**5.1. Biomedical applications**

by 104 and 46%, respectively as compared to electrospun pure polyurethane membranes. The tangent moduli of as-prepared and ester functionalized SWNT-PU membranes were also

**Figure 10.** (a) TEM images of MWNTs/PU nanofibers and multi-wall carbon nanotube (MWCNT) [94]. (b) Schematic

Liu and Pan [95] produced MWNTs/PU composite nanofibrous membranes (**Figure 10b**). They used a thermal treatment method to improve the comprehensive properties of the membranes. They reported that the proposed thermal treatment method effectively improved the conductivity and mechanical properties of the nanomaterials, with 3 wt% of MWNTs, the conductivity of the membranes reached 8.29 × 10−5 Scm−1, which was nearly three orders higher than that of the untreated sample and the tensile strength and the modulus increased more than 50% after thermal treatment. PU and PU/multi-walled carbon nanotube (MWCNT) nanocomposite nanofibers, both with diameters of 350 nm, were prepared by Kimmer et al. as well [40]. The appearance of smaller nanowebs in PU/MWCNT nanofiber structures with diameters of 20–40 nm was observed. They attributed the existence of these structures to the occurrence of strong secondary electric fields, which were created between individual conducting MWCNTs (distributed in the PU/MWCNT nanocomposites). From the TEM images individual and very well aligned MWCNTs can be seen in the outer surface of the main nanofiber from which nanoweb fiber was created. However, the authors did not investigate the

Cross-linking the nanofibrous mats is another way to improve the mechanical properties. Theron et al. [65] modified a medical standard TPU (Pellethane 80A) with latent cross-linkable groups; and they determined the effect of subsequent cross-linking on viscoelastic properties and degradation resistance. They confirmed the successful cross-linking by insolubility of the materials. Pellethane was cross-linked with containing an increasing number of pentenoyl groups. Cross-linking decreased (up to 42%, p < 0.01) the hysteresis and creep (44%, p < 0.05), and significantly improved the degradation resistance in vitro. Modified Pellethane was also electrospun into tubular grafts and with UV irradiation they were cross-linked to make them insoluble. Prototype grafts had a burst pressure of >550 mmHg, and for uncross-linked and cross-linked samples, it was 12.1 ± 0.8 and 6.2 ± 0.3%/100 mmHg, respectively. They concluded that the modification of Pellethane with PCL occurred on the carbamate nitrogen and cross-linking resulted in improved viscoelastic properties. Although there were some

higher than the control PU membranes and were 215 and 250%, respectively.

diagrams of single-wall carbon nanotube (SWCNT) [95].

34 Aspects of Polyurethanes

mechanical properties of the prepared electrospun fiber mats.

The importance of electrospinning, in general, for biomedical applications like wound dressing, drug release, tissue engineering, medical implants etc. is emphasized in this part of the chapter. The focus is on the active substances combined with PU and blends of PU that have been electrospun and also on the modifications that have been carried out in conventional electrospinning apparatus.

PUs, due to their structure/property diversity, are considered one of the most bio- and bloodcompatible materials known today. Properties like durability, fatigue resistance in tensile, compression or shear, elasticity, compliance, "elastomer character," and propensity for healing became attainable via PU. Furthermore, modification via hydrophilic/hydrophobic balance or by attachments of biologically active species to the PUs is possible [37].

