Applications of Electrospinning

## **Chapter 4**

## Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0%

*Manuel F. Piñón-Espitia, Guillermo M. Herrera-Pérez and Matha T. Ochoa-Lara*

## **Abstract**

The copper (II) oxide nanofibers (NFs) synthesized with the electrospinning method showed a necklace-like morphology and nanometric size. The use of the XPS (X-ray Photoelectronic Spectroscopy) technique allowed the analysis of the Cu 2p and O 1s orbitals showing a CuxO type stoichiometry (x = 1, 2, 3), in turn, the UPS (Ultraviolet Photoelectronic Spectroscopy) region determined the conduction state associated to the dielectric function. These data are compared with the EELS technique. The NFs have presented a behavior with double magnetic phase associated to the non-stoichiometry and oxygen vacancies, and the non-presence of the AFM phase due to the increase of the vacancies. In addition, their electronic and magnetic structure reveal spin-orbit related changes shown in the Cu 2p spectra. The results showed in the conduction band holes and the Cu 2p and O 1s orbitals.

**Keywords:** NFs, CuxO, XPS, UPS, EELS, AFM, electrospinning, Cu 2*p*,O1*s*

## **1. Introduction**

The electrospinning technique has been widely used in recent years for the synthesis of nanomaterials, especially micro and nanometer scale fibers for a wide range of applications in areas such as biotechnology, spintronics and electronics. The technique is characterized by being versatile and easy to assemble, allowing the processing of a wide variety of polymers, integrating in recent years ceramics, semiconductors and dielectrics [1]. The technique consists of using polar solutions (PVP or PVA) in which acetates are dissolved, once mixed, the solutions are placed in a syringe connected to a hose and needle, the latter placed at a certain distance to be deposited on an aluminum plate. To this process an electric field is applied between (5 to 20 kV), the process is diversified in terms of uses, time, synthesis process.

The CuO study is a p-type semiconductor with a monoclinic crystal structure, with a *C*<sup>6</sup> <sup>2</sup>*<sup>h</sup>* (C2/c space group. The copper atom is coordinated to four coplanar oxygen atoms located at the corner of a rectangular parallelogram and the oxygen atom is coordinated by four copper atoms located at the corner of a distorted tetrahedron. These chains traverse the [110] and 110 directions, respectively [2].

The crystallographic structure is octahedral. The molecule has 4 Cu atoms in the Wickoff position 4c (1/4,1/4,0) and 4 O atoms in the Wickoff position 4e (0, y, 1/4) where y = 0.4184 [3]. The lattice parameters in the unit cell are a = 4.6837 Å, b = 3.4226 Å, c = 5.1288 Å, the angle β = 99.45° between a and c.

In current reports Cu shows three oxidation states Cu1+, Cu2+ y Cu3+ [4–6] and excess holes in its valence band structure (VC) which are associated with the presence of Cu3+ microtraces [7]. The copper oxide faces VO due to the synthesis process the crystalline structure undergoes cation exchanges. This originates changes in its chemical coordination octahedral (Oh) or tetrahedral (D4h) generating a superexchange thus giving the magnetic origin [8–11].

In recent studies the oxide has been highlighted by various nanostructures (nanosheets, nanoflowers, nanoparticles, nanorods, etc.) [7, 8, 12–15]. The study of the surface of these nanostructures has shown relevance through X-ray Photoelectron Spectroscopy (XPS) showing a stoichiometric quantification approach and identification of cations/anions. The analysis of CuO has focused on the Cu 2*p* and O 1*s* orbitals, due to its physical characteristics (hybridization and high energy edges). In addition, it is a transition metal because it has incomplete *d* level, therefore, its study is focused on showing its configuration (1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>2</sup> 3s<sup>2</sup> 3p<sup>6</sup> 3d<sup>9</sup> 4s2 ) and the acceptance of electrons from the O<sup>2</sup> ion, this phenomenon allows charge transfer. However, this is not orange blossom, because a chemical coordination Oh and D4h is governed. These coordination's show distortions caused by the packing of ions of different sizes generating the Jahn-Teller effect. Other authors have shown that the 3*d* orbital shows perturbations due to the possibility of displacements due to bond distortion, clarifying that it is not due to the generation of VO [12–16]. Some authors have focused on studying the Cu 3*d* orbital because of its proximity to the VB [17]. Some authors have shown modifications in their forbidden gap (Eg) because of quantum effects forbidden in the continuum. These changes are due to the quantum confinement of the electronic states which are modified by states not yet clarified in the literature because on the one hand the crystal structures are modified due to the nanometric dimensions and their resonance from the VB to the CB [9–11, 18–24].

XPS is used to understand the oxidation behavior of metals. The study of CuO NFs has led to the elucidation of the initial excitation processes [5, 6, 24–26].

The analysis of the Cu 2p3/2 and Cu 2p1/2 doublets shows changes in the electrical behavior. In addition, the association of the O 1*s* orbital, which is quantified to obtain the stoichiometry of the oxide, has been added to this study. The spectroscopists suggest to calculate these by the block method which provides higher accuracy 4.0% error [27]. On the other hand, the background of the spectra is important to associate chemical species, this quantification is relevant due to the resonance of electrons in the valence band [28].

The 2*p* photoemission spectra of the transition metals in the first row are distinguished by being highly complex, showing a large and complex background, peak asymmetries and a broad multiplet structure. However, the Cu 2*p* spectrum is particularly peculiar, even among them. We will discuss these peculiarities and how the associated difficulties can be overcome by using the Shirley - Vegh - Salvi - Castle (SVSC) based fitting methods under the active approach, as well as compare with the Tougaard contribution, in order to know the electronic contribution associated with the chemical species in the CuO [5, 29, 30].

The study for the identification of the chemical state and its quantification by XPS, using the NIST database [31] and Electron Effective Attenuation Length (EAL), generally provide the necessary information for the identification of metal oxides.

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

Investigations of multiplet structure calculations suggest that transition metals exhibit charge transfer which can complicate the intensity of the spectral multiplet peaks. Analysis of 2p spectra can be complicated to distinguish the ion structure and charge effect of neighboring bonded ions as both the oxidation state and the multiplet splitting can be affected by this perturbation. These phenomena have been observed principally in copper oxide [5, 32, 33].

The multiplet structure in recent years has been analyzed using CTM4XAS (Charge Trasfer Multiplet) software. The software solves quantum data through density functional theory (DFT) and Hartree-Fock function to calculate the spin-orbit entanglement.

DFT (Density Functional Theory) and the Hartree-Fock function to calculate the spin-orbit entanglement. The calculation is used to determine the final energy of the orbital to be treated using three primitives: (a) atomic multiplet, (b) crystal field and (c) charge transfer. Employing the Schrodinger equation, the minimum energy, and e-e interactions and spin-orbit interaction are determined by providing information of the electron location employing the atom symmetry and charge fluctuation in the energy states 3*dn* ! <sup>3</sup>*dn*þ<sup>1</sup> *L* , considering L as a hole, respectively. The multiplet structure is important in the study of XPS due to the contribution of the VB electrons and the core-hole (generated from the photoelectric effect). Moreover, in transition metals the 3d (L3,2) edge is the most important due to the unpaired electron, which provides electronic information [30, 31]. Stavitski and de Groot [32], point out that one of the first features of XPS is the absorption of electrons in the BV and the corehole effect, because of this the L3,2 edge is important due to the 2*p*63*d<sup>n</sup>* ! <sup>2</sup>*p*53*dn*þ<sup>1</sup> transition, due to this absorption the multiplet effect is affected in the deeper 2*p*, 3 *s* or 3*p* levels [30, 32].

The calculation process using CTM4XAS software employs empirical data: a reduction parameter of the Slater integral, which refers to the final configuration of the calculated electronic structure. The crystal field (10 Dq) would indicate the separation of eg and t2g. Δ (charge transfer energy) refers to the average energy for the 3*d* orbital, Udd (the core hole potential) is the energy transferred to a hole (unoccupied state) and Upd (Hubbard) is a potential related to the charge fluctuation in the 3d orbital. In addition, the Lorentzian and Gaussian values taken from some database are fixed [32].

Furthermore, the study of the multiplet structure of CuO has not been generated in recent years unlike the undersigned of this manuscript [26, 33], therefore, authors Okada and Kotani to extend and determine the data obtained [25]. These authors studied three Cu oxides by approximation calculations using a Hamiltonian proposing the energy of the free ion (Cu) and the gap (electronic repulsion due to its neighboring O 2p atom) in the BV, binding the energy level Cu 2p<sup>6</sup> 3d<sup>9</sup> 4s2 and its final state 3d<sup>8</sup> L (where L denotes the gap and the relationship with O 2*p*). This spectrum has been discussed by several authors due to the importance of the Columbian interaction, spin-orbit entanglement and the screening shielding effect [25].

The EELS technique evaluates the energy loss of inelastic scattered electrons passing through the sample in the transmission electron microscope (TEM). The valence electron energy loss study (VEELS) focuses on the lower energy loss spectrum, typically <50 eV, this region shows the valence and conduction band characteristics due to electron beam interaction. These are appreciated using scanning transmission electron Microscopy (STEM) Park and Yang [34]. Egerton mentions that the use of STEM provides nanometer resolution spectra, thus allowing surface and crystal structure information to be obtained [35]. The author Herrera-Pérez et al. presents the VEELS

technique as a approach to obtain Eg characteristics, electronic and electrical properties through the cole-cole diagram (the graph is obtained from the Im vs. Re function), from the Single Scattering Distribution (SSD) [36]. This analysis is important to determine the resolution of the Zero Loss Peak (ZLP) from the method proposed by Park and Yang [34]. In addition to the above, obtaining the modern spectra and analysis proposed by Eljarrat et al. from the Kramers-Kronig analysis (KKA) and the elimination of the relativistic effects (Cerenkov effect) [37]. Herrera-Pérez et al. shows in their optoelectronic studies the elimination of this effect, as well as convenient methods to calculate the complex dielectric function (CDF) of the materials [36]. In recent years, the electronic study has been complemented by joint density of states (JDOS) convolution showing the electrons present in the conduction band [38].

On the other hand, the theoretical calculations obtained by means of density functional theory (DFT) show similarities to the experimental ones by EELS and XPS, techniques that are exposed in this research, but how to approximate it, for years it has been tried to solve the Schrodinger equation, Born-Oppenheimer in the early 30's proposed an equation to model multielectronic systems (a many-body wave solution) with N variables. The first-principles or ab initio method is based solely on the laws of physics, without reference to empirical parameters. Kohn-Sham to give solution to this uncertainty treats the set of N particles as electron density, broadens the potential energy with a potential that has been neglected to obtain the noninteracting parts (VXC Exchange-correlation potential) in the Hamiltonian (the Hamiltonian supplements ψ in the Schrödinger equation; the latter has no physical meaning); relative to the term shows that the motions of the electrons are correlated with each other. Software (CASTEP -Cambridge Serial Total Energy Package-, Wien2K, VASP) have implemented for such theory two approximations: Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA), which perform estimates considering variables for Eg's energy solution, density of states (DOS). However, the calculations have shown estimates that do not agree with those measured experimentally, especially for the d and f orbitals. In the last two decades Hubbard - U effects implemented in DFT have been shown, described as DFT + U in strongly correlated systems that approximate the d and f systems to the expected ones. What does the Hubbar value in the approximation mean, it is a value that serves to describe the electron-electron interaction without shielding (e.g., in the CTM4XAS software it uses the Slater integral to consider such interaction to estimate the type of chemical bond), this interaction is important to determine the magnetic moment and Eg.

The aim of this work is to determine by modern fits to XPS and EELS spectroscopies the Cu 2*p*,O1*s* electronic states and the interband transition states. Furthermore, to calculate the stoichiometry of the A-NFs and the reference (Sigma Aldrich). The EELS section will show a comparative study of CuO and CuO doped with 3.0% Mn to know the changes associated with Mn compared to that calculated with CASTEP 7.0 software. Finally, the magnetic study will show the change of magnetization with respect to temperature and the association of the magnetic field with respect to the shape of the NFs.

## **2. Experimental procedure**

For the synthesis of polymeric fibers by the electrospinning method, the following reagents were used:

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

1.PVA (High purity, 130,000 Da, Sigma Aldrich)

2.Tri-distilled water (1.1 μohms/cm, J. T. Baker)

3.Copper Acetate II (99.6% of purity, Sigma Aldrich)

The 8.0% PVA polymer solution was made by weighing 8.0 g of PVA in tridistilled water at 100°C with constant agitation at 100 rpm for 24 hours.

For the polymeric solution of copper acetate II, 1.0 g of it was weighed and added over 2 ml of tri-distilled water at 50°C and left stirring for 2 hours. Finally, 10 g of PVA was added and the whole solution was stirred for 24 hours.

Finally, the polymer solution was placed in a 10 ml syringe connected to a hose for dosing by means of a number 22 needle. The parameters used in the pump were 0.3 ml/hr. and the distance from the needle to the collection plate was 20 cm.

#### **2.1 Characterizations and computational methods**

#### *2.1.1 Scanning electron microscopy (SEM)*

The sample used was a piece of aluminum with an area of 1 cm<sup>2</sup> , taken from the collector sheet, and used as an electrode for electrospinning. The collected images were taken from the SEM Hitachi SU3500 equipment used to verify that the material was obtained in the form of fibers.

#### *2.1.2 TGA-DSC analysis*

The TGA-DSC analysis aimed to show the chemical reactions with their weight distribution in relation to the heat of the reaction (entropy).

A simultaneous thermal thermogravimetric difference test (TGA-DSC) was performed using the SDT-TGA Q600 equipment of TA instruments, through the air and a temperature ramp of 10°C/min, with a range of 25–1000°C, placing 0.25 mg of the synthesized material in a sample holder of the equipment, to determine the calcination temperature of the study compound.

#### *2.1.3 Structure characterization and XRD analysis*

Structure characterization was performed by X-ray diffraction (XRD) using an X'Pert Pro diffractometer equipped with an X'Celerator detector. Diffraction patterns were taken in an interval 2θ = 30°–65° using a step size of 0.05 s<sup>1</sup> with a Cu – Kα radiation source λ = 1.5418 Å.

From the lattice parameters obtained from the XRD characterization, these spectra were used for Rietveld refinement using a Pseudo-Voight peak shape (least squares method) in Fullprof suite software version 2022 [39]. A CIF structure was obtained from the refinement, which was used to determine the 2-D and 3-D electron density using VESTA software (free version provide by VESTA) [40]. Especially this analysis took into account the thermal factors of the crystal structure of Arbrik et al. to optimize the calculated versus experimental spectrum using the above-mentioned software [3].

#### *2.1.4 High resolution-transmission electron microscopy (HR-TEM)*

The synthesized samples were dispersed at 10 mgL�<sup>1</sup> isopropanol for 20 min, then deposited on a 3 mm diameter nickel grid with carbon membrane.

