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The effect of hard segment size on the hydrolytic stability of polyether-urea-urethanes when exposed to cholesterol esterase.

Previous studies have shown that both polyester and polyether-based polyurea-urethanes are susceptible to cleavage by hydrolytic enzymes. Furthermore, it has been hypothesized that the degree of hard segment micro-domain formation in polyurethane materials, as well as its structure, influences the ability of enzymes to degrade the polymers. The current study has investigated a series of segmented polyether-urea-urethanes synthesized with the same reagents but having different hard segment content. Using these materials, the relationship between the formation of hard segment domains and the hydrolysis of urea/urethane groups was specifically addressed. Both differential scanning calorimetry and X-ray photo-electron spectroscopy data indicated that the three materials differed significantly in the extent of hard segment domain formation and the nature of the chemical groups located in the top 10 nm of the surface. Biodegradation studies showed a strong dependence on hard segment domain formation and indicated that the polymer containing the highest number of hydrolytically labile urea and urethane bonds exhibited the least degradation. The ability of a polyurethane material to form hard segment micro-domains may contribute to the formation of a protective structure for the hydrolysable hard segment linkages located within the micro-domains.