Hydrolytic and enzymatic degradation of linear segmented polyurethane block copolymers studied by ToF-SIMS and atomic force microscopy

Hydrolytic and enzymatic degradation of linear segmented polyurethanes with differing compositions were studied by atomic force microscopy and time-of-flight secondary ion mass spectroscopy. Poly (ester urethane urea)s (PEUUs) with two different molecular ratios of polycaprolactone diol (PCL) soft segments and L-lysine diisocyanate/hydrazine hard segments were exposed to aqueous conditions (water or phosphate buffered saline), and the changes in their surface chemistry and morphology were studied. It was found that polymer surface roughness in aqueous conditions is significantly affected by its bulk composition. After soaking in an aqueous buffer solution, the surface of PEUU with higher PCL concentration became significantly rougher compared to PEUU with lower PCL concentration. This surface roughening can be attributed to PCL lost from the surface during hydrolytic degradation. Despite the surface roughness changes, the rate of the hydrolytic degradation of PEUUs was found to be independent of bulk polymer composition. Enzymatic degradation of a linear segmented PEUU containing an oligopeptide segment [poly(peptide urethane urea) (PPUU)] in a collagenase solution was also investigated. The PPUU oligopeptide segment contained proline, hydroxyproline, and glycine amino acids. In a collagenase solution, the PPUU polymer exhibited a significantly higher degradation rate and surface roughness compared to a PEUU polymer that did not contain the oligopeptide segment.