that the surface tension of the drop formed in the tip of the needle be overcome by the force of the electric field. On this way, the polymeric solution is continuously stretched to produce a jet with a conical structure named "Taylor's cone", where the solvent is evaporated to obtain the fibers [12].

Characteristics of the fibers depend on the control of the electrospinning parameters. In this context, a change of the properties of the polymeric solution (polymer concentration, viscosity, electrical conductivity, type of solvent) or the operational parameters (flow rate, voltage and the height also known as the distance between the tip of the needle and the collector) can affect the size and morphology of the fibers [20]. This fact will be detailed in the following section.

*Active Electrospun Mats: A Promising Material for Active Food Packaging DOI: http://dx.doi.org/10.5772/intechopen.101781*

#### **3.1 Influence of the properties of the polymeric solution**

#### *3.1.1 Polymer concentration*

The concentration of the polymer is one of the main parameters that affects the size and the morphology of the fibers, and it is closely related to the viscosity of the solution. If the solution concentration is very low, the jet cannot be continuously stretched, and thus, uniform fibers cannot be obtained. This fact in turn can produce a decrease in the diameter of the fibers and the presence of beads in their surface. On the contrary, an increase of the concentration can result in thicker structures, and in some cases, the non-formation of the fibers due to high viscosity of the solution. A recent study evidenced the decrease of the diameter and the presence of beads in polycaprolactone (PCL) nanofibers when the polymeric concentration decreased from 13 to 8 wt% [21]. A similar result was also obtained in the processing of cellulose acetate (CA) and poly(vinyl chloride) (PVC) nanofibers. In both cases, the use of CA and PVC concentrations at 12 wt% resulted in thinner and beaded fibers, while an increase to 16 wt% produced structures with smooth surfaces and large diameters [22].

#### *3.1.2 Electrical conductivity*

The increase of electrical conductivity in the polymeric solution has been mainly related with the increase of the concentration of the polymer, favoring the electrospinning process and the formation of the fibers. For example, gelatin nanofibers were only obtained with acid solutions at high gelatin concentrations. The low electrical conductivity obtained with the lowest gelatin solution (7 wt%) did not allow to produce fibers. On the contrary, the increase of polymeric solution concentration to 20 wt% produced an increase of electrical conductivity and the formation of nanofibers [23].

#### *3.1.3 Type of solvent*

The type of solvent has an important role during the electrospinning process. It is stretched related with the surface tension of the solution, and several investigations

have shown changes of this parameter by the use of different solvents or the mix of them. This fact in turn has derived in different morphologies and sizes of fibers. Thus, the combination of formic acid (FA) and dichloromethane (DCM) at different ratios as solvent system for producing PCL nanofibers produced changes on the diameter of the structures. A higher amount of FA produced an increase of electrical conductivity solution, while an increase of the amount of DCM increased its surface tension. These effects in turn produced fibers with diameters between 1.5 μm and 220 nm [21]. Likewise, the use of the following solvent systems: acetone/N,Ndimethylacetamide, acetone/N,N-dimethylformamide and tetrahydrofuran/dimethylformamide at different ratios changed the morphology of PCL nanofibers. Beaded, beaded-free, thin, thick and smooth nanofibers were obtained with these different combinations, and this fact could be associated to the changes on the surface tension of polymeric solutions [22].

#### **3.2 Influence of operational parameters**

#### *3.2.1 Flow rate*

The flow rate is considered a key parameter because controls the diameter of the fibers, the trajectory of jet, initial droplet shape, maintenance of Taylor's cone and the collection area. A high flow rate produces larger droplets in the tip of the needle and favors the formation of thicker and beaded fibers due to minimum solvent evaporation. On the contrary, a low flow rate facilitates the evaporation of solvent, obtaining uniform and smooth structures [24]. This effect has been observed when a poly(vinylidenefluoridene-hexafluoropropylene) solution was electrospun at different flow rates. An increase of flow rate from 0.1 to 0.7 mL/h produced an increase of fiber diameter [25]. The same result was also obtained when the flow rate of a poly(vinyl alcohol) (PVOH) solution increased from 0.75 to 1.5 mL/h [19].

#### *3.2.2 Collection distance*

The distance between the needle and the collector has a great effect on the diameter and the shape of the fibers. A small distance avoids the total evaporation of the solvent, and thus, the collection of wet and thicker fibers can occur. In this way, the presence of beads or the formation of ribbon-flat fibers have been the most common results. On the contrary, a high distance can improve the stretching of the jet and favor the formation of uniform and thinner structures. Furthermore, the increase of distance can also increase the needed voltage to produce the fibers [19, 26]. A recent study obtained thinner polyacrylonitrile nanofibers when increased the collection distance from 15 to 45 cm [27]. Similarly, the increase of collection distance from 8.5 to 10 cm produced smaller diameter in PVOH nanofibers [19].

#### *3.2.3 Voltage*

Despite of several studies have demonstrated that voltage has a minimum impact on the diameter and morphology of fibers, it is an important parameter to be considered during processing of electrospun materials. This fact is due to its increase can produce change the diameter of fibers and produce the presence or absence of beads in the structures [26]. Some studies have evidenced the effect of this parameter on such characteristics [23, 27].

#### **3.3 Active electrospun materials**

As it was earlier mentioned, electrospinning is able to produce smaller and thinner mats composed by fibers with high aspect ratio. In order to functionalize these mats, active compounds can be incorporated into them. These materials in turn could be converted to active packaging materials or be part of an active packaging system, exhibiting the following advantages [11]:


Despite of active electrospun materials are an excellent alternative to develop active packaging materials in comparison with other traditional techniques (melting processes, coating, casting), their processing remain one of the main challenges. This fact is mainly because the addition of the active compound can produce changes in the properties of the polymeric solution, and therefore, the electrospinning process can be affected. In order to deepen in the topic, the following section will discuss the effect of adding active compounds in the development electrospun materials.

#### **3.4 Influence of active compounds during electrospinning process**

The incorporation of an active compound to the polymeric solution to be electrospun can mainly change their physicochemical properties and affect the development of electrospun packaging material as follows.

#### *3.4.1 Viscosity*

The viscosity of the polymeric solution is related to the concentration and molecular weight of the polymer. A polymeric solution with an optimum viscosity can be electrospun in order to obtain the active mat. On the contrary, solutions with very high or low viscosities affect the electrospinning process and the obtaining of homogenous fibers [28]. Depending on the type of the active compound, the viscosity of the polymeric solution can be increased or decreased, and the morphology and diameter of the fibers are affected. As is shown in **Table 1**, the use of essential oils has mainly produced an increase of solution viscosity, which has derived in an increase of fiber diameter. This effect has been mainly associated to a less stretching of the jet [30]. For example, the increasing addition of angelica essential oil into gelatin solutions produced high viscosities which resulted in thicker fibers [30]. Altan et al. also evidenced this same effect when active PLA fibers loaded with carvacrol were developed [29]. Likewise, thicker fibers of glycyrrhiza polysaccharide and polyoxide ethylene (PEO) loaded with tea tree essential oil encapsulated into gliadin nanoparticles were obtained by Cai et al. Like above mentioned studies, the active compound increased the solution viscosity and affected the diameter of the fibers [31].

On the other hand, the effect of incorporating plant extracts in the viscosity of the polymeric solutions has produced different behaviors. A clear tendency of increase or decrease of viscosity by the incorporation of plant extracts has been not obtained.


*V = viscosity, ST = surface tension, EC = electrical conductivity. Trends:* **↓** *= decreased,* **↑** *= increased, M = maintained, C = constant.*

#### **Table 1.**

*Influence of the active compound incorporation on properties of polymeric solution.*

A work about PCL fibers loaded with sage extract evidenced that the incorporation and increase of extract concentration in the polymeric solution decreased its viscosity and favored the production of thinner fibers [33]. Likewise, an increase of concentration of jaboticaba peel extract in a zein solution decreased its viscosity and the diameter of the fibers [35]. Meanwhile, an increase of concentration of tomato peel extract in a polymeric solution of zein produced an increase of its viscosity and the development of thicker fibers [34]. Yang et al. also obtained a similar result when *Coptis chinensis* extract was incorporated in a zein solution. Similarly, the extract increased the viscosity of the solution, but favored the decrease of diameter of the fibers [36].

The use of nanoparticles has also influenced the diameter and the morphology of the fibers, and this fact has been mainly related to changes in the solution viscosity. For example, although an increase of TiO2 nanoparticles concentration into zein solutions caused high viscosity values, thinner fibers were obtained [37]. A similar effect was also observed in the development of PVOH/gum karaya nanofibers loaded

#### *Active Electrospun Mats: A Promising Material for Active Food Packaging DOI: http://dx.doi.org/10.5772/intechopen.101781*

with silver (Ag) nanoparticles, whose resulting nanofibers showed roughness in their surface, and this fact was attributed to an increase of the viscosity of the polymeric solution. Meanwhile, Liu et al. evidenced a contrary effect because the viscosity of a blend of ethylcellulose and gelatin decreased with the increase of ZnO nanoparticles concentration, but the diameter of fibers increased [39].

The development of fibers loaded with peptides and enzymes has also been an excellent strategy for producing potential active electrospun materials. Most studies have evidenced a decrease of the polymeric solution viscosity after their incorporation, which in turn has affected the size of fibers. A decrease of diameter of amaranth protein/pullulan nanofibers was evidenced by Soto et al. when nisin was incorporated to the polymeric solution. The increase of nisin content decreased the viscosity of the solution due to the molecular entanglement among the components, and this in turn influenced on the diameter of the fibers [40]. Likewise, a work about active nanofibers of chitosan/PVOH loaded with lysozyme showed a result similar. In this case, the incorporation and increase of the lysozyme concentration caused a decrease of viscosity, and therefore, a decrease of the nanofiber's diameter [42].

#### *3.4.2 Surface tension*

This parameter is closely related with the nature of the solvent. Surface tension shows the strong cohesiveness of the molecules in the solution, which allows the formation of the drop on the tip of the capillary before to be formed the jet by action of electric field [43]. A decrease of surface tension results on bead-free fibers while its increase produces instability of the jet and avoids the formation of the nanostructures [44]. As can be seen in **Table 1**, the incorporation of active compounds has mainly produced a decrease of surface tension of polymeric solutions due to their behavior as surfactant. Despite of this, the morphological properties of the fibers have been not affected. This effect was recently evidenced when essential oils of *Laurus nobilis* (LEO) and *Rosmarinus officinalis* (REO) were added to an aqueous PVOH solution [32]. The surface tension value was significantly lower than the solvent, and it decreased even more when the essential oils were added [32]. Horuz et al. also obtained a similar result in their study about active fibers of zein loaded with tomato peel extract. In this case, the addition of the extract decreased the surface tension without affecting the morphology of the fibers [34]. Likewise, the incorporation of sage extract into an organic PCL solution did not produce changes on the morphology of the fibers although its surface tension was decreased [33].

#### *3.4.3 Electrical conductivity*

Another of the key parameters for the development of electrospun active fibers is the electrical conductivity. The value in this parameter influences on the fiber's morphology. Generally, an increase of electrical conductivity facilities the elongation of the droplet and jet formation, therefore, thinner and bead-free fibers are reached [45]. **Table 1** shows that the incorporation of an active compound into a polymeric solution has generally produced an increase of its electrical conductivity. Despite of this, the morphology and the diameter of the fibers have shown different trends. For example, although the addition and increase of angelica essential oil concentration into gelatin solutions produced higher electrical conductivity values, an increase of diameter of the fibers was mainly influenced by the increase of the viscosity [30]. A similar result was recently obtained in a study about active nanofibers of glycyrrhiza

polysaccharide and PEO loaded with tea tree essential oil encapsulated into gliadin nanoparticles. As the above-mentioned study, the active compound significantly increased the electrical conductivity of the polymeric solution. However, the increase of fiber diameter was attributed to the higher solution viscosities [31]. Meanwhile, a contrary effect was obtained in the study of Avila et al. In this case, the incorporation and increase of jaboticaba peel extract concentration into zein solutions increased their electrical conductivity, which favored the formation of thinner fibers [35]. The same effect was also evidenced in the electrospinning process of chitosan nanofibers loaded with lysozyme [42].

On the other hand, few studies have evidenced a decrease of this parameter when the active compound has been added to the polymeric solution, resulting in the formation of thicker structures. The increase of the diameter of the fibers due to the decrease of electrical conductivity has been explained because static charges of the solution are oriented to jet surface during the electrospinning process. In this way, the capacity of polymer solutions to be electrospun is increased [34]. For example, the adding of TiO2 or tomato peel extract in a zein polymeric solution has evidenced such effect [34, 37].

#### **3.5 Application of active electrospun materials on food packaging**

Although electrospinning has been a novel tool for developing active food packaging materials, their application to industrial scale has been not still largely exploited. This fact has been mainly associated to its low technological readiness level (TRL) in the food area due to low-yield in the production of packaging materials [11]. However, the numerous researches about the application of this technology in real matrixes reveal their promissing and potential application in the food packaging area in the future. In this sense, the most recent developments that involve the application of active electrospun materials on different foodstuffs, the type of formats used for packaging and the principal assay experimental are shown in **Table 2**.

