## 4 Chitosan/Graphene Oxide Films for Biomedical Applications
### Other Types of Chitosan/Graphene Oxide Composites  
[PERSON] et al. [43] fabricated biocompatible graphene oxide nanocomposite membranes cross-linked with chitosan, which can be used in various applications. A schematic diagram of the reaction is shown in Figure 7. The tensile strength of the membranes was significantly improved with the incorporation of GO. By adding 1 wt% GO, tensile strength improved from 43.2 MPa to 104.2 MPa, an increase of 141%, which can be explained by the formation of covalent bonds formed during the chitosan/GO cross-linking reaction. The authors claimed that by controlling other physicochemical properties of GO, such as the density of the functional groups and particle size, superior nanocomposite properties could be achieved. Chitosan/GO and chitosan/reduced GO (rGO) hybrid nanocomposites were fabricated by [PERSON] et al. [60]. Reduced graphene oxide was synthesized by \"green\" reducing agents such as L-ascorbic acid (LAA), grape extract, and green tea extract. Among these three reducing agents, the nanocomposites prepared with rGO-LAA had good wettability and a regular, homogeneous microstructure, indicating that such nanocomposite materials may be considered as potential tissue-engineering scaffolds. The composites prepared from grape and green tea extracts were less homogenous and formed visible agglomerates. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ingredients** & \begin{tabular}{c} **Potential** \\ **Applications** \\ \end{tabular} & **Characterization** & **Reference** \\ \hline \multirow{4}{*}{\begin{tabular}{c} Chitosan/polyvinyl \\ pyrrolidone/ \\ polyethylene \\ oxide/GO \\ \end{tabular} } & \multirow{4}{*}{Wound dressings} & Enhanced elastic modulus and & \multirow{4}{*}{[54]} \\  & & tensile strength & \\  & & controllable water permeability & \\  & & Biocompatible & \\  & & Accelerated in vivo wound & \\  & & closure rate & \\ \hline \multirow{4}{*}{\begin{tabular}{c} Chitosan/levorotatory \\ poly-L-lactide/GO \\ \end{tabular} } & \multirow{4}{*}{Wound dressings} & Excellent antimicrobial activity & \multirow{4}{*}{[55]} \\  & & Promoted proliferation of pig & \\  & & iliac endothelial cells & \\  & & Improved in vivo wound healing & \\ \hline \multirow{4}{*}{Polyvinyl alcohol/  chitosan/GO} & Tissue engineering, & \multirow{4}{*}{Improved mechanical properties} & \multirow{4}{*}{[56]} \\  & wound healing, and & & \\  & drug delivery & & Effective antibacterial activity & \\  & systems & & \\ \hline \multirow{4}{*}{\begin{tabular}{c} Chitosan/bacterial \\ cellulose/GO \\ \end{tabular} } & Skin tissue & Adding GO reduced nanofiber & \multirow{4}{*}{[57]} \\  & engineering and & & size \\  & wound dressing & & Water vapor permeability and \\  & & wound dressing & hydrophilicity decreased by \\  & & adding GO & \\ \hline \multirow{4}{*}{\begin{tabular}{c} Polylide-co- \\ glycolide/chitosan/ \\ \end{tabular} } & \multirow{4}{*}{Biomedical} & Improved wettability of & \multirow{4}{*}{[58]} \\  & & magnolishers & \\  & & & Enhanced antimicrobial function & \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Chitosan/gelatin/ \\ GO-silver \\ \end{tabular} } & \multirow{4}{*}{Tissue engineering, & \multirow{4}{*}{
\begin{tabular}{c} Improved tensile strength and \\ Young’s modulus \\ Enhanced antimicrobial activity \\ Improved thermal stability \\ \end{tabular} } & \multirow{4}{*}{[59]} \\  & & & Improved thermal stability \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chitosan/GO nanofiber webs and their biomedical applications. Chitosanan/hyaluronic acid wound dressings were prepared with GO/copper using sodium trimeta-phosphate (STMP) as the crosslinking agent, followed by vacuum freeze-drying [61]. The reason for using copper was that it is a cheaper antimicrobial agent with the ability to kill pathogens on its metallic surface. The prototype dressings had excellent antimicrobial activity against two strains of _Staphylococcus aureus_, usually found in wound infections, and good cytocompatibility when cultured with NIH/3T3-L1 mouse fibroblasts.