The effect of poly(trimethylene carbonate) molecular weight on macrophage behavior and enzyme adsorption and conformation

Poly(trimethylene carbonate) (PTMC) with molecular weights greater than 100 kg/mol is known to degrade readily in vivo while PTMC of less than 70 kg/mol is resistant to degradation. The reason for the molecular weight dependent degradation rate of PTMC is unclear, and may be due to differences in macrophage behavior or enzyme adsorption or activity. Macrophage number and production of reactive oxygen species (ROS) and esterase were measured when cultured on 60 and 100 kg/mol PTMC. Cholesterol esterase and lipase were adsorbed to 60 and 100 kg/mol PTMC and mass and viscoelastic properties of the adsorbed enzyme layers were measured. No significant differences were observed in macrophage number or production of degradative species. Significant differences were measured in mass, shear modulus and viscosity of the adsorbed cholesterol esterase layer, suggesting that the cholesterol esterase is adsorbing in a different conformation on the 60 and 100 kg/mol PTMC. Despite similar bulk moduli, the surface modulus of 60 kg/mol PTMC was significantly lower than 100 kg/mol. It is proposed that the difference in surface stiffness and polymer chain flexibility affect the arrangement of water bound to and freed from the polymer chains during adsorption, thus affecting enzymatic adsorption, conformation, and activity.