Enzyme-induced biodegradation of polycarbonate polyurethanes: dependence on hard-segment concentration.

Polycarbonate-based polyurethanes with varying hard segment contents were synthesized. The physical and chemical structures were characterized by using gel permeation chromatography, differential scanning calorimetry, water uptake testing, Fourier transform infrared, and attenuated total reflectance--Fourier transform infrared. The polymers were incubated with cholesterol esterase in a phosphate buffer solution at 37 degrees C over 10 weeks. A higher resistance to hydrolytic degradation was observed in polycarbonate-based urethanes with higher hard segment content. The analysis of the material structures revealed that the degradation of polycarbonate-based urethanes was preferentially initiated at non-hydrogen-bonded carbonates and urethanes. Although the crystallinity of the polycarbonate soft segment may contribute to reducing the hydrolytic degradation catalyzed by cholesterol esterase, it was found to be relatively minor in comparison to the importance of hydrogen bonding between the carbonate and urethane groups. These observations suggest that the biostability of polyurethanes and specifically polycarbonate-based polyurethanes can be improved by manipulating the degree of hydrogen bonding within the materials. Copyright 2001 John Wiley & Sons, Inc. J Biomed Mater Res 56: 516--528, 2001