The BF-HR-TEM micrographs were obtained in the JEOL-JEM-2200FS equipment operated at 200 kV. In addition, JImage software was used to determine the average particle size distribution by entering the micrographs and calibrating each one. In this way a histogram was constructed using a Log Normal function [26].

#### *2.1.5 X-Ray photoelectronic spectroscopy (XPS)*

The XPS study was obtained using the following parameters: scan energy 10 eV, resolution 0.1 eV, dwell time 200 msec, 40 scanning scans per spectrum and a 90° angle. The monochromatic source used was an Al Kα (*hν* ¼ 1486*:*6 eV).

The nanofibers were deposited on a graphite tape, adhered to the sample holder of the XPS equipment, introduced into the pre-chamber at a vacuum pressure of 10�<sup>6</sup> Torr, and finally into the analysis chamber at a pressure of 10�<sup>10</sup> Torr.

The peak analysis of the spectra was calculated using AAnalyzer® software (DEMO version) by means of Gaussian and Lorentzian functions (block method, which consists of assigning individual values to each peak, that is, it is not cumulative [27]), these areas obtained were used to calculate the stoichiometry of the oxide. In addition, the convolution considered the Shirley model type SVSC (Shirley-Vegh-Salvi-Castle) suggested for high resolution spectra (in this case Cu 2p), also, for the case of O 1s a Slope line was applied. The data were plotted in Origin Pro 8.6 software [26].

To calculate the chemical composition of NFs, a spherical model was used (model suggested by Shard et al. [41] for 1D materials) that considers the electron attenuation effect (λ), in relation to this Bravo-Sánchez et al. [42] and German-Cabrera et al. [29], relate the λ factor for 2D materials (the difference of this method to the one mentioned above is that it does not consider the shape) as the effect of electron interactions with the atoms of the material, thus affecting the binding energy (Eb) [43, 44].

#### *2.1.6 CTM4XAS*

The free version of CTM4XAS software was used to elucidate the multiplet structure (possible energy states calculated by the Schrodinger equation) for the Cu 2p spectrum. The calculation procedure consisted of choosing the Cu element with valence 2+, then the XPS 2p option. By choosing XPS, the charge transfer flag was automatically activated. In addition, the stacks options (to plot the multiplet structure) were selected. To accurately determine the theoretical spectrum, a tetrahedral symmetry was chosen as suggested by Okada et al. [25], the spectrum obtained was calibrated at 933.60 eV to compare the experimental (A-NFs) and reference spectra (Sigma Aldrich) [43].

#### *2.1.7 Electron energy loss spectroscopy (EELS)*

The study of NFs by EELS spectroscopy was carried out on a Gatan spectrometer (Tridiem 866 ERS), coupled to a Titan G2 60–300 transmission electron microscope. A Wien monochromator was used to correct the electron beam, the operating

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

conditions were carried out at 200 kV, the collection angle was 17 mrad (corresponding to a parallel beam α = 0 mrad), in diffraction mode at 0.05 eV/Channel, a pitch of 5.0 nm and 2.0 s per pixel.

Through the valence electron energy loss spectroscopy (VEELS) method, and using a scanning transmission electron microscope (STEM), the spectra of A-NFs and B-NFs (CuO, doped with 3.0% Mn) were fitted to the center of the zero loss peak (energy calibration) using the asymmetric Pearson VII function to calculate the experimental resolution, this calculation will be carried out through Origin Pro 8.6 software [44].

On the other hand, the data obtained were processed in the DigitalMicrograph software where the measurement noise in the spectrum was subtracted. Also, the dielectric function and the loss function were obtained mainly by means of the Kramers-Kronig analysis. To remove the relativistic effect, they were treated through a difference method working with angles of: β1 = 17.3 mrad and β2 = 9.1 mrad, that is, two spectra taken with different angles were subtracted. This method is used to determine the bandgap [36].

On the other hand, the thickness value of the samples was calculated using the Log-ratio method (absolute, with relative thickness), taken from the author Egerton [35], from the parameters of: electron beam energy E0 (kV), the effective collection angle (β), and the effective atomic number Zeff. In addition, take into account t = λ/ 0.75, where λ is an attenuation factor of the electron on the sample (statistical value, this value is taken from a graph proposed by the author Egerton [35]. To obtain the single scattering distribution (SSD), it was analyzed by means of the Fourier function using the following equation:

$$S\left(E\right) = \frac{I\_0 t}{\pi a\_0 m\_0 v^2} \operatorname{Im}\left(\frac{-1}{\varepsilon\left(E\right)}\right) \ln\left(\mathbf{1} + \left(\frac{\beta}{\theta\_E}\right)^2\right) \tag{1}$$

where *I*<sup>0</sup> is the intensity of the zero-loss beam, t is the thickness of the sample, *v* is the incident electron velocity, *β* is semi-angle of collection, *a*<sup>0</sup> is the Bohr radius, *m*<sup>0</sup> is the rest mass of the electron and *θ<sup>E</sup>* is the characteristic scattering angle for energy loss [34, 45].

To obtain the electron loss function (ELF) was from the SSD employing Kramers-Kroning [35] given by:

$$1 - \frac{1}{n^2} = \frac{2}{\pi} \left[ \operatorname{Im} \left[ \frac{-1}{\varepsilon(E)} \right] \frac{dE}{E} = \frac{2}{\pi} \left[ \left[ scale\\_Factor \times \text{SSD} \right] \frac{dE}{E} \right] \tag{2}$$

The scale factor was determined using the refractive index of CuO (2.3), the same as that used for the doped material. Then the real function of the dielectric function, Re 1½ � *=*εð Þ E , experimentally obtained from the loss function, Im ½ � �1*=*εð Þ E , using the Kramers-Kronig transformation.

$$\operatorname{Re}\left[\frac{\mathbf{1}}{\varepsilon(E)}\right] = \mathbf{1} - \frac{2}{\pi} P \int\_0^\infty \operatorname{Im}\left[\frac{-\mathbf{1}}{\varepsilon(E)}\right] \frac{E^\prime dE^\prime}{E^{\prime 2} - E^2} \tag{3}$$

where P denotes the Cauchy integral part (it is a weighting to correct for any imbalance in the sample data). Finally, the complex dielectric function ð Þ *ε* ¼ *ε*<sup>1</sup> þ *iε*<sup>2</sup> , ε<sup>1</sup> and ε2, was obtained from the relation Re 1½ � *=*εð Þ E and Im ½ � �1*=*εð Þ E [34].

To distinguish the inter-band transitions from the imaginary function, according to the equation [35, 36]:

$$J\_{CV} = J\_{cv1} + i \, J\_{cv2} = \frac{m\_o^2}{e^2 \hbar^2} \frac{E^2}{8\pi^2} i (e\_2(E) + i e\_1(E)) \tag{4}$$

where *m*<sup>0</sup> is the electron mass, *e* is the Charge and *E* is the energy, *JCV* ¼ Re½ � *JCV* is the joint density function of states, these provide the inter-band transitions obtained from the imaginary part of the dielectric function.

As a comparative method to the complex dielectric function and the joint state function, these were calculated using Materials Studio 7.0 software, through the CASTEP (Cambridge Serial Total Energy Package) program using 10 cores on the Xeon10 server of the CIMAV cluster, Chihuahua, Mexico. This was possible using a P1 crystal structure, and atomic positions of Cu (0.25, 0.25, 0) and O (0, 0.4185, 0.25). The structure was optimized and energized using the GGA (Generalized Gradient Approximation) method and the PBE (Perdew Burke Ernzerhof) functional. The convergence was place at 2∙10�<sup>5</sup> *eV=*a*tomo*, the force on the atom 0.01 eV/Å, the stress on the atom less than 0.02 GPa, and the maximum atomic displacement no more than 5∙10�4Å. The electron exchange of the correlation energy was treated in the GGA framework using PBE, as well as a U potential (7.5 eV) as a correction method in the forbidden band, the energy cutoff of the plane wave basis set was chosen at 500 eV. Directions over the Brillouin zone (BZ) were fixed by the Monkhorst-Pack method with a grid (k-points) of 8 � 8 � 8. In addition, the convergence criterion for the total energy was set with a self-consistent field (SCF) tolerance at 2∙10�<sup>6</sup>*eV=*a*tomo*. For the calculation as an antiferromagnetic structure without fixed spin orientation. The DOS (density of states) values were taken from the calculations suggested by the author Absike et al. [46].

## **3. Results and discussion**

#### **3.1 SEM analysis**

The polymeric fibers obtained by the electrospinning technique were analyzed through SEM, in the secondary electron mode, at magnifications of 5000�. The images are shown in **Figure 1a**, by means of JImage software calculated the average sizes of the fibers (panel b), resulting to be 47.24 nm.

### **3.2 TGA-DSC analysis**

The graphs shown in **Figure 2** present the result of the simultaneous TGA-DSC test. The same figure illustrates the synthesized and calcined material (panels a and b).

This technique was used in the thermal analysis to find the calcination temperature, which after analyzing panel d illustrating the different chemical reactions of decomposition in the polymeric fibers until CuO was obtained, was found after 650°C. Temperatures from 40.5–650°C show the decomposition of the organic and inorganic groups that compose the polymeric fibers such as: alcohol, water, chemically bound water, acetate, and PVA, mainly (see panel d). The analysis was complemented with a DSC that exhibits two types of reactions for the research materials: positive enthalpy

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

*Polymeric fibers obtained by electrospinning method, CuO (panel a), and average diameter quantified by JImage software shown in panel b.*

#### **Figure 2.**

*Panel (a) illustrates an example of the finished polymer solution for use in electrospinning. Panel (b) shows the electrospun polymeric fibers and panel (c) shows the calcined polymeric fibers. Finally, panel (d) illustrates the TGA-DSC analysis showing the decomposition of the precursors of the polymer solution.*

(exothermic), related to the release of thermal energy, manifested by the peak at 230 J/g (180°C), and a negative enthalpy (endothermic), related to energy adsorption 25 J/g, at 650°C. The final concentration shows thermal stability for pure CuO, corroborating that, from 650°C, there are no energy and mass changes, respectively.

On the other hand, the authors Kroger et al. [47], Jeong et al. [18], and Piñon-Espitia et al. [26] indicate that the negative enthalpy energy is related to the formation of VO (oxygen vacancies) from an uncontrolled atmosphere.

Based on the results shown in **Figure 2d**, in an uncontrolled atmosphere, the defects associated with VO are corroborated by TGA due to a negative enthalpy.

## **3.3 DRX analysis**

**Figure 3** shows the XRD obtained from the NFs, indicating that the predominant phase is tenorite (panel a), which was corroborated with PDF 80–1268 (panel b). Relation to the fits by the Rietveld method show agreement with the experimental result (Yobs-Ycalc), which is shown in the same figure.

In **Table 1**, the variations related to the Rietveld refinement settings for the XRD spectra are presented. Their variants allow elucidation of their crystal structure with respect to the average crystallite size, lattice parameters, and changes in the O<sup>2</sup> anion in the crystal structure.

The parameters a, b, and c of the structure are compared with those of the reference sample of Asbrik [3], showing consistency with the calculated ones. In addition, the Y parameter shows changes due to the presence of oxygen vacancies [40, 48].

#### **Figure 3.**

*Experimental XRD data are shown (panel a), which are compared with the PDF (power diffraction file) data shown in panel b.*

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*


**Table 1.**

*The data obtained from the Rietveld refinement for the NFs under study compared with two references (sigma Aldrich and S. Asbrik) are shown.*

#### *3.3.1 Electron density in the tenorite structure*

According to the XRD results explained above, the structure obtained from the refinement is shown in **Figure 4**. The 3-D structures exhibit the (110) plane. In panel a shows the comparison of the electron density for the A-NFs and the references (Asbrik [3], Cao et al. [49]), indicating charge transfer from oxygen to Cu2+. In relation to this point, this phenomenon is characteristic of MOs as a consequence of thermal treatment, nanometric dimensions, and thermodynamic changes (the oxide formation energy change generally presents negative peaks associated with endothermic absorption) [16, 32, 40, 48, 50, 51]. In addition, the energies exhibited in panel a suggest a covalent bond, increasing due to energy transfer this suggests an increase in the forbidden Eg and a greater number of defects [40, 48].

#### **3.4 TEM analysis**

According to the XRD analysis, morphological changes were studied compared to the Sigma Aldrich reference sample.

The bright field (BF) analysis by HR-TEM shows in **Figure 4b** the formation of fibers in the form of a collar, which shows the characteristic planes of the tenorite phase (diffraction pattern attached to the image) compared to the Sigma Aldrich reference (panel b). In addition, an analysis was performed concerning the defects shown in panel c (it was amplified in panel d) and utilizing the edge marked with the yellow arrow in panel c. An EELS analysis (high energy between 400 and 700 eV) was performed to identify oxygen, this data corroborates the TGA-DSC analysis explained in Section 3.2.

The distribution and elemental composition of the NFs, using the EDS of the Hitashi 7700 TEM. Panel a show the pure CuO NFs showing the Cu (yellow) and O (red) components, furthermore, this can be corroborated with the signals obtained from the EDS analysis (see panel b). The distribution of the elements in the mapping NFs showed homogeneity, in a 1:1 ratio (see reference [33]).

#### **3.5 XPS and CTM4XAS analysis**

The XPS results are displayed in **Figure 5**, these plots show the spectral differences and spin-orbit coupling energy for the A-NFs and the Reference (Sigma Aldrich). The spectra in panels a and b show the contributions of Cu1+, Cu2+, and Cu3+ cations in the main Cu 2p3/2 and Cu 2p1/2 peaks. The presence of Cu1+ and Cu2+ cations are bound to oxygen (panel c and d), this can be corroborated by the NBD diffraction patterns in

#### **Figure 4.**

*In panel (a) the comparison of the electron density of S. Asbrik [3] and A-NFs is observed, in panel b and c the 3-D crystal structures of CuO in the (110) plane are shown, respectively. Finally, in panels (d) and (e) the 2-D electron density is plotted for the reference and experimental structure.*

Refs [48, 52]. These spectra show a spin-orbit splitting *J* ! ¼ *L* ! þ *S* ! at the peaks located at: 19.97 and 19.91 eV, respectively. Furthermore, it can be corroborated that in the left panel of **Figure 3**, the thin films reported by Pauly et al., up on oxidation of the orbitals also present a splitting attributed to the thermal treatment of the material [53].

Three settings indicating three valence states for Cu (1+, 2+ and 3+) have been proposed in the main branches, reported by the authors: Piñon-Espitia, et al., Ochoa-Torres, et al., Pauly, et al., Sarkar, et al., [5, 26, 50, 53]. These authors have also discussed the presence of mixed oxides by the chemical reaction Cu2O.

