# Electrospinning of Chitosan for Antibacterial Applications--Current Trends
## 7 Application Fields of Electrospun Chitosan Nanofibers and Chitosan Derivatives
### Water Filtration
#### 7.1.2 Electrospun Fibers from Chitosan-Polymer Mixtures for Water Filtration  
Preparing electrospun nanofiber mats from pure chitosan is difficult due to its cationic character and high crystallinity. Therefore, various experiments were performed with mixtures with different synthetic polymers:  
The addition of chitosan to the nylon-6 nanofiber membrane enhanced its hydrophilicity and mechanical strength. Due to the presence of functional groups such as primary amino and hydroxyl groups, increasing the chitosan concentration significantly improved the hydrophilicity of the membrane for pure nylon-6 nanofiber. Increasing the chitosan concentration resulted in an increase in the tensile strength of the chitosan-nylon-6 electrospun membrane. The inhibition zone of chitosan-nylon-6 nanofibers with a polymer ratio of 30:70 on _E. coli_ bacteria measured up to 8 mm, while increasing the chitosan amount improved the antibacterial activity to 96%. As a result, the electrospun nanofibers were able to capture bacteria, which prevented them from polluting water. The nanofiber membrane's increased hydrophilicity can increase the antifouling effect, making the electrospun nanofibers a potential candidate for water filtration and improving the membrane performance at low pressures [161]. Due to its hydrophilic nature, the addition of chitosan enhances the membrane's hydrophilicity [158]. In addition, it is assumed that chitosan-modified membranes withstand biofouling for longer periods. Chitosan and polycaprolactone (PCL) were electrospun from a formic acid-acetone solvent combination. In terms of the fiber morphology, samples with 25 wt% chitosan produced the best results. The electrospinningning of chitosan-incorporated PCL nanofibers with a diameter range of 200 to 400 nm resulted in a 50% improved effect against _S. aureus_ colonization compared to membranes made of pure PCL fibers. They also seemed promising as pre-filters for water filtration, since they allowed for a high water flux while removing all 300 nm particles [162]. The water transport process through the membrane involves three stages: sorption, diffusion, and desorption. The hydrophilicity of the membrane serves as a driving factor \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Water** & **Technology** & **Species size** & **Filtered** & **Advantages** & **Disadvantages** \\ \hline Microfiltration & Membrane & 0.1–5 μm [160] & Particles, large bacteria and pathogens, grease & Low-pressure filtration, low energy consumption, no chemicals required, low production costs [160] & (Bio)fouling reduces efficiency, pre-treatment and chemical cleaning are necessary [156; 160] \\ \hline Ultrafiltration & Membrane & 0.01–0.1 μm [160] & High-molecular weight material, colloids, particles, endosomes, some viruses, oil & No chemicals required, low-pressure filtration, low energy consumption, low production costs [155; 156] & (Bio)fouling limits performance, pre-desinflection or membrane modification is necessary [155] \\ \hline Reverse Osmosis & Membrane & 0.0001–0.001 μm [160] & Salts, metal ions, solids, colloids, organics & Most important probable system, ultra-pure water [157] & (Bio)fouling limits performance, pre-treatment is necessary, eg. by UV-irradiation [157] \\ \hline Nanofiltration & Nanofibers, nanofibrens membranes & 0.001–0.01 μm [160] & Particles, endotoxins, microorganisms, dyes, desalination & High surface-to-area ratio, high porosity, small driving forces needed, high water flux, low energy consumption, usage of antimicrobial chitosan reduces biofouling, no further treatment necessary, improved hydrophobicity [158; 161; 162] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of different water filtration systems. for water sorption into the membrane. Usually, biofouling decreases as the hydrophilicity of the polymeric material increases, resulting in an increased flux ratio.