#### *3.5.1 Meat products*

In the food industry, chicken, meat and pork are considered the most appreciated and chosen meat products by the consumers due to a 15% preference of world population [68]. These food have been usually packaged into trays and bags through different systems in order to ensure their quality and safety [69]. Despite of this, microbial contamination, oxidation processes and loss of the sensory properties are still some of main issues that produce their spoilage. In order to avoid such complications, several developments based on the direct application of active electrospun materials as wraps or films has allowed their protection, as **Table 2** shows. In this way, the quality, safety and shelf-life of these products have been guaranteed during long-time in a cold storage condition. A wrapper active film based on PVOH electrospun nanofibers loaded with LEO and REO was used to protect chicken breast fillets against oxidation and microbial contamination during cold storage. The active mat inhibited their lipid oxidation up to 68% and decreased their microbial growth [32]. Likewise, an active electrospun wrap composed by PLA nanofibers loaded with inclusion complexes of γ-cyclodextrin/α-tocopherol was able to reduce the lipidic oxidation of beef up to 50% during its storage at 4°C for 21 days [48]. Li et al. also prepared active gelatin/zein fibers with resveratrol in order to wrap small pieces

*Active Electrospun Mats: A Promising Material for Active Food Packaging DOI: http://dx.doi.org/10.5772/intechopen.101781*


**Table 2.**

*Application of active electrospun materials on different food matrices.*

of pork. Samples were stored at 4°C and the active mat was able to extend their shelf-life by 3 days [51].

#### *3.5.2 Freshwater and sea products*

Fish and seafood are the main products obtained from salt and fresh water. They constitute a great source of animal protein and essential micronutrients, such as minerals, vitamins and essential fatty acids [70]. However, their high fatty content is one of the main reasons of decay, principally evidenced through changes of their sensory properties due to oxidation processes. Furthermore, their deterioration is also related to the presence and growth of pathogens and microorganisms. Therefore, and as **Table 2** shows, the latest developments about electrospun active materials have been mainly focused on the protection of freshwater and sea products against such deterioration processes. In order to achieve this, these products have been wrapped with developed active electrospun mats containing different polymers and active compounds. A work about the development of sodium caseinate/gelatin nanofibers loaded with essential oil of *Mentha spicata* L. and magnesium oxide nanoparticles evaluated their effectivity as fresh trout fillets packaging during cold storage for 13 days. This active material was able to reduce the oxidation in the fillets up to 93% and the presence of microbial population up to 5 log CFU/g [54]. In the same way, *Mentha longifolia* L. essential oil was encapsulated into carboxymethyl cellulose/gelatin nanofibers in order to produce a nanofibrous film able to improve the shelf-life of peeled freshwater prawns during 14 days in refrigeration. A low microbial growth and oxidation of the samples during the storage was reflected with the high sensory scores in terms of odor, color, texture, taste, and total acceptance [57]. Likewise, active electrospun mats composed by PVOH fibers loaded with poly(hexamethylene biguanide) hydrochloride or nisin have also protected these food against microbial growth [55, 56].

#### *3.5.3 Fruits and vegetables*

Another important group of food used for evaluating the effectivity of packaging systems are fruit and vegetables. Different strategies, such as the use of active sachets or packages with improve physical properties, have been applied for protecting them and extending their shelf-life [71, 72]. Despite of this, their weight loss, textural changes and fungal contamination are still the principal issues causing of their spoilage. In this sense, the most recent developments about wrapper films, bags, films and active sachets obtained through electrospinning have shown their potential application for active food packaging (**Table 2**). These materials have been mainly applied on strawberries, grapes, tomatoes and mushrooms, and promising results have been obtained. For example, an active electrospun sachet composed by PLA and PVOH/ poly(ethylene glycol) nanofibers loaded with thyme essential oil was able to maintain the freshness and prolong the softening rate of strawberries stored at 20°C for 5 days [73]. Likewise, active zein fibers with allyl isothiocyanate were applied as a sachet into a package containing strawberries. In this case, the active sachet reduced the weight loss up to 36% and maintained their firmness during 15 days at 4°C [58]. On the other hand, two recent developments based on PVOH nanofibers loaded with inclusion complexes of β-cyclodextrin with cinnamon essential oil (CEO), and zein and ethyl celullose fibers loaded with CEO demonstrated their excellent effectivity during the storage of mushrooms. In both cases, the weight loss of the vegetables decreased, and therefore, their shelf-life was prolonged [62, 63].

#### *3.5.4 Dairy and bakery products*

As **Table 2** shows, cheese and bread have been the main food models used for evaluating the antimicrobial effectivity of active electrospun packaging materials. In order to avoid the bacterial and fungal contamination in this food category, wrapper films and sachets obtained from such materials have been developed. Cheese has been mainly wrapped with the active mats to avoid the growth of pathogens microorganisms. For example, a total inhibition of microbial growth of *Salmonella typhimurium*, *Listeria monocytogenes* and *Leuconostoc mesenteroides* was obtained by Soto et al. when cheese cubes stored at 4°C for 7 days were covered with active amaranth protein isolate and pullulan nanofibers loaded with nisin [65]. A study based on PEO nanofibers containing nisin-loaded poly-γ-glutamic acid/chitosan nanoparticles also evidenced a similar behavior. In this case, the strong antibacterial activity of the active mat against *L. monocytogenes* was observed on cheese samples stored at 4 and 20°C for 7 and 15 days, respectively [66].

On the other hand, active electrospun sachets have been the preferred format packaging for protecting bread samples. Contrary to cheese, the sachets have been applied without direct contact, avoiding mainly the fungal contamination. This fact was evidenced in the studies developed by Altan et al. and Fonseca et al. Both researches evidenced that the active sachets obtained from starch, zein and PLA nanofibers loaded with carvacrol were able to inhibit the growth of molds on bread stored at 25°C for 7 days [29, 64].

#### **4. Conclusions**

Electrospinning has been one of the most recent and novel technologies used in the packaging research area. This technique has allowed the development of

#### *Active Electrospun Mats: A Promising Material for Active Food Packaging DOI: http://dx.doi.org/10.5772/intechopen.101781*

electrospun mats composed by fibers with high aspect ratio. During their development, the modification of electrospinning parameters in turn have generated changes on the morphological characteristics of resulting fibers. Moreover, electrospun mats have been also functionalized through the incorporation of active compounds into polymeric solutions. This fact has eventually modified the viscosity, surface tension and electrical conductivity of the polymeric solutions, and therefore, the morphology and sizes of electrospun structures.

On the other hand, although this technique presents a current low technological readiness level in the food packaging area, the interest and projection of this technology to be applied is growing in an exponential way. This fact has been mainly evidenced by the diverse developments of active electrospun materials able to protect different products, such as meat, chicken, fish, pork, fruits, vegetables, bread, cheese, among others. Therefore, electrospun mats could be proposed as the new generation of materials to be used in the active food packaging.

#### **Acknowledgements**

The authors acknowledge the financial support of Agencia Nacional de Investigación y Desarrollo de Chile (ANID) through the Doctoral Scholarships CONICYT-PFCHA/Doctorado Nacional/2019-21190316, CONICYT-PFCHA/ Doctorado Nacional/2019-21190326 and Fondecyt Regular 1200766.

#### **Conflict of interest**

The authors declare no conflict of interest.

### **Author details**

Cristian Patiño Vidal1,2\*, Cristina Muñoz-Shugulí1,2, Marcelo Patiño Vidal3 , María José Galotto1,2,4 and Carol López de Dicastillo1,2,4

1 University of Santiago of Chile (USACH), Packaging Innovation Center (LABEN), Chile

2 University of Santiago of Chile (USACH), Center for the Development of Nanoscience and Nanotechnology (CEDENNA), Chile

3 Escuela Superior Politécnica de Chimborazo (ESPOCH), Faculty of Mechanics, Industrial Engineering School, Ecuador

4 University of Santiago of Chile (USACH), Technological Faculty, Food Science and Technology Department (DECYTAL), Chile

\*Address all correspondence to: cristian.patino@usach.cl

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Active Electrospun Mats: A Promising Material for Active Food Packaging DOI: http://dx.doi.org/10.5772/intechopen.101781*

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### **Chapter 2**

## Electrospun Polymeric Substrates for Tissue Engineering: Viewpoints on Fabrication, Application, and Challenges

*Azadeh Izadyari Aghmiuni, Arezoo Ghadi, Elmira Azmoun, Niloufar Kalantari, Iman Mohammadi and Hossein Hemati Kordmahaleh*

#### **Abstract**

Electrospinning is the technique for producing nonwoven fibrous structures, to mimic the fabrication and function of the native extracellular matrix (ECM) in tissue. Prepared fibrous with this method can act as potential polymeric substrates for proliferation and differentiation of stem cells (with the cellular growth pattern similar to damaged tissue cells) and facilitation of artificial tissue remodeling. Moreover, such substrates can improve biological functions, and lead to a decrease in organ transplantation. In this chapter, we focus on the fundamental parameters and principles of the electrospinning technique to generate natural ECM-like substrates, in terms of structural and functional complexity. In the following, the application of these substrates in regenerating various tissues and the role of polymers (synthetic/natural) in the formation of such substrates is evaluated. Finally, challenges of this technique (such as cellular infiltration and inadequate mechanical strength) and solutions to overcome these limitations are studied.

**Keywords:** electrospinning process, parameters of electrospinning technique, synthetic/natural polymers, electrospun scaffolds, Tissue engineering

#### **1. Introduction**

Nowadays, tissue engineering is known as a multi-disciplinary science that leads to the regeneration of damaged/lost tissues via combining the cell and scaffold [1, 2]. In this technique, the engineered scaffolds act as micro/nano/smart environments for improving the interactions of cell-scaffold and cellular functions (such as proliferation, adhesion, differentiation, and growth) [3]. The methods that can be led to the design of scaffolds similar to extracellular matrices (ECM), with the properties of mechanical/biochemical support from the cells and imitation of architecture/structure and function of the tissues, play an important role in this field [4–7].

Electrospinning is one of the unique approaches in this field that lead to the production of polymeric fibers with interconnecting pores and the opportunity to control the network and morphology of scaffolds, especially in bio-polymers processing. Such that, the polymeric solutions with low viscosity lead to shorter and finer scaffolds/substrates, while, more viscous solutions provide a relatively continuous scaffold. However, the morphology and diameter of the produced fibers depend on the processing conditions and the type of the polymer [8].

These conditions can be provided via controlling parameters of the solution, process, and ambient, such as an electric-field application, distance between the needle and collector, needle diameter, and flow rate, solution conductivity, the concentration of the polymeric solution, materials molecular weight, and solution viscosity [9–13].

In recent years, many studies have been carried out on electrospun substrates and their functions for tissue engineering applications, such as the regeneration of the blood vessels, skin tissue, cartilage, and bone, as well as muscle [14–23]. However, a better understanding of cellular responses to sophisticated structures derived from this technique can be effective in reaching ECM-liked substrates.

Hence, in this chapter, we discuss the principles of the electrospinning technique to analyze these sophisticated structures and generate natural ECM-like substrates. In the following, the application of these substrates in regenerating various tissues and

#### **Figure 1.**

*(A) Schematic of electrospinning process, (B) Taylor cone formation via increasing the voltage, (C) the fibers derived from electrospinning process with different collectors.*

the role of polymers (synthetic/natural) in the formation of such substrates is evaluated. Finally, challenges of this technique and solutions to overcome these limitations are studied.

#### **2. Electrospinning process**

In this simple technique (spinning technique), a very high electrical field (high voltage), in the range of 10–50 kV, is applied for accelerating the charged polymer jet and producing ultrafine fibers (**Figure 1A**). Moreover, the electrospinning machine includes a syringe pump along with a syringe (with a metallic needle) that is loaded with the polymeric solutions, so that the tip needle is attached to one of the negative or positive terminals of the high-voltage electrical field, and pendant-shaped droplets of the polymer solution are held through surface tension. Notably, the needle tip is usually attached to the positive terminal of the electrical field [24]. In these conditions, the increase of the voltage is led to the formation of the Taylor cone in the needle tip [25]. Afterward, increased voltage leads to the creation of the critical value above which the electrostatic forces can overcome the surface tension forces so that it results in ejecting out the fine-jet of the solutions from the tip of the Taylor cone (**Figure 1B**). In the following, solvents are evaporated at a low boiling point due to contact with the atmosphere and subsequently the charged polymeric strands deposited on the collector. The collectors can play a crucial impact in reaching the various structures of the scaffold. Such that, unidirectionally oriented nanofibers, aligned nanofibers, and nonwoven nanofibers can be designed by square frame collector, rotating collector-drum, and flat plate stationary collector [26], respectively (**Figure 1C**).

#### **3. Electrospinning parameters**

The parameters of the electrospinning process play an important role in understanding the nature of this process and conversing polymeric solutions into nanofibers. Indeed, control of these parameters can be led to electrospun fibers with a desired morphology and diameter. Hence, this section has been focused on these parameters and their influence on the properties of produced fibers. The mentioned parameters have been listed in **Table 1**.

