In vivo kinetic degradation analysis and biocompatibility of aliphatic polyester polyurethanes

Polyester polyurethanes incorporating polyhedral oligosilsesquioxane (POSS) as the crystalline hard block were evaluated for biocompatibility and degradation over 24 weeks in vivo. In vitro studies were also used to predict the onset of mass loss. The molecular weight of each sample was found to decrease quickly over an 8 week period and then became constant due to the nondegrading POSS hard block. Kinetic analysis of the initial molecular weight change indicated that the degradation rate was dependent on the soft block composition. Crystallinity, melting temperature, and heat of fusion of the polyurethanes were found to increase during degradation as the amorphous polyester soft segments were hydrolyzed. The histological analysis of each polymer demonstrated rapid resolution of the acute and chronic inflammatory responses and the development of expected, normal foreign body reaction, consisting of adherent macrophages and foreign body giant cells on the surface of the polymers, and fibrous capsule formation around the polymer. No acute and/or chronic inflammation was seen after 3 weeks, indicating that the polymers in film form and biodegraded form, that is, particles, were biocompatible and did not elicit inflammatory responses expected for toxic or nonbiocompatible materials.