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Nanofibers for Medical Textiles

  • Muhammad Qamar Khan
  • Davood Kharaghani
  • Zeeshan Khatri
  • Ick Soo KimEmail author
Reference work entry

Abstract

This chapter introduces the nanofibers for medical textiles. Nanofibers possess the various unique characteristics, which enable them to be used for different fields of advanced textiles. The structure of nanofibers plays an important role to achieve the functional applications for technical medical textiles (Medtech). The key formation mechanisms of structured functional nanofibers such as core-shell, aligned, porous, composite, tubular, mechanical, and chemical are reviewed, including the briefed information on the processes involved. Recently, many researchers are focusing on nanofibers as the suitable methods and materials for Medtech which enhance the scope of medical textiles. Biocompatibility, biodegradability, and mechanical properties are the main issues for biomedical textile products as scaffolds. To overcome these issues, electrospun nanofibers could be very suitable for medical textiles, because the electrospun nanofibers are continuous nanofibers meshes that mimic the extracellular matrix as the medical textiles product. The main features of advanced examples and innovative applications are reviewed, and at the end of this chapter, the future of medical textiles is also discussed.

Keywords

Structure of nanofibers Drug release Medical applications Composite Dual network 

Introduction

Nanofibers possess high surface area to volume area and small pore size with significantly improved chemical, mechanical, and biological properties as diameter decreases to nanoscale [1, 2, 3]. Therefore, nanofibers have attracted an attention of research over the few decades in the various fields of life. One of them is the medical textile, due to nanofibers’ biocompatibility, biodegradability, non-biodegradability, strength, elongation, and porosity [4, 5]. The medical textile (Medtech) is a class of technical textiles, in which medical field-related products are technically fabricated for stated and implied needs with natural fibers, regenerated fibers, and synthetic fibers. In these fields, there are wound dressings, sutures, surgical apparels, membranes, artificial blood vessels and nerves, drug delivery, and tissue engineering [2, 3, 4, 6]. Biocompatible and biodegradable polymeric biomaterials are the main source for the fabrication of Medtech by nanofibers as scaffolds or biological matrices [7]. These biomaterials include the synthetic polymers such as PVA, polylactic acid, PVP, polyglycolic acid, poly-lactide-co-glycolide, polycaprolactone, chitosan, and cellulose and also include the natural biopolymers due to their superior structure and biocompatibility such as silk, mussel adhesive protein, keratin, zein, collagen, and elastin [8]. In this chapter, we tried to introduce the parameter to make the spinning solution and nanofibers for biomedical applications. Herein, we also tried to introduce the influence of structure on the applications of Medtech. Therefore, authors focused on tubular structure, core and sheath structure, layer-by-layer structure, and composite structure feature, which have great influence on the different applications of medical fields.

Parameters of Nanofibers for Medtech

There are some important parameters for fabricating the Medtech by nanofibers. These parameters have the direct effect on the structure of nanofibers.

Molecular Weight of Solution

Fabrication of nanofibers from electrospinning mostly depends on molecular weight of solution. It demonstrates the number of entanglement of polymer chain in the spinning solution. Many researcher claimed in their work that solutions having low molecular weight tend to create beads instead of nanofibers and also high molecular weight solutions tend to form course/thick nanofibers [9]. So, molecular weight of polymer is important to form the suitable viscous solution for fabrication of nanofibers. If polymer molecular weight is low and the researcher blended the nanoparticles/drugs, then it can be possible to obtain the suitable viscosity for the spinning solution, and also sometimes polymer concentration is low, but suitable number of entanglements of polymer chain can ensure the suitable viscosity level for electrospinning. Therefore, molecular weight of polymer is not important, but molecular weight of spinning solution is important. There are some biocompatible polymers for biomedical application such as PVA, PVP, zein, and chitosan which have high molecular weight, but some like PAN, cellulose, PCL, etc. have lower molecular weight, but they are used as a part of composite or can be used with high concentration.

Concentration

The concentration of polymer in the spinning solution plays an important role in the electrospinning for biomedical applications. When the concentration is high, then nanofiber properties are changed, and the diameter of nanofibers becomes thick which changed the scope of study. If the concentration of polymer in the solution is very low, then also properties changed, and at low concentration, there is most probability of bead formation rather than nanofibers. Therefore, a suitable concentration of required biocompatible polymer is required to fabricate composite for medical applications. At high concentration the spinning solution also become very thick to be stretched into nozzle tip and require high electric force to fabricate the nanofibers. So, there should be a suitable concentration of polymers and also suitable concentration of drugs and nanoparticles in the polymer solution to fabricate the functional nanofibers.

