Nanofibers for Medical Textiles
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.
KeywordsStructure of nanofibers Drug release Medical applications Composite Dual network
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 . 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 . 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 . 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.
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 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.
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
Layer by Layer
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.
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.
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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