PROPERTIES OF BIODEGRADABLE HYDROGELS PREPARED BY GAMMA-IRRADIATION OF MICROBIAL POLY(EPSILON-LYSINE) AQUEOUS-SOLUTIONS

Poly(epsilon-lysine) (PL) hydrogels have been prepared by means of gam ma irradiation of PL produced by Streptomyces albulus in aqueous solut ions. When the dosage of gamma irradiation was 70 kGy or more and the concentration of PL in water was 1-7 wt %, transparent hydrogels (opaq ue hydrogels for 1-3 wt % PL concentration) could be produced. In the case of 70 kGy of gamma irradiation and 5 wt % PL concentration, the s pecific water content (wt of absorbed water/wt of dry hydrogel) of the PL hydrogel was approximately 160. Specific water contents of PL hydr ogels decreased markedly with an increase in the dosage of gamma irrad iation. The specific water contents were increased with an increase in PL concentration in the irradiated solution. This result indicates th e presence of a radical scavenger in the PL solution. Swelling equilib ria of PL hydrogels were measured in water or in aqueous solutions of various pHs or concentrations of NaCl, Na2SO4, and CaCl2. Under acid c onditions, the PL hydrogel swelled due to the ionic repulsion of the p rotonated amino groups in the PL molecules. The degree of deswelling i n electrolyte solution was smaller than that of other ionic hydrogels [poly(gamma-glutamic acid), poly(acrylic acid) etc.]. In addition, the enzymatic degradations of PL hydrogel were studied at 40 degrees C an d pH 7.0 in an aqueous solution of the neutral protease [Protease A (A mano)] produced from Aspergillus oryzae. The rate of enzymatic degrada tion of the respective PL hydrogels was much faster than the rate of s imple hydrolytic degradation. The rate of enzymatic degradation decrea sed with the increase in gamma-irradiation dose during preparation of the PL hydrogel. (C) 1995 John Wiley & Sons, Inc.