Viscosity of the Solution

Viscosity of the electrospinning solution is very important parameter to fabricate the nanofibers. Molecular weight, polymer concentration, and viscosity are correlated to each other. For obtaining the good and clean nanofibers, neither low viscosity nor high viscosity is required. It is little difficult to maintain the suitable viscosity for the spinning solution. Therefore, researchers tried on an optimum condition before going ahead for experiment. Generally, a high viscosity has a bad effect on the deposition of nanofibers because instability can be happened with jets and droplets can be formed.

Conductivity

Conductivity or surface charge density of the solution is very important for the fabrication of nanofibers through electrospinning. It can be determined through the nature of polymer and solvent which are used to form the solution. Conductivity has a great effect on the diameter of nanofibers; if conductivity of solution increased, the diameter of the nanofibers reduced, but electrospinning of highly conductive solution has a negative effect on the bending stability and diameter distributions of nanofibers. Fabrication of nanofiber-based scaffolds is necessary to minimize nanofiber diameter distributions and ensure bending stability. Therefore, a suitable or sufficient conductivity of spinning solution is required to fabricate the nanofibers.

Applied Voltage

It is more important parameter for fabrication of nanofibers for Medtech. Applied voltage has great influence on electrospinning and also on nanofibers properties. The initiative voltage for electrospinning is related to the material’s properties, distance from nozzle tip to collector, humidity, and environmental temperature. The high voltage is required where polymer’s solution viscosity increased or their concentration in solution was increased; then high voltage is required to create the nanofibers scaffolds. PVA, PVP, PAN, zein, chitosan, and cellulose require average applied voltage 12 kV to fabricate nanofibers for scaffolds. The collector distance also has a great effect on the voltage. If we increase the distance from the nozzle tip to the collector, a high electric force to fabricate and collect the nanofibers on the collector is also required.

Flow Rate of Solution

Flow rate of solution during electrospinning is very important to fabricate the desired type of structure for nanofibers. If flow rate is low, then it can help to evaporate the solvent from the solution during ejection of nanofibers. It is very good to obtain the biocompatible scaffolds. In some solution there are toxic solvent to dissolve the polymer. If we do electrospinning on low flow rate, then resultant scaffolds can be free of toxicity and well-proliferation rate of cell attachments.

Distance Between Nozzle and Collector

Collecting distance is very important parameter to fabricate the appreciable solid nanofibers. To fabricate the solid nanofibers, the distance from the nozzle tip to collector must be large enough to evaporate the solvents from the jet before collection. The minimum collecting distance depends on the material properties and geometry of electrospinning. The most used collecting distance is 10–15 cm for PVA, PVP, PAN, zein, cellulose, and chitosan. If we increase the distance, then high voltage is required to fabricate the nanofibers. Therefore, a good balance should be maintained for fabrication of appreciable nanofibers as scaffolds.

Temperature and Humidity

It has been noticed that temperature and humidity have great influence on the fabrication of nanofibers for biomedical products/applications. For biomedical nanofibers, the solution temperature should be up to 25 °C for better electrospinning. When temperature increased, then nanofibers’ morphology, mechanical properties, and structure are disturbed. If these types of nanofibers are used for biomedical application, then MTT and in vivo analysis will provide un-expectational results. Humidity also has a great influence on morphology and mechanical properties of nanofibers. At a very low humidity, the volatile solvent will dry rapidly as the evaporation will be faster. In this way ejection will be unstable and within insufficient time to deposit on the collector, and high humidity can create discharge of the electrospun nanofibers.

Structure of Nanofibers for Medtech

Core and Sheath

The core and sheath structure has very important role in the fabrication of scaffolds for medical applications because in the structure of core and sheath nanofibers there are two different functions of nanofibers at the same time by using the two different materials in the same nanofibers. Electrospinning is the best option to fabricate such type of nanofibers. The coaxial electrospinning is used to prepare core and sheath nanofibers with outstanding and multifunctional for additional functional applications such as biotechnology scaffolds, membranes, and other composites. In the coaxial electrospinning, a bi-component needle (core material flow in the core needle and external material flow in the outer needle) is used as shown in Fig. 1.
Fig. 1

Illustration scheme of coaxial electrospinning [10]