Due to their higher surface area to volume ratio, nanofiber mats have been studied for applications as drug delivery carriers. The blending (or mixing) technique is a common choice for the nanofiber functionalization [9]. Verreck et al. [96] prepared PU nanofibers containing model drug itraconazole and ketanserin, using DMF and dimethylacetamide (DMAc) as solvent, respectively. The collected non-woven fabrics released the drugs at various rates and profiles based on the nanofiber morphology and drug content. They used a specially designed release apparatus based around a rotating cylinder for release studies. They loaded 10% ketanserin and 10 and 40% itraconazole to the PU nanofibers. At low drug loading, itraconazole was released from the nanofibers as a linear function of the square root of time. They did not observe initial burst release. They explained the faster initial release of ketanserin versus itraconazole with (1) higher drug solubility of the ketanserin in the polymer and (2) increased drug diffusivity in the polymer. They also observed that the obtained fiber diameters did not significantly influence the initial release rate. Fiber diameters for the ketanserin loaded samples were between 0.5 and 2 μm, 10% itraconazole loaded were 2 μm and 40% loaded samples were 0.3–0.7 μm. They observed a biphasic release pattern for ketanserin in which two sequential linear components. The authors correlated these release phases temporally with (1) drug diffusion through the polymer and (2) drug diffusion through formed aqueous pores.

Akduman et al. [99] prepared nanofiber mats of TPU containing naproxen (NAP) from 8 to 10% (w/w) TPU/DMF solutions. The amount of NAP in the solutions was 10 and 20% based on the weight of TPU and the collection periods were changed to 5, 10, and 20 h. The diameters of the nanofibers were significantly affected by the TPU concentration; however, the NAP loading and percentage of NAP did not have a significant effect on the fiber diameters. They investigated the release characteristics of fiber mats by the total immersion method in the phosphate buffer solution at 37°C and performed the characterization of the produced NAP-loaded TPU mats. They observed that the diffusion paths correlated to the nanofiber collection period has a significant effect on the release characteristics of the drug. Short collection periods resulted burst release of the drug. Beside, higher drug loading (20% w/wpolymer) caused higher drug release rate. The drug that had previously leached from the nanofiber mat formed channels through the matrix and that these channels lead to higher release rates of the drug. As a result, the authors suggested that in drug-loaded electrospinning studies, the produced mats should be collected for at least 20 h for a one needle electrospinning system, and drug loading should not exceed 10% for better controlled release rates (**Figure 11**).

Polymeric nanofiber matrix has similar structure with the nano-scaled non-woven fibrous extra cellular matrix (ECM) proteins, thus it can be considered as potential candidate for ECMmimetic material [115]. A successful tissue engineering nanofibrous material should allow cell attachment and proliferation. Most of the surface modifications are related to the biocompatibilities of polymeric tissue engineering scaffold and to the immobilizations of biomolecules that can be specifically recognized by cells on the biomaterials [9]. In the study of Unnithan et al. [43] prepared an antibacterial electrospun scaffold by electrospinning of a solution composed of dextran, polyurethane (PU), and ciprofloxacin HCl (CipHCl) drug. They used dextran, which is a versatile biomacromolecule. Dextran can be used by blending with either water-soluble bioactive agents or hydrophobic biodegradable polymers for biomedical applications for preparing electrospun nanofibrous membranes. They investigated the interaction

**Figure 11.** (a) Percentage release of NAP from (■) 5 h collected-, (●) 10 h collected-, and (▲) 20 h collected 10TPU/ NAP10 mats by the total immersion technique during (b) SEM image of a NAP-loaded TPU nanofibers [99].

parameters between fibroblasts and the PU-dextran and PU-dextran-drug scaffolds such as viability, proliferation, and attachment. Their results indicated that the cells interacted favorably with the scaffolds especially the drug containing one. The authors concluded that the introduced scaffold might be an ideal biomaterial for wound dressing applications.

two sequential linear components. The authors correlated these release phases temporally with (1) drug diffusion through the polymer and (2) drug diffusion through formed aqueous