On the other hand, these peaks are related to phenomena such as: paramagnetism and electrical conductivity, due to the presence of the Cu2+ cation associated to the

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

**Figure 5.**

*An analysis of the A-NFs is shown regarding the corroboration of the tenorite phase shown in panel b, compared with the sigma Aldrich reference (panel a), these show the electron diffraction pattern which shows the characteristic planes (111) and (111). In panel c and d, a surface analysis of the A-NFs due to the defects shown in the edges is exhibited, panel e shows by EELS (high energy edges) the presence of oxygen.*

CuO [54, 55]. In **Figure 5** The contributions of the chemical species present in the peaks (Cu1+, Cu2+, Cu3+) given by the areas (see **Table 2**) indicate that the greatest contribution to the conductivity is due to the cations of the A-NFs, which coincides with their geometry that includes a greater area-volume ratio compared to the Reference (Sigma Aldrich).

In the case of Cu-bonded oxygen, the evolution in **Table 2** of sample A and the commercial sample is presented. There is a relationship between the areas between the cation and the anion (oxygen). In the particular case of oxygen, the reactions obtained for this work have been shown in Section 3.2, as well as their derivatives (e.g., enthalpy and entropy). Sample A showed a higher amount of Cu1+ as well as a tendency to decrease the amount of the other cations, so according to the author Chusei et al. [56] there is a tendency to higher reactivity because the surface oxygen area increases according to the Cu1+ peak, meaning that it increases. While the amount of oxygen vacancy is like the Reference.


**Table 2.** *Analysis of areas for the adjustments made.*

On the other hand, as mentioned in the experimental part, the Shirley of the spectra was analyzed by modifying the block method and the SVSC function proposed by Herrera-Gómez et al. [28], adding the Tougaard function to the analysis. The calculated values for the A-NFs and the Reference were: 0.24 to 0.04 eV<sup>1</sup> and 3864 to 2000 eV<sup>1</sup> , respectively, associated with recombination of the 2*p* band with the conduction band (see **Figure 5**), which is corroborative with **Figure 3** of author Herrera-Gómez et al. [28].

#### *3.5.1 Analysis of O 1*s *spectra and Vo contributions*

**Figure 5c** and **d** show the results of the O 1*s* spectrum and its homogeneity in the samples by means of the Background Slope calculation. In addition, this analysis is supported by the TGA-DSC technique (see Section 3.2) that other authors have related to XPS, especially on the generation of vacancies in the tenorite structure [55, 57].

The vacancies have been located in the O 1*s* spectra between 531 and 533 eV and are related to the enthalpy due to the negative reaction suggested by the authors [48, 55] in the formation of the oxide, being the TGA-DSC technique an alternative for the detection of vacancies (they have been identified as S2 in panels c and d). The importance of the generation of V0 is how they influence its physical properties such as magnetic, in addition to the electrical properties of the material indicated by the literature [41, 58–61].

**Table 3** shows the percentage variations of Cu1+ and Cu2+ cations related to the O2- ion, which are compared with the Reference (Sigma Aldrich). The A-NFs have a Cu1+/O2 ratio of 0.92 and 0.72% for the Reference. The percentage corresponding to the Cu2+/O2 ratio is 1.08% in the A-NFs, and 1.38% for the Reference. These nonstoichiometric ratios are associated with structural and surface defects and other phenomena related to the nanometer dimensions of the material (e.g., plasmonic effects) [62, 63].


These percentage ratios show that the A-NFs presented an increase of Cu1+ in the crystalline structure, compared with the Reference which has a lower amount and a

#### **Table 3.**

*Percentage of Cu1+ and Cu2+ spices associated with oxygen (O1(S0)-O2(S1)), respectively.*

## *Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

higher amount of Cu2+; in relation to this, the research samples have slightly an excess of Cu2+, this shows that the presence of both cations are important for their electrical, magnetic and optical properties, mainly [12, 54, 61, 64].

#### *3.5.2 Multiplete structure analysis*

In this section we show evidence of changes in chemical coordination, binding energy, hybridization, and charge transfer (Δ), related to the nanometer dimensions of the synthesized material compared to the Reference (Sigma Aldrich). Other related changes are: scramming shielding effect, electronic changes in the main 2*p*3/2 peak (Cu 2*p* – L3,2 edge electrons) and satellites (holes).

**Figure 6** shows the final states of the NFs compared to the commercial and calculated material (CTM4XAS). Image a show the set of study spectra compared to the calculated one (spectral shape and multiplet structure). In addition, the panels show the changes mainly in the satellites discussed in the previous section [32, 65, 66].

In **Figure 6a** the Δ according to the obtaining of the materials is exposed, which is seen to be higher for the A-NFs and much lower for the commercial one. According to Okada and Kotani [25] the Δ effects are due to the electron donors (in this case the two oxygens located in the c plane), data that agrees with the percentages presented in **Table 3**, which would show that the A-NFs show higher charge transfer due to the proximity of the oxygen ion to Cu and generating a higher scramming shielding.

The authors showed that the satellites are due to the holes in the oxide, which is observed in panel a that physically exemplifies the effect of the exposed edge related to electrons and holes in the BV. Finally, the leading-edge shifts and hole variation are

mainly due to the hybridization of the Cu 2*p* and O 1*s* edges, and their shift to higher binding energy, as is the case in the experimental sample exhibiting the screening shielding effect.

About the satellites, it can be appreciated that according to the ions and their coordination, variations were obtained with those shown in **Figure 5** (image a and b), indicating for the experimental ones a D4h type structure (tetrahedral) and the Reference type Oh (octahedral). On the other hand, the screaming shielding effect is directly related to electronic effects related to electron and hole resonance.

## *3.5.3 Chemical composition analysis based on a spherical model*

The chemical composition of NFs has been calculated through the spherical model. This proposal is derived from recent reports by Shard et al., and Cardona, [61, 67]. In **Table 4** shows that A-NFs do not retain stoichiometry.

According to the geometries estimated with the spherical model of Shard [41, 61] the compositions were for A-NFs: Cu1.02O1.16, Cu2.22O2.12, and for the Reference (Sigma Aldrich): Cu0.97O1.02, Cu2.43O2.01, with a 4.0% error, respectively. The chemical composition was related to the E\_k and to the photoelectric effect applied to the sample (cross section).

## **3.6 EELS analysis**

For this analysis, two samples, A-NFs and B-NFs (CuO doped with 3.0% Mn) were taken for comparison. To corroborate the distribution of Mn and its percentage can be observed in the reference [33].

**Figure 7** shows the inelastic contributions of the electrons in the A-NFs and B-NFs, respectively. The resolution of the peaks exhibited in panels a-b was 0.97 eV, as an asymmetric result of the deconvolution. In addition, the loss function (blue line) is shown in both panels, in panel a a a plasmon is exhibited at 22 eV, in panel b 2 plasmon peaks are exhibited, 10.0, 22 eV, while the 32.0 eV peak represents a M2,3 Mn [35]. On the other hand, the analysis using the Pearson VII function allowed us to clean the spectra obtained, and thus obtain the single scattering distribution (SSD) (blue line).


*Note: the data obtained in SF, were obtained from calculating λ = 1.25 (Electron attenuation factor in the LEA sample), this factor was used to calculate the chemical composition by means of the MML model which was proposed as a bulk model, without layers. XCuO is the Cation compositional factor, I1/I2 are the intensities of these, A% is the atomic percentage and SF is the final stoichiometric factor.*

#### **Table 4.**

*Primary XPS signal data for Cu 2p and O 1s spectra used to calculate the chemical composition in the nanopowders.*

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

#### **Figure 7.**

*Multiplet structure for the A-NFs and the reference (sigma Aldrich), compared to the calculated one (panel a). In addition, in panels b and c it differentiates the Oh and D4h structures.*

In addition, the relative thickness calculated by the Log-ratio method yielded values of: 35.55 (A-NFs) and 38.72 nm (B-NFs) suitable for analysis.

#### *3.6.1 Surface and bulk plasmon analysis*

Egerton reports plasmons for all materials between 10–30 eV [35], while Charles, 1996 by means of an analysis of metals and EELS analysis determined an energy of 0 to 10 eV for these metals [35]. In the study materials, plasmons were found to be associated at 22.52 and 22.15 eV, for materials A and B, respectively. Material B showed a signal of 10 eV which is consistent with being doped.

**Figure 7** (Panels a,b) show the collective excitations of electrons (plasmons) where they interact in low regions in the BC and BV, known as bulk plasmon and surface plasmon, respectively. In this regard, the authors Herrera-Pérez et al., Egerton, [35, 36] propose to evaluate the energy of the free electron plasmon as:

$$\mathbf{E\_p} = 28.82 \text{ eV} \ast \left(\frac{\mathbf{z}\rho}{\mathbf{A}}\right)^{1/2} \tag{5}$$

Where z is the number of electrons per molecule, ρ is the density of A-NFs = 6.520 g/ cm3 and B-NFs = 6.473 g/cm3 (these values were calculated by Fullprof suite software), respectively and A is the molecular weight 79.57 and 134.483 g/mol, respectively.

According to the calculations proposed by the authors Herrera-Pérez et al., Egerton [35, 36] the plasmon energy for A-NFs and C-NFs turn out to be: Ep = 16.49 eV and Ep = 17.88 eV, respectively. The change between these values is due to the interband transition below the plasmon peak [35].

These results suggest that the plasmons found are transiting in low regions between the valence and conduction bands. According to Egerton, this would indicate that they are semiconducting materials [35].

## *3.6.2 Comparative analysis of the dielectric function and the edges obtained from XPS-survey*

**Figure 8** shows the dielectric function, the peaks associated with the interband transitions obtained in EELS compared to the XPS survey spectra, for the A-NFs and C-NFs. This comparison indicates according to the author Meyer and co-workers [63], the data obtained showed a similarity.

ε<sup>1</sup> is the real part of the dielectric function which presents in this case a negative transition indicator showing a response below the value of the semiconductive behavior [37]. In addition, the authors Johann Toudert and Rosalía Serna [64], performed a study of the effects of collective oscillations (free charges) in Ag and Au oxides to know the optical and interband and intraband transition effects by means of the complex dielectric function (ε ¼ ε<sup>1</sup> þ iε2) [64]. The discussion focuses on the plasmonic effect, because on electromagnetic radiation, especially the infrared and UV-Vis zones. The results of those authors show similarity to those presented for the real function (see panels a and b), ε<sup>1</sup> being negative suggesting that it has the metallic character [68–71]. However, the relationship does not comply with what is exposed by these authors because ε<sup>1</sup> >1 so such harmonic dispersion is in the UV-Vis region, but it complies with the imaginary relationship due to its growth [66]. In addition, the authors mention that this effect is for alternative plasmonic materials. In studies with doped materials, they improve the response to such an effect [72]. The author Manuel Cardona, 1986, finds that the negative value for ε<sup>1</sup> is related to excitons (phonon-electron) [67].

On the other hand, the peaks of the imaginary function (**ε2**) were associated with the Cu 2p, 3d, and O 2p transition interbands in the conduction band, and the peaks A, D, E, H, and I are associated with the holes. In Figure 26 of reference Meyer et al. [63] present the imaginary part of the dielectric function pointing out five transition states, associated with the Cu 2*p*, 3*d*,O2*p*, and holes bands.

#### **Figure 8.**

*Valence energy loss spectra (VEELS) of A-NFs (a) and B-NFs (b), extracted from the zero peak and dispersion spectrum (SSD).*

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

Moreover, the bands obtained by XPS in the UPS (Ultraviolet Photoelectronic Spectroscopy) region (see panels e and f) show similarity to those reported in CuO [41, 46, 67]. Furthermore, Wang and co-workers, [73], performed the theoretical and experimental study of CuO by XPS- UPS, finding that the obtained peaks corresponded to the Cu 2p, 3d and O 2p orbitals [46, 67]. On the other hand, panel f shows the oxidative evolution of metallic Cu to the study oxides. In the study materials the leading edge presented a Cu-2p and Cu-3d splitting, while the O-2p shows an overlap with these orbitals (A-NFs and Reference), while for doping there is slightly a peak associated with it (hybridization), which agrees with the model of Wang et al. [73]. In addition, in the case of metallic Cu, the peak corresponding to oxygen was not present.

**Table 5** shows the values of the electron transition shifts in the conduction band. When Mn is added to the NFs, it is observed that the main peak shows a smaller peak width (0.25 eV) and a smaller number of holes. It is also seen that the number of peaks for the A-NFs is like the theoretical one. The Cu 3d transitions for the study materials with respect to O 2p, mainly, are exposed. In **Figure 8c** and **d** a shift from 1.33 to 3.69 eV (transition Cu 2*p* ! Cu 3*d*, see DOS in **Table 5**) in the doping with respect to pure is shown. For the case of Cu 2p with the O 2p of materials A and C there was a shift between these peaks due to doping [74–82].

**Figure 9** shows the joint density of states calculated for the interband transitions. In the A-NFs (panel a), three states corresponding to those calculated by CASTEP (panel c) were observed, which coincide with those presented by the authors [41, 46, 67, 73], furthermore, the O 2p shift coincides with that of Meyer et al. [63]. In the case of the doped material, the Cu 3d transition increased the energy (see panel b) and decreased the number of holes (see **Figure 9d**). Panel c shows the holes obtained, similar to those reported by the author cited above [63]. On the other hand, the DOS model of CuO is calculated by Meyer et al. [63]. Absike, et al., [46], by calculating the TDOS and PDOS show agreement with the results (see panels c and d) [46]. Panel d shows the agreement with the one calculated by CASTEP through the GGA-PBE (Generalized Gradient Approximation - Perdew Burke Ernzerhof) functional and the one reported by Meyer and collaborators, [69].


*In addition, the DOS-CASTEP label shows the energy obtained from the model by this software and compares it with the authors mentioned in the Table.*

#### **Table 5.**

*Proposed inter-band transitions and compared to references A[73], <sup>B</sup> [63].*

#### **Figure 9.**

*Panels a and b indicate the dielectric functions* ^*ε*ð Þ¼ *E ε*1ð Þþ *E iε*2ð Þ *E , for the A-NFs and C-NFs, respectively. In panels c and d, the interband transitions are exhibited. Panel e shows the survey spectra of: Cu metallic, A-NFs, B-NFs, and the reference. Panel f shows the Cu 3d and O 2p bands for the materials in the UPS region.*

#### *3.6.3 Bandgap determination*

**Figure 10** compares the normalized ELF (Energy Loss Function) (black dotted line) calculated using the KKA (Kramers-Kronig Analysis) logarithm in the 0–10 eV range with the VEELS spectra using the difference method (red line). This method allows us to calculate the onset energy associated with the (optical) bandgap in the ELF. The Eg energy was determined using the method of Rafferty and Brown [38] as the intercept of a polynomial fit *A* þ *E* � *Eg <sup>n</sup>* (A is the background level), the plots suggest an indirect Eg of 2.03 and 2.85 eV, respectively. The Eg reported by Meyer et al. is 1.0 eV [69], which we attribute to working with bulk material. The calculated bandgap and that obtained in our materials suggest that the bandgap values may be associated with electronic resonance problems at the Cu 3*d* and Cu 2*p* levels due to its nanometer character, which generates changes in the orbitals, for this reason, the curve was not entirely possible to smooth it [26, 28].

