Biodegradation of chitosan-graft-polymethylmethacrylate films

Methylmethacrylate was graft copolymerized onto chitosan, the N-deacetylated derivative of chitin, by persulfate-induced free radical initiation to get chitosan-graft-polymethylmethacrylate (C-g-PMMA), which could be thermo-pressed into thin films. Screening of known microorganisms for in vivo degradation of C-g-PMMA copolymer showed maximum activity (11.3 μg glucosamine released min−1 ml−1 at 37 °C) for Bacillus subtilis. Aspergillus flavus which colonized on C-g-PMMA films was isolated and purified. The fungus degraded the graft film by 40-45% over 5-25 days of aerobic cultivation. Infrared spectral data of the treated film showed absorption above 3000 cm−1 due to hydrogen bonding of −OH groups, 1650 cm−1 due to amide group of chitosan diminished, and 1730 cm−1 absorption due to -C0 group of polymethylmethacrylate became broader as biodegradation increased. SEM of treated film revealed preferential utilization of chitosan moieties. HPLC data showed chitotetraose due to initial (day 5) endo-hydrolase activity, and after 20 days glucosaminidase activity converted this to glucosamine in the culture medium. No monomer (MMA) was released into the medium even after incubation for 25 days. In vitro degradation of C-g-PMMA (27% grafting) with chitosanase, pepsin and lysozyme released chito-oligomers (HPLC), whereas these enzymes showed no activity towards highly grafted copolymer.