Synthesis and properties of chitosan-silica hybrid aerogels

Chitosan, a polymer that is soluble in dilute aqueous acid, is derived from chitin, a natural polyglucosamide. Aquagels, where the solid phase consist s of both chitosan and silica, can be easily prepared by using an acidic so lution of chitosan to catalyze the hydrolysis and condensation of tetraethy lorthosilicate. Gels with chitosan/tetraethoxysilane (TEOS) mass ratios of 0.1-1.1 have been prepared by this method. Standard drying processes using CO2 give the corresponding aerogels. The amount of chitosan in the gel play s a role in the shrinkage of the aerogel during drying. Gels with the lowes t chitosan/silica ratios show the most linear shrinkage, up to 24%, while t hose with the highest ratios show only a 7% linear shrinkage. Pyrolysis at 700 degreesC under nitrogen produces a darkened aerogel due to the thermal decomposition of the chitosan, however, the aerogel retains its monolithic form. The pyrolyzed aerogels absorb slightly more infrared radiation in the 2-5 mum region than the original aerogels. B.E.T. surface areas of these a erogels range from 470 to 750 m(2)/g. Biocompatibility screening of this ma terial shows a very high value for hemolysis, but a low value for cytotoxic ity. (C) 2001 Elsevier Science B.V. All rights reserved.