## 6 Modifications of Chitosan
### Blending Modification of Chitosan  
The blending modification is a common method of polymer modification. Through some physical and chemical methods, chitosan is blended with other natural polymer materials or synthetic polymer materials, including starch, glucomannan capsule, gelatin, glycerin, cellulose, polyvinyl alcohol, polyacrylamide, etc., which can synthesize the excellent characteristics of each component to prepare for the needs of various fields, expanding the application range of polymer materials effectively. The blending modification of chitosan can not only give new excellent properties to new materials but also greatly reduces the cost of polymer materials. It is extensively used in adsorption of heavy metal ions, biomedical membrane materials, biological tissue functional materials, environmental protection fresh-keeping materials and other fields. [PERSON] et al. [57] fabricated chitosan biomaterials with collagen using a cross-linker alginate dialdehyde (ADA) that has been presented in Figure 7. Intact retaining of the classical triple-helical structure after crosslinking was confirmed by in vitro fiber formation and FTIR analysis. More compact microfibril structural interactions of collagen side-chains established by SEM analysis. Crosslinking of chitosan and collagen could improve the thermostability of final products. There was no significant effect of ADA in chitosan/collagen scaffolds on antibacterial activity. Accordingly, the fabrication of chitosan/collagen composites crosslinked with ADA improves stabilization, conserves the standard triple-helical structure, sustains good biocompatibility and discloses the new medical uses. Figure 6: Schematic representation of subsequent covalent reaction between single-walled carbon nanohorns (SWCNH) and the amine group of chitosan (CS) during CS-SWCNH hybrid scaffolds fabrication. Chitosan and carboxymethyl glucomannan are two kinds of polyelectrolytes with an opposite charge, which can form the polyelectrolyte complex and cross-linked membrane with the network structure in the process of film formation. [PERSON] et al. [58] prepared the chitosan carboxymethyl glucomanan blend film by solution blending (Figure 8). The results showed that there was durable communication and better compatibility between chitosan and carboxymethyl glucomannan in the blend membrane and the mechanical properties of the blend membrane increased with the increase of the carboxymethyl glucomannan content. [PERSON] et al. [59] reported that collagen, glucomannan and chitosan have good compatibility, and there are strong interactions among the three polymers, such as an electrostatic attraction and hydrogen bond. It is precise because of this interaction that the membrane has a uniform and smooth cross-section, high transmittance and better mechanical properties than a single polymer and binary blend membrane, the adsorption and permeability were also significantly lower than that of the glucomannan collagen binary membrane. The blend membrane containing glucomannan has good compatibility with endothelial cells and can be used as the carrier of endothelial cells. These characteristics indicated that the blend membrane of glucomanan collagen and chitosan has broad prospects as a potential scaffold material for tissue engineering, membrane carrier for cell transplantation, or biomaterial for organ damage repair. Although chitosan has outstanding advantages such as non-toxicity, degradability, biocompatibility, does little damage to the drug and is suitable for drug release, it also has disadvantages such as poor solubility, poor mechanical properties and too much dependence on pH. Blending with PVA can improve these disadvantages of chitosan. Chitosan was easy to accumulate on the surface of the airside when it was blended into the film, which indicated that chitosan was more hydrophobic than PVA.