Akduman et al. [99] prepared nanofiber mats of TPU containing naproxen (NAP) from 8 to 10% (w/w) TPU/DMF solutions. The amount of NAP in the solutions was 10 and 20% based on the weight of TPU and the collection periods were changed to 5, 10, and 20 h. The diameters of the nanofibers were significantly affected by the TPU concentration; however, the NAP loading and percentage of NAP did not have a significant effect on the fiber diameters. They investigated the release characteristics of fiber mats by the total immersion method in the phosphate buffer solution at 37°C and performed the characterization of the produced NAP-loaded TPU mats. They observed that the diffusion paths correlated to the nanofiber collection period has a significant effect on the release characteristics of the drug. Short collection periods resulted burst release of the drug. Beside, higher drug loading (20% w/wpolymer) caused higher drug release rate. The drug that had previously leached from the nanofiber mat formed channels through the matrix and that these channels lead to higher release rates of the drug. As a result, the authors suggested that in drug-loaded electrospinning studies, the produced mats should be collected for at least 20 h for a one needle electrospinning system, and drug loading should not exceed 10% for better controlled release rates (**Figure 11**).

Polymeric nanofiber matrix has similar structure with the nano-scaled non-woven fibrous extra cellular matrix (ECM) proteins, thus it can be considered as potential candidate for ECMmimetic material [115]. A successful tissue engineering nanofibrous material should allow cell attachment and proliferation. Most of the surface modifications are related to the biocompatibilities of polymeric tissue engineering scaffold and to the immobilizations of biomolecules that can be specifically recognized by cells on the biomaterials [9]. In the study of Unnithan et al. [43] prepared an antibacterial electrospun scaffold by electrospinning of a solution composed of dextran, polyurethane (PU), and ciprofloxacin HCl (CipHCl) drug. They used dextran, which is a versatile biomacromolecule. Dextran can be used by blending with either water-soluble bioactive agents or hydrophobic biodegradable polymers for biomedical applications for preparing electrospun nanofibrous membranes. They investigated the interaction

**Figure 11.** (a) Percentage release of NAP from (■) 5 h collected-, (●) 10 h collected-, and (▲) 20 h collected 10TPU/

NAP10 mats by the total immersion technique during (b) SEM image of a NAP-loaded TPU nanofibers [99].

pores.

36 Aspects of Polyurethanes

Amoroso et al. [116] utilized two fabrication modalities to induce controlled alterations in fiber network topology. They investigated the variation of collecting mandrel translation velocity, and concurrent electrospraying of cell culture medium with or without cells or rigid particulates to emulate the maximum possible micro-inclusion stiffness. Once, they electrospun poly(ester urethane) urea (PEUU) without modifications to the process, then electrospun it "wet" by concurrently electrospraying cell culture medium onto the target. The authors studied the effect of cell and particulate inclusion into the fiber scaffold matrix. Authors used either vascular smooth muscle cells or polystyrene microspheres. They electrosprayed the cells at concentrations of 2 and 6 million/mL and electrosprayed the microspheres at 7 million/mL into the cell culture medium. The inclusion of cell culture medium into the construct resulted in a dramatic change in scaffold microarchitecture. Particulates and cells would act as additional fiber bonding sites, increasing the effective fiber intersection density and consequently raising the level of mechanical anisotropy. Practically, wet processing and mandrel rastering can be successfully implemented as tools to reliably modify scaffold microarchitecture without altering fiber alignment.

In the study of Carlberg et al. [117], electrospun fibrous PU scaffolds have been studied as substrate for embryonic stem cells cultivation and neuronal differentiation. The authors prepared electrospun scaffolds composed of biocompatible PU resin (Desmopan 9370A) with a vertical electrospinning setup. They showed that the embryonic stem cells displayed favorable interaction with the substrate, spreading outgrowths, establishing connections to adjacent cells and attaching to individual fibers. Immunocytochemistry results showed that fibers can support neuronal differentiation in embryonic stem cell cultures. Their results indicated that physical cues induced by the fibrous scaffolds affect stem cells toward a neuronal cell fate. Hence, they claimed that these scaffolds are potential cell carriers in neural tissue engineering repair and rehabilitation of the adult human nervous system.