#### **3.7 Magnetic analysis**

**Figure 11** shows the paramagnetic behavior shown by the magnetic susceptibility of A-NFs and C-NFs (panel b). Mariammal et al. [83] performed a study with CuO and Mn-doped CuO in nanoflakes, which suggests the coupling of Mn on CuO creates spin decompensation at the surface (superparamagnetism) and spin-glass behavior that the antiferromagnetic phase disappears. According to Zhao et al., possible couplings can appear when CuO is doped with Mn, are: Cu-O-Cu-O-Mn-O-Cu-O-Cu-O-Cu, Mn-O-Mn, and Mn-O-Cu-O-Mn attributed to paramagnetic or spin-glass, antiferromagnetic, and ferromagnetic behaviors, respectively [70]. On the other hand, at d levels of Mn a strengthening in the magnetic aspect was expected, however, the antiferromagnetic effect did not occur, as in the case of NPs mentioned by Zhao et al. [70], above.

**Figure 12a** and **b** show the magnetization versus temperature (ZFC-FC) results of A-NFs and B-NFs pointing to temperatures of 58 and 60 K, corresponding to

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

#### **Figure 10.**

*Panels a and b show the joint density of states for A-NFs and B-NFs, respectively. Panel c exhibits the DOS for CuO calculated by CASTEP. In addition, the BC region with the interband transitions is exposed. Panel d shows the interband region obtained by Mayer and the gaps obtained from this model [69].*

#### **Figure 11.**

*In panels a-b, the comparisons of the VEELS spectra with deconvoluted ZLP and the fit of these with the difference method are shown. In addition, the blue dashed line indicates the polynomial fit for Eg. a) Corresponds to the A-NFs and b) are the B-NFs.*

ferromagnetic behavior. This behavior is also observed in the results of NPs in CuO and Mn-doped CuO (nanowires) of the author Han et al. [12] shown in panel c. Similar to this work, it shows a blocking T greater than 80 K which is attributed to the different grain size and higher doping than this work.

Recalling that bulk CuO exhibits two antiferromagnetic phases at 213 and 230 K it is remarkable that the same in **Figure 12a** and **b** no such phases are observed in both cases due to spin decompensation at the surface of the nanostructures [84]. The absence of these phases also in the work of Narsinga Rao et al., [71] in nanoparticles shown in the image d.

**Figure 12.** *Magnetic susceptibility from 2 K to 300 K, a) for CuO NFs, pure and doped with Mn (2.5%).*

**Figure 13a** and **b** show the magnetic behaviors using hysteresis loops for A-NFs and B-NFs at 300 K, which were found to be superparamagnetic and paramagnetic, respectively. The superparamagnetic behavior is comparable with that obtained for NPs by Narsinga Rao et al. [71].

In **Table 6**, the data of magnetic saturation variations and coercivity for the synthesized materials and CuO NPs of authors Borzi et al. [85] and Narsinga Rao et al.

*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*


#### **Table 6.**

*Coercivity and Remanence for A and B materials, compared with Borzi et al. and Narsinga Rao et al. [71, 85].*

[71] at room T are shown. It is observed that the coercivity is higher in A-NFs than those reported by those authors. The difference is attributed to the nanometer dimensions between the nanostructures handled and the difference in the geometries between the NFs and the NPs of these mentioned authors. On the other hand, C-NFs present higher remanence with respect to A-NFs, but also lower coercivity.

## **4. Conclusions**

The synthesis of A-NFs by electrospinning showed a monoclinic phase corresponding to tenorite. These NFs show multivalent states (Cu1+, Cu2+ and Cu3+). Their lattice parameters calculated by the Rietveld method suggest lattice distortion. This was corroborated by the electron density in the crystal structure with charge transfer from O<sup>2</sup> to Cu2+ appreciated as peanut shape which is characteristic in semiconducting materials [1].

The XPS study showed the identification of the cations/anions in the Cu 2p and O 1s orbitals, corroborated with the authors [1–7], respectively. The distances of the main branches (Cu 2*p*3/2 and Cu 2*p*1/2) were: 19.97 and 19.91 eV, respectively, because of the Jahn-Teller effect [6, 86, 87]. The increase in the distance of the main branches is a consequence of paramagnetism in CuO. The spectra were used to calculate the stoichiometry using the geometrical topofactor (sphere) method showing non-stoichiometric oxides: Cu1.02O1.15 and Cu2.06O2.03, and the reference: Cu0.97O1.02 and Cu2.43O2.01. The CTM4XAS software corroborated the cationic states in the Cu 2*p* orbital through the multiplet structure. In addition, the calculation employed a higher charge transfer than previous reports. Moreover, the multiplet structure of A-NFs suggests a D4h structure presents higher number of holes (this chemical coordination is suggested as the one with the lowest energy according to the experimental spectral shape). On the other hand, the O 1*s* spectra allowed us to calculate the oxygen vacancies generated in these, found in the same samples at 533.17, 532.22 eV. These energies agree with previous reports.

The difference method in VEELS spectra allowed to calculate the onset energy associated with Eg (optical) using the energy loss function (EFL). In addition, this method suggests the elimination of the relativistic effect of the electrons (10<sup>6</sup> ) from the spectra [13, 14]. The polynomial fit for the spectra presented an indirect Eg, in agreement with that calculated by CASTEP agrees and differs with previous reports.

The comparative XPS-EELS study for A-NFs and B-NFs (3.0% Mn-doped CuO) in the UV-VIS region (0–50 eV) through the dielectric function showed similarity in spectral shape, deconvolution of the EELS spectra determined the interband states in the CB for Cu 3d, Cu 2s and O 2p orbitals. Furthermore, the comparative study of the A-NFs and B-NFs suggests changes in the interband transitions in agreement with those calculated, the Eg by CASTEP and VEELS obtained were: 1.27, 2.03, 2.85 eV. Meyer et al. [63, 69] shows.

According to the magnetization study, it was observed that sample A and B Ferromagnetism and Paramagnetic (mixed phase) behavior, which is attributed to the change obtained in the Cu 2p multiplet peaks of XPS (change in electric current arises due to changes in *J* ! ¼ *L* ! þ *S* ! ). These results are compared to those of reference [16], finding a mixed phase. This is due to the spin decompensation at the 3d<sup>9</sup> orbital, which is attributed to its nanometer size and doping and B a paramagnetic behavior, which is attributed to its nanometer size and doping. In addition, the antiferromagnetic phase that normally appears in a CuO (II) bulk material at 232 K, in these samples is not present. This is attributable to the nanometer size, particle geometry, oxygen vacancies, charge decompensation (Cu3+) and occurs in other nanostructures [16, 70, 88].

## **Acknowledgements**

The author M. Piñón-Espitia thanks the Ph.D. CONACYT scholarship grant No. 467043. We would like to make two important mentions for the completion of this work: to Dr. Francesca Péiro and Dr. Luis Gerardo Silva for the support received in the EELS and XPS studies. As well as to the national laboratory of nanotechnology CIMAV, S.C. Chihuahua.

## **Conflict of interest**

The authors have no conflicts to disclose.

## **Abbreviations**


*Electronic and Magnetic Contribution for CuO and CuO Nanofibers Doped with Mn at 3.0% DOI: http://dx.doi.org/10.5772/intechopen.112897*

## **Author details**

Manuel F. Piñón-Espitia<sup>1</sup> \*, Guillermo M. Herrera-Pérez<sup>2</sup> and Matha T. Ochoa-Lara<sup>1</sup>

1 Departament of Physics of Materials, Centro de Investigación en Materiales Avanzados, Chihuahua, Mexico

2 Catedra CONACYT asignada al Departamento de Físcia de Materiales, Centro de Investigación en Materiales Avanzados, Chihuahua, Mexico

\*Address all correspondence to: freunfide@gmail.com; manuel.pinon@cimav.edu.mx

© 2023 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 5**

## Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review

## *Isabel C. Gouveia and Cláudia Mouro*

## **Abstract**

Electrospinning, a remarkable and versatile technique has been related to medical textiles, aiming to produce nanomaterials for drug delivery and tissue regeneration applications. Furthermore, electrospun nanofibrous materials with unique properties as favorable pore size distribution, porosity, surface area, and wettability, along with effective mechanical properties, are the frontrunner solutions. Also, the features of the nanofibrous structures can be designed and optimized by controlling electrospinning parameters related to the solution properties, the setup parameters, and the environmental conditions to design nanofibrous textile materials for the desired applications. Further, to accomplish the required functionality of the drugdelivery systems, a rather broad range of drugs have been loaded into the nanofibers using different electrospinning techniques, namely the blending, side-by-side, coaxial, tri-axial, emulsion, and multi-needle electrospinning, in order to accomplish specific drug-release profiles of the designed nanofibrous textiles. Thus, this chapter describes the different electrospinning techniques that have been utilized in the production of the textile nanofibrous materials as the application of these materials in bone, nerve, periodontal, and vascular regeneration, as well as in wound dressings, personal-protective-equipment (PPE), and cancer treatment, providing an overview of the recent studies and highlighting the current challenges and future perspectives for their medical applications.

**Keywords:** emulsion electrospinning (ES), coaxial ES, blend ES, encapsulation ES, drug delivery, medical textiles, wound dressing, personal protective equipment

## **1. Introduction**

During the last years, the huge and rapid development in nanotechnology has greatly contributed to the production of new functional materials with enhanced properties to be effectively and efficiently used in numerous fields [1–3]. Nevertheless, the development of medical textiles through the intervention of nanotechnology has been highlighted, in order to improve the health and quality of life of patients [3, 4].

Medical textiles, due to their distinctive features, such as their flexibility, wide range of sizes, and light-weight, physical, structural, and surface properties, have been produced with different materials (synthetic and/or natural) and with various structures (woven, knitted, braided, nonwoven, and composites) for different purposes, namely for advanced biomedical applications, like drug-delivery systems for tissue regeneration and wound healing [4–6]. However, developing advanced biocompatible, biodegradable, nontoxic, and nonallergic materials with desirable properties for drug loading and delivery in biomedical fields is still one the major challenges faced by the researchers, and thus, to minimize this gap, textile-based drug-delivery materials have been designed [3, 6, 7].

Among the different types of medical textiles, electrospun textiles fabricated from natural polymers, like proteins and polysaccharides, have gained increasing interest due to their low cost, biocompatibility, biodegradability, bioactivity, and unique properties, like the high surface area-to-volume ratio, smaller and more uniform fiber diameters, highly interconnected porous structures, and similarity to the extracellular matrices (ECMs) of tissues in the body [3, 8–11]. Moreover, electrospinning has been revealed to be a simple and versatile method to produce drug-delivery systems, and hence the nanofibrous materials developed from the electrospinning are a unique and exceptional platform for loading and delivery of multiple therapeutic agents due to their performance and intrinsic nanoscale morphological characteristics [3, 8–11]. Furthermore, the nanofibers drug loading has been achieved using different electrospinning techniques that comprise the incorporation of these therapeutic agents prior to the electrospinning process through the blended, coaxial, side-by-side, emulsion, and tri-axial electrospinning in order to deliver the appropriate amount of drug over the desired period of time and with a specific release profile [3, 5, 11]. Therefore, textile-based drug loading and delivery materials have been designed according to the medical conditions in order to improve the effectiveness of the drugs and reduce costs and the toxic side effects [5].

In the following sections of this chapter, an overview is provided which focuses on the fundamentals of the electrospinning technology, the different parameters that influence the diameter and arrangement of the produced nanofibers, and the main medical textile materials (e.g., cellulose, chitosan, collagen, alginate, keratin, and silk) used to produce textile-based drug loading and delivery nanofibers. In addition, the drug-release mechanisms and kinetics, as well as the different electrospinning techniques used to incorporate different therapeutic agents and produce electrospun nanofibers to act as drug-delivery textile materials, are described in detail. Finally, a brief outline of the recent studies concerning the production of textile-based drug loading and delivery materials for medical fields, namely for applications in bone, nerve, periodontal, and vascular grafts tissue engineering, wound dressings, and other textile-based materials, like personal protective equipment (PPE) and cancer treatment is presented, as well as the conclusions, challenges, and future perspectives of this emerging research field.

## **2. Electrospinning technology to produce textile-based drug-delivery materials**

Electrospinning is a simple, versatile, and cost-effective manufacturing method that uses high voltage to produce an electrically charged jet of polymer toward the collector, where the continuous nanofibers are collected and interconnected

### *Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

nanofibrous structures produced (**Figure 1**) [3, 5, 8, 9, 12–15]. Therefore, in the electrospinning process, a charged polymer jet is ejected when the electrostatic forces overcome the surface tension of the polymer solution and a Taylor cone-jet, subjected to a variety of forces, like an electric force imposed by the external electric field, a Coulomb force, a surface tension force, a viscoelastic force, and gravitational forces, is formed to produce the high-quality nanofibers [3, 8, 9, 12–14].

In addition, the electrospun textiles have been recognized by their superior structural properties, like the high surface area-to-volume ratio, tunable porosities, morphologies, and diameters, as well as the ability to carry large amounts of drugs or to be chemically modified using wet chemical methods, oxygen plasma treatments, and in situ grafting polymerization for specific applications, such as drug loading and delivery materials [3, 5, 8, 9, 12, 14]. Moreover, there are various parameters that affect the morphology, diameter, distribution, and orientation of the produced textile nanofibers, namely the properties of the solution (e.g., viscosity, conductivity, and surface tension), the operating/process parameters (e.g., applied voltage, distance between the capillary tip and the collector, and the flow rate), and environmental conditions (e.g., humidity and temperature), and therefore, optimizing the variables that affect the electrospinning process is expected to develop textile nanofibrous materials with the specific features (porosity, wettability, mean diameter, and mechanical strength) desirable for tissue regeneration and wound-healing applications, as well as for PPE [3, 5, 8, 9, 12, 14].

Furthermore, the type of collector that is used in the electrospinning process determines the alignment of the electrospun nanofibers. Thus, using a stationary collector, the jet of the polymeric solution is directed to the collector, the solvent evaporates, and a dry and randomly oriented nanofibrous structure is obtained, mimicking ECM's threedimensional structures [3, 5, 12, 14]. On the other hand, using rotating collectors (e.g., discs, rotating drums, and rotating wire drums), nanofibers are deposited with a specific orientation and, consequently, are more prone to medical textiles for nervous and muscle tissue regeneration. Also, when the collector rotation speed is increased, the nanofibers diameter reduces, and the alignment improves [3, 5, 12, 14].

Additionally, electrospun textiles have also been produced from a broad range of polymer materials. Among them, synthetic polymers approved by the US Food and

#### **Figure 1.**

*Scheme of the basic device of electrospinning composed of four major parts: A spinneret, a syringe pump, a highvoltage source, and a collector.*

Drug Administration (FDA), such as polycaprolactone (PCL), poly(L-lactic acid) (PLLA), polylactic-co-glycolic acid (PLGA), polyvinyl alcohol (PVA), polyethylene oxide (PEO), and polyurethane (PU) have been explored for drug loading and delivery and biomedical applications due to their biocompatibility, excellent thermal stability, mechanical properties, and proper biodegradation rates [5, 8, 10, 12, 16]. Nevertheless, more recently, researchers started to explore natural biopolymers, such as proteins (e.g., hyaluronic acid, collagen, and silk fibroin) and polysaccharides (e.g., chitosan, alginate, and gelatin) according to their inherent nontoxicity, biocompatibility, bioactivity, sustainability, and eco-friendliness, as well as blending of synthetic and natural polymers to design electrospun nanofibrous textiles with notable medical properties [5, 8, 10, 12, 16].

