Chitin and Chitosan and Their Polymers
It has become necessary to obtain economic culture media that promote the growth of fungi and stimulate the production of the polymers. Recently, microbiological processes were used for chitin and chitosan production by Cunninghamellaelegans grown by submerse fermentation in economic culture medium, with yam bean as substrate. In order to improve the solubility or impart new properties to chitosan, modification of the chitosan chains, generally by either grafting of small molecules or polymer chains onto the chitosan backbone or by alkylation, sulfation, thiolation, carboxymethylation, etc. of the amino groups, has been investigated. Chitosan-4-thio-butylamidine conjugates provide 140-fold stronger mucoadhesion than unmodified polymers. The mannose-bearing polymers exhibit enhanced macrophage-specific bioactivity both as a gene delivery system and as a vaccine. Major obstacles for large-scale technical applications of high quality chitin/chitosan are the high prices of the polymers and the difficulties in preparing uniformly reproducible charges in bulk quantities from various marine organisms.