Preparation of Chitin Hydrogel Under Mild Conditions

Abstract

Both the amount of water and the number of calcium ions are main factors affecting the dissolution of chitin in calcium chloride dihydrate-saturated methanol (calcium solvent). The higher degree of N-acetylation of the chitin was also indicated by its higher solubility in calcium solvent. The chitin hydrogel was prepared by adding a large excess of water to the chitin solution with vigorous stirring, followed by extensive dialysis against water or by filtration to remove the methanol and calcium ions. The water content of the chitin hydrogel was approximately 94 -96% (w/v) and could be controlled by centrifugation. The chitin gel was also prepared by the addition of a large excess of alcohol, such as ethanol and iso-propanol, and these protocols were found to be effective under anhydrous conditions because the alcohols were exchangeable with other organic solvents in solution. The chitin hydrogel was more susceptible to lysozyme than to chitinase, and showed and a poor susceptibility to chitosanase. A a-chitin-type crystalline structure was regenerated from chitin sheets prepared from both a-chitin and b-chitin solutions in calcium solvent, but the b-chitin-type sheet was formed from the b-chitin hydrogel prepared by mechanical agitation in water. The a-chitin hydrogel solidified when thawed after freezing, but the b-chitin hydrogel prepared by mechanical agitation maintained its gel form even after prolonged freezing. Animal studies revealed a low toxicity for the chitin sheet and an acceleration of epidermal cell regeneration.

A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields

“…Chitosan can also form gels that absorb substantial volumes of water due to its high molecular weight, and porous structure [191]. These "hydrogels" can improve the water retention levels of soils [192].…”

Chitin-chitosan nanocomposite gels: reinforcement of chitosan hydrogels with rod-like chitin nanowhiskers

“…Methanol saturated with calcium chloride dihydrate was prepared according to the previous report. 31 Two gels with whisker content of 2.97 and 0%, respectively, (namely, the latter is a cross-linked chitosan gel), swollen with water, were cut into cubical pieces of about 8 mm length, and immersed in the 20 ml of methanol/ CaCl 2 solvent separately. These gels were refluxed for 2 days in an oil bath at 90 1C with an exchange of the solvent at 24 h heating.…”

“…A chitin nanowhisker/chitosan nanocomposite gel and a cross-linked chitosan gel were refluxed in methanol saturated with calcium chloride, which is reported to be a good solvent for chitin. 31 If chitin nanowhiskers are free from crosslinking and are embedded separately in the nanocomposite gel, the methanol/CaCl 2 solvent penetrated into the gels will readily dissolve chitin nanowhiskers and make the gel transparent. The result was quite opposite; appearances of the both gels did not change as shown in Figure 2b, although they were slightly shrunk according to solvent exchange.…”

Chitosan, Chitosan Derivatives and their Biomedical Applications

“…Chitin can be dissolved in solutions with high ionic strength as hexaluoroacetone or dichloroethane with mineral Biological Activities and Application of Marine Polysaccharidesacids, and 5% lithium chloride in dimethylacetamide [2]. In 2006, Tamura and coworkers solubilized chitin in saturated methanol with dihydrate calcium chloride [8]. The insolubility of chitin is associated with a high degree of crystallinity due to the formation of diferent hydrogen bonds between the N-acetyl groups (N-H…O=C) at C-2 and hydroxyl group at C-3 and C-6 with N-acetyl group (O-H…O=C), keeping chitin chains tightly bound.…”