Grasl et al. [118] in vitro studied the mechanical homogeneity of electrospun small diameter polyurethane grafts as well as spontaneous attachment, proliferation, and adhesion molecule expression of endothelial cells. They prepared the prostheses from 5% (w/w) PU (Pellethane 2363-80A; DOW Plastics) in 1,1,1,3,3,3-hexafluoro-2-propanol and used a mandrel with the diameter of 2.1 mm and the length of 170 mm. It was rotated at 200 rpm and oscillated 150 mm in the transverse direction at a speed of 8 mm/s. The authors measured the axial and circumferential tensile strengths and they found that they were two-fold higher in the circumferential direction. They fabricated highly uniform small diameter polyurethane grafts and easily achieved the endothelial cells attachment without precoating the fiber matrix. They also observed that the synthetic graft surface neither impaired the endothelial response toward IL-1b stimulation nor did it adversely affect the regulation of expression of endothelial adhesion molecules.

To assess mesh architecture sensitivity to manufacturing parameters, Mitchell and Sanders [119] developed a system for controlled electrospinning of fibro-porous scaffolds for tissue engineering applications. Their intent was to achieve scaffolds with well-controlled fiber diameters and inter-fiber spacing. They used a custom, closed-loop controlled, electrospinning system. With their system, they were capable of producing TPU meshes with fiber diameters ranging from 5 to 18 m with variability less than 1.8%; inter-fiber spacing ranged from 4 to 90 m with variability less than 20.2%. They concluded that their system has potential use in biomedical applications where meshes with controlled fiber diameter and interfiber spacing are needed.

Antibacterial and antimicrobial agents such as silver (Ag) nanoparticles [120], 4-vinylpyridine (4VP) [36], or streptomycin sulfate [87] loaded electrospun PU nanofibers were also developed for biomedical applications. Some of these studies combined the antibacterial properties of PU nanofibrous membranes with wound dressing applications.

Yao et al. [36] developed a novel antibacterial material by surface modification of electrospun PU fibrous membranes, using a plasma pretreatment, UV-induced graft copolymerization of 4-vinylpyridine (4VP), and quaternization of the grafted pyridine groups with hexylbromide. Poly(4-vinyl-*N*-hexyl pyridinium bromide) was grafted to the surfaces to achieve antibacterial activities. They showed that the morphologies of PU fibrous membranes changed slightly during the modification process. The tensile strength of PU fibrous membranes decreased after surface modification. After the modification, the tensile strength of PU fibrous membranes from 7% (w/v) decreased from 3.27 to 1.99 MPa, losing almost 40% of tensile strength. They observed smaller decreases in the tensile strength with the increasing solution concentration. The largest diameter of fibers belongs to a concentration of 11% (w/v) and the loss of tensile strength was approximately 16%. They carried out the antibacterial assays with surface modified PU fibrous membranes electrospun from 10% (w/v). Their modified PU fibrous membranes possessed highly effective antibacterial activities against Gram-positive *Staphylococcus aureus* (*S. aureus*) and Gram-negative *Escherichia coli* (*E. coli*) and the authors claimed that these fibrous membranes may have a wide variety of potential applications in high-performance filters, protective textiles, and biomedical devices.

Sheikh et al. [120] synthesized PU nanofibers containing silver (Ag) nanoparticles. They carried out the synthesis of silver nanoparticles by exploiting the reduction ability of DMF, which is used mainly to decompose silver nitrate to silver nanoparticles. Typically, a sol-gel consisting of AgNO<sup>3</sup> /PU was electrospun and aged for 1 week. Ag nanoparticles were created in/on PU nanofibers. They examined the durability of the silver NPs on the PU nanofibers by harsh successive washing. Their results confirmed the good stability of the nanofiber mats. The authors used *E. coli* and *Salmonella typhimurium* to check the antimicrobial influence. Consequently, antimicrobial tests indicated that the prepared nanofibers have a high bactericidal effect and they have potential for using as antimicrobial agents.