#### **4. Polymers for electrospun fibers**

Nowadays, natural and synthetic polymers are widely used in the design of electrospun scaffolds for tissue engineering applications [6, 51–56]. In this field, synthetic polymers possess high flexibility in the electrospinning process and can provide fibers with better mechanical properties [56, 57]. Although, these polymers are also highly cost-effective than bio/natural polymers, however, a comparison of these two polymers indicates that synthetic polymers lack bioactivity and need more modification to improve biological properties [53, 56, 58]. In contrast, natural polymers possess the properties of inherent bioactive and can be led to an increase in the interactions of scaffold-cell and cell–cell (i.e., adhesion, proliferation, differentiation) [3]. These polymers have a relatively low immune response (in terms of chemical degradation) and can provide a structure similar to native ECM. In recent years, more



**Table 1.**

*The important parameters in the electrospinning process, as well as the morphology of electrospun fibers.*

than 200 natural/synthetic/copolymer/hybrid polymers have been designed and studied to obtain electrospun scaffolds with suitable physicomechanical and biological properties for use in tissue engineering [16, 17, 59–65]. Some of these polymers and their applications have been listed in **Table 2**.

#### **4.1 Natural polymers**

#### *4.1.1 Collagen*

Collagen is one of the main components of the native ECM with diameters in the range of 10–500 nm that plays an important role in providing mechanical strength of tissue and stimulating cell attachment and its proliferation [67, 83, 84]. Generally, type I collagen is the most common type of this protein in the dermis (70–80%),





*Electrospun Polymeric Substrates for Tissue Engineering: Viewpoints on Fabrication… DOI: http://dx.doi.org/10.5772/intechopen.102596*

#### **Table 2.**

*The used polymers in the electrospinning process to produce nano/microfibers.*

compared to other types of collagens (i.e., type II and type III) [85]. Given that collagen possesses a low young modulus (0.8 GPa) [83], the processes, such as chemical modification [by covalent of amine/imine linkage], cross-linking [by Glutaraldehyde (GA), NHS, and EDC, genipin as the cross-linking agent], and physical treatment [by UV irradiation, gamma radiation and dehydrothermal treatment (DHT)], can be led to an increase in mechanical properties of electrospun nanofibers based on this biopolymer [84, 86–96].

#### *4.1.2 Gelatin*

Gelatin derived from collagen is also one of the other biopolymers whose surface charge depends on the gelatin processing methods, such as acidic/alkaline processing [97]. The mechanical strength of this biopolymer can also increase via the physical mixing with other polymers or cross-linking process and immersing of gelatin-based scaffolds into glutaraldehyde (25%), carbodiimides, and genipin [83, 98].

#### *4.1.3 Chitosan*

Chitosan is another biopolymer that is widely used in biomedical/tissue engineering applications due to its low toxicity, non-immunogenic, biodegradability, and antibacterial properties [51, 98]. This polysaccharide as a cationic biopolymer can interact with structural molecules of the ECM due to having positively charged and be led to the formation of two-component scaffolds with suitable physicomechanical/ biological properties when mixed with other anionic biopolymers [99].

#### *4.1.4 Fibrinogen*

Fibrinogen is a soluble biopolymer derived from the blood plasma and plays an important role in tissue engineering applications and the development of electrospun substrates/scaffolds [100, 101]. Based on the reports, fibrinogen electrospun fibers are more extensible and elastic compared to other biopolymer-based electrospun fibers [98, 102]. Notably, the mechanical resistance of this biopolymer and its degradation rate can be controlled by crosslinking process or supplementing culture medium [103].

#### *4.1.5 Elastin*

Elastin is a biopolymer of highly insoluble with difficult processing, hence the approaches, such as cross-linking and blending with other polymers can be effective in reaching elastin-based scaffolds [104].

#### *4.1.6 Silk fibroin*

Silk is a protein-biopolymer derived from Bombyx more (most commonly)/other insects and included two proteins of fibroin (70–80%) and sericin (20–30%) or other insects [105–109]. This biomacromolecular possesses suitable biocompatibility, biodegradability, and mechanical properties and plays an important role in the biomedical applications and development of engineered scaffolds [110–114]. Based on the reports, the electrospun nanofibers of this biopolymer can modulate cellular interactions (such as adhesion, spread, the expression level of genes and proteins) [115, 116]. *Electrospun Polymeric Substrates for Tissue Engineering: Viewpoints on Fabrication… DOI: http://dx.doi.org/10.5772/intechopen.102596*

#### *4.1.7 Hyaluronic acid*

Hyaluronic acid (HA) is known as a linear polysaccharide and plays an important role in the ECM structure [117, 118]. This glycosaminoglycan (GAG) is a suitable candidate for hydrogel production and tissue regeneration due to its molecular weight (100–8000 kDa) and hygroscopic nature [118–120]. However, the high viscosity of produced hydrogels leads to limitations in the electrospinning process, hence, the electrospun fibers can form by blending/dissolving this hydrogel with other polymers/ in other solvents [65].

#### *4.1.8 Alginate*

Alginate is a copolymer derived from β-D-mannuronic acid and α-L-guluronic acid that is widely used in tissue engineering applications [121, 122]. This biopolymer is known as one of the other polysaccharides that are commercially produced from brown algae or some bacteria, such as *Azotobacter chroococcum*, *Azotobacter vinelandii*, and some species of *Pseudomonas* [121, 123]. The salt of this polymer (alginate sodium) is water-soluble and can also form a highly viscous solution at very low concentrations [124]. Moreover, the electrospinning of alginate sodium solutions carries out in presence of synthetic polymers (PVA, PEO, etc.), owing to the reduction of the repulsive forces among the poly-anionic chains of alginate. Methods, such as cross-linking, are also necessary for resulting scaffold stability in the aqueous environment [65].

#### **4.2 Synthetic polymers**

#### *4.2.1 Polylactic acid (PLA)*

PLA as thermoplastic polymer fabricates from the polymerization of lactic acid and possesses isomers of poly(L-lactic acid) and poly(D-lactic acid) [125, 126]. This aliphatic polyester possesses biodegradability properties and plays a critical role in the design of tissue-engineered scaffolds [127]. However, PLA is usually copolymerized with other polymers or made as a composite due to its low modulus, especially in bone tissue engineering [128, 129].

#### *4.2.2 Polycaprolactone (PCL)*

This polymer is a semicrystalline polyester that is widely used in the applications of tissue engineering due to its biodegradability, nontoxicity, and biocompatibility properties, as well as mechanical strength [130–132]. This synthetic polymer can improve cellular penetration into the engineered scaffolds due to the presence of cell recognition sites [51, 133, 134]. However, the degraded product of this polymer (the acids of polylactide and glycolide) affects on stability and functions of proteins and bioactive molecules. PCL is also known as the most famous synthetic polymer in the design of bone-engineered scaffolds, due to its low degradation rate and high modulus [83].

#### *4.2.3 Polyglycolic acid (PGA)*

PGA is the aliphatic thermoplastic polyester (simple linear) that is usually applied in the applications of bone tissue engineering. This polymer possesses a high young modulus (7 GPa) and can be completely degraded within 4–6 months [133, 135].

#### *4.2.4 Polyethylene glycol (PEG)*

PEG is known as one of the most popular synthetic polymers in tissue engineering applications and can lead to a promotion of cellular adhesion and improvement of cell–cell signaling, due to its hydrophilic properties and interactions with the chains of polysaccharides or peptides [51, 136]. Notably, copolymerization of this polymer with other hydrophobic polymers, such as polyglycolic acid, polycaprolactone, and polylactic acid, can lead to an increase in the degradation rate of these polymers and neutralization of their acidic products [137, 138].

#### **4.3 Copolymer/hybrid polymers**

Tissue engineering is a strategy for the design of tissue-liked scaffolds/ substrates (in terms of biological and physiological functions). In this field, the combination of natural or synthetic polymers as copolymers or hybrid scaffolds can be played an important role in overcoming the limitations of mono-component systems and improving the interactions of cell/cell and cell/scaffold. Sodium alginate/PVA electrospun mats are a sample from these copolymers that aimed to prepare the antibacterial substrates [79]. Such substrates can be used in wound dressings to reduce wound infection and prevent scars [79, 139]. PCL/HA nanofibrous scaffolds are also one of the other composite scaffolds that can provide substrates with better mechanical and biochemical properties. Based on the reports, such scaffolds lead to an increase in fibroblasts infiltration into the scaffold, cellular proliferation, and consequently tissue regeneration [77]. In this field, the combination of HA and collagen has been reported as an ideal matrix in electrospun dressings that play an important role in reducing scar via proteinase secretion and metalloproteinase inhibition [78]. Alginate-PEO nanofibers containing lavender essential oil are another scaffold that can be used for wound healing and reducing the production of pro-inflammatory cytokines [80]. The PLLA-gelatin scaffold with a layer of electrospun PDLA is one of the other samples in this field [82].

#### **5. Application of electrospun polymers in tissue engineering**

The cells play an important role in the formation of organ-dependent extracellular matrix (ECM), and to this end, they need microenvironments to improve their functions. However, the body is unable to repair damaged tissue when tissue damage is severe or extensive. In this field, although, the xenografts, autografts, and allografts approaches can be used, however, the problems of donor sites, antigenicity, and immunogenicity have been limited to the use of these therapeutic methods [51]. In recent years, tissue engineering as a new method has been overcome the mentioned problems via designing engineered substrates with suitable physicomechanical and biological properties [3, 51]. There are many studies that show electrospun substrates can be effective in this field. Such that, the electrospinning process of natural and synthetic polymers can help to address cell requirements, improve its functions, and finally regenerate damaged tissue.

Blood vessels are one of the important organs in the body that need to be repaired quickly in case of damage. Vascular-engineered scaffolds play a key role in this regard so that electrospun matrices based on the natural/synthetic/hybrid polymers can support the adhesion, differentiation, and proliferation of vascular cells and be led to

#### *Electrospun Polymeric Substrates for Tissue Engineering: Viewpoints on Fabrication… DOI: http://dx.doi.org/10.5772/intechopen.102596*

tissue regeneration [140]. Accordingly, the study of Bondar et al. shows that there is ideal intercellular contact between endothelial cells on the nano/micro-scale electrospun silk fiber that led to vascular endothelial cadherin expression [141]. Soffer et al. also designed silk fibroin into a tubular structure (inner-diameter: 3 mm, the average wall thickness: 0.15 mm). They reported that the average strength of such scaffolds is much more than collagen scaffolds [142].

Skin is another organ that possesses an important role in the protection of the body against infection and environmental agents. Such that, loss of a large surface of the skin due to burn, wound, etc. can lead to patient death. However, dermis-engineered scaffolds can be an ideal therapeutic option for skin regeneration [6]. In this field, Min et al. stated that silk electrospun substrates with coating collagen I can increase adhesion and spreading of keratinocytes. Moreover, they found that laminin coating can stimulate cellular spreading, but not cellular adhesion [112]. Based on the studies of Pezeshki-Modaress et al., the gelatin/chitosan electrospun scaffolds as the structures containing protein and polysaccharide play a crucial role in the proliferation of dermal fibroblast cells and wound healing. Such scaffolds can maintain their morphology in culture medium and increase the proliferation and attachment of cells [143]. Law et al. also assessed electrospun collagen nanofibers for applications of skin tissue engineering. They stated that collagen nanofibers possess low mechanical properties, hence are usually cross-linked/blended with synthetic polymers [144]. In this field, Jin et al. showed that collagen/poly(l-lactic acid)–co-poly(3-caprolactone) electrospun scaffolds can differentiate mesenchymal stem cells to epidermal and lead to an increase in cell proliferation [145].

One of the other applications of electrospun scaffolds is related to the design of calcified extracellular matrices. These substrates consist of calcium phosphates, carbonated hydroxyapatite, growth factors, and bone marrow stromal cells (MSCs) or osteoblasts and osteoblast-like cells, such as osteoprogenitors and osteocytes [140]. In this regard, Ki et al. designed the 3D silk matrices to produce bone with MC3T3-E1 cells. They found that cell proliferation and spreading increase on the 3D matrices compared to 2D matrices. This can be due to the higher porosity of 3D matrices that provides better cellular adhesion [146]. In another study, Yin et al. showed that electrospun scaffolds can be effective on the regeneration of various tissues, via topography-dependent induction of lineage-specific differentiation [147]. They evaluated the differentiation pathway of MSCs in forming new tissues and observed that these scaffolds can lead to the formation of tendon-like tissue in the Achilles tendon injury models, as well as, chondrogenesis and bone tissue formation via ossification. Delgado-Rangel et al. also developed collagen/poly (vinyl alcohol)/ chondroitin sulfate and collagen/poly (vinyl alcohol)/hyaluronic acid 3D electrospun scaffolds to apply tissue engineering [148]. Based on their reports, these scaffolds can increase the biocompatible cross-linker. Moreover, the scaffolds possess the behavior of pH-sensitive swelling and can be used in drug delivery systems.

