# Electrospinning of Chitosan for Antibacterial Applications--Current Trends
## 7 Application Fields of Electrospun Chitosan Nanofibers and Chitosan Derivatives
### Biomedicine
#### 7.4.2 Tissue Repair by Controlled Drug Release via Coaxial Electrospinning  
When medicines are electrospun from biodegradable polymers, an effective drug release mechanism may be achieved. Additionally, it is feasible to alter the drug release kinetics and concentration by changing the parameters of the electrospinning process More precisely, by regulating the diameter of the fibers, biodegradable polymers in a fiber structure allow for smooth and controlled medication release [203].  
The technique of coaxial electrospinning offers the possibility of preparing fibers with a core-shell structure and allows the combination of the advantageous properties of two different materials within one fiber (see Figure 10). Nanofibrous scaffolds produced with the coaxial electrospinning technique can be effectively used for the construction and implementation of biodegradable antimicrobial layers because they are lightweight and can incorporate antimicrobial agents inside their large surface area.  
An example of the advantages of utilizing core-shell fibers was published by [PERSON] et al. [204]. Here, nylon-6 (PA6) in the core provides mechanical stability and the mixture of chitosan and PEO in the shell provides bacteriostatic action and hydrophilicity. The addition of 5-chloro-8-hydroxyquinoline (SCLO8Q) and poly(hexamethylene biguanide) (PHMB) to the chitosan or to PA-6, respectively, resulted in the preparation of a binary antimicrobial system that was tested against _S. aureus_ and _P. aeruginosa_. These are two of the most prevalent pathogenic bacteria, which are often found in surgical infection sites. PHMB is a well-known polycationic disinfect of mucous membranes and wounds that can permeabilize and destroy bacterial membranes and is used as an antiseptic in wound dressings [205]. Furthermore, 5 CLO8Q is an aromatic nitrogen molecule that is slightly soluble in water with antibacterial, fungal, and amoebic activities. The antibacterial  
Figure 10: Coaxial electrospinning. Adapted from [204], originally published under a CC-BY 4.0 license.  
effect of chitosan, which may permeabilize the cell membrane of prokaryotes by creating ionic compounds with its negative charges, was significantly increased by 5 CLOSQ. Pure PA6 did not have an effect on bacterial growth. The chitosan in the structure's shell was used to regulate and guide the drug release model. With this technique, it was possible to protect sensitive substances from the outside environment by placing the drug within the fibers, provide programmable release kinetics for defined concentrations of drugs [206], and improve the mechanical behavior by incorporating a mechanically strong polymer into the core. For homogeneous fiber production, PEO was added to the chitosan solution as a carrier polymer [204].  
The encapsulated composite nanofibers seemed to totally resist the development of both bacteria strains, demonstrating that an anti-adhesive surface may be obtained in addition to the biocompatibility of chitosan and the synergistic antibacterial characteristics of these two substances. Meanwhile, the control electrospun mat chitosan/PA6 only delayed _S. aureus_ growth but had no effect on the more robust strain _P. aeruginosa_[204]. The findings showed that this electrospun composite material may be used to avoid bacterial infections on surgical mesh surfaces in the future.  
For biomedical applications, nanofibers have been shown to be superior to films in the areas of wound coverage and tissue engineering [207]. The nanofibrous structure is similar to that of collagen fibrils and can guide cell proliferation. Additionally, the porosity ensures breathability and fluid transport, but also protects the wound from bacterial penetration. The inclusion of chitosan supports these effects via its antimicrobial properties.