In the study of Unnithan et al. [87], an antibacterial electrospun nanofibrous scaffolds with diameters around 400–700 nm were prepared by physically blending PU with two biopolymers, cellulose acetate (CA) and zein. They used PU as the foundation polymer, blended it with CA and zein to achieve better hydrophilicity, cell attachment, proliferation and blood clotting ability. They incorporated an antimicrobial agent, streptomycin sulfate into the electrospun fibers and characterized the interaction between fibroblasts and the PU-CA and PU-CA-zein-drug scaffolds. They investigated the viability, proliferation, and attachment of the fibroblasts on the nanofiber scaffolds and observed that the produced composite nanoscaffold has better blood clotting ability than pristine PU nanofibers. They found that the incorporation of CA and zein to the nanofiber membrane enhanced the bioactivity of nanofiber mats, as weel as the hydrophilicity. CA and zein also provided a moist environment for the wound.

engineering applications. Their intent was to achieve scaffolds with well-controlled fiber diameters and inter-fiber spacing. They used a custom, closed-loop controlled, electrospinning system. With their system, they were capable of producing TPU meshes with fiber diameters ranging from 5 to 18 m with variability less than 1.8%; inter-fiber spacing ranged from 4 to 90 m with variability less than 20.2%. They concluded that their system has potential use in biomedical applications where meshes with controlled fiber diameter and inter-

Antibacterial and antimicrobial agents such as silver (Ag) nanoparticles [120], 4-vinylpyridine (4VP) [36], or streptomycin sulfate [87] loaded electrospun PU nanofibers were also developed for biomedical applications. Some of these studies combined the antibacterial properties

Yao et al. [36] developed a novel antibacterial material by surface modification of electrospun PU fibrous membranes, using a plasma pretreatment, UV-induced graft copolymerization of 4-vinylpyridine (4VP), and quaternization of the grafted pyridine groups with hexylbromide. Poly(4-vinyl-*N*-hexyl pyridinium bromide) was grafted to the surfaces to achieve antibacterial activities. They showed that the morphologies of PU fibrous membranes changed slightly during the modification process. The tensile strength of PU fibrous membranes decreased after surface modification. After the modification, the tensile strength of PU fibrous membranes from 7% (w/v) decreased from 3.27 to 1.99 MPa, losing almost 40% of tensile strength. They observed smaller decreases in the tensile strength with the increasing solution concentration. The largest diameter of fibers belongs to a concentration of 11% (w/v) and the loss of tensile strength was approximately 16%. They carried out the antibacterial assays with surface modified PU fibrous membranes electrospun from 10% (w/v). Their modified PU fibrous membranes possessed highly effective antibacterial activities against Gram-positive *Staphylococcus aureus* (*S. aureus*) and Gram-negative *Escherichia coli* (*E. coli*) and the authors claimed that these fibrous membranes may have a wide variety of potential applications in

Sheikh et al. [120] synthesized PU nanofibers containing silver (Ag) nanoparticles. They carried out the synthesis of silver nanoparticles by exploiting the reduction ability of DMF, which is used mainly to decompose silver nitrate to silver nanoparticles. Typically, a sol-gel

in/on PU nanofibers. They examined the durability of the silver NPs on the PU nanofibers by harsh successive washing. Their results confirmed the good stability of the nanofiber mats. The authors used *E. coli* and *Salmonella typhimurium* to check the antimicrobial influence. Consequently, antimicrobial tests indicated that the prepared nanofibers have a high bacteri-

In the study of Unnithan et al. [87], an antibacterial electrospun nanofibrous scaffolds with diameters around 400–700 nm were prepared by physically blending PU with two biopolymers, cellulose acetate (CA) and zein. They used PU as the foundation polymer, blended it with CA and zein to achieve better hydrophilicity, cell attachment, proliferation and blood clotting ability. They incorporated an antimicrobial agent, streptomycin sulfate into the electrospun fibers and characterized the interaction between fibroblasts and the PU-CA and

/PU was electrospun and aged for 1 week. Ag nanoparticles were created

of PU nanofibrous membranes with wound dressing applications.

high-performance filters, protective textiles, and biomedical devices.

cidal effect and they have potential for using as antimicrobial agents.

fiber spacing are needed.

