The stability of methacrylate biomaterials when enzyme challenged: kinetic and systematic evaluations

This study addressed whether methacrylate monomers and polymers used in dentistry might degrade from enzymolysis by acetylcholinesterase (ACHE), cholesterol esterase (CHE), porcine liver esterase (PRLE), and a pancreatic lipase (PNL). Short (hour) and long-term (day) exposures were performed. Product ratios were used to determine surface hydrolysis of the polymeric materials. Enzyme kinetics were studied for the monomers when challenged by ACHE, CHE, and PRLE. In the case of PRLE, the V(max) for the dimethacrylate substrates varied slightly, but amounted to as much as 10% of that of p-nitrophenylacetate. The K(m) for triethylene glycol dimethacrylate (TEGDMA) was 197 microM for ACHE and 1107 microM for CHE. The V(max) was 2.7 nmol/min for ACHE and 3.5 nmol/min for CHE. TEGDMA was converted by CHE at 2% the rate of cholesteryl oleate. Long-term incubations of monomers with CHE and ACHE produced degrees of hydrolysis that evidenced structure dependency in the ability of the enzymes to effect hydrolysis. Particularly resistant were aromativ derivatives and those with branching in methacrylate linkages. Overall, the study confirms the ability of physiologically important esterases to catalyze the hydrolysis of biomaterial methacrylates.