Han et al. in 2017 studied the core and sheath nanofibers for chem/bio/med applications. In this work their objective was delivery of targeted functional molecules to the specific region where pH response was required. For this purpose, two types of solutions were prepared for coaxial electrospinning. The illustration scheme of their work is shown in Fig. 1. The resultant scaffolds fulfilled the stated and implied needs of Han et al. which they reported novel multi-pH-responsive Eudragit nanofiber membranes using two Eudragit polymers such as EL 100 and ES 100 which were dissolved at pH 6 and ph 7, respectively. The combination of EL 100 and ES 100 into different layers of core and sheath nanofibers, different dissolution, and release kinetics at different pH environment could be obtained. It was showed that at pH 6, EL 100 core was dissolved and released in a sustained manner due to protection from ES 100 sheath, and the sheath and remaining core were completely dissolved and released at pH 7. When the combination of material was switched between core and sheath, different responses of pH were observed as shown in Fig. 2b.
Fig. 2

Cross-sectional scheme of core and sheath [10]

Li et al. in 2017 prepared the core and sheath yarn by electrospinning for enhancement of biomedical properties. Herein, they introduced a novel method of electrospinning to fabricate the core and sheath structure as shown in Fig. 3. In this method, the polycaprolactone (PCL) solution was ejected by syringe pump. The PCL nanofibers were deposited over the surface of PGA-MFs yarn at room temperature and 65 ± 5% humidity.
Fig. 3

Apparatus design for core and sheath structure [11]

Li et al. claimed that obtained scaffolds from this method have the great potential for the enhancement of biomedical properties. For this purpose MTT analysis was done as shown in Fig. 4. It was observed that there are high difference of optical density between PCL-NCYs & PGA-MFs, at day 1 indicates high proliferation rate with BALB/3 T3 cells on PCL-NCYs due to nano surface offering more suitable places for cell attachment or cell culturing. After days 3 and 5, this proliferation rate was higher than PGA-MFs as shown in Fig. 4. So, it was prove that cell attachment and culturing on PCL-NCYs nanofibers have a high proliferation rate than PGA-MFs yarn.
Fig. 4

MTT analysis with BALB/3 T3 cells on PCL-NCYs, PGA-MFs & TCP [11]

Layer by Layer

The layer-by-layer structure is the architecture of an engineered tissue substitute which plays an important role in fabrication of tissue or loading drug for the treatment of tissues. In this type of structure, different types of materials are used for specific functions. It is also a composite structure, but its design is unique which known as layer-by-layer structure of scaffolds or vascular tissue engineering. The natural artery is the complex of so many layered tissue composed of various cells and proteins which play an important role in the mechanical behavior of the native artery. In order to bear the high pressure and pulsatile blood flow rate, an artery is composed of three different layers; intima, media, and adventitia. Each of them has a different composition and function in an artery. Therefore, Michael et al. in 2012 prepared a trilayered vascular graft which was composed with polycaprolactone, elastin, collagen, and silk. In this research authors designed an electrospinning setup for making trilayered nanofibers as shown in Fig. 5. It was claimed that through this method the resultant graft could mimic the native artery.
Fig. 5

Schematic illustration of electrospinning for trilayered grafting (Michael et al. 2012)

Michael et al. studied the burst behavior of this scaffold in which they analyzed that burst strength properties of graft were near to media and adventitia. For this purpose they studied over the 4-week period. It was expected that if there is any degradation noticed, then a decrease in burst strength must be noticed. In the case of PCL-ELAS-COL graft in Fig. 6a, there was a significant decrease (p ≤ 0.05) between week 0 and 2, week 0 and 1, and week 0 and 4 for 65-10-25 adventitia with 45-45-10 media. Furthermore, 45-10-45 adventitia and 45-45-10 media grafts significantly increased (p ≤ 0.05) in burst strength from week 0 to 4, but there were no differences among week 1, 2, and 4. Figure 6b demonstrate a significant decrease (p ≤ 0.05) in burst strength for grafts with a 55-10-35 adventitia and a 45-45-10 media between week 0 and week 4, while 45-10-45 adventitia with a 55-35-10 media effectively increased in burst strength from week 0 to 2, but average burst pressure from week 4 is still smaller than week 1 and similar to week 0.
Fig. 6

Results of burst pressure for trilayered specimens: (a) PCL/ELAS/COL trilayered, (b) PCL/ELAS/SF trilayered scaffolds (Michael et al. 2012)