38 Aspects of Polyurethanes

consisting of AgNO<sup>3</sup>

Nanofibrous materials provide a realistic representation of the native tissue than any other substrate with respect to general cell culture. An advantage of using nanofibrous material is they can also be produced in a highly aligned orientation. The orientation of the nanofibers plays an important role in the study of cell behavior whose native environments consist of highly aligned ECM [121]. Most researchers carried out cell culture tests to characterize the developed nanofibers for wound dressing and scaffold purposes. In **Figure 12**, representative cell-cultured images of nanofibers were given.

Khil et al. [21] prepared PU nanofibrous membrane and evaluated its performance as a wound dressing. They saw that the produced nanofibrous wound dressing showed controlled evaporative water loss, good oxygen permeability, and promoted fluid drainage ability due to porosity of nanofibrous membrane. Neither toxicity nor permeability to exogenous microorganism was observed with the nanofibrous membrane. They also observed that the epithelialization rate was increased confirmed by histological examination, and they were able to control the exudate in the dermis by covering the wound with the electrospun membrane. Thus, they claimed that nanofibrous PU membrane prepared by electrospinning could be properly employed as wound dressings.

Kim et al. [39] prepared a blended nanofiber scaffold using synthetic and natural polymers, PU and gelatin, respectively, to prepare a material for wound dressing. They produced a gelatin/PU blended nanofiber scaffold and examined these scaffold by contact angle, water uptake, mechanical property, recovery, and degradation tests, and cellular response. They observed that, with the decreasing amount of gelatin in the blended solution, the contact angle increased, in the meanwhile water uptake of the scaffold decreased. The mechanical tests showed that, the blended nanofibrous scaffolds had an elastic character, as expected, and the elasticity of the scaffold increased with the increasing amount of PU. Beside, gelatin

**Figure 12.** SEM images of (a) cells on randomly oriented nanofibers, (b) cells on aligned nanofibers and their fluorescence images [121].

amount increased the cell proliferation with the same amount of culture time. These results indicated that produced gelatin/PU blended nanofiber scaffold has a potential for wound dressing applications.

Lee et al. produced nanofiber-based artificial renal microfluidic chip by electrospinning method [122]. Authors have developed polyethersulfone and PU-based nanofibers and combined these webs with the poly(dimethylsiloxane)-based microfluidic platform top to create a chip-based portable hemodialysis system. They measured the filtration capability of this dialyzing chip and found that during the filtration and the transportation of the blood cells, they were not mechanically affected.

### **5.2. Other applications**

In addition to biomedical applications, other application fields such as filtration, sensors, nanoweb lamination based on electrospun PU polymer nanofibers have been steadily extended in recent years. One main interest of electrospun polymer nanofiber non-woven mesh is for filtration application and it is best represented by relevant academic researches, in which many applications are in the field of filtration systems.

Filtration efficiency is closely associated with the fiber fineness and it is one of the most important concerns for the filter performance [10]. In general, due to the nanodimensions of the nanofiber, nanofiber mats have very high surface area to volume ratio and which results in high surface cohesion. Hence, tiny particles of the order of <0.5 mm can be easily trapped in the electrospun nanofibrous-structured filters. Thus, it is possible to improve the filtration efficiency with nanofibrous materials. In this manner, PU-based electrospun nanofibers could also be used as a filtration material because they are resistant to microorganisms and abrasion, and also have high hydrolytic stability [40].

