# Electrospinning of Chitosan for Antibacterial Applications--Current Trends
## 5 Electrospinning of Chitosan
### Auxiliary Solvents and Composites  
Molecular modification of chitosan was also proven to improve its spinnability. For example, the addition of carboxymethyl to the chitosan structure significantly influences its water solubility [98]. The degradation temperature of chitosan below its melting point limits its processability as a casted film and its application development on a wide scale. On the other hand, the advantage of electrospinningning chitosan nanofibers is their high surface area to weight ratio, biocompatibility, and physicochemical properties, and their particularly small diameter, which makes them functional for several biomedical applications, such as in wound dressings, sensors, water filtration, and food protection. However, since CS is a cationic polyelectrolyte, it only becomes positively charged when dissolved in water, resulting in poor electrospinningning capabilities [111; 112]. By tweaking the electrospinningning process and solution parameters, the anticipated and final geometry of the processed solution may be estimated and controlled. It was shown that the molecular adhesion between chitosan chains is poor at low polymer concentrations, resulting in bead formation. Uniform and beadless nanofibers were effectively produced when the polymer content or Mw increased. The longer polymer chains allow sufficient chain entanglement and result in a stable filament with avoidance of fragmentation. However, high Mw chitosan produces extremely viscous and rigid systems that are difficult, if not impossible, to electrospun. Similarly, stronger chitosan content solutions have higher repulsive forces, which results in more stretching and elongation, leading to nanofibers with a narrower fiber diameter distribution [111; 112]. As the chitosan concentration increases, the average fiber diameter becomes smaller due to the increase in electrical conductivity. However, a very high content will increase viscosity. This critical variation of factors makes the electrospinningning process of chitosan discouraging. Researchers have experimented with a variety of techniques to enhance the electrospinningability of chitosan. To dissolve chitosan, some researchers utilized trifluoroacetic acid (TFA) for one-step electrospinningning [113; 114; 115]. The use of anionic polyelectrolyte hyaluronic acid is known for neutralizing cations in chitosan solution [112; 113; 114; 115; 116; 117]. However, hazardous solvents should not be used, particularly in biomedical applications [118]. TFA is cytotoxic, caustic, and ecologically damaging, making it unsuitable for uses such as food packaging [94]. Auxiliary solvents such as PEO and PVA have been presumed to interact with chitosan through hydrogen bonding [119; 120], resulting in reductions in electrostatic repulsion and surface tension, lowering the system's viscosity while increasing its flexibility and promoting fiber production. PVA (polyvinyl alcohol) is a water-soluble polymerized alcohol that can improve the capability of the prepared nanofibers. The areas of application of PLA are numerous and this polymer is used in solvents, dispersions, paper manufacture, electronics, cosmetics, medicine, textile impregnation, as well as aerospace [121; 122]. PVA is also widely used in biomedical fields due to its non-toxic, hydrophilic, and biocompatible properties [123]. Related research studies [124; 125; 126] have described some cases of nanofibers made by electrospinningning PVA and chitosan, whereby the aqueous PVA solution also removes potential organic solvent residues. As a result, antibacterial materials made of PVA and CS are considered harmless, are biocompatible, and offer easy adaptation for defined applications. With increasing CS content ratio in the mix, the fiber diameter decreased progressively. However, no fiber was produced when the CS content was more than 30% [127]. This means that a very high content of chitosan in a copolymer solution induces repulsive interaction between ionic groups inside the polymer backbone and obstructs the electrospinning process.