Biodegradation evaluation of polyether and polyester-urethanes with oxidative and hydrolytic enzymes

Enzyme-induced liberation of components from seven different radiolabeled polyurethanes was monitored by radiolabel counting of the incubation solutions and product isolation by high performance liquid chromatography (HPLC). The polyurethanes were selected to reflect variations in the hard-segment chemistry, soft-segment chemistry, and polyurethane hydrophilicity resulting from combinations of hydrophobic/hydrophilic soft segments. All materials were characterized using electron spectroscopy for chemical analysis, differential scanning calorimetry, size exclusion chromatography, and Fourier transform infrared spectroscopy. The material surfaces were examined both before and after incubation with enzyme and control solutions using scanning electron microscopy. Biodegradation assays were carried out at 37 degrees C using cholesterol esterase (CE) and horseradish peroxidase (HRP) under optimal pH conditions for each enzyme. The hydrolytic enzyme (CE) was effective in releasing degradation products that contained hard-segment components from some of the polyurethanes. HPLC analysis of products for a polyesterurethane synthesized with toluene diisocyanate (TDI) suggested that the bulk of the incorporated radiolabeled TDI was still covalently bonded within the cleaved chain segments of the original polymer and was not released as pure toluene diamine (TDA). The data suggest that urethane linkages in the soft-segment domains of phase separated polyetherurea-urethanes may be more prone to cleavage by CE than are the urea/urethane groups in the hard-segment domains. This could be related to the nature of the hard-segment domain structures. The oxidative enzyme (HRP) was not able to induce liberation of radiolabeled segments from either the polyether or polyester-based polyurethanes.