Herein, some materials for release function can also be loaded within the polymers. This type of structure has great influence on medical-related products which are fabricated by electrospinning. Lee et al. in 2017 fabricated the trilayer for drug releasing, in which they loaded ketoprofen (KET) as a drug; first layer was fabricated by zein/ketoprofen (zein/KET), second layer of PVP/GO/KET, and third layer of zein/KET as shown in Fig. 7. This scaffold was good for drug releasing purpose. Lee et al. claimed that this scaffold has good profile of release behavior and KET release from trilayer is better than PGK and ZK. It means for release profile layer-by-layer structure is a better option. Authors claimed that trilayered nanofibers exhibited appreciable release profile because trilayered nanofibers showed combined release of PGK; in PK within 1 h, the release profile was 60% and then 100% in 16 h as shown in Fig. 8.
Fig. 7

Illustration scheme of making trilayered scaffolds [9]

Fig. 8

Release profile of trilayered nanofibers (zein/KET), PVP/GO/KET, and PK [9]

Liu et al. in 2018 studied the release behavior of glial cell line-derived growth factor (GDNF) and nerve growth factor (NGF) from the fabricated multilayered bicomponent electrospun scaffolds. In this research, GDNF and NGF were incorporated into PLGA and PDLLA nanofibers, respectively. Liu et al. studied the release behavior of tetra-layered scaffolds from both top and bottom sides in 42 days. They claimed that released profile of GDNF and GNF was good because the cumulative release % of NGF was 13.5 in 7 days; after 42 days it was 25.6%, but from side B, there was 3.3% cumulative release of NGF. Release profile showed that GDNF release was more rapid than NGF because after 42 days it was 61.1%, but from the bottom side, it was also same like NGF as shown in Fig. 9.
Fig. 9

Release profile of GDNF and NGF from both sides of tetra-layered scaffolds [12]

Nanofiber Tubes

The tubular structure based on nanofibers is vital factor to develop the scaffolds or Medtech products for the applications of biomedical fields. Tubular structure is used to develop the artificial tissues like the blood vessel, nerve, axon, or any other organs where tubular structure is required. Tubular structure can be manufactured or fabricated by electrospinning. Figure 10 showed the illustration scheme through which a tubular structure can be fabricated based on electrospun nanofibers.
Fig. 10

Illustration scheme of electrospinning for fabrication of tubes

Tan et al. in 2017 fabricated the electrospun vein for blood vessel applications. In this research authors claimed that bilayer tubular scaffolds could enhance the growth of endothelial cells and promote infiltration of cell and also tissue growth. Tan et al. tried a new method which showed in Fig. 11 to fabricate the tubular structure which is appreciable way for scaffolds application in vascular tissue engineering. In this method a wooden box designed with strips of aluminum in the parallel series was used to collect the fibers which were ejected from needle as shown in Fig. 11, the fibers collected and aligned between strips. The internal layer of longitudinally aligned scaffolding (ILASL) is obtained around the mandrel collector; then through co-electrospinning, an external layer of randomly oriented fibers is collected over the ILASL. At the end, a bilayer scaffold was obtained which consisted of aligned internal and external layers made of two materials.
Fig. 11

Illustration scheme of vein (a) wooden box designed with strips of aluminum in the parallel series was used to collect the fibers which were ejected from needle, (b) fibers collected and aligned between the strips. (c) The spaced fibers adhere uniformly around a mandrel collector, (d) an internal layer of longitudinally aligned scaffolding, (e) co-electrospinning, and (f) bilayer scaffolds [13]

Through this innovative method, the tubular structure was investigated by several characterizations and showed that it is aligned, and bilayer tubular structure has no toxicity and great potential for enhancement in the growth of endothelial cells and promoting infiltration of cell and also tissue growth.

Bini et al. in 2004 [14] fabricated the tubular structure as a nerve guide by electrospun poly(l-lactide-co-glycolide). Authors claimed that nanofiber based tubes for nerve guidance channels. They also investigated the feasibility of in vivo on rat sciatic nerve model with a gap length of 10 mm. Bini et al. also claimed that these types of tubes are flexible and permeable and have no swelling capacity. Wu et al. in 2018 designed a tubular structure for vascular tissue engineering by poly(l-lactide-co-glycolide)/collagen and poly(l-lactide-co-glycolide)/silk fibroin. Authors claimed that it was novel tubular scaffolds for blood vessel applications with highly profiled mechanical and biocompatible properties. Xue et al. in 2018 [15] prepared the tubular conduits based on nanofibers with a honeycomb structure for nerve repair applications. Authors used PCL materials to fabricate the electrospun nanofibers for multitubular phenomenon like honeycomb structure as shown in Fig. 12.
Fig. 12

Schematics illustration showing (a) cross-sectional view, (b) side view of single tube, (c) cross-sectional view of multitubular, and (d) photograph of multitubular conduit [16]

