Effects Of Different Solvents On The Stability And The Biological Properties Of Chitosan

Chitosan, a biocompatible and biodegradable natural biological polysaccharide,not only has less immunogenicity and nontoxicity, but also has functions of balancingcholesterol, anti-cancer and coagulation. It is a good health care product andbiomedical material. But there are strong hydrogen bondings between intramolecularand intermolecular of chitosan, thus the chitosan is only soluble in several specificacidic solvents.The ionic liquid is a new type of green solvents which has developed in therecent years. The previous studies also showed that chitosan has good solubility in it.In this thesis, three different solvents which are traditional chitosan solvent acetic acidsolution, GlyCl solution prepared by the HCl and glycine, and the ionic liquidEmimAc were used to dissolve the chitosan. NaOH solution and ethanol were used toregenerate the dissolved chitosan. Molecular weight and de-acetylation degree ofdetermination were used to visualize the changes in the process of dissolution.Wide-angle X-ray diffraction(WAXD) and Fourier transform IR(FTIR) were used tovisualize the different structures after the dissolution of three different kinds ofsolvent. The results showed that the regenerated chitosan had a molecular weightreduced to a certain extent, but no significant difference between the three. WAXDand FTIR results clearly suggested that the H-bond networks formed in the nativechitosan have been greatly destroyed in the dissolution process by the EmimAcsolvent, and the H-bond network could not be completely reconstituted during theregeneration process by the coagulants.The antibacterial experiment of the regenerated chitosan on E. coli was evaluated.Regenerated chitosan had stronger antibacterial activity than the native chitosan. Theantibacterial activity of the regenerated chitosan dissolved in ionic liquid is strongerthan that dissolved in the other two. Because the antibacterial activity of chitosantowards Gram-negative bacteria is mainly based on the amino, further explained that H-bond networks formed in the native chitosan have been greatly destroyed in thedissolution process, which increased the number of the exposed amino.Hemolysis experiments, endotoxin experiments, cytotoxic assays were tested todetect the biological performance of regenerated chitosan. The hemolysis rate of theregenerated chitosan was lower than1.5%, which is far below the national standard ofbiological material and also had a decline compared to the original chitosan. Thedetermination of endotoxin content in the chitosan was generally ignored in-vitroexperiments. In the paper, the endotoxin content of the renewable and originalchitosan was detected. The results showed that the endotoxin content of theregenerated chitosan was much lower than the original chitosan. MTT assay of theregenerated and the native chitosan showed that the relative cell growth was morethan75%, which indicated that the cytotoxicity of all materials were at a lower level.ILs are usually considered as green solvents, toxicity studies have shown that in thecase of very low concentration (0.1mg/mL) the cells had good cell viability.Chitosan had become more widely used in industry. The chitosan solution weretend to be stored in a short time and maintain its stability. Chitosan in acid solutionwas prone to degradate, the chitosan solution is not conducive to the storage inindustry. Glycine was added in acetic acid solution as a buffer, within the first12hours the chitosan solution has remained relatively stable with no significantdegradation. After12hours, chitosan degraded significantly. Sodium acetate wasadded in the acetic acid solution to form buffer solution of different pHs. The stabilityof the chitosan in acetic acid-sodium acetate solution was the best，which isconducive to the storage of chitosan solution in the industry.