Besides, textile nanofibers have been successfully electrospun and loaded with different drugs, including water-soluble, water-insoluble, anticancer, and antibacterial drugs through distinct techniques (see Section 3) in order to protect these agents from decomposition within the body before reaching the target site and produce textile-based drug loading and delivery nanofibers with varied drug-release profiles and kinetics, such as biphasic release, prolonged release, immediate release, and targeted release [3, 12]. These strategies can also control the incorporation of multiple agents in order to achieve the desired therapeutic effect and reduce the number of dosing times, improving patient compliance [3, 11, 12]. In this way, the electrospun nanofibers produced from biodegradable and biocompatible polymers using different electrospinning techniques have received increasing attention as carrier materials for drug loading and delivery in medical fields due to their flexibility, effectiveness, and unique physicochemical properties. **Table 1** presents the different types of biocompatible synthetic and natural polymers that have been electrospun into nanofibers with controlled-release functions.

#### **2.1 Mechanisms and kinetics for drug release**

Textile nanofibers produced through the electrospinning process have been highlighted in the development of new nanomaterials, being able to provide improved drug-delivery systems with immediate- or prolonged-release profiles, minimum toxicity, and reduced dosage frequency due to their intrinsic properties (e.g., porosity, wettability, fiber diameters, and specific orientation), as described above [3, 5, 8, 10, 11, 17]. Besides, textile-based drug loading and delivery nanofibers fabricated from different types of polymer-carriers have been proposed to accurately predict the diverse drug-release kinetics from the polymeric matrix since the drug can interact with the polymer carriers in several manners and be released from nanofibers based on drug diffusion from pores, drug desorption from the surface layer, and/or polymer matrix degradation. Hence, different release mechanisms will be achieved depending on the characteristics of the drugs and the produced nanofibers (**Table 2**) [3, 5, 8, 11, 12, 17].

For example, occasionally, it is desirable that the incorporated drug has the ability to produce rapid effects, being released in an immediate form. In these cases, a faster rate of drug diffusion from polymer structure should be achieved by using watersoluble and biodegradable polymers, like PVA, PEO, and Polyvinylpyrrolidone (PVP), being largely influenced by several factors, such as polymer swelling, wettability, porosity structure, polymer erosion, and drug dissolution/diffusion and distribution [3, 5, 8, 11, 12, 16]. On the other hand, a prolonged drug release, also denoted as a


**Table 1.**

*The most common biocompatible polymers used as drug-delivery carriers.*

controlled, extended, and sustained release, requires the use of polymers or polymeric blends with a gradual degradation profile [3, 8, 11]. In addition, the electrospun nanofibers with an extended drug-release profile should display an adequate wettability and a thickness appropriate, as well as exhibit a core–shell structure containing a drug-loaded layer and an outer polymer layer that acts as a rate-controlling barrier. Moreover, core–shell nanofibers could provide biphasic drug-release profiles, which consist of an initial burst release followed by a sustained release (**Figure 2**) [3, 8, 11].

More recently, pulsatile drug-release profiles, where a sharp burst release is observed after a lag phase with no release, have gained increasing interest in various drugs or therapies. Besides, stimulus-responsive drug-release profiles have also been explored, and in these cases, responsive polymers after exposure to different stimuli, like pH, light, temperature, water, and CO2, can change their physicochemical properties (**Figure 2**) [3, 5, 8, 9, 11].

Therefore, the solubility of the drug in the polymeric solution and the structure of the drug-loaded fibrous matrix can give valuable information about the release kinetics and consequently allow to tune of the desired behavior [3, 5, 8, 9, 11]. Concerning that, controlling the multiple electrospinning parameters that affect the nanofiber's features, such as fiber diameter, morphology, porosity, and wettability, and selecting the most suitable electrospinning technique for drug loading and subsequent


#### **Table 2.**

*Effect of the drug and nanofibers-related factors on the release kinetics.*

controlled release can produce good-quality textile-based drug loading and delivery materials [3, 5, 8, 9, 11]. In addition, the choice of the drug molecules and methodology applied to incorporate the drugs into the textile electrospun nanofibers can favor the location, amount, and timing of drug release needed to modulate the release profiles and achieve the desired effects [3, 5, 8, 9, 11].

*Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

**Figure 2.**

*Classification of the electrospun drug-loaded nanofibers based on their release profiles.*

## **3. Electrospinning techniques for drug loading and delivery**

A wide range of drug molecules, such as antibacterial molecules (e.g., antibiotics, nanoparticles (NPs), and natural extracts), molecules with biological activities, including anti-inflammatory, growth factors, vitamins, enzymes, and other proteins, as well as anticancer drugs, and nucleic acids (DNA and RNA) have been loaded into electrospun textile nanofibers through different electrospinning techniques, that comprise needle-based electrospinning and needleless electrospinning systems (**Figure 3**), in order to predict the location of drugs in the nanofibers and control the drug-release profile [3, 5, 8, 10–12, 16]. The drug loading using needle-based electrospinning techniques, like blending, side-by-side, coaxial, tri-axial, emulsion, and multi-needle electrospinning, add the drugs to the polymer solution before the electrospinning process and use a needle-like spinneret [3, 11, 12, 15, 18, 19]. On the other hand, needleless electrospinning methods, like the needle-free Nanospider technology, allow that multiple Taylor cones to be spun at the same time using a rotating electrode instead a needle, and hence this methodology is highly productive [3, 11, 12, 14, 18, 19]. In this way, the selection of the electrospinning technique can affect the role of the drug for its intended uses and manipulate its release rate and profile from the textile nanofibers [3, 11, 12, 14, 18, 19]. To accomplish that, the most common electrospinning methodologies for loading the drugs into electrospun textile nanofibers are described in detail below and their main advantages and disadvantages are summarized in **Table 3**.

## **3.1 Needle-based electrospinning**

The needle-based electrospinning techniques would have a direct impact on the drug loading and release behavior from the electrospun nanofibers. The needle-based

**Figure 3.** *Schematic representation of several electrospinning techniques for the preparation of drug-loaded nanofibers.*

systems can result in simple, core-shell, and multi-axial nanofibers comprising more than one textile material [3, 11, 14, 18]. However, in the needle electrospinning techniques, capillary tubes, such as a needle-like spinneret, are required to form the nanofibers [3, 11, 14, 18].

## *3.1.1 Blending electrospinning*

Blending electrospinning is the simplest and most basic method that uses a single nozzle to incorporate drugs into the electrospun nanofibers by blending them into the polymeric solution before the electrospinning process [14, 15]. In addition, different types of carrier materials and drugs can be processed by blending electrospinning, and hence it is the most researched and applied strategy for loading drugs into electrospun nanofibers. However, when this technique is used, in general, the drugs loaded are rapidly released from the nanofibers due to their homogeneous distribution all over the surface of the polymeric nanofibers and their high surface-to-volume ratio that favors the drug release. Nonetheless, their release depends on the degree of drug encapsulation into the polymeric matrix and the affinity between the drug and the polymer [14, 19]. Thus, to avoid an initial burst effect and ensure a more sustained release, the drugs absorbed and/or encapsulated into nanostructures, like NPs, nanospheres, nanomicelles, and nanotubes, can be added to the polymeric solution before the electrospinning process [14, 19].

Moreover, drugs with different properties can be blended into the same polymer carrier, and nanofibers with a biphasic drug release are obtained. For example, Li et al. dissolved PLGA (25% (w/v)) in a mixture of acetone and N,N-dimethyl formamide (DMF) with a volume ration of 3:1, and dexamethasone (DEX) at a concentration of 15% and green tea polyphenols (GTP) at concentrations of 5%, 10%, and 15% by weight of PLGA were added to the blend [22]. Afterward, the polymeric solutions were electrospun at a flow rate of 0.5 mL/h, using a working distance of 18 cm and an applied voltage of 23 kV. The results revealed that the DEX and GTP released from the electrospun nanofibers in PBS at pH 7.4 achieved a biphasic release profile. The hydrophilic GTP drug exhibited a faster release, while the hydrophobic DEX was successfully released from the channels formed by the fast-released GTP molecules. Thus, drugs with different hydrophilicity were used to achieve a biphasic release profile from the same polymer solution, which was controlled by the drugs' diffusion rate and the


*Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

## *Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

degradation of the polymer carrier [22]. Furthermore, stimuli-responsive nanofibers could also be produced by blending electrospinning. Li et al. produced electrospun silk fibroin/PEO (SF/PEO) nanofibers with a pH-responsive controlled-release behavior [23]. For this purpose, 5 mol% strontium or copper-doped hollow bioactive glass nanospheres (5Sr/Cu-HBGNs), synthesized via a sol–gel method, were loaded with a 2.5 mg/mL aqueous solution of vancomycin hydrochloride (VAN), a glycopeptide antibiotic that inhibits bacterial cell wall synthesis, and incorporated in a mixture of 10% SF/3% PEO to produce 2% w/v solutions. The release kinetics behavior of VAN from VAN@5Sr/Cu-HBGNs/PEO/SF nanofibers in PBS at pH of 4.5 and 7.4 demonstrated that VAN@doped HBGNs/PEO/SF nanofibers presented a slower and sustained release rate in comparison with VAN@HBGNs/PEO/SF. Besides, the cumulative release of VAN from the electrospun VAN@5Sr/Cu-HBGNs/PEO/SF nanofibers at pH 7.4 was faster than at acidic microenvironments (pH 4.5), indicating that the drug release increased with an increase in pH along with a quick VAN desorption release. Thus, their pH sensitivity can be explained by the different solubility and both hydrophilic nature and amphoteric properties of SF under acid and alkali conditions [23].

#### *3.1.2 Side-by-side electrospinning*

The side-by-side electrospinning technique is a variation of the basic single nozzle electrospinning comprised of two capillaries placed one adjacent to the other to produce nanofibers with Janus structures and materials with two distinct layers [3, 14, 18]. However, this method is not easy to perform, since both capillaries, containing different polymer solutions, are controlled by the same pump, and the same voltage is applied to both solutions, which causes repulsion between the two different polymers and separate from each other [3, 14, 18]. Hence, few studies have been developed in order to fabricate electrospun textile nanofibers with a Janus structure [3]. However, the side-by-side bi-component fibers exhibit the characteristics of both polymers, and consequently, we can achieve a biphasic drug-release profile required for a particular type of drug and application [14]. Thus, a biphasic drug release can be achieved by incorporating the drug on both sides of the fiber, where one side consists of a watersoluble polymer and the other side of a water-insoluble polymer [14]. On the side composed of the water-soluble polymer, the drug diffusion rate will be affected by polymer erosion and will be faster, while on the side containing the insoluble polymer, the drug release will be extended [14].

Shi et al. used side-by-side electrospinning to combine a solution of 10% (w/v) PLGA with an anti-inflammatory drug (0.2% (w/v) valsartan, V) and a solution of 15% (w/v) PVA with copper sulfide nanoparticles (CuS NPs) and an antibacterial drug (mupirocin, M) [24]. Both solutions were placed in two different syringes with 26 G blunted spinning needles and electrospun at a constant feeding rate of 1.0 mL/h, using a working distance of 20 cm and an applied voltage of 15 kV. The Janus amphiphilic nanofibers composed by a hydrophobic side of PLGAV-CuS NPs and a hydrophilic side of poly(vinyl alcohol) mupirocin nanofiber (PVAM) exhibited a biphasic drug release mechanism. The cumulative release of the hydrophilic antimicrobial drug, mupirocin, from PLGAV-CuS/PVAM nanofibers enabled a continuous and slow release, reaching 89.36% after 24 h of incubation [24]. The sustained release of mupirocin can be attributed to the hydrogen bonding between the drug and the PLGAV-CuS/PVAM. In addition, the water uptake ability of the PLGAV-CuS/PVAM nanofibers could have a certain blocking effect on the release of mupirocin. In turn, the release profile of valsartan reached only 23.77% after 24 h, providing a slow release of drug from nanofibers. This result confirms that the diffusion of hydrophobic drugs in a hydrophilic environment is hindered. Therefore, the PLGAV-CuS/PVAM Janus nanofibers initially released mupirocin more quickly, and then, the valsartan and remaining mupirocin were continuously released, achieving tunable antibacterial and anti-inflammatory gradient drug release systems [24].

#### *3.1.3 Coaxial electrospinning*

Coaxial electrospinning technique also uses two capillaries, like side-by-side electrospinning, however, in coaxial electrospinning the capillaries are arranged one inside the other. In addition, the concentric capillaries, i.e. the inner capillary coaxially placed inside the outer one, are connected to two independent reservoirs, with controllable flow rates [11, 14, 18]. Concerning that, coaxial electrospinning allows the production of core-shell nanofibers with different core and shell compositions, including functional fibers encapsulated with different drugs and hollow nanofibers with adjustable shell thickness by selectively removing the core from as-spun core-shell nanofibers [11, 14, 18].

Hence, core-shell nanofibers produced from coaxial electrospinning provide an added advantage as carriers for drug delivery, protecting the drugs' native structure and their bioactivity from harsh environments during textile nanofibers production [11, 14, 19]. In addition, the drugs loading into the core of the textile nanofibers can significantly reduce and/or prevent the initial burst release rate from the polymeric matrix and maintain a sustainable drug release for an extended and controlled time [11, 14, 19]. Moreover, this technique contributes greatly to the high loading capacity of diverse drugs and allows susceptible drugs to be delivered. Furthermore, core-shell nanofibers prepared from miscible and immiscible polymers can be produced through coaxial electrospinning, as well as from nonspinnable solutions and polymers and drugs with low compatibility [11, 14, 19]. However, this technique requires a special apparatus, and the operating conditions should be carefully chosen to ensure desirable results [11, 14]. Nevertheless, coaxial electrospinning has the ability to adjust the thickness of both layers *by changing the flow rate*, particularly the shell thickness that acts as a barrier to diffusion, controls the release kinetics of the encapsulated drugs, and enables the potential to simultaneously load various components [14, 19]. Therefore, core-shell nanofibers fabricated from the coaxial electrospinning technique can effectively avoid the initial drugs' explosive release and achieve a sustained release profile. For example, Li et al. successfully produced Xylan/PCL core–shell nanofibers using coaxial electrospinning. In this study, Xylan aqueous solution (20 *w/w*%) containing the antiinflammatory drug levofloxacin (LEV) was used as core and coated by (12 *w/w*%) PCL solution (shell). The solutions were placed in two coaxial injectors and electrospun at an applied voltage of 14 kV, using a collecting distance of 15 cm, a constant flow rate of 1.0 mL/h for the Xylan solution and a flow ration between Xylan and PCL of 1:1.1, 1:1.2, and 1.1.4, respectively. The results obtained revealed that the hydrophobicity of the PCL prevents a burst release and short diffusion of the LEV loaded into the watersoluble Xylan core. Additionally, the increase in PCL's flow rate resulted in a lower degradation rate of the nanofibers due to the thicker fibrous shell layer and consequently can be used to produce a slow drug release [25].