Composite

The composites nanofibers are the vital structure to fabricate the product for Medtech. In this type of structure, two or more than two materials are composed/blended together to form the highly profiled product. Herein nanoparticles or some types of drugs can be blended with other polymers for fabrications of nanofibers for medical applications because metal nanoparticles have great potential for medical applications. Kharaghani et al. [17] blended Ag nanoparticles with PAN nanofibers to organize the high-profiled antibacterial composite nanofiber membranes. There was uniform dispersion of nanoparticles on the nanofibers with acceptable size distributions as shown in Fig. 13.
Fig. 13

TEM images with distribution graphs of PAN/Ag nanofibers [17]

Kharaghani et al. claimed that a composite made from polymers and metal nanoparticles has a good application for Medtech with suitable mechanical strength because it showed the high-profiled data for antibacterial properties as shown in Fig. 14.
Fig. 14

Results of antibacterial of PAN/Ag nanofibers against E. coli and S. aureus, (a) neat PAN nanofibers, (b) PAN/Ag with one immersing cycle, (c) PAN/Ag with two immersing cycles, and (d) PAN/Ag with three immersing cycles [17]

A composite can also be fabricated by two or more polymers for medical applications. For example if one polymer has biocompatibility and other has no these properties but its mechanical properties are better, so they can be showed the all properties of both polymers. In 2017 Khan et al. fabricated the composite of natural and synthetic polymers. In which honey was natural and PICT was synthetic polymer. Honey has the antibacterial properties but low mechanical properties. Therefore authors blended honey with PICT to fabricate the composite for biomedical application with high mechanical strength as shown in Fig. 15.
Fig. 15

Tensile strength data of neat PICT nanofibers, 10% wt PICT/honey nanofibers, and 20% wt PICT/honey nanofibers [1]

Hakro et al. in 2018 blended the zein with nylon to enhance the mechanical properties of the composite. Authors claimed that zein nanofibers have very low tensile strength than nylon nanofibers. Therefore, they blended them and fabricated the composite of them which showed 2.9 MPa strength, which is greater than zein 0.6 MPa and lower than nylon 5.7 MPa as shown in Fig. 16b.
Fig. 16

(a) Cell viability data of zein and PCL and (b) tensile strength data of zein and nylon nanofibers (Hakro et al. 2018)

Liao et al. in 2016 developed the composite by blending of zein with PCL, and they claimed that composite properties of biocompatibility and mechanics were increased as shown in Fig. 16a.

So, it can be concluded that composite structure of nanofibers with different category of materials has a great importance for the fabrication of Medtech products.

Future of Nanofibers for Medtech

With this versatility, the functional nanofibers have been explored for applying in different areas of medical field due to their different structure. Recently, most researchers have been focused on the fabrication of compound/combined structure such as tubular, core and sheath, layer by layer, composite membranes by modifying the electrospinning illustration scheme. For example, the fabrication of triangular or square nanofiber membranes depends on the rebuilding collector. Therefore, electrospinning process still needs modifications and manipulations to fabricate new structure for scaffolds of medical applications. The hybrid technology is also being processed to fabricate the structure nanofibers. However, in order to enhance the properties of medical products or introducing new Medtech, future work concentrates on better analysis of the shape formation mechanism and technical properties.

Conclusion

Herein, the influence of nanofibers structure has highlighted for the researchers that how a design or structure can provide the different types of function from same origin. The nanofibers have great potential to mold in a required structure with the alignment of illustration scheme of apparatus such as forming tubes from nanofibers for vascular tissue engineering is an appreciable feature of nanofibers, similarly core and sheath structure is the credit of coaxial electrospun nanofibers. Therefore, through different structures, we can get different medical product for different functions.

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Muhammad Qamar Khan
    • 1
  • Davood Kharaghani
    • 1
  • Zeeshan Khatri
    • 2
    • 3
  • Ick Soo Kim
    • 2
    Email author
  1. 1.Nano Fusion Technology Research GroupDivision of Frontier Fibers, Institute for Fiber Engineering (IFES), Interdisciplinary Cluster for Cutting Edge Research (ICCER), Shinshu UniversityUedaJapan
  2. 2.Nano Fusion Technology Research Group, Division of Frontier FibersInstitute for Fiber Engineering (IFES), Interdisciplinary Cluster for Cutting Edge Research (ICCER), Shinshu UniversityTokidaJapan
  3. 3.Center of Excellence in Nanotechnology and MaterialsMehran University of Engineering and TechnologyJamshoroPakistan

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