Flaig et al. also studied the application of electrospun scaffolds in cardiac tissue engineering. They found that electrospun scaffolds based on poly (glycerol sebacate) elastomer and poly (lactic acid) can induce neovascularization without the inflammatory responses and support cardiomyocyte development [149]. Moreover, Vogt et al. stated that poly (ε-caprolactone)/poly (glycerol sebacate)-based electrospun scaffolds possess better mechanical properties compared to native myocardium; hence can be potentially suitable to apply cardiac tissue engineering [150].

Collectively, the studies indicate that electrospun scaffolds possess an inductive role in the regeneration of tissues and the use of hybrid polymers can provide effective insight into the design and development of smart scaffolds for applications of tissue engineering.

#### **6. Challenges and resolutions of the electrospinning process**

The techniques of tissue engineering hold promise for developing functional networks similar to native tissue. The designed substrates in this technique can support the formation of 3D tissues by mimicking ECM functions. Among the fabrication techniques of the engineered scaffold, the electrospinning process is known as an outstanding one that can produce a nonwoven structure.

Although this method is considered as the potential technique in the design of tissue-engineered scaffolds, however, it possesses limitations of mechanical strength and cellular infiltration in the application of load-bearing.

Based on the reports, the optimum size of pores for cell infiltration to tissue is in a range of 100–500 μm [151], while, the size of pores in electrospun scaffolds is much lower than the mentioned size. This can lead to inhibition of vascular growth and the creation of the hypoxic region. Moreover, the density of the fibers in electrospun substrates can be one of the reasons for poor cellular infiltration [152].

There are several solutions to overcome these limitations that pore architecture of scaffolds and their surface morphology control are some of the most important solutions. Generally, the diameter of fibers strongly relates to the pore diameter in the electrospun substrates, so that, fibers with smaller diameters lead to smaller pores. Hence, attention to surface topography plays a crucial role in the removal of waste and diffusion of nutrients [153, 154].

Indeed, the manipulation of characteristics of the electrospun scaffolds for enlarging the diameter of pores or reduction of the fibers density, help migration of cells into internal parts of the scaffold. There are other four approaches in this field, including [155]:


#### **7. Conclusion**

The electrospinning process is known as the powerful, simple, and inexpensive tool to fabricate tissue-engineering substrates that are capable of the formation of ECM-mimicking networks. Although, this technique, in clinical applications; has the limitations, such as low cellular infiltration, high-density of fibers, possible toxicity of solvent/cross-linker, and insufficient mechanical strength. However, some solutions, such as the increased diameter of pores, reduced density of fibers, and electrospinning polymers along with cells can overcome these problems. Combining robust materials or structures also provides the more robust electrospun substrate for the design and production of tissue substitutes with the desired target.

*Electrospun Polymeric Substrates for Tissue Engineering: Viewpoints on Fabrication… DOI: http://dx.doi.org/10.5772/intechopen.102596*

### **Author details**

Azadeh Izadyari Aghmiuni<sup>1</sup> \*, Arezoo Ghadi<sup>2</sup> , Elmira Azmoun<sup>3</sup> , Niloufar Kalantari<sup>2</sup> , Iman Mohammadi<sup>2</sup> and Hossein Hemati Kordmahaleh<sup>2</sup>

1 Department of Nanobiotechnology, Pasteur Institute of Iran, Tehran, Iran

2 Department of Chemical Engineering, Ayatollah Amoli Branch, Islamic Azad University, Amol, Iran

3 Department of Chemical Engineering, Islamic Azad University, Gaemshahr branch, Mazandaran, Iran

\*Address all correspondence to: azadeh.izadyari@gmail.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 3**

## Production of Nanofibers from Plant Extracts by Electrospinning Method

*Nilşen Sünter Eroğlu*

#### **Abstract**

The fact that different plants grow in each climate type, that each plant has different and many benefits, and that it can obtain bio-structured, sustainable, economic, and ecological products has increased the work of researchers in this field. The long-term toxicity and harmful side effects of herbal extracts are generally less compared to synthetic drugs. Studies on the production of nanofibrous membrane structures from plant extracts are relatively limited and are an emerging field. Herbal extracts have a positive effect in electrospinning applications with their biodiversity, ability to maintain biological functionality, and wound healing effects against pathogenic microorganisms. With the creation of nanofiber structures of plants obtained from natural sources, applications in fields such as wound healing, tissue engineering, drug release are increasing day by day.

**Keywords:** nanofiber, polymer, electrospinning, herbal extract, electrospun

#### **1. Introduction**

Electrospinning is the most preferred method because of its low cost compared to nanofiber production methods, production of long and continuous nanofibers, controllable nanofiber diameter, and industrial processing potential. When all these properties are evaluated, it would be appropriate to produce a nanofiber for wound healing by electrospinning. On the other hand, in recent years, interest in polymer materials obtained by the electrospinning method has increased significantly. Materials such as polymers and nanofiber composites can be produced directly by electrospinning. The post-processing of electrospun fibers forms other materials, such as ceramics and carbon nanotubes [1]. Polymer nanofibers obtained by the electrospinning method have a high surface area-volume ratio, flexible in surface functions, have superior mechanical performance, and are versatile in design [2].

Because of all these advantages, the most common and simple method used for tissue framework production is electrospinning. The principle of operation is based on filling the syringe with the polymer solution or melting in the high potential area and spraying it from the tip of the syringe to the collector by applying a voltage to an electrode connected to the tip of the syringe (**Figure 1**). Here, since the solution sprayed

#### **Figure 1.** *Schematic representation of the electrospinning process.*

from the syringe is subjected to an electrical field, it elongates at the tip of the needle, and a conical appearance called a Taylor cone is obtained. A typical electrospinning process must be between a high voltage source with positive or negative polarity and a grounded surface so that the fibers can clump together. Spraying the solution in the syringe starts when the potential difference applied from the voltage source reaches the threshold value and equalizes to the electrostatic forces, and is completed by spraying it on the grounded surface. Since the fibers collected on the surface are sprayed with a high amount of pulling, they should be in a fine and regular structure [3–5].

The surface tension of the liquid (γ), and the gravitational force (Fg) affect the droplet when the solution, which is the first step of the electrospinning process, comes out of the syringe by forming a droplet. The capillary of internal radius (R), density of the liquid (ρ), and gravitational constant (g) values of the pipe through which the polymer flows are effective in the formation of the radius of the droplet (r0).

$$\mathbf{r}\left(\mathbf{r}\_{\circ}\right) = \left(\mathbf{\mathcal{R}}\mathbf{\hat{R}}\mathbf{\hat{y}} / \mathbf{\hat{z}}\mathbf{\hat{p}}\mathbf{g}\right)^{\omega/3} \tag{1}$$

When a sufficiently high voltage is applied, the electric force FE, the gravitational force Fg encounter surface forces (Fγ = FE + Fg), and the radius of the droplet decreases from (r0) to r (r < r0) [6].

After droplet formation, the polymer solution overcomes the surface forces under the influence of Coloumb repulsive forces, forming a Taylor cone with an apex angle of 49.3°. Initially straight, the jet segment may become unstable over time and may show twisting and undulating movements as it passes toward the collector. The jet in this region exhibits components of predominantly non-axial electrostatic repulsion forces. Three types of instability can occur as demonstrated by the polymer jet. These instability forms are listed as classical Rayleigh instability, axisymmetric electric field current, and whipping instability. Whipping instability results in a radial torque from the center of the jet, resulting in a high degree of bending instability. The resulting radial jets push each other and separate from the main jet. The interaction between increasing charge density on the one hand and viscous and surface tension forces resisting elongation on the other determines the complexity of the resulting instability [6, 7].

This chapter focused that the electrospinning process, parameters affecting the process such as solution and ambient. After then, it was explained herbal extracts

were used to obtain nanofibers by electrospinning method and their application areas. This chapter will provide an overview of the principles of the electrospinning process with various herbal extracts for potential applications in many fields especially biomedical areas.

#### **2. Parameters affecting electrospinning process**

There are three main parameters of the electrospinning process. These are due to the polymer solution, process, and environmental conditions. In this section, the factors affecting each parameter will be discussed in detail. These parameters and their effects in **Table 1** are also shown.

#### **2.1 Solution parameters**

To carry out the electrospinning process, the polymer must be in liquid form, in the form of a molten polymer or polymer solution. The physical and chemical properties of the solutions play an active role in the electrospinning process and the resulting fiber morphology. During the electrospinning process, the polymer solution is drawn from the tip of the needle. For this reason, the electrical properties, surface tension, and viscosity of the solution determine the amount of stress in the solution. The evaporation rate also affects the viscosity of the solution as it is stretched. The solubility of the polymer in the solvent determines not only the viscosity of the solution but also the types of polymers that can be mixed with each other [1].

#### *2.1.1 Solution viscosity, molecular weight, and concentration*

Viscosity is the most important factor determining the flow rate of the solution. In the electrospinning process, the flow rate increases at low viscosity [8]. However, when the viscosity of the solution is too low, fluidity may occur and polymer particles may form instead of fibers. In solutions with lower viscosity, the polymer chain is generally less synthesized with each other [9], less chain entanglement occurs, and thus jet stability is lost. The fibers are collected into the collector as droplets, which


#### **Table 1.**

*Electrospinning parameters affecting fiber morphology.*

first turn into spindle-like structures and then into beaded nanofibers [3]. As the viscosity increases, the formation of the bead structure decreases, and more regular nanofibers are obtained [9]. Therefore, factors that affect the viscosity of the solution also affect the electrospinning process and the resulting fibers.

The molecular weight of the polymer used in the electrospinning process has a direct effect on properties such as viscosity, surface tension, and conductivity, and this interaction determines the nanofiber formation. Molecular weight is explained as the length of the chains of the polymer from which nanofibers will be obtained [4]. The length of the polymer chain will determine the amount of entanglement of the polymer chains in the solvent [1]. Since the viscosity will be higher in polymer solutions with high molecular weight, the formation of beads decreases [10]. Although the increase in molecular weight provides regular fiber formation, if this increase is high, it causes the formation of microstrip structure [11, 12].

#### *2.1.2 Surface tension*

When a very small drop of waterfalls into the air, the droplet usually takes on a spherical shape. The liquid surface property that causes this phenomenon, which occurs when the electrical forces are around zero, is known as surface tension [1]. An excessive increase in surface tension adversely affects the electrospinning process. Some surfactants with low concentrations are used to lower the surface tension. The decrease in the surface tension of the solution ensures the formation of finer and smoother fibers and a problem-free electrospinning process [4]. The concentration change in the solutions used directly affects the surface tension [13].

#### *2.1.3 Solution conductivity*

Electrospinning is a method of obtaining nanofibers that repel the charges on the surface by stretching the solution and transfer the electric charge from the electrode to the polymer solution [1, 14]. In the electrospinning system, low electrical conductivity can form beaded fibers as it will create instability and cause the jet to not be able to extend sufficiently, while with high electrical conductivity, the polymer jet can stretch more with the loads it carries and form fibers with a smoother and finer structure [3]. For this reason, it is aimed to increase the electrical conductivity by increasing the concentration. Some additives can also be added to increase conductivity in low-concentration or insufficiently ionic solutions [4]. If the conductivity of the solution increases, the electrospinning jet can carry more charge. For example, the conductivity of the solution can be increased by the addition of ions [1]. By adding salt to an uncharged solution, although electrical neutrality is maintained, salt molecules can dissociate into independently acting positive and negative ions, thereby increasing the electrical conductivity of a solution [15, 16]. These ions can also be obtained by dissolving most drugs or proteins in water. As a result, when a small amount of salt or polyelectrolyte is added to the solution, the increased loads carried by the solution will increase the stretching of the solution and the formation of beaded fibers will be prevented [1].

#### *2.1.4 Solution dielectric constant*

The insulation constant or dielectric constant is defined as a coefficient that measures the ability of a material to store charge on it [17]. As the dielectric constant of the solutions increases, the charge distribution across the surface of the bubble formed

at the needle tip will be more uniform, as there will be more net charge density. Therefore, the ordered structure of the obtained nanofiber is also increasing [3, 4]. It is thought that as the dielectric constant increases, obtaining finer and smoother fibers is due to the application of more tension force to the fluid jet [18].

#### **2.2 Processing variables**

Another important parameter affecting the electrospinning process is various external factors applied to the electrospinning jet. These factors are voltage, flow rate, temperature, collector effect, nozzle diameter, and the distance between the tip and the collector. Although these parameters are less important than solution parameters, they have a certain effect on fiber morphology.

#### *2.2.1 Voltage*

Voltage is a parameter that induces charges in the solution, overcomes electrostatic forces, and initiates the electrospinning process [1]. As the amount of applied voltage increases, the diameters of the obtained nanofibers will decrease [4]. There are three main reasons for this. The first reason is because of a higher voltage will lead to greater stretching of the solution due to the larger columbic forces in the jet and the stronger electric field. This will reduce the fiber diameter. The second factor is that by using a lower viscosity solution, at a higher voltage, the formation of secondary jets during electrospinning is achieved. Thus, the fiber diameters can become narrower. Another factor that can affect the fiber diameter is the flight time of the electrospinning jet. A longer flight time will allow more time for the fibers to stretch and elongate before being placed on the collecting plate. Therefore, at a lower voltage, the diminished acceleration of the jet and the weaker electric field can increase the flight time of the electrospinning jet, facilitating the formation of finer fibers [1].