## *3.1.3.1 Tri-axial electrospinning*

Coaxial electrospinning can be used to produce textile nanofibers with more complex architectures, namely by using a tri-axial electrospinning technique, composed of

## *Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

three concentric capillaries [3, 14]. The three-layer core-shell nanofibers are formed from an external polymeric solution, an intermediate polymeric solution, and a core polymeric solution controlled by different pumps [3, 14]. Besides, the tri-axial nanofibers can be produced with the core enclosed by two different polymer layers or with two layers of the same polymer. Moreover, the core polymers can also be surrounded by an outer polymer layer and a layer of void areas. In turn, different drugs can be incorporated into the core, or in each different layer, and released by diffusion and degradation [3, 14]. The three-layer textile nanofibers can be also prepared with targeted drug-release functions for medical applications in order to improve the drug efficacy and reduce its toxicity and side effects, as well as with a linear and constant release rate in order to eliminate the drug burst release [3, 14]. Likewise, the drug content can be changed by using a tri-axial electrospinning technique, creating an increased drug gradient distribution from the outer layer to the inner layer. Thus, in comparison with the double-layer core-shell nanofibers produced from coaxial electrospinning, the tri-layer core-shell nanofibers prepared by tri-axial electrospinning provide more potential to overcome the limitation of poor drug solubility, protect drugs from the adverse environments, and control the drug-release kinetics for developing functional textile-based drug loading and delivery materials [3, 14, 26].

Ding et al. compared the capacity of aspirin-loaded ES100 core-shell nanofibers (produced with an improved tri-axial electrospinning system) (CSFs) with the monolithic composite (prepared with the same material using a traditional blended single-fluid electrospinning) (MCFs) for a sustained drug release. The CSFs revealed better results than the MCFs, although the release of aspirin from both occurred through an erosion mechanism [27]. The CSFs exhibited a prolonged release of the drug and showed a lower release rate during the first 2 h under acidic conditions. In addition, in a posterior neutral environment, a prolonged drug release was obtained by an extended-release effect [27].

#### *3.1.4 Emulsion electrospinning*

Emulsion electrospinning is a uniaxial electrospinning technique, which has attracted growing interest in the production of core-shell textile nanofibers without the use of specific coaxial apparatus [11, 14, 18, 19]. This method is similar to conventional electrospinning, apart from that the polymeric solution is replaced by a water-in-oil (W/O) or oil-in-water (O/W) emulsion [14]. In the emulsion electrospinning, most emulsions are of the W/O type, where the drug is usually dissolved in an aqueous phase composed mainly of water-soluble polymers (i.e., the water phase) and then dispersed in a continuous-phase composed of an organic polymer solution (i.e., the oil phase) [14, 19]. The droplets of the water phase dispersed in the oil phase evaporate more slowly than the organic polymer solution, resulting in a viscosity gradient between the two different phases. Subsequently, this gradient guides the droplets of the water phase from the surface to the center, the droplets are stretched into elliptical shapes along the axial region under a high voltage and the core-shell nanofibers containing the drug into the core are formed [14]. Hence, W/O emulsions, in which the hydrophilic drugs are dissolved in an aqueous polymer solution, while hydrophobic polymers are dissolved in organic solvents, are particularly useful for a drug continuous and sustained release, avoiding the initial burst release, typical of most drug-delivery materials, as well as play a role in protecting the drugs in the core from the harmful effects of the external environment, enhancing their bioactivity and effectiveness [11, 14, 19]. Moreover, the drugs are released faster in the shell than in the core layer; once the drugs are loaded into the core have to pass through the core-shell matrix before being released. Furthermore, good-quality core–shell nanofibers can be produced through emulsion electrospinning using diluted polymer solutions [19]. Various combinations of hydrophilic drugs and hydrophobic polymers with low compatibility and affinity can also be explored, removing the necessity of using a common solvent for both the drug and the polymer [18]. However, emulsifiers such as surfactants are frequently used to stabilize the emulsions and the encapsulated drugs [11, 19].

Weng et al. prepared camellia oil-loaded zein nanofibers with a core-shell structure using an emulsion electrospinning technique. For this purpose, zein (30% *v/v*) aqueous solution was firstly prepared in acetic acid (70% *v/v*) and then camelia oil was dropped at 10, 20, 40, and 60% (*v/v*) based on the zein solution. After stirring for 1 h, 30% (*w/w*) of glycerol (based on the weight of zein) was added as a plasticizer. The blends were mixed with a high-speed homogenizer at 1000 rpm for 3 min and then treated by ultrasonic for 2 min at 250 W at 25°C to obtain the required O/W emulsions. Afterward, the emulsions were placed in the syringe and electrospun at a flow rate of 0.5 mL/h, using a working distance of 12 cm and an applied voltage of 20 kV. The results of this study demonstrated that core–shell nanofibers of zein with camellia oil could be used as a promising controlled-release carrier for hydrophobic bioactive compounds [28].

#### *3.1.5 Multi-needle electrospinning*

The multi-needle electrospinning is one of the simplest techniques to achieve nanofibers with high throughput [20]. This electrospinning technique implies passing a polymeric solution through multiple needles connected to a high-voltage supply. In addition, the flow rate is controlled by a single pump and is required the application of a higher voltage to continuous electrospinning due to the large mass of the spinning solution [20]. Nevertheless, multi-needle electrospinning presents several drawbacks, such as unstable electric field strength, changes in fiber size distribution, clogging at the tip of the needles, and cleaning of multiple needles. In addition, the multi-needles may also provide repulsion from adjacent jets. Nonetheless, multiple drugs can be added, and diverse release profiles can be achieved [20].

Varesano et al. tested several multi-jet electrospinning setups using a 7 wt% PEO aqueous solution and varied the number of nozzles between 2 and 16. The data obtained showed that when increasing the number of jets above 6 was imperative to increase the collector dimensions because the deposition area also increased [29]. Hence, multi-needle electrospinning systems have great potential for large-scale nanofibers production. Moreover, Yoon et al. fabricated Polystyrene (PS)/Polyamide 6 (PA6) nanofibers using multi-jet electrospinning and revealed that the fiber content was directly related to the syringes' number used for PS and PA6, respectively [30].

#### **3.2 Needleless electrospinning techniques**

The needleless electrospinning does not use a needle-like spinneret but static or rotating spinnerets, which can be a cylinder, a ball, a disc, and/or a rotating electrode, immersed into an open container with the polymeric solution in order to produce nanofibers in higher quantities for industrial range [18, 20]. Nevertheless, when the open container is filled with a polymer solution dissolved in volatile solvents, the

### *Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

solvent evaporates quickly and can affect the reproducibility of fiber morphology. Moreover, in needleless electrospinning, many Taylor cones (the source of nanofibers) are created simultaneously on the surface of the spinnerets, and hence these techniques are highly productive and more effective in producing high-quality nanofibers [20, 21]. For example, in the Nanospider technology, a needleless electrospinning technique, a rotating electrode/roller transport the polymer solution from the container, allowing industrial-scale production of nanofibers [20, 21]. In this way, Nanospider is a pilot electrospinning equipment, already used on an industrial scale, which allows an easy scale-up. Furthermore, this is a simple and versatile technique for textile nanofibers production from a wide range of materials [20, 21]. Regarding that, Mouro et al. incorporated *Hypericum perforatum* L., a medicinal plant extract, in a PLLA/PVA/CS emulsion via Nanospider, a needleless electrospinning technology. The results obtained showed a controlled and sustained release profile of the *Hypericum perforatum* L. from the produced nanofibers for 72 h. In addition, the release speed was dependent of the content of plant extract incorporated and the swelling of the produced nanofibers [31].

Recently, electrospinning derivative technologies, such as melt electrospinning and centrifugal electrospinning, have also arisen as promising approaches [3, 8, 14, 32, 33]. The melt electrospinning is a solvent-free process and hence a more efficient and environmentally friendly technique. A typical melt electrospinning setup includes a heated polymer fed into a spinneret. However, like traditional electrospinning, a high electric potential is applied between the spinneret and the collector for producing the textile nanofibers [8, 14, 33]. Moreover, melt electrospinning enables the production of nanofibers in the absence of residual solvents because it does not require the dissolution of the polymers in organic solvents. In addition, various materials can be used to fabricate nanofibers. However, this technique only uses materials that melt, and polymer degradation or denaturation can occur because high temperatures are applied [8, 14, 33]. On the other hand, the centrifugal electrospinning technique combines the electrostatic force of the electrospinning and the centrifugal force to promote jet stretching [3, 32]. Centrifugal electrospinning is a simple and cost-effective method that allow the fabrication of highly aligned and small-diameter textile nanofibers, upon applying adjusted rotational speeds and voltages, for drug delivery and regenerative medicine applications [3, 32]. Regarding that, in centrifugal electrospinning, the electrical fields allow the spinneret to rotate at a slower speed and simultaneously a lower voltage to overcome the surface tension of the spun solution is required [3, 32].

## **4. Applications of the electrospun textile drug-delivery materials in medical fields**

The unique features of the electrospun textile materials, namely the high surface area, tunable porosity, and smaller diameter of the fibers, as well as the easy optimization of the nanofiber's properties through controlling the different parameters, like the solution properties, processing parameters, and environmental conditions, made them ideal for drug loading and delivery applications [3, 5, 8, 9, 12, 14]. Moreover, the various electrospinning techniques allow for incorporating a wide range of drugs with high loading and encapsulation efficiencies into diverse polymer-textile nanofibers [3, 5, 11, 12, 14, 18, 19].

Therefore, this section is focused on the textile-based drug loading and delivery of nanofibrous materials produced from the different electrospinning techniques for

medical applications. Regarding that, it is provided an overview of the recent studies for applications in bone, nerve, periodontal, and vascular regeneration, as well as in wound dressings and other textile-based materials, like PPE and cancer treatment. Furthermore, **Table 4** are presented several studies where the authors prepared drug-loaded nanofibers using different electrospinning technologies for medical applications.

#### **4.1 Bone tissue regeneration**

Nanofibers produced from electrospinning have been investigated for bone regeneration due to their intrinsic properties, such as biocompatibility, highly porous structure, small pore size, high surface area, three-dimensional (3D) architecture, and mechanical features that are compatible with the natural nanostructure of bone. In addition, different drugs have been incorporated into these nanofibrous structures to improve bone regeneration [8, 16].

In 2022, Canales et al. produced electrospun fibers of Poly(lactic acid) (PLA) containing bioactive glass (n-BG) and magnesium oxide (n-MgO) NPs to be used in bone tissue engineering applications [49]. Their results showed that the electrospun PLA/n-BG and PLA/n-BG/n-MgO fibers presented a significant increase in fiber diameter with mean diameter values of 3.1 0.8 μm, while the neat PLA and the PLA/n-MgO displayed an average fiber diameter of 1.7 0.6 μm [49]. Besides, the electrospun PLA/n-BG/n-MgO fibers presented a high porosity and an interconnected pore structure required for tissue engineering applications. However, the incorporation of the NPs affected the thermal properties and mechanical properties [49]. All the composite fibers containing n-BG showed the capability to precipitate hydroxyapatite on the surface, demonstrating their bioactivity, while the addition of the n-MgO to PLA provides antibacterial properties against *S. aureus* [49]. Moreover, the osteoblastic phenotype expression ability of the produced composite fibers was assessed in comparison with the neat PLA fibers measuring the alkaline phosphatase expression (ALP), a marker of osteoblastic activity known for its capacity to promote cell differentiation, and the results indicated that the PLA/n-BG presenting the highest osteoblastic expression. Therefore, this study revealed that the incorporation of both n-BG and n-MgO NPs into the PLA can be considered to produce a synergic effect increasing its bioactivity and antimicrobial behavior [49].

Huang et al. encapsulated citrate-stabilized gold-nanoparticles (GNPs) into PVP/ Ethylcellulose (EC) by coaxial electrospinning technique in order to create core-shell nanofibrous membranes [50]. In this study, the core-shell nanofibers were prepared by coaxial electrospinning with EC as the core and PVP containing GNPs as the shell. The GNPs-loaded electrospun PVP/EC nanofibers were prepared by changing the feeding GNPs to 0.5:1, 1:1, and 1.5:1 (P/E-0.5, P/E-1, and P/E-1.5), respectively [50]. The data obtained revealed that the GNPs were successfully encapsulated into the electrospun nanofibers. Besides, the GNPs addition did not significantly affect the morphology of the nanofibers, although it improved the porosity and the mechanical properties of the nanofibers [50]. Furthermore, the presence of the GNPs in electrospun PVP/EC membranes triggered a higher alkaline phosphatase activity, mineralized nodule formation, and osteogenic-related genes expression, thus confirming the excellent biocompatibility and osteogenic bioactivities of the produced composite material [50]. The *in vivo* studies also confirmed that GNP-incorporated electrospun PVP/EC nanofibers accelerate bone regeneration. Hence, the produced coaxial electrospun membranes demonstrated the appropriateness for being


*Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*






#### **Table 4.**

*Several drug-loaded nanofibers using different electrospinning techniques for medical applications.*

considered as a promising material for bone repair [50]. In a similar way, Alam et al. produced coaxial PCL/Gelatin/Poloxamer 188 (P-188) nanofibers for duel release of βlactoglobulin (a hydrophilic protein) and vitamin K2 (a hydrophobic agent) from core and shell fibers [51]. The coaxial electrospun nanofibers produced from the PCL/P-188 shell and Gelatin/P-188 core displayed superior stability, average weight loss, no water uptake ability, and a sustained, controlled release of both β-lactoglobulin and vitamin K2 [51]. Moreover, these nanofibers also significantly enhanced alkaline phosphatase activity and promoted higher cell viability for human osteogenic sarcoma cells (Saos-2 cells), and thereby, coaxial PCL/Gelatin/P-188 nanofibers can release both hydrophilic and hydrophobic bioactive compounds and be a promising bioactive material for bone tissue engineering with improved osteogenic properties [51].