Sambaer et al. [45], synthesized a PU based on 4,4′methylenebis(phenylisocyanate) (MDI), poly(3-methyl-1,5-pentanediol)-alt-(adipic, isophtalic acid) (PAIM) and 1,4 butanediol (BD) in molar ratio 9:1:8 at 90°C for 5 h. They used needless electrospinning apparatus and a supporting polyester fabric for collecting nanofibers with a speed of 0.16 m/min. Nanofibers were collected on the fabric with square ordering of electro conductive 9601 of fiber resistant, 95 g/m2 of area mass, electro conductive 5 mm of thread distance. They evaluated the filtration efficiency of the nanofibers by experimental particle penetration efficiency according to EN 779 standard at the constant air flow rate 5.7 cm/s with aerosol particles. They also created 3D structure model from SEM image of the filter and compared this 3D structure model representing real filter structure with the corresponding experimental data. They obtained good agreement between both datasets.

In addition to fulfill the more traditional purpose in filtration, the nanofiber membranes fabricated from some specific polymers or coated with some selective agents can also be used as, for example, molecular filters or affinity membrane applications. Such filters can be applied to the detection and filtration of chemical and biological weapon agents [10].

Air filters separate particles mainly by the physical entrapment but also electrokinetic capture plays an important role in the air filter [46]. Through the filtration process particles collide with the filter medium. The filter medium that has an electrical charge and has attractive forces on the surface capture the particles. Due to attractive forces between charges or induced forces, particle deposition can occur on the surface. PU cationomers (PUCs) containing different amounts of quaternary ammonium groups were synthesized and successfully electrospun into non-woven nanofiber mats for use in antimicrobial nanofilter applications in the study of Jeong et al. [46]. The PUCs showed antimicrobial activities against *S. aureus* and *E. coli*. Due to the increased charge density of the PUC solutions, the average fiber diameters decreased with increasing quaternary ammonium group content. The PUC nanofibers showed adhesion between nanofibers with various bonding sites, yielding mats with a film-like character and structural integrity. The authors specified that, particle deposition could occur due to attractive forces between charges or induced forces. Therefore, they expected that the developed PUC nanofiber mats can exhibit a better performance as air nanofilters due to their surface electrical charges.

amount increased the cell proliferation with the same amount of culture time. These results indicated that produced gelatin/PU blended nanofiber scaffold has a potential for wound

Lee et al. produced nanofiber-based artificial renal microfluidic chip by electrospinning method [122]. Authors have developed polyethersulfone and PU-based nanofibers and combined these webs with the poly(dimethylsiloxane)-based microfluidic platform top to create a chip-based portable hemodialysis system. They measured the filtration capability of this dialyzing chip and found that during the filtration and the transportation of the blood cells,

In addition to biomedical applications, other application fields such as filtration, sensors, nanoweb lamination based on electrospun PU polymer nanofibers have been steadily extended in recent years. One main interest of electrospun polymer nanofiber non-woven mesh is for filtration application and it is best represented by relevant academic researches, in which many

Filtration efficiency is closely associated with the fiber fineness and it is one of the most important concerns for the filter performance [10]. In general, due to the nanodimensions of the nanofiber, nanofiber mats have very high surface area to volume ratio and which results in high surface cohesion. Hence, tiny particles of the order of <0.5 mm can be easily trapped in the electrospun nanofibrous-structured filters. Thus, it is possible to improve the filtration efficiency with nanofibrous materials. In this manner, PU-based electrospun nanofibers could also be used as a filtration material because they are resistant to microorganisms and abra-

Sambaer et al. [45], synthesized a PU based on 4,4′methylenebis(phenylisocyanate) (MDI), poly(3-methyl-1,5-pentanediol)-alt-(adipic, isophtalic acid) (PAIM) and 1,4 butanediol (BD) in molar ratio 9:1:8 at 90°C for 5 h. They used needless electrospinning apparatus and a supporting polyester fabric for collecting nanofibers with a speed of 0.16 m/min. Nanofibers were collected on the fabric with square ordering of electro conductive 9601 of fiber resistant, 95 g/m2 of area mass, electro conductive 5 mm of thread distance. They evaluated the filtration efficiency of the nanofibers by experimental particle penetration efficiency according to EN 779 standard at the constant air flow rate 5.7 cm/s with aerosol particles. They also created 3D structure model from SEM image of the filter and compared this 3D structure model representing real filter structure with the corresponding experimental data. They obtained good