In many studies [19–21], it was observed that the formation of beads on the surface formed with the increase of voltage increased. The increase in bead density due to tension is explained because of increased instability of the jet as it is drawn into the syringe needle in the Taylor cone [1]. Here, bead formation occurs with the excessive acceleration of voltage increase, jet movement, and evaporation [4]. It is also suggested that increasing voltage will increase bead density and at even higher voltage, beads will form fibers of thicker diameter [1].

Despite these studies that the voltage increase creates a bead surface, it has been observed that the production of nanofibers at very low voltage also creates a beaded surface [22]. In this sense, the important thing is to work at a voltage where the flow balance will be stable. With the increase in voltage, the jets coming out of the cone tip reach the collector in an orderly manner, increasing their speed in the electrical field. Here, excessive speed increase or decrease is a factor that will lead to the formation of a beaded surface. In other words, the applied voltage must have an upper and lower limit.

#### *2.2.2 Feeding rate*

The feeding rate determines the amount of feed in the electrospinning system. A certain feeding rate is needed to maintain the Taylor cone in the system. When the feeding rate increases, there will be an increase in the fiber diameter or the size of the beads formed in the fibers, as there will be more solution volume at the nozzle tip [1]. At low feeding rate, nanofiber production will not be possible because there will not be sufficient feed for the Taylor cone.

As the applied voltage changes, the resulting Taylor cone will also change. At low applied voltages, a hanging drop forms at the tip of the array. The Taylor cone is then formed at the tip of the array. However, as the applied voltage increases (moving from left to right), the volume of the hanging drop decreases until a Taylor cone is formed at the tip of the array. Increasing the applied voltage results in the ejection of the spray through the syringe, which is associated with an increase in bead formation [5].

#### *2.2.3 Temperature*

The temperature parameter consists of three environmental variables: melt temperature, solution temperature, and ambient temperature. As the melt temperature increases, less tension is required due to the decrease in viscosity and fiber diameters decrease [7]. Similar to melt temperature, the temperature of a solution has the effect of both increasing the evaporation rate and reducing the viscosity of the polymer solution. This is because the solution has a lower viscosity and greater solubility of the polymer in the solvent, allowing the solution to be stretched more evenly. With a lower viscosity, Columbic forces can exert a greater tensile force on the solution, thus resulting in smaller diameter fibers [1].

#### *2.2.4 Effect of the collector*

There must be an electric field between the source and the collector (collector) for the electrospinning process to start. Therefore, in most electrospinning systems, the collector plate is made of a conductive material such as aluminum foil, which is electrically grounded such that there is a constant potential difference between the source and the collector. If a non-conductive material is used as a collector, charges from the electrospinning jet will quickly build upon the collector, resulting in less fiber deposition. Fibers collected on non-conductive material generally have a lower packing density than those collected on a conductive surface. This is due to the repulsive forces of the loads that build upon the collector as more fibers accumulate. For a conductive collector, the loads on the fibers are distributed so that more fibers are drawn into the collector. As a result, the fibers can be wrapped closely together [1].

The most commonly used collector types in the electrospinning method are generally flat plates, grids and frames. Apart from these, rotating cylinder, rotating disc, rotating cones, parallel rings, liquid bath and wrapper, pyramid-shaped platform, conveyor belt, two parallel frames, rotor, and thin conductive rod are listed as [7].

#### *2.2.5 Nozzle (needle) diameter*

The nozzle diameter has a certain effect on the electrospinning process. As the nozzle diameter gets smaller, it provides clogging of the diameter and reduces the amount of beads on the nanofibers. The reduction in occlusion is due to less exposure of the solution to the atmosphere during electrospinning. The decrease in the inner diameter of the hole causes a decrease in the diameter of the nanofibers. As the size of the droplet at the tip of the hole decreases, the surface tension of the droplet increases. It reduces jet acceleration when the same amount of voltage is applied, allowing more time for the solution to stretch and stretch before the collector. The nanofibers formed in this way are finer [1].

#### *Production of Nanofibers from Plant Extracts by Electrospinning Method DOI: http://dx.doi.org/10.5772/intechopen.102614*

The nozzle could be blockage when electrospinning with electrospinning chloroform solutions of PLA. When more than one nozzle is formed, the solvent density may increase, but this will increase the difficulty of solvent removal and nozzle cleaning and compose the deposition of nonwoven fiber in thicknesses >10 mm [23].

#### *2.2.6 Distance between tip and collector*

The distance between the needle tip and the collector provides the necessary time for the solvent in the polymer jet sprayed from the nozzle tip to evaporate [4]. Changing the distance between the tip and the collector has a direct effect on both the flight time and the electric field strength. As the distance between the tip and the collector decreases, the jet will have a shorter distance to travel before reaching the collector plate. In addition, the electric field strength will increase at the same time, which will increase the acceleration of the jet going to the collector. As a result, there may not be enough time for solvents to evaporate when they hit the collector. When the distance is too low, excess solvent causes the fibers to coalesce where they come into contact [1].

#### **2.3 Environmental conditions**

Environmental conditions in the electrospinning process are the factors affecting the electrospinning process. In this sense, humidity, atmospheric type, and pressure cause physical and morphological changes in the formed fibers.

#### *2.3.1 Humidity (moisture)*

The increase in humidity in the environment adversely affects the electrospinning process. High humidity causes circular pores to form on the nanofiber surfaces obtained. The pore depth increases with increasing humidity. However, the depth, diameter, and number of pores remain constant above a certain humidity [1]. It is not possible to carry out the electrospinning process at very high humidity values [3]. As the humidity level decreases, volatile solvents evaporate quickly, causing drying and making the electrospinning process difficult [9]. For this reason, keeping the humidity level at an optimum level is an important factor.

#### *2.3.2 Type of atmosphere*

The type of atmosphere in which the electrospinning process takes place is very important for the smooth running of the process. Different gases have different behavior under the high electrostatic field. For example, helium decomposes under a high electrostatic field and therefore electrospinning is not possible [1]. For another example, with excessively volatile solvents the Taylor cone could dry out. To prevent evaporation in the cone, it is feasible to introduce a local stream of solvent-saturated gas around the cone [23]. The decrease in pressure in the environment adversely affects the electrospinning process [1].

#### *2.3.3 Pressure*

Pressure changes in the electrospinning process make it difficult to ensure the stability of the drafting process. The reduction in pressure surrounding the electrospinning jet adversely affects the electrospinning process. When the ambient pressure drops below atmospheric pressure, the polymer solution in the syringe will have a greater tendency to flow through the needle, resulting in an unstable spray start. As the pressure decreases, rapid solution foaming occurs at the needle tip. At very low pressure, electrospinning is not possible due to the direct discharge of electric charges [1].

#### **3. Herbal extracts used to obtain nanofibers by electrospinning method**

Reasons such as health problems, population density, environmental pollution, and increased consumption have encouraged people to seek natural solutions. The use of herbal products in the field of health for their healing properties is increasing day by day. In recent years, plants derived from natural substances such as flavonoids, terpenoids, steroids have received considerable attention due to their different pharmacological properties, including antibacterial, antioxidant, and anticancer activity.

The olive leaf plant, which draws attention with its biocompatible, biodegradable, antioxidant, and antimicrobial properties, has been used by many researchers [24–27] in the electrospinning process for use in the biomedical field. Similarly, because of its biocompatible, biodegradable and antimicrobial properties, and rosemary plant [28, 29] has been used as a bioactive packaging material and to obtain nanofibers by electrospinning for use in the biomedical field. Many plant extracts such as aloe vera [30, 31], thyme [10], grape seed [32], chamomile [33], green tea [34], grewia mollis [35], gotu kola [36], calendula [37], mangosteen [38], lavender [39] are mixed with different polymers and used in the production of nanofibers for use in the medical field.

#### **4. Application areas of nanofibers obtained from plant extracts by electrospinning method**

The fact that different plants grow in every geography, each plant has different and many effects and the ability to obtain biocompatible, sustainable, organic, and environmentally friendly products have encouraged researchers to work in this field. The use of plants obtained from natural sources as active agents is increasing day by day in areas such as wound healing, tissue engineering, and drug release.

#### **4.1 Wound healing**

The skin forms the largest part of body weight and is very vulnerable to external forces and effects such as tissue traumas and injuries. Today, wound dressings play a vital role in the healing of such wounds, and wound healing depends on several factors such as selection of wound dressing, physiological state of the wound, and degree of damage. An ideal wound dressing should facilitate wound healing, remove exudates from the wound bed, be non-toxic and allergenic, and act as a barrier against microbes [4, 30]. Conventional wound dressings are generally used to close the wound and absorb the excess discharge. Although in previous studies, it was stated that the dressing should keep the wound dry, it is known that a warm and moist environment on the wound increases the healing of the wound [40]. However, it is a fact that excessive moisture causes wetting and softening of the scar tissues and prolongs the wound healing process [4]. Keeping the humidity level at an optimum level is very important for wound treatment. In addition to the ideal moisture level of modern

#### *Production of Nanofibers from Plant Extracts by Electrospinning Method DOI: http://dx.doi.org/10.5772/intechopen.102614*

wound dressings, effective oxygen circulation, air permeability, and low bacterial contamination are the essential qualities sought [40].

Modern wound dressings are composed of water-absorbent granular hydrocolloids, alginate containing mannuronic and guluronic acids, and hydrogel, in which water-absorbing polymers are structured into a three-dimensional network [40]. In recent years, with the rapid development of tissue engineering, nanofiber-based ECM (extracellular matrix) scaffold structures have become widespread [4]. ECM is a collagenous substance commonly found in skin, tendons, cartilage, and bone [11]. Compared to other wound dressings, nanofiber wound dressings have advantages such as hemostasis, high porosity, good fluid absorption capacity, small pore sizes, and large surface area [4]. Hyaluronic acid, collagen, chitosan-based nanofibers are generally used in new generation nanofiber-containing bioactive wound dressings due to their biocompatible, biodegradable, and antibacterial properties [40]. Thus, it ensures the healing of the wound by releasing the active substance in the nanofiber structure onto the wound in a controlled manner.

In recent studies [24, 29, 41–43], herbal extracts seem to be helpful in fighting infection and accelerating the wound healing process. The use of herbal extracts as wound dressings can nourish the wound site with healing properties such as antimicrobial, anti-inflammatory, analgesic, and tissue regeneration [30]. The long-term toxicity and harmful side effects of herbal extracts are generally insignificant compared to synthetic drugs. The main disadvantage of herbal medicines is that they need to be used in higher dosages than synthetic medicines. Large amounts of herbal medicines extracted from plants reduce their solubility in water or other chemical solvents. Therefore, dissolution of plant extracts almost never occurs in polymer-carriers such as capsules, nanofiber mats, and casting films containing herbal medicines. This may cause adverse effects in applications such as drug release behavior. Despite these problems, herbal drugs promise great success compared to chemical drugs due to their superior performance in wound treatments [10]. The important point here is to extract the herbal extracts in a suitable solvent, to obtain a biocompatible polymer and a nanofibrous structure that preserves its existing effects such as anti-inflammatory and antibacterial and supports the repair of opened wounds.

#### **4.2 Tissue engineering**

Tissue engineering is a field that aims to heal damaged or diseased tissues/organs, to maintain, regenerate and develop the functions of normal tissues/organs, and to form tissue scaffolds with repair capability for this purpose. Electrospinning is an application with high potential in many tissue engineering fields such as vasculature, bone, neural, and tendon/ligament. With the electrospinning process, the ability to form aligned scaffolds for anisotropic mechanical and biological properties in the field of vascular grafts, as well as the ability to inhibit smooth muscle cell migration, is provided. In addition, possibilities have been presented to improve vascular grafts with tissue scaffolds that can be obtained by tissue engineering [5, 44].

Nanofibers in tissue engineering must have such as biocompatible, biodegradable (with an acceptable shelf life), tissue-appropriate degradation rate, tissueappropriate mechanical (strength, stiffness, and modulus) and structural (pore sizes, shape, and structure) properties, and sterilizability [45]. Tissues consist of multiple cell types and works in conjunction with the cell-surrounding extracellular matrix (ECM), which is the tissue scaffold, concealed by regular, micro-sized cells. The ECM is responsible for providing the cells with the needed mechanical support

and protecting the cells. The materials used in tissue engineering applications should allow a certain interaction with the cell, the cell's attachment, proliferation, change, ECM production, and proper progression of this process should be ensured. It should form a supporting function in the formation of new tissues [3, 44].

Approximately, 25% of current prescription drugs are derived from trees, medicinal plants, shrubs, and herbs in nature. The use of herbal extracts with nanofibers produced by electrospinning provides a good potential to form scaffolds for skin regeneration [46]. For example, it has been seen that the nanofibrous structure of the chamomile plant supports collagen fiber accumulation and tissue formation in the dermis [33], and the olive leaf plant has a good potential for tissue scaffolding in biomedical applications thanks to its high antioxidant effect [3]. There are studies on tissue scaffolds containing edible, non-toxic, biocompatible, biodegradable plant extracts with many different contents. It is thought that the applications of plantbased tissue scaffolds will increase in future studies.

