Degradation of five polyurethane gastric bubbles following in vivo use: SEC, ATR-IR and DSC studies

Five Garren-Edwards Gastric Bubbles were characterized, following up to 4 months use in vivo, using size exclusion chromatography, differential scanning calorimetry and attenuated total reflectance infrared spectroscopy. These techniques show that the material used to construct the bubble is probably an aromatic polyester urethane and revealed a 39-55% decrease in number average molecular weight, a 9 degrees C decrease in glass transition temperature, the disappearance of soft segment crystallinity and a broadening of the hard segment melting region after exposure to highly acidic (approximately pH 1.2) gastric fluid. The results indicate that significant chemical and morphological changes have taken place in the bubble material, including loss in chemical functionality, phase separation and increased hard segment aggregation. A comparison of the decrease in glass transition temperature as a function of molecular weight suggests that glass transition temperature is a sensitive predictor of this material's stability. Additionally, evidence is provided that the broad infrared absorption at 1077-1067 cm-1 normally assigned to C-O-C hard segment may represent two types of C-O-C stretching: (1) C-O-C stretching of the free urethane carbonyl, and (2) C-O-C stretching of the hydrogen bonded urethane carbonyl.