Biodegradation of ornithine-containing polylysine hydrogels

The degradation of the cross-linked cationic poly(amino acid)-glutaraldehyde (GA) hydrogels by two kinds of proteolytic enzymes, trypsin and Aspergillus Protease Type XXIII, and by seven species of soil filamentous fungi has been investigated using homo- and copolypeptides of lysine (Lys) and ornithine (Orn). Trypsin degraded the hydrogels prepared from poly(Lys) and copoly(Lys Orn)s but not poly(Orn), while Aspergillus protease degraded all of them. Degradation time of hydrogels by the two proteases became longer with increasing Orn content in the gel. Seven species of soil filamentous fungi were cultured with hydrogels on Czapeck medium to evaluate the degree of microbial degradation of the hydrogels, and the three species of the fungi, Aspergillus oryzae, Penicillium citrinum and Curvularia sp., were grown in culture with an accompanying degradation of the gel matrix, while the other four species, Mucor sp., Rhizopus sp., Cladosporium sp., and Trichoderma sp., were not. The degree of degradation of gel matrix with growth of the three fungi became lower with increasing Orn content in the gel matrix. The results might offer some clues to the applications for the controlled biodegradation of cationic poly(amino acid) hydrogel by introduction of Orn, suggesting that unnatural amino acid resists hydrolysis by proteases or microorganisms.