#### **4.3 Drug delivery systems**

Drug delivery systems aim to deliver the drug to the unhealthy region in a controlled and regular manner and to ensure its effectiveness in this region. While drug delivery is generally associated with the delivery of therapeutic agents for the treatment of certain disease states such as cancer, the delivery systems for tissue engineering applications can also apply to the delivery of bioactive agents such as proteins and DNA [5].

In conventional drug delivery systems, successive doses of the drug cause a fluctuating profile of the drug concentration in the blood throughout the treatment period. Therefore, at certain times, concentrations may exceed the recommended maximum (Cmax) concentration with the risk of biotoxicity or fall below the minimum concentration (Cmin), limiting the therapeutic effect. To obtain the highest therapeutic value from the drug, the optimum concentration (C), (Cmin < C < Cmax) in body tissue should be maintained throughout the entire treatment period. Via controlled delivery techniques, the bioavailability of the drug has been designed throughout to be close to this optimum value. In addition, the amount of drug required to be administered is relatively lower in the controlled release mode, minimizing potential side effects [6].

In tissue engineering, the design of the polymer scaffold requires the release of growth factors and other bioactive substances into the growing tissue over a period of time. In nanofiber applications such as wound dressings or artificial leather, the local controlled release of antibiotic substances can aid the healing process. Polymer-based delivery systems can produce controlled drug release by diffusion or chemical bioerosion of the matrix or biodegradation of the linkages connecting the drug to the matrix [6]. These advantages are of great importance in their preference and use.

Polymer-based drug delivery systems; nano or microparticles, hydrogels, micelles, and fibrillar systems. Fibrillated systems form nanofiber-based drug release systems [3]. The release kinetics of the drug is controlled by the morphology of the polymer/ drug composite as well as the semi-crystalline structure of the polymer. First, the drug is dissolved at the molecular level in the polymer matrix. The drug is separated as crystalline or amorphous particles in the polymer matrix [6, 47].

The use of herbal-based nanofiber structures in drug delivery systems has increased in recent years. There are different applications such as designing coaxial nanofibers by using olive leaf extract as a bioactive agent [25], producing nanofiber membranes containing aloe vera [48], using nanofibers prepared using the bark of

Tecomella undulate (rohida) plant in in-vitro drug release [49]. It is expected that nanofiber drug delivery systems containing herbal extracts will increase therapeutic efficacy, reduce toxicity and ensure compatibility with patients by delivering drugs to the affected area at a controlled rate for a certain period.

#### **5. Conclusion**

Electrospinning is a nanofiber production method that is the most preferred because it is simple, economical, and environmentally friendly, and has many production parameters including solution, process, and environmental conditions. Production of nanofibers by electrospinning process; It is a subject that draws attention with its applications in many fields such as tissue engineering, drug release, filtration, automotive, energy, food industry, cosmetics, agriculture, biosensing. Although polymer contents with synthetic infrastructures are generally preferred in these applications, approaches to using natural agents with few side effects, biocompatible, sustainable, economical, biodegradable, and free from toxic components are increasing [10, 27, 33, 41, 42]. The use of natural components containing active agents in the production of nanofibers is becoming more and more common in the fight against potential health problems that may occur due to the rapidly increasing world population and environmental pollution. Herbal extracts are promising in electrospinning applications with their biodiversity, ability to maintain their biological functionality even after exposure to high electrical voltage, and wound healing effects against pathogenic microorganisms. In addition, it is thought that the use of herbal extracts in different applications in the field of health will become widespread, as they have fewer side effects, and versatile therapeutic properties compared to chemical agents.

### **Conflict of interest**

The authors declare no conflict of interest.

#### **Author details**

Nilşen Sünter Eroğlu Haliç University, İstanbul, Turkey

\*Address all correspondence to: nilseneroglu@halic.edu.tr

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 4**

## Biomass Electrospinning: Recycling Materials for Green Economy Applications

*Farai Dziike, Phylis Makurunje and Refilwe Matshitse*

#### **Abstract**

The development and advancement of electrospinning (ES) presents a unique material technology of the future achieved by fabricating novel nanofibrous materials with multifunctional physical (three-dimensional [3D] structure, nanoscalable sizes) and chemical characteristics (functional groups). Advancing the possibility of preparing various classes of novel organic and inorganic electrospun fiber composites with unique features such as polymer alloys, nanoparticles (NPs), active agents, and devices. This feature gives provision for internal access of the setup parameters such as polymer precursor material, polymer concentration, solvent, and the method of fiber collection that consequentially improves the intrinsic control of the construction mechanism of the final nanofibrous architecture. In synthetic electrospinning, the nanofibrous material processing allows for internal control of the electrospinning mechanism and foster chemical crosslinking to generate covalent connections between polymeric fibers. Comparing technologies according to materials of the future revealed that electrospinning supports the formation of micro-scale and in some cases nano-scale fibers while the formation of thin films is facilitated by the electrospraying system. Recent innovations point to various biomass waste streams that may be used as an alternative source of polymeric materials for application in electrospinning to produce materials for the future.

**Keywords:** electrospinning, biomass, nanofibrous, material mimicking, electrospraying, scaffold, nanostructures

#### **1. Introduction**

Electrospinning (ES), as a nanotechnology, exhibits strong evolution of materials used across a broad spectrum from bioactive (microorganisms-infused for biomedical applications) to manufacturing (adhesion, proliferation, and differentiation of the mimetic for mechanical, chemical and electrochemical applications) nanofibers [1]. The advent of bioeconomy and innovation technological development presented opportunities for remarkable progress in the expansion of methods and multiple applicability for the electrospun nanofibers. Waste biomass and other recyclable materials are also finding use in ES as an adaptable and sustainable innovative approach for making ultrathin fibers [2]. Valorization of biomass waste materials such as plant biomass, waste plastic, industrial effluent and other waste biomass streams have been processed through various technologies to produce a wide range of higher hierarchical recycled fibrous products. These including biodegradable bio plastic, filtration membranes, nanofibers as macro, micro and nanomaterials. Advancement in innovative ES techniques allows for intrinsic control of the physicochemical factors, including physical (morphology, diameter, orientation); surface (volumetric dispersion, porosity and thickness) and chemical (functional groups) characteristics of the final product [2].

Electrospinning method entails the utilization of voltage to create an electric field, polymer solution of specific concentration and electrospinning pump to introduce the spinneret onto collector plate. The resulting products are electrospun nanofibers characterized by their fibrous morphology, three-dimensional (3D) porous framework, nanoscale and chemical character that enable unique capabilities across multiple fields; which are difficult to create using conventional methods. Thermally induced phase separation nanofibers, and electrospun nanofiber scaffolds, for example, are being developed and are widely regarded as an emerging technology and a potential strategy for biosensing, drug delivery, soft tissue regeneration, hard tissue regeneration, and wound healing. The capacity to alter numerous control aspects of the functional scaffold, such as fiber geometrical features and alignment, architecture, and subsequent material performance, is the technique's most prominent feature [1]. More importantly, electrospinning allows for the creation of a wide range of novel materials, including polymer alloys, nanoparticles, and active agents.

Nanofiber preparation employing the ES method has proved to be a future-proof materials technology, with numerous appealing characteristics such as outstanding mechanical properties and large specific surface areas. Due to the versatility, utility, and simplicity of the ES technology, the fibers produced are particularly appealing for numerous applications from a simple process capable of producing diverse morphologies [3]. The use of metal organic frameworks (MOFs) due to its flexible and functionalized molecular structures, nanofibers composites were fabricated as a novel molecular system with highly engineered structures for tailored applications. The usage of MOFs/carbon nanofibers (CNFs) as good electrode materials in energy transformation and storage technologies that include supercapacitors, sensors, and electrocatalysts is one of the most basic applications [4].

Electrospinning for materials technology of the future have seen a wide range of innovations of the technology including home-made re-designing of the technology to improve the ES apparatus reproducibility. Thus hybrid electrospun structures on different types of polymers have been developed and optimized to create products for various applications [5]. This chapter explores electrospinning innovation technology and the materials of the future, their properties and characteristics and applications. The focus materials of the future will be products fabricated from recyclable waste biomass materials as a way of valorization for higher hierarchical bioeconomic products.

#### **2. Advances in electrospinning technology**

The ability to tailor structural and morphological aspects of electrospun materials, such as the surface topography of nanofibers, and their porosity that allows enhanced mimicking of the manufactured material matrix, has sparked interest in the ES technology. This is accomplished by the ability to modify the electrospinning

#### *Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

assembly in numerous ways in order to combine polymers with a wide range of materials (incorporate active materials such as drugs, inorganic catalysts, growth factors, functional groups and DNA/RNA as necessary in the various applications of the fabricated nanofibers [6]. **Figure 1** is a schematic diagram showing a simple set up of the electrospinning system.

Mokhtari et al. compared the technical assembly of the electrospraying and the electrospinning systems. This is because the two systems have different mechanisms of performing the fabrication of carbon materials they produce in unique distinct ways as shown in **Figure 2**. Electrospinning (**Figure 2a**) supports the formation of micro-scale and in some cases nano-scale fibers while the formation of thin films is facilitated by the electrospraying system (**Figure 2b**) aids in the formation of thin films [7]. As a result of insufficient polymer-chain entanglements in the polymer chains network, it was discovered that applying a high voltage below the minimum concentration causes electrospraying rather than electrospinning.

It was observed that varying the ratio of the polymer solution and the electrospinning potential difference results in the formation of unique materials ranging from beaded carbon deposits, heterogeneous fibers, uniform fibers, and entangled fibers [7]. Advanced efforts to improve electrospinning performance and the quality of the nanofibers while increasing cost-effective productivity of electrospinning and other nanofiber assembly technologies include integration of key concepts of conventional fiber production methods with nanotechnology. Electro-blowing, gas-jet/gas-assisted

**Figure 1.** *Schematic illustration of vertical electrospinning setup [6].*

**Figure 2.**

*(a) Schematic drawing of a typical electrospray setup. (b) Schematic drawing of a typical electrospinning setup.*

electrospinning, and solution blowing, which advanced from melt blowing, combined with electro-centrifugal processing, centrifugal spinning, near field electrospinning with dip-pen nanolithography, and XanoShear, which combines shearing with wet spinning, are among the merged electrospinning conceptual technologies [8].

A look into a study of electrospinning as a versatile technique for fibrous material manufacturing in advanced fabrication of the electrospun biopolymer-based biomaterials compared the conventional needle-based and an innovative needless-based electrospinning processes. **Figure 3** presents the unique feature of the needless-based ES process is that the polymer solution is positioned in a bath and a high voltage polarized spinning mandrill is immersed into the bath.

When the rotating mandrill comes into contact with the grounded collection electrode, it collects a thin layer of polymer solution, which is subsequently subjected to an electric field. The electrostatic forces of the field at the needle's tip, or the thin layer of polymer solution at the rotating mandrill, overcome the solution's surface tension, pushing it to form several or a single Taylor cone, as illustrated in **Figure 4**. On its way to the collector, the charged polymer jet from the cones is ejected and extended.

**Figure 3.**

*Electrospinning setups needle-based (left) and needleless (right) [2].*

*Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

**Figure 4.** *Needleless roller for electrospinning of polymer solutions.*

The solvent evaporates from the solution, weakening the continuous jet of pure polymer and depositing it in a fibrous form on the collector [2].

A needleless mechanism performs the electrospinning of the polymer solution from the surface of a revolving roller. The roller is partially immersed in a tank containing material to be electrospun, as shown in **Figure 4**. On the roller's surface, a layer of consistently new material is generated by a rotating roller. When compared to needle electrospinning, the technique produces a large number of Taylor cones on the roller's surface, resulting in the technology's industrial applicability in mass manufacture of nanofibers materials [9].

Complex fibrous nanostructures have been prepared through manipulation of many experimental parameters of a multifluid electrospinning process. This is an innovative shift from the traditional single-fluid blending electrospinning process. However, there are difficulties in using multifluid processes, such as compatibility concerns of set up parameters including fluids, rate of stock feed and average proportions, interfacial tensions, and electrospinning sustainability [10]. Mass production of nanofibers using electrospinning was determined through the development of the macromolecular ES principle. The molecular flow in the spinning process, as well as the molecular direction in nanofibers, can be tailored to advance the electronic, and physico-chemical properties of nanofibrous materials, which influence their applications, molecular orientation in nanofibers, and structural hierarchical significance [11]. Several recent methods were developed to manufacture nanofibers using macromolecular ES processes. For example, industrial yarn production processes were only applicable for solution electrospinning via the innovative conceptualized gas-assisted melt ES. (GAME) as shown in **Figure 5**.

The unique characteristic of the innovative technique is the observed occurrence that turbulent air applies a pulling force, subsequently leading to an increase in output and a 10% reduction in melt jet width, with an additional 20-fold thinning when the air jet temperature is increased [12].