In addition to fulfill the more traditional purpose in filtration, the nanofiber membranes fabricated from some specific polymers or coated with some selective agents can also be used as, for example, molecular filters or affinity membrane applications. Such filters can be applied to

Air filters separate particles mainly by the physical entrapment but also electrokinetic capture plays an important role in the air filter [46]. Through the filtration process particles collide

the detection and filtration of chemical and biological weapon agents [10].

dressing applications.

40 Aspects of Polyurethanes

**5.2. Other applications**

they were not mechanically affected.

applications are in the field of filtration systems.

sion, and also have high hydrolytic stability [40].

agreement between both datasets.

Ouyang et al. [123] reported the preparation of PU filled with carbon nanotubes and Ag nanoparticles (PU-MWCNT-AgNP) and the subsequent fabrication of a novel non-enzymatic amperometric biosensor for analytical determination of hydrogen peroxide. They conducted cyclic voltammetry experiments to indicate PU-MWCNT-AgNP nanofiber-modified electrodes have high electrocatalytic activity on hydrogen peroxide. The authors also carried out chronoamperometry measurements to illustrate developed electrospun sensor has high sensitivity for detecting hydrogen peroxide. Their study confirms that there is a remarkable synergistic effect of MWCNTs and AgNPs on the significant improvement of the conductivity of electrospun nanofibers. MWCNTs and AgNPs filling also affect the electrocatalytic activity, and the sensitivity of the fabricated non-enzymatic sensor. Their results indicated that the created biosensor for detecting hydrogen peroxide has a sensitivity of 160.6 μA mM−1 cm−2, a wide linear range from 0.5 to 30 mM and a detection limit of 18.6 μM (S/N ¼ 3) and they claimed that PU–MWCNT–AgNP nanofibers have wide potential applications in bio-analysis and detection.

In most electrospinning setup, a conductive material is used as a collector, then produced nanofiber mat is removed from this material. But for some applications it is possible to use a nowoven or casual fabric as supporting material. US20100304108 describes a stretchable, non-woven nanofiber fabric. It allows vapor transport, capable of conforming to body parts but is impermeable to water. This breathable fabric could be useful in high-performance apparels and personal care products [124]. Inventors combined the fabric with different substrates to form a laminate (**Figure 13a**). Illustration of a composite breathable fabrics with electrospun membrane is given in **Figure 13b** [125]. Ahn et al. [24], electrospun PU nanofibers on to a water repellent nylon fabric and compared its waterproof and breathable properties with sole nylon fabric and polytetrafluoroethylene laminated nylon fabric. The aim of the authors is to develop an outdoor clothing with increased performance. A nanoweb laminate was prepared by laminating a PU electrospun nanoweb to the face fabric followed by heat treatment at 160°C in a tenter. The authors evaluated the water resistance and water vapor transmittance of the fabrics were under simulated microclimate. They examined the clothing microclimate and subjective sensations under normal and rainy atmospheric conditions. Their results indicated that the nanoweb laminate compared to the polytetrafluoroethylene laminate, had a higher water

**Figure 13.** (a) A non-woven layer laminated fabric (US20100304108). (b) Illustration of a composite breathable fabrics with electrospun membrane [125].

vapor transmission rate but lower water resistance. They conducted wearing tests in a normal, warm environment to simulate exercising or sweating, to reveal the PU nanoweb-laminated clothing provided a more comfortable clothing microclimate than polytetrafluoroethylenelaminated clothing. In the rainy test conditions, they did not observe any difference between the polytetrafluoroethylene and the nanoweb-laminated clothing.
