In vitro degradation of novel medical biodegradable aliphatic polyurethanes based on ε-caprolactone and Pluronics® with various hydrophilicities

Linear biodegradable polyurethanes with varying ratios of the hydrophilic-to-hydrophobic segment were obtained in the study. The hydrophilic segment was based on poly(ethylene oxide-propylene oxide-ethylene oxide) diols (Pluronic (R)). The hydrophobic segment was based on poly(epsilon -caprolactone) diol. Viscosity-average molecular weights and the polydispersity index of the polyurethanes were in the range of 38.000-85.000 daltons and 1.2-3.2, respectively. The polymers absorbed up 3.9% of water depending on the chemical composition. Tensile strength, Young's modulus and elongation at break of the polymers were in the range of 11-46 MPa, 4.5-91 MPa and 370-960%, and the glass transition and soft segment melting temperatures were -60 to-21.5 degreesC and 30-55 degreesC, respectively. Degradation in vitro caused 2% mass loss, 15-80% reduction of molecular weight and slight reduction of polydispersity at 48 weeks. The extent of degradation was dependent on the polymer composition and the hydrophilic segment content. At a comparable degradation time the materials containing Pluronic (R) were degraded most. Degradation of polyurethanes caused insignificant changes of the pH of the medium. (C) 2001 Elsevier Science Ltd. All rights reserved.