Multi-temperature control electrospinning (MTCES) is a practical way to spin molten polymers on a submicron level fiber than the conventional molten/solution ES. The molten precursor polymer was treated to quad-heating regions in the proposed MTCES design: needle, nozzle, rotating area, and collector to augment and regulate fiber size and morphology. The nozzle, spinning thermal parameters and dimensions, electric field, and flow rate of the MTCES are all adjusted to change the fiber diameter [13]. The MTCES setup is depicted in **Figure 6**. The technical mechanism demonstrates that the jet propagation begins to bend significantly near the collector at 25°C, and at 80°C, a strong melt jet propagation increases the dwelling time of the jet in the rotary region, demonstrating a distinct multi-control ES scheme, which was characterized by extensive preliminary work and models that used the same or similar setup schemes.

Energy materials have been fabricated by ES techniques as an alternative to fossil fuels and environmental mitigation initiatives. The nanofibrous materials produced by ES are extensively used in electrochemical energy storage devices. This is because the materials have inherent excellent properties, including an increased surface area, high dimensional ratio, good flexibility, high permeability, with several functionalities. A shift from the conventional ES methods saw the development of innovative enhanced ES techniques that produce nanofibers with novel special hierarchical nanostructures [14].

The core-shell structure was chosen because of its distinctive features, which can help to improve the preferred properties. Co-electrospinning creates core-shell fibers by filling two distinct precursor solutions into the double nozzles, as shown in **Figure 7** [14].

*Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

**Figure 6.**

*The multi-temperature control electrospinning setup showing the multi-heating zone melt electrospinning [13].*

The simplicity of setup and low cost, together with the ability to fabricate nanofibers with a wide range of compositions and morphologies, has aided ES technology's innovative advancement. Electrospinning-created nanofibrous structures provide appealing extracellular matrix conditions for the fixing, migration, and variation of materials matrix, including those giving rise to hard structure regeneration. The creation of structural materials regenerating nanofibers has been utilized by ES technology developments, which include material simulating composite/hybrid configurations and surface functionalization such as mineralization [16].

A special trifluid electrospinning technology was also developed as an innovation to the co-electrospinning process. This advancement provided for complex multi-chamber nanostructures for designing novel functional nanomaterials. The complex structure consisted of a collective shell and two independent openings of a multi-chamber

nanostructure, with each having its own unique complex property, and these compartments form a total composite assembly within a region limited by nanofiber diameter. The sheath-separate-core fused nanostructure synchronized the functionalities of the three ES monolithic nanocomposites to afford a smart regulated release profile of a multi-chamber nanostructure, with each chamber characterized by distinct intrinsic complex property, and the structural compartments constituting a whole fused structure inside a section restricted by the diameter of nanofiber as shown in **Figure 8** [17].

Precision electrospinning, enabled by recent improvements in ES technology, is being envisioned as a viable option for fabricating 3D nanofibrous materials with a desired microstructure. Internal access to setup parameters such as solvent and fiber collecting method has increased intrinsic control of final nanofibrous architecture creation mechanism, as shown in **Figure 9** [18].

Plastic and other waste materials from industrial, domestic and agricultural activities, are the modern scourge on the face of the planet. The global call for re-use and recycle is gaining tremendous recognition with scientist scrambling for innovative ways of using waste materials in the circular economy. Waste biomass has been explored as an alternative source of polymers that may be used in wide range of ES processes targeting specific valorized products. As new materials use emerge and novel materials are electrospun into nanofibers, it is becoming increasingly critical to grasp current breakthroughs in biomass conversion into polymer sources for nanofibrous structures in order to fully exploit their potential. Advancements in waste

#### **Figure 8.**

*Designs of the complex spinneret for implementing trifluid electrospinning: (a) a digital image showing a full view of the spinneret; (b) front view; (c) side view; and (d) a diagram about the organization of a structural outlet from three inlets [17].*

*Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

**Figure 9.**

*Setup used to form 3D nanofibrous scaffold using a negatively charged electrode or negative ion generator [18].*

biomass conversion technologies such as bio digestion, pyrolysis of plastic, and waste agricultural plant biomass wastes into bio oils and other polymers have preceded this.

#### **3. Waste biomass feedstock for electrospinning nanofibers**

Biomass is organic substances that is renewable and comprises plants and animals matter and may be combusted for heat or treated into renewable polymeric materials or fuels using a range of technologies. Most of the biomass end up as environmental waste materials that contaminate the land, rivers and oceans. Waste biomass include waste plant materials from crops, animal waste (dung and sewage), industrial waste in the form of effluent coming from industries such as petrochemical, food processing, textile dye effluent, pharmaceutical, and solid waste biomass including plastics, plant residues, (bagasse and other dregs), timber offcuts and sawdust, pulp and paper processing waste etc. These various biomass waste streams may be used as an alternative source of polymeric materials that may be used in electrospinning to produce materials for the future. Three classes of the waste biomass will be discussed namely synthetic waste biomass, natural flora waste biomass and natural fauna-based waste biomass.

#### **3.1 Synthetic waste biomass**

Plastic is the largest solid waste biomass on the face of the earth's surface while textile and pharmaceutical effluent are major synthetic liquid waste biomass. Unless great strides are made to valorize these waste streams and find hierarchical bioeconomic applications of these materials, they will persist in the environment as contaminants. Due to its tunable features, including wettability, surface charge, transparency, elasticity, porosity, and surface to volume proportion, various polymeric fibrous nano materials have been developed as simulated extracellular matrix. Using ES nanofibers of natural polymers (NPs) and synthetic polymers (SPs) as simulated extracellular matrix for tissue regeneration, a comprehensive investigation identified five basic kinds of nanofibrous polymers. NP–NP composites, NP–SP composites, SP–SP composites, cross-linked, and modified polymers with mineral materials are

some of the polymers available [19]. Polycaprolactone (PCL), polylactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA), and polyethylene terephthalate (PET) are some of prevalent well-known synthetic polymers [20, 21].

In recent years, a variety of processing technologies have been utilized in the manufacture of polymeric fibrous nano materials, including drawing, 3D printing, template synthesis, phase separation, self-assembly, ES, and so on. Synthetic ES nanofibrous materials processing allows for internal control of the electrospinning mechanism and foster chemical crosslinking to generate covalent connections between polymeric fibers. In either in situ electrospinning or post-spinning crosslinking, this manipulation is done to target qualities of the material of application in which the fibers will be used. Highly porous electrospun nanofibrous membranes, for example, have sparked a lot of interest in water filtering applications. **Figure 10** presents some of the common synthetic biomass materials used in ES of nanofibers. The creation of a reduced pore size and its distribution is highly favored by a thicker membrane with a lower mean fiber diameter, albeit the influence of membrane thickness is rather restricted. A high flux microfiltration (MF) sheath was fabricated based on efficient control of the total composite structure containing the electrospun layer thickness of 200 ± 10 m and a mean fiber diameter of 100 ± 20 nm [22].

A previous study looked at the spinnibility of various polymers, such as aqueous poly(ethylene oxide) (PEO) dispersed in alcohol-to-water mixtures. Fiber production was found to be possible with viscosities ranging from 1 to 20 poises and superficial tensions

**Figure 10.**

*Synthetic polymers used in electrospinning of nanofibrous materials.*

*Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

of 35−55 dynes/cm. Electrospinning, however, was not feasible at viscosities more than 20 poises due to flow instability produced by the solution's high cohesiveness [23].

#### *3.1.1 Natural flora waste biomass for electrospinning: material technology of the future*

Spongy pomelo peels, rice husk, rice straw, sugar cane bagasse, coffee beans, coconut shells, and peanut shells have all been investigated as alternative sources of carbonaceous materials from biomass. In comparison to other carbonaceous precursors, these and other natural plant/floral biomass resources have grown increasingly appealing due to their availability, low cost, easy accessibility, and environmental friendliness. As a result, floral biomass has gotten a lot of attention in the electrospinning, biomedical, and energy storage fields [24]. Okara, soy pulp, or tofu dregs, for example, is a pulp made up of insoluble components of the soybean that remain after pureed soybeans are filtered for soy milk and tofu manufacture. Recent reviews have reported on the feasibility of ES fibrous nano materials made from a variety of decomposable and biocompatible matter, including natural proteins like floral and faunal collagen, gelatin, silk, chitosan, and alginate [25].

The preparation of the waste floral/plant biomass for ES of nanofibrous materials involves a number of steps that extract plant proteins in the insoluble parts of the waste biomass. Silk fibroin (SF), for example, is made by degumming raw silk fibers twice with a 0.5% (W/W) NaHCO3 base medium at 100°C, over half an hour period followed by

#### **Figure 11.**

*SEM micrographs of electrospun SF nanofibers with concentration of (a) 3%, (b) 6%, (c) 9%, and (d) 12% [26].*

rinsing with warm dH2O. At 70°C for 6 h, degummed silk (SF) is dispersed in a ternary aqueous medium of calcium chloride-ethanol-water (1:2:8 in molar ratio). The SF was filtered and lyophilized after 3 days of dialysis using cellulose hollow sheath (250-7u; Sigma) in dH2O to get the regenerated SF sponges. Dispersing the SF sponges in 98% methanoic acid (Aldrich) for 3 h makes SF solutions. The molar quantities of SF solutions for electrospinning range from 3% to 15% by weight [26].

Extracted silk fibroin was used to prepare silk electrospinning as presented in **Figure 11**. Electrospun SF nanofibers with varied silicon fibroin concentrations of 3%, 6%, 9%, and 12% are shown in SEM micrographs. The most prevalent natural polymers used as ES nanofiber materials include chitosan, collagen, gelatin and silk [20, 21]. Natural polymer nanofibers present distinguished features like biodegradability and biocompatibility, a phenomenon that makes them suitable materials in biological environments. **Figure 12** presents some of the abundant natural polymers adapted for ES nanofibers production. Chitin and its over 50% deacetylated derivative, chitosan, for example, are commonly used natural polysaccharides as scaffolds. Blending with other materials are thus required to tailor-make materials with a set of acceptable features and attributes in order to achieve a stronger composite. Chitin/silk fibroin (chitin/SF) nanofibers, for example, were used to make novel ECM scaffolds [27].

**Figure 12.**

*Natural polymers used in electrospinning of nanofibrous materials.*

#### *Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

Biocompatibility and biological activity are two characteristics of natural polymers. However, these polymers have some drawbacks, such as engineering and processing difficulties due to poor mechanical strength, restricted processing and manufacturing capacities, batch-to-batch variability, and the possibility of pathogen transmission [20]. Collagen and proteoglycans, for example, make up the majority of the body's natural extracellular matrices (ECMs), which vary in composition depending on tissue type. Nanofibrous scaffolds made of collagen fused with glycosaminoglycans (GAGs), the major constituent of proteoglycans like condroitin sulfates and hyaluronic acid, are suitable for creating a perfect scaffold that mimics the natural ECM. Collagen and GAGs' utility, on the other hand, has been limited because of their exorbitant price and poor mechanical qualities. In biomedical applications, this phenomenon can be addressed by fusing natural polymers such as proteins polymeric strands and polysaccharides fibrous materials, which can improve biotic transformation of cells and accelerate tissue development [27].

Most of the insoluble floral biomass is in the form of lignocellulosic and chitin material. The success of tapping into the floral biomass as a resource for ES of nanofibrous material depends on the ability to depolymerize the lignin and chitin long polymer chains. It is these polymers that will be used for ES processes to produce electrospun nanofibers. Recently, there has been renewed interest in producing carbon fibers from sustainable cellulosic precursors [28]. The abundance and cost effectiveness of cellulose as a material generator, as well as the relatively ecologically friendly fiber production methods used preceded this interest. Recent research on regenerated cellulose fibers from a fluid crystalline fabrication route as a carbon fiber precursor generated strands with a modulus of 140 GPa for the shell area and 40 GPa for the core area, indicating that CNFs resulting from nano-sized cellulosic precursors are even more competent as physical reinforcement than micron-sized fibers; because of their reduced diameters, providing a greater surface area for bonding and stress transfer [29].

#### *3.1.2 Natural fauna waste biomass for electrospinning: material technology of the future*

Animal manure, agricultural residues, organic portion of municipal solid garbage, industrial waste biomass, and natural vegetation cycle waste are all examples of enormous amounts of organic waste produced by many sectors. Similarly, fauna waste biomass, primarily in the form of keratin, a durable, fibrous protein found in advanced vertebrates (mammals, birds, and reptiles) and human epithelial cells, has been widely employed in ES for the creation of nanofibrous materials. Millions of tons of keratincontaining biomass are produced by the food business, particularly the meat market, slaughterhouses, and wool manufacturers. These sectors are rapidly expanding, with the United States, Brazil, and China accounting for more than 40 million tons of faunabased biomass annually [30]. Inadequate management of these organic wastes can harm the environment by polluting water and air, lowering people's quality of life [31].