Electrospun nanofibers with a core-shell structure have also been produced by emulsion electrospinning for bone tissue regeneration. For example, Boraei et al. fabricated core-shell nanofibers from PVA and PCL by water-in-oil electrospinning encapsulated with strontium ranelate (SrR), an osteogenic agent [52]. The authors successfully obtained nanofibers with a shell of PCL (the oil phase) and a core of PVA incorporated with SrR (the water phase). In addition, higher contents of SrR induced the formation of fibers with increased diameters and decreased the crystallinity of the nanofibers [52]. Moreover, the SrR release from the electrospun core-shell nanofibers occurred through a Fickian diffusion mechanism, and it was more evident a quicker drug dissolution in the samples with higher SrR content [52]. Additionally, the incorporation of the SrR improved mesenchymal stem cell proliferation and enhanced the expression of ALP, Runx2, Col I, and OCN genes. The *in vivo* assays also showed that animal models treated with the core-shell nanofibers displayed an increased bone formation of calvarial defects [52]. Further, Al-Baadani et al. investigated the suitability of the electrospun PCL/Gelatin membranes containing different drugs/proteins, like fluorescein isothiocyanate-bovine serum albumin (FITC-BSA), vancomycin hydrochloride (Van), and simvastatin (Sim) to improve the antibacterial and osteogenic activities [42]. This approach combined the biocompatibility of the Gelatin, namely its ability to improve the adhesion and differentiation of osteoblasts, with the mechanical properties of the PCL. The results showed that the produced membranes from coaxial electrospinning could be utilized as drug-carriers for slow-release hydrophobic drugs, like Sim, loading in the PCL solution, and for controlled-release of hydrophilic drugs/proteins, like FITC-BSA and Van, loading in Gelatin solution, adjusting the PCL content [42].

Additionally, the electrospun nanofibers have also been applied to restore other structural tissues, namely skeletal muscle and cartilage ligament.

#### **4.2 Nerve tissue regeneration**

Neural tissue repair is one of the major challenges faced by the researchers because the most common neural injuries result in an irreversible loss of function [16]. In this context, biocompatible polymer nanofibrous conduits, with customized lengths and sizes and controlled delivery of drugs for nerve regeneration, have recently been investigated using different electrospinning techniques. In addition, both aligned and randomly oriented nanofibers have been further explored in order to improve neural stem cell adhesion and differentiation, as well as neural tissue regeneration [8, 16].

Alipour et al. explored the encapsulation of fingolimod-loaded PLGA nanoparticles into electrospun PU/PCL/Gelatin nanofibers for promoting neurite formation and axonal regeneration. Different amounts of fingolimod (0.01, 0.02, and 0.03%), a useful drug in nerve regeneration, were studied. The increased content of drug loaded into the membranes resulted in an increase in the nanofiber's mean diameter [53]. Nevertheless, the nanofiber's diameters of the produced membranes are in the acceptable range displayed by nerve tissues, as well as the degradation rate, the mechanical properties, and the water uptake behavior [53]. Besides, the electrospun PU/PCL/Gelatin nanofibrous membrane loaded with 0.01% fingolimod through PLGA NPs provided a more favorable environment for cell growth and proliferation. Moreover, the release profile of the fingolimod from this membrane displayed a burst release behavior during the first 24 h, and then a slow release occurred for up to 5 days [53]. Therefore, the electrospun PU/PCL/Gelatin nanofibers loaded with fingolimod NPs can be a suitable candidate for application in neural tissue engineering [53].

Xia et al. incorporated the recombinant human vascular endothelial growth factor (VEGF) and the recombinant human nerve growth factor (NGF) on the shell and in the core of the PLLA nanofibers by emulsion electrospinning [54]. The electrospun coreshell nanofibrous membranes with VEGF on the shell and NGF in the core displayed a sequential release profile, in which most of the VEGF was released in the first few days, and the NGF could be gradually released from the PLLA core nanofibers for >1 month [54]. Besides, the nanofibers containing the NGF and VEGF encouraged the nerve differentiation of induced pluripotent stem cells-derived neural crest stem cells (iPSCs-NCSCs) in vitro [54]. Moreover, in vivo data showed that, after 3 months, animals treated with the dual-delivery of VEGF and NGF membrane showed a significant improvement in neovascularization and nerve healing postoperation [54].

In turn, Alipour et al. reported the incorporation of vitamin C (VC) at concentrations of 5, 10, and 15 wt.% into PCL/Polyglycerol Sebacate (PGS) nanofibers [55]. The nanofibers produced from a rotating drum collector presented an aligned and uniform appearance, although the incorporation of the VC induced a decrease in the nanofibers' mean diameter. In addition, the electrospun membranes exhibited appropriate properties for nerve applications, namely mechanical properties, wettability, water uptake capability, and degradation [55]. Furthermore, the release profile of VC was characterized by an initial burst, followed by a gradual release, which is fundamental for more beneficial therapeutic effects on peripheral nerve regeneration. However, the electrospun PCL/PGS nanofibers containing 5 wt.% VC provided a more favorable environment for PC12 cell adhesion and migration [55].

### *Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

Chen et al. prepared multilayered membranes with a PCL outer layer, a Fe3O4 magnetic NPs (Fe3O4-MNPs)/PCL middle layer, and a melatonin (MLT)/PCL inner layer for peripheral nerve regeneration [40]. The results obtained revealed a sequential and sustainable drug release appropriate for mitigating oxidative stress and inflammatory response and inducing a microenvironment suitable for nerve regeneration [40]. In fact, the composite nanofibrous membranes showed satisfactory mechanical strength, in vitro biocompatibility in contact with rat Schwann cells (RSC 96), and beneficial effects for nerve regeneration in vivo [40]. Further, Mohamadi et al. obtained electrospun conduits from the PCL/collagen/nanobioglasses (NBG) blends, and the NGF was loaded in the structure of conduits [56]. Their results showed that the PCL/Collagen/NBG containing NGF revealed the potential to be applied to promote sciatic nerve regeneration. In addition, the NGF-loaded conduits exhibited the ability to enhance the recovery of the injured sciatic nerve [56].

In 2023, for the first time, Puhl et al. delivered mRNA encoding NT-3 from the aligned electrospun PLLA fibers for peripheral nerve regeneration [57]. In this approach, the PLLA fiber's surface was functionalized with poly(3,4-dihydroxy-Lphenylalanine) (pDOPA) or coated with dextran sulfate sodium salt (DSS). Then, lipoplexes were obtained by complexing the synthesized pseudouridine-5'-triphosphate (Ψ)-modified mRNA encoding NT-3 (ΨNT-3mRNA) with the cationic delivery vehicle JetMESSENGER® and immobilized to the fiber PLLA surface [57]. The cationic lipoplexes containing ΨNT-3mRNA complexed to JetMESSENGER® were immobilized into PLLA fibers resulting in detectable ΨNT-3mRNA release for 21 days. Moreover, the ΨNT-3mRNA/JetMESSENGER® lipoplex-immobilized pDOPA-coated aligned electrospun PLLA fibers showed the capability to support Schwann cell secretion of NT-3 and enhance neurite outgrowth from dorsal root ganglia (DRG) neurons [57].

### **4.3 Periodontal tissue regeneration**

Periodontal tissue is a complex tooth-supporting connective structure, in which soft, mineralized connective and epithelial tissues are structured to form a dentogingival junction [8]. However, it is highly susceptible to chronic periodontal diseases, like periodontitis, resulting in irreversible tissue destruction. Thus, to restore tissue integrity and improve periodontal regeneration, researchers have produced diverse nanofibrous membranes via electrospinning and incorporated different drugs with antibacterial, anti-inflammatory, and tissue regeneration properties [8].

Ranjbar-Mohammadi et al. prepared a PLGA/Gum tragacanth (GT) blend via blending electrospinning and PLGA/GT core-shell nanofibers via coaxial electrospinning at various ratios [58]. The tetracycline hydrochloride (TCH), a hydrophilic model drug, was incorporated within these nanofibers in order to investigate the drug-release kinetics displayed by the produced membranes. The authors obtained uniform nanofibers of PLGA, blend PLGA/GT, and core-shell PLGA/GT [58]. Moreover, the drug release of the TCH from the blend nanofibers and the coreshell structures can be controlled throughout both membranes. However, the incorporation of the TCH into PLGA/GT core-shell nanofibers exhibited a more prolonged release for 75 days with a smaller burst release within the first 2 h [58]. Thus, the more sustained release of the TCH from the core-shell membranes allied with their proven biocompatibility, antibacterial, and excellent mechanical properties make them suitable for periodontal regeneration purposes [58].

In turn, Chachlioutaki et al. used silk sericin, a natural protein derived from silkworm cocoons, and PLGA to incorporate an anti-inflammatory drug, ketoprofen, by blending electrospinning [59]. Their results revealed an increase in the hydrophilic character of the composite membranes, good mechanical properties, and a sustaining drug release for up to 15 days [59]. Besides, the in vitro assays demonstrated that the silk sericin-PLGA composite membranes promote the attachment and proliferation of human gingival fibroblasts and induce a significant downregulation of the specific pro-inflammatory markers MMP-9 and MMP-3 and an upregulation of the antiinflammatory gene IL-10 on lipopolysaccharide-simulated RAW 264.7 macrophages [59]. Further, Zupančič et al. incorporated resveratrol (RSV) at different quantities (1, 5, 10, and 20% (w/w)) into PCL electrospun nanofibers. RSV loaded into the PCL nanofibers below 5% resulted mostly in the form of solid dispersion, while at higher loading were observed nanocrystals on the fibers surface [60]. The PCL nanofibers loaded with RSV showed a bi-phase release kinetic due to the drug dissolution and cleavage of hydrogen bonding and hydrophobic interactions between the PCL and the RSV. Thus, the RSV-loaded PCL nanofibers showed their suitability to be used as drug-delivery systems for the treatment of periodontal disease [60].

In 2022, Zhong et al. produced via electrospinning a bi-layered nanofibrous membrane composed of an antibacterial layer of PLGA/Gelatin loaded with nano-silver (nAg) and an osteoconductive layer of PLGA/Gelatin loaded with nanohydroxyapatite (nHA) for periodontal tissue regeneration and reestablishment [61]. Both nAg and nHA were successfully incorporated into the electrospun PLGA/Gelatin nanofibers. Additionally, in vitro assays indicated that the nanofibrous membranes displayed excellent cytocompatibility and the PLGA/Gelatin nHA-PLGA/Gelatin osteoconductive layer exhibited an improved osteogenic ability for human osteoblastlike cells (MG63), as confirmed by the good cell viability and the increased alkaline phosphatase (ALP) activity, respectively [61]. On the other hand, the nAg-PLGA/ Gelatin antimicrobial layer of the bi-layered nanofibrous membranes presented an effective antimicrobial capability against *S. aureus* and *E. coli* [61]. Jenvoraphot et al. combined poly(l-lactide-co-ε-caprolactone) (PLLCL) with Tetracycline to produce electrospun membranes that promote periodontal regeneration and deliver an antiinflammatory and antibiotic drug [62]. The release profile of TC from the electrospun PLLCL membranes was characterized by a controllable slow release of the drug from the nanofibers. Besides, the in vitro assays demonstrated that the electrospun PLLCL membranes containing TC promote the proliferation of human oral fibroblast (HOF) and human oral keratinocyte (HOK) cells and exhibit antibacterial properties [62].

Peng et al. produced coaxial magnesium oxide (MgO) NPs-incorporated PCL/ Gelatin core-shell nanocellulose membranes for periodontal tissue regeneration [63]. The encapsulation of the MgO within the core-shell PCL/Gelatin nanocellulose nanofibrous membranes assured their sustained release and promoted the adhesion and proliferation of human periodontal ligament stem cells (hPDLSCs) due to the biocompatibility and hydrophilicity of the Gelatin shell layer [63]. Furthermore, in vitro osteogenic and antibacterial activities were enhanced in the PCL/Gelatin nanocellulose membranes containing MgO nanoparticles [63]. Additionally, Pouroutzidou et al. reported the incorporation of the Moxifloxacin-loaded Silica-based mesoporous nanocarriers (MSNs) in PLGA composite membranes produced through electrospinning [64]. The produced drug-loaded composite fibrous membranes presented a controlled and prolonged release profile, ensuring a desirable antibacterial activity against a wide range of periodontal pathogens, good hemolytic behavior, and a protective effect on the erythrocytes [64].

*Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

#### **4.4 Vascular grafts tissue regeneration**

The electrospun nanofibers have emerged as a promising alternative to produce vascular grafts due to their ability to control the mechanical properties, the fiber diameters, the porosity, and the pore size [16]. In addition, electrospinning is a highly versatile method and allows to produce of materials with different structures and forms, as well as combining the advantages of synthetic and natural materials, which are vital for tissue-engineered grafts. Moreover, the different electrospinning techniques offer control over the alignment of the nanofibers, which can result in the orientation of the cells in a specific direction, able to provide the anisotropy encountered in certain organs including blood vessels [16].

Yang et al. prepared PCL solutions containing rapamycin (RM) that were electrospun outside the decellularized vascular graft in order to produce an RM-loaded vascular graft [65]. A small-diameter RM-loaded vascular graft showed superior mechanical properties and a sustained drug-release profile, which is considered ideal for prolonged bioactivity. Moreover, in vivo assays demonstrated that, 12 weeks after implantation, the hybrid electrospun RM-loaded decellularized vascular grafts were able to significantly reduce intimal hyperplasia without impairing reendothelialization and M2 macrophage polarization [65]. Kuang et al. combined the electrospinning and freeze-drying technology to create core-shell structures of poly(l-lactide-cocaprolactone) (PLCL) (core) nanofibers coated with heparin/silk gel (shell) [66]. The core PLCL nanofibers were designed to provide mechanical support during vascular reconstruction, while the shell heparin/silk gel layer improved the biocompatibility of the grafts. The release of heparin from silk gel-PLCL composite nanofiber graft could regulate the microenvironment in the early stage after transplantation and inhibit intimal proliferation [66]. Besides, the graft showed an auspicious biodegradation rate and was safe. Furthermore, the composite nanofiber graft provided to be a useful model for remodeling vascular structures, and in vivo assays demonstrated that the graft remained unobstructed for a long period of time (for more than 8 months) [66].

In 2021, Han et al. produced coaxial electrospun core-shell structure fibers for small-diameter vascular grafts incorporated with puerarin (PUE) [67]. The gelatin by taking PLLA was used as a carrier material, while multi-walled carbon nanotubes (MWNTs) were used as reinforced materials. The obtained results revealed that the produced Gelatin/PLLA/MWNTs-PUE fiber membranes displayed wettability, degradability, and mechanical properties similar to those presented by the natural blood vessels [67]. Besides, the PUE release from the Gelatin/PLLA/MWNTs grafts occurred in an effectively prolonged and highly efficient manner. Moreover, the fiber membrane did not induce any cytotoxic effects or side effects on endothelial cells, as well as any hemolytic activity [67]. Likewise, Maleki et al. explored the electrospinning and freeze-drying methods to fabricate a bilayer vascular graft with a core-shell structure [68]. An anticoagulant core layer composed of electrospun nanofibers of silk fibroin (SF) and thermoplastic polyurethane (TPU) containing Heparin (Hep) and a shell highly porous hydrogel layer fabricated by the freezedrying method was used to produce a bilayer tubular vascular graft [68]. Their results revealed that the electrospun TPU-SF-Hep fibers showed robust mechanical properties, while the hydrogel layer increased the viability of the smooth muscle cells (SMCs) [68]. The Hep displayed a sustained release from the proposed graft over 40 days, as well as excellent cell and blood compatibility, as shown by 3-(4,5 dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and platelet adhesion test [68].

