Selected properties of pH-sensitive, biodegradable chitosan-poly(vinyl alcohol) hydrogel

Chitosan and poly(vinyl alcohol) (PVA) were used to form a semi-interpenetrating polymeric network with glutaraldehyde as the cross-linker. The molecular weight and degree of deacetylation of the chitosan were 612 kDa and 72 %, respectively. The chemical bonds formed by the cross-linking reaction and transition of these bonds in different pH media were investigated. The gelation property of the chitosan-PVA pregel solution and mechanical properties of the hydrogel were studied. The FTIR spectra of the hydrogel before and after swelling at pH 3 and pH 7 indicated formation of Schiffs base (C=N) and -NH3+. They also showed pH-induced transition of C=N to C-N, and -NH3+ to -NH2, as well as the instability of the Schiffs base. The chitosan is essential for hydrogel formation through Schiffs base reaction between the amino groups of the chitosan and the aldehyde groups of the glutaraldehyde. The addition of PVA improved the mechanical properties of the hydrogel. However, PVA tends to leach out at longer swelling times in the acidic medium due to hydrolysis of the gel networks, Schiffs base. (C) 2004 Society of Chemical Industry.