If controlled with scientific interventions, organic waste no longer persists as garbage, but instead becomes a rich source of substrate, polymers, and molecules for the production of a variety of value ES nanofibrous products [32]. Detailed studies explored potential applications of the fauna generated organic waste in the production of biogas for energy production. Human waste is disposed of as sewage in the form of biological wastewater. Technological advances unravelled biological wastewater treatment plants (WWTP) as an approach to converting biomass into rich materials for precursor molecules for polymerization in ES nanofibrous material fabrication or for energy production [33]. Fauna waste biomass in the form of dung (**Figure 13**), piggery or fowl wastewater treatment with purple phototrophic bacteria was explored as a promising platform for electrospinning biomass resource recovery process under optimized operational conditions [34].

**Figure 13.** *Fauna biomass: cow dung is co-digested with sewage for production of gas in an anaerobic bio digester.*

**Figure 14.** *Sewage treatment plant for gas production.*

#### *Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

It is important to note that fauna waste biomass is a natural phenomenal bio digestive process of converting lignocellulosic and chitin organic biomass and transform it into shorter chains of polysaccharides and other polymeric substrates for ES nanofibrous materials production. Anaerobic bio digestion followed by catalytic polymerization of biogas molecules such as methane, ethane and propane, will produce tailor-made polymeric materials that may be used in electrospinning production of carbon nanofibrous materials. **Figure 14** is an advanced industrial scale bio digestion plant for production of biogas.

Bio digestion of fauna waste biomass is a significant alternative supply of materials for electrospinning of nanofibrous materials when modern methods are used. Previous research on bio digestion of fauna waste biomass for methane production found that the influence of pre-treatment results in a substantial increase in gas production of up to 67%, with a 52% methane content in the biogas. As a result, it was determined that pretreatment of both feed and biomass improves biogas output but not methane content [35]. According to recent studies, the valorization of bio or organic waste is being prioritized in order to tackle the rapid accumulation of waste generated from food production activities, as well as to create sustainable feedstock for industrial materials and chemicals in place of fossils and synthetic materials (see Section 3.1). Biogas, compost, and small platform molecules are currently produced from biowaste via anaerobic bio digestion, fermentation, and thermo-chemical methods as shown in **Figure 15**. There are currently no commercial low-temperature chemical methods for valorizing organic lignin fractions as feedstock for modified compounds. Thus, research has been conducted to fill this technological gap, demonstrating that moderate thermal hydrolysis of municipal bio-waste manure reserve is a safe, environmentally sustainable, and affordable process for transforming lignin-like material from compost into value-added specialty chemicals for the production of ES nanofibrous materials (**Figure 15**) [37].

Biomass is a readily available and long-lasting ES material that may be turned into carbon based smart energy storage device and other uses. For carbon nanofiber manufacture, many strategies were used to meet various goals, including an increased productivity, easy dimensional parameters manipulation, energy efficient, and a high turnover. Nonetheless, several critical features of biomass-based fibrous carbon nano materials

#### **Figure 15.** *Auger/screw pyrolysis reactor concept using heat carrier [36].*

**Figure 16.** *An α-helix and β-pleated sheet keratin and the molecular structure [40].*

are yet to be extensively studied, thus information gaps still exist for each process to be supplied. As a result, more research is needed to expand our knowledge of the essential characteristics of various processes in order to generate highly desirable precursor materials for ES fibrous carbon nano materials manufacture from organic matter for sustainable materials manufacturing and energy smart storage applications [38].

An example of fauna waste biomass material rich in extractable materials for ES nanofibers materials is feathers from the poultry industry. Chicken feathers, comprises 90% raw keratin protein and 70% amino acids, can be employed as one of the primary sources for extracting keratin. Keratin is used in a variety of industries, including biotechnology, waste management, cosmetics, and medicine [39]. Waste feathers can be converted into keratin in a cost-effective and environmentally beneficial manner. Keratin is an insoluble protein of the cytoskeletal element with a size of 8–10 nm that belongs to a group known as intermediate filaments (IFs). Keratin is a fibrous protein with a helical structure, as seen in **Figure 16**, and is the ecosystem's third most prevalent natural biomass polymer after chitin and cellulose [41].

#### **4. Innovative waste biomass-sourced electrospun products**

Electrospun fibers fabricated from waste biomass sources has resulted in manufacturability of bioactive electrospun nanofibers and has been reported as potential drug delivery agents [42], wound dressing with antibacterial activity, filtration, cosmetics, protective clothing, electrical applications [43] catalysis [44], food industry [44], facial mask [45], and smart energy storage devices, such as supercapacitors as illustrated in **Figure 17**.

Natural biopolymer electrospun products are made up of ultrafine fibers that are reusable, nontoxic, biocompatible, biodegradable and antibacterial properties. The fibers have been reported to possess excellent physical and chemical characteristics such as high degrees of crystallinity, aspect ratio, large specific surface area, number of surface hydroxyl groups, thermal resistance and excellent mechanical properties [45, 46]. However, the substantial chemical and energy consumption associated with the isolation of macro-sized fibers to nano-sized fibers creates manufacturing hurdles for waste bioactive electrospun nanofibers [46]. As a result, findings on waste bioactive electrospun nanofibers are still in their infancy in the literature [46].

*Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

#### **Figure 17.**

*Applications of nanofibers in different fields for day to day activities.*

#### **4.1 Biomedical product**

In the biomedical field, literature reports on manufactured products made from biomass electrospun fibers range from medication delivery agents to biomaterials [42], wound dressing with antibacterial activity, facial mask [45], and tissue regenerative biomedical applications as presented in **Figure 18**.

The ultrafine fibers have been previously reported to result in high-performance filters and applicability in facial masks [45, 47]. Various ultrafine fiber filters have been created that can filter particles larger than 10 nm with excellent efficiency. Spider-web network filters are described in the literature as having a combination of extremely efficient, long-range electrostatic property, low air resistance, and great transparency [45, 47]. Viruses can be blocked by ultrafine fiber filters [47]. Irrespective of the challenges associated with the fabrication of bioactive electrospun fibers products. The choice of polymer used aid in fabricating fibers with antimicrobial activities [45].

**Figure 19a** presents a typical electrospinning technology. Choice of polymer, concentration, flow rate, needle, and tip-to-collector distance all affect fiber quality. **Figure 19b** shows various types of electrospun fibers. The structure of a hybrid filter that works as both a filter and a hydrophobic layer is shown in **Figure 19c** and **d**.

Facial masks constructed from electrospun biomass possess key characteristic performance features that has the potential to outcompete with the masks in the market. Advantages of biomass electrospun masks vary from the transparent, reusability, antiviral, degradable smart masks that possess filtration, thermal stability, and water resistance [45]. The facial mask technique has a wide range of possible uses, including filtration systems in water treatment, protective garments, and cosmetics [45].

#### **Figure 19.**

*(a) Scheme of electrospinning technology. (b) Various SEM images of electrospun nanofibers. (c) Scheme of generally utilized masks. (d) The proposed structure of electrospun ultrafine fibrous masks.*

As a result of the structure and bioactivity of loaded pharmaceuticals remaining unaltered during the spinning process, electrospun drug-delivery agents drew interest. They also reduced in vitro drug burst release and can contain a range of biomolecules [48]. Drug delivery agents fabricated from all forms of cellulose polymer results in drug delivery systems that are hydrophilic, eco-friendly, bio-degradable, and biocompatible [42].

#### **4.2 Renewable energy products**

Incorporation of NPs, natural biomass onto the polymer through the electrostatic interaction between their functional groups has a stabilizing effect on NPs [44, 49]. These electrospun catalyst found application in catalysis, supercapacitors, corrosion inhibition, and within the food industry natural polymers [44, 49].

Carbon-based supercapacitors with a large interactive surface and high permeability have sparked interest in natural floral and faunal waste materials, owing to the growing ecological consciousness. Electrospun cellulose-based supercapacitors are still in the laboratory stage, despite their rich carbon abundance of roughly 44%, great stability, and exceptional permeability linked with its hierarchical conformation and exceedingly efficient rigid lateral chains in cellulose [49]. The energy density of cellulose-based supercapacitors is low [49]. Hence the poor electrical performance and cell voltage. Another limitation is time consumption associated with economic factor in the optimization stage of cellulose electrospun mats.

As an alternate technique for increasing the electrochemical properties of lignin/ cellulose nanofiber electrodes, creating compound electrode materials with a lignin/ cellulose backbone can be used to address these constraints [49, 50]. Literature presented flexibility, wide surface area, outstanding mechanical flexibility, and particularly good electrical conductivity, composite nanofibers and ES activated carbon fiber network (ACFN) as attributes to improved performance. When employed as supercapacitor electrodes, they have a high electrical performance, a phenomenon attributed to their pseudo-capacitance [51, 52]. As a result, ACFNs lignin/cellulose nanofiber composites could be an attractive electrode material for biomass-based flexible supercapacitors [49]. Furthermore, when the electrolyte penetrates the micropores of the electrospun mats, as shown in **Figure 20**, the characteristics of the electrospun biomass composites can be adjusted, allowing for the wettability feasible with the preferred electrolyte [53].

#### **Figure 20.**

*Supercapacitive cell with thin film-coated carbon powder-based electrodes and free-standing and flexible flexible carbon nanofiber electrodes in conjunction with a polymer electrolyte [50].*

In aqueous electrolytes, heteroatoms have been reported to enhance wettability of carbonaceous surfaces [54]. Lignin has a lot of oxygen functional groups and a lot of active hydrophilic surface. However, biomass-derived ECNF p-doped performed worse relative to the commercial CF. The lower performance could be attributable to the starting material's higher number of oxygen functional groups. P-doping has been reported to block micro/mesopores, reduce conductivity and electron transport [50]. Jet viscosity of the polymer was not measured, as such further research still has to be done.

As a result, environmentally friendly biomass electrospun fibers with improved performance in working electrochemical devices have demonstrated that the fabrication of future smart energy storage materials will be ecologically viable, providing a completely green alternative to the powering of transportation and conventional storage [50].

#### **4.3 Electrical products**

The versatility of waste biomass electrospun fibers, as well as their controllable physical and chemical properties, make them a model technique for electrode fabricating and flow media for a variable of smart energy devices, with the ability to reduce mass transport and activate overpotentials, thereby increasing competence [50]. Natural biomass is being used as a polymer of choice because of its capacity to infuse sustainable principles in electrochemical device materials. This also contributes to their capacity to increase the use of renewable electricity through their application [50]. Lignin is a waste by-product derived from natural flora that has been documented to exist in three different types: Different molecular weights and mechanical and thermal stabilities of kraft (KL), ethanol organosolvents (EOL), and phosphoric acid lignin (PL) [50]. For vanadium redox couples, electrospun carbon nanofibers produced from PL and KL at 9 kV demonstrated excellent cyclic voltammetry electrochemical performance. **Figure 20** clearly illustrates potential electrical products that can be fabricated from waste biomass electrospun fibers. Redox flow batteries (RFBs), fuel cells, and metal air batteries are some of the potential products shown in **Figure 20** [50]. The use of electrospun material in RFBs is still in its infancy and requires further development. Nonetheless, the improved redox couple's catalytic activity of waste biomass electrospun fibers provides an alternate solution to commercial electrodes' high overpotential when discharge current density is large [50].

Electrospun fibers made from waste biomass have the potential to be used in redox flow batteries because they form microstructures with large surface areas and mass transport qualities in the electrodes. Similarly, improved biomass electrospun fiber applicability in fuel cells and metal air batteries offers a conductive-advanced structure for the gas diffusion layers that can dope and/or support catalytic nanoparticles, as well as electrochemically active fibers [50].

#### **5. Conclusion and future works**

The advancement of electrospinning (ES) technologies and the industrial production of ES fibrous carbon nano materials to suit or facilitate different bioeconomic uses was aided by technical innovation. It may be inferred that the capacity to change the electrospinning assembly in various ways, in order to combine different materials with a wide variety of properties as well as incorporate active elements, will have a substantial impact on the production of materials in the future. By combining essential

#### *Biomass Electrospinning: Recycling Materials for Green Economy Applications DOI: http://dx.doi.org/10.5772/intechopen.103096*

concepts from traditional fiber manufacturing techniques with nanotechnology, the performance of electrospinning technology and the quality of nanofibers can be increased. In comparison to other carbonaceous precursors, natural flora and fauna waste biomass for future electrospinning material technology has become increasingly appealing due to its abundance, low cost, easy accessibility, and environmental friendliness. Most of the insoluble floral biomass is in the form of lignocellulosic and chitin material while the soluble biomass is in the form of proteins and polysaccharides. Fauna waste biomass is mainly in the form of keratin. Millions of tons of keratin biomass are produced by industry, particularly the meat market, slaughterhouses, and wool manufacturers. The determination of marketable low thermal chemical procedures to valorize bio and organic waste lignin fractions as feedstock for commercial chemicals will be the focus of future work aimed at advancing electrospinning materials.

#### **Author details**

Farai Dziike1 \*, Phylis Makurunje2 and Refilwe Matshitse3

1 Technology Transfer and Innovation Directorate, Durban University of Technology, Durban, South Africa

2 Nuclear Futures Institute, Bangor University, Gwynedd, Wales, United Kingdom

3 Department of Chemistry, Rhodes University, Grahamstown, South Africa

\*Address all correspondence to: faraid1@dut.ac.za

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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### Section 2