#### **4.5 Wound dressings**

The electrospun nanofibrous membranes have been widely used for efficiently wound healing and skin regeneration due to their ability to mimic the randomly oriented 3D structure of the collagen fibers found within the skin's ECM and suitable mechanical properties [8, 16]. Moreover, these membranes display high porosity, small and interconnected pore size, and high surface area, which provide a suitable microenvironment for cell adhesion and proliferation, as well as excellent nutrients/ oxygen permeability, controllable evaporative water loss, and fluid drainage ability [8, 16]. Furthermore, various drugs, including antimicrobials, anti-inflammatories, growth factors, vitamins, and even cells, have been loaded into electrospun nanofibers for achieving antibacterial, antifungal, anti-inflammatory, antioxidant, analgesic, and anesthetic properties, which are vital for wound dressing applications [8, 16].

Yao et al. prepared peanut protein isolate (PPI)/PLLA nanofibers loaded with f 5, 10, and 15% of tetracycline hydrochloride (TCH) for being applied as wound dressing materials [69]. The PPI was developed using the alkali-dissolved acid precipitation method, and then the blend PPI/PLLA containing TCH was obtained via electrospinning. The incorporation of TCH did not affect the morphology of the nanofiber membranes, although the fiber diameter decreased when TCH content increased, while the wettability and mechanical properties improved [69]. Besides, the TCH was released from the PPI/PPLA composite nanofibers through a Fickian diffusion process. Moreover, the hemolysis rates were below 5%, which indicated the safety of the drug-loaded PPI/PLLA nanofibers, and the TCH-loaded PPI/PLLA composite nanofibers maintained the anticoagulant effect and showed low toxicity to cells [69]. The TCH/PPI/PLLA nanofibers also exhibited an inhibitory effect on *S. aureus* and *E. coli* growth and promoted skin wound healing in mice [69]. In turn, Yang et al. produced electrospun Janus nanofibers composed of PVP and EC loaded with a ciprofloxacin (CIP) and silver NPs (AgNPs) via a side-by-side electrospinning process as an effective antibacterial wound dressing [70]. The nanofibers presented a uniform appearance and cylindrical morphology with a clear Janus structure. The AgNPs were distributed on the EC side, while the drug was present in the PVP fibers [70]. In vitro assays demonstrated that over 90% of CIP was released within the first 30 minutes, confirming a strong antibacterial effect against both *S. aureus* and *E. coli* at the initial stages of the wound-healing process [70]. Lan et al. designed coreshell PVA/PCL nanofibers through coaxial electrospinning with dual release of tea polyphenols (TP) and ε-poly (L-lysine) (ε-PL) as antioxidant and antibacterial wound dressing materials [71]. The antioxidant TP incorporated in the PVA core showed a sustained release profile, while the antibacterial ε-PL in the PCL shell presented a fast release, allowing to achieve an antibacterial effect toward *S. aureus* and *E. coli* in the initial phase of the healing process and prolonged antioxidant activity [71]. Furthermore, the prepared coaxial core-shell nanofibers simultaneously incorporated with ε-PL and TP presented excellent cytocompatibility [71].

Zhong et al. fabricated through coaxial electrospinning PVA/PLA nanofibers embedded with *Bletilla striata polysaccharide* (BSP) and *Rosmarinic acid* (RA) to promote the wound-healing process [72]. Their results showed that the core-shell RA-BSP-PVA@PLA membranes were able to control the water vapor transmission rate (WVTR), and exhibited excellent flexibility, as well as better accommodate wounds [72]. Moreover, the MTT assay revealed that the RA-BSP-PVA@PLA nanofibers exhibited good biocompatibility and safety properties, as well as induced wound tissue growth in rat dorsal skin wound models and tissue sections [72]. Furthermore, the histological examination showed that the produced nanofibers enhanced the

*Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

collagen deposition, the epidermal thickness, and the granulation tissue formation, as well as promoting the conversion of M1 macrophages into M2 macrophages, reducing the release of inflammatory factors, and promoting the occurrence of an effective wound-healing process [72].

Moreover, Mouro et al. incorporated *Chelidonium majus* L. into electrospun nanofibrous membranes composed of PCL, PVA, and Pectin (PEC) through emulsion electrospinning [73]. The electrospun PCL/PVA/PEC membranes exhibited suitable morphological, chemical, physical, and mechanical features for application as wound dressing materials [73]. Moreover, these membranes displayed excellent biological properties, namely antibacterial activity against *S. aureus* and *P. aeruginosa,* and the cytocompatibility assay provided no evidence of cytotoxicity in normal human dermal fibroblasts (NHDF cells) [73].

Recently, Sarviya et al. evaluated the performance of an ultrafine three-layer polymer nanofiber membrane produced via electrospinning [74]. In this approach, the first layer was produced with Polystyrene (PS) to act as a carrier layer and confer a suitable mechanical strength, the second layer consisted of PCL containing AgNPs endowing it with antibacterial properties, and finally, the third layer comprised of PEO act as a nonadhesive hydrophilic barrier layer with the potential to further support the healing process [74]. The cumulative Ag<sup>+</sup> release was improved for a period up to 84 days and the findings highlight the importance to balance the antibacterial properties with the low toxicity in order to produce a biocompatible three-layer wound dressing material containing antibacterial properties [74].

#### **4.6 Other textile-based applications**

The electrospinning technique has allowed the creation of different textile materials with controllable diameters by changing several parameters, such as the solution properties, processing conditions, and environmental variables [8]. Besides, electrospun nonwoven membranes have displayed remarkable features, like high porosity, small pore size, high surface area, and good interconnected pore structure, which permits to efficiently capture ultrafine particles, like particulate and microbial contaminants [75, 76]. Moreover, these nonwoven structures are flexible, breathable, and comfortable, and therefore electrospinning has become a promising technique for producing PPE, particularly face masks [13, 75, 77].

In 2022, Geetha et al. dispersed Zinc Oxide (ZnO) NPs into a PVA/PVP polymer blend solution through electrospinning to produce efficient antimicrobial face masks [75]. The results obtained revealed that the produced ZnO/ PVA/PVP composite nanofiber displayed a pronounced antibacterial effect against different pathogenic bacterial strains [75]. In turn, Salam et al. incorporated different concentrations of Viroblock (VB) (0.5, 1.5, 2.5, 3.5, and 5.0%) into a Polyacrylonitrile (PAN)/ZnO solution via electrospinning [78]. The electrospun nanocomposite reached an antibacterial efficiency of 92.59% against *S. aureus* and 88.64% against *P. aeruginosa*, when the higher amount of VB (5.0%) was incorporated in the nanofibers, as well as a significant reduction in virus titer (37.0%) [78]. Hence, the VB-loaded PAN/ZnO nanofibers showed the potential to develop nanofiber-based personal protective equipment, such as facemasks and surgical gowns, due to their ability to kill enveloped viruses, such as coronaviruses and influenzas [78]. Further, Ferreira et al. produced an antibacterial face-mask filter composed of PCL combined with MgO and CuO NPs using an electrospinning technique [76]. The PCL filter dopped with CuO/MgO NPs exhibited structural stability up to 2 h of washing, offered filtering

capacity, and additional antibacterial activity against two different bacteria strains, *E. coli* and *S. aureus* [76].

More recently, researchers started to explore the use of electrospun nanofibers as promise carriers for the local delivery of anticancer agents in order to circumvent some of the limitations presented by the simple nanostructures, like the low stability and the burst drug-release features, and effectively prevent cancer progression and improve their therapeutic index [79]. In fact, electrospun nanofibers have many advantages in cancer treatment due to their nanofibers size, surface modification, alignment variation, and drug molecules incorporation.

In this sense, Ahmady et al. investigated the release profile of capsaicin-loaded alginate (ALG) NPs from the PCL/chitosan (CS) nanofibers. Firstly, ALG NPs were prepared using different concentrations of cationic gemini surfactant and nanoemulsions as templates. Then, the optimized ALG NPs were loaded with 20 wt% capsaicin, a pharmacological natural agent with potent anticancer activity, into a blend of PCL and CS prepared at 2:1 volume ratio. The Cap-ALG NPs @ PCL/CS nanofibers were fabricated at a constant flow rate of 0.2 mL/h, using a working distance from the needle to the rotatory drum collector of 14 cm, with a rotation speed of 300 rpm, and a voltage of 16 kV [79]. The results obtained revealed a prolonged capsaicin release from 120 h to more than 500 h when capsaicin-loaded ALG NPs were incorporated into PCL/CS nanofibers. In addition, in vitro assays also demonstrated that The Cap-ALG NPs @ PCL/CS nanofibers could effectively inhibit the proliferation of MCF-7 human breast cells and did elicit any cytotoxicity effect on human dermal fibroblasts (HDF). Therefore, the long-term and controlled release of capsaicin from the electrospun nanofibers has a high potential for the prevention and treatment of cancer [79]. In turn, Seyhan et al. prepared PLA/ Polyethylene glycol (PEG) nanofibers loaded with amygdalin (AMG) and bitter almond kernel extract in order to prevent local breast cancer recurrence [80]. The produced electrospun PLA/PEG nanofibers containing AMG exhibited a sustained and controlled release extending up to 10 h. Additionally, the acquired in vitro data revealed that the nanofibers were able to induce cytotoxicity against MCF-7 breast cancer cells [80]. Therefore, AMGloaded nanofibers arise as a highly promising approach for reducing the risk of local recurrence of cancer after surgery and can be directly embedded into solid tumor cells for treatment. Thus, electrospun nanofibers, particularly polymeric nanofibers, can be used to incorporate antitumor drugs for sustained and controlled release of chemotherapeutic compounds at a particular site over a specific period of time with low risks of toxicity and side effects to the healthy cells. Besides, the electrospun nanofibers have received increasing consideration as promising implantable textile-based materials for the on-site delivery of chemotherapeutic drugs in a sustainable release manner after surgical resection to inhibit tumor recurrence and prolong drug release at the tumor site [81].

## **5. Conclusions and future outlook**

Medical textiles are a field within the textile industry that has received increasing attention from researchers in recent years. Besides, the textile industry can benefit from nanotechnology, since it provides better functionalities and properties to the materials. Regarding that, tremendous efforts have been made to produce drug loading and delivery systems for tissue regeneration and wound healing able to release the drug in a controlled manner over the desired period of time.

Among the diverse methods used until now to manufacture nanoscale materials, electrospinning has been recognized as a viable technique to fabricate nanofibers from

### *Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

various types of textile materials that can act as carriers for the delivery of drugs due to their intrinsic properties, such as high surface area, high porosity, and small pore size. Moreover, the electrospun nanofibers have been loaded with a wide range of drugs using different electrospinning techniques, namely through blending, side-byside, coaxial, tri-axial, emulsion, multi-needle, and needleless electrospinning. However, although the electrospinning techniques have the inherent benefits of simplicity, low cost, and versatility, all the techniques exhibit advantages and disadvantages depending on the polymeric solution and desired drug-release behavior. In fact, although the electrospun nanofibers produced by blending electrospinning are the most researched and applied for loading drugs by direct dissolving or dispersing in the polymeric solution; usually a rapid drug-release rate is observed. Thus, core–shell nanofibers produced by coaxial electrospinning and emulsion electrospinning have been highlighted to slow down the drug release. In addition, the coaxial and emulsion electrospinning provides an additional advantage for encapsulating fragile drug molecules, like growth factors, enzymes, and DNA, into the core protected by a shell, avoiding their denaturation. Further, these electrospinning techniques can involve the simultaneous use of two immiscible polymer solutions. Nonetheless, coaxial electrospinning needs a special syringe tip, while emulsion electrospinning requires the same basic setup as blending electrospinning. Moreover, side-by-side, tri-axial, and multi-needle electrospinning techniques offer the advantage of providing richer functionality from the different polymers and may result in biphasic and prolonged sustained release profiles. In turn, needleless electrospinning techniques addressed the limitations of traditional needle-based electrospinning and can produce highthroughput nanofibers using a wide variety of spinneret shapes and methods.

In addition, it is possible to tailor the properties of the electrospun textile materials by optimizing the parameters that influence the electrospinning (properties of the solution, processing variables, and environmental conditions), as well as the materials and configuration used in order to obtain the textile nanofibers with the desired morphology, size, orientation, porosity, wettability, mechanical properties, and degradation and drug-release kinetics for biomedical applications, including for bone, nerve, periodontal, and vascular tissue regeneration, wound dressings, and other textile-based materials, like PPE and cancer treatment.

However, until now, the data available concerning the nanofibers' applications at the industrial scale are still very poor, being almost limited to the laboratory scale. Thus, preclinical and clinical assays are required for further validation of these materials and to help their transition to the market. Another future outlook with the potential to revolutionize various fields could be the application of electrospun nanofibers that exhibit changes in their physicochemical properties in order to respond to environmental stimuli, where the incorporation of drugs into smart electrospun nanofibers will enable precise activation-modulated or feedback-regulated control of the drug release. As research into this technology continues to progress, the potential applications for textile electrospun nanofibers will likely expand, ranging from drug loading and delivery systems to tissue regeneration and beyond.

## **Acknowledgements**

Financial support was provided by the Portuguese Foundation for Science and Technology (FCT), I.P./MCTES through national funds (PIDDAC), in the scope of the FibEnTech Research Unit project (UIDB/00195/2020).

## **Author contribution**

Invited author for book contribution—Isabel C. Gouveia; Pedagogical content and methodology—Isabel C. Gouveia and Cláudia Mouro; Scientific supervision and editing—Isabel C. Gouveia; Figures and tables layout—Cláudia Mouro.

## **Conflict of interest**

The authors declare no conflict of interest.

## **Author details**

Isabel C. Gouveia\* and Cláudia Mouro FibEnTech Research Unit, Faculty of Engineering, University of Beira Interior, Covilhã, Portugal

\*Address all correspondence to: igouveia@ubi

© 2023 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.

*Development of Drug-Delivery Textiles Using Different Electrospinning Techniques: A Review DOI: http://dx.doi.org/10.5772/intechopen.112788*

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## *Edited by Khalid S. Essa and Khaled H. Mahmoud*

*Electrospinning - Theory, Applications, and Update Challenges* is a comprehensive guide that delves into the principles, techniques, and applications of this cutting-edge technology. Electrospinning, a versatile and innovative process, has revolutionized industries such as health care, textiles, and materials science. The first section presents a detailed overview of electrospinning, covering topics ranging from the fundamentals of electrostatics and polymer science to advanced electrospinning techniques and industrial applications. The second section covers the intricacies of fiber formation, the influence of process parameters, and the wide array of materials that can be spun into fibers. The book provides valuable insights into the latest developments and future prospects of electrospinning.

Published in London, UK © 2024 IntechOpen © Dr\_Microbe / iStock

Electrospinning - Theory, Applications, and Update Challenges

Electrospinning

Theory, Applications, and Update Challenges

*Edited by Khalid S. Essa and Khaled H. Mahmoud*