Influence of well-defined hard segment length on the properties of medical segmented polyesterurethanes based on poly(ε-caprolactone-co-L-lactide) and aliphatic urethane diisocyanates

This work describes the preparation, characterization, mechanical properties, in vitro degradability, and cytocompatibility of two aliphatic segmented polyesterurethanes (SPEU-II, SPEU-III) based on poly(epsilon-caprolactone-co-L-lactide) and aliphatic urethane diisocyanate chain extenders. Two novel chain extenders containing two and four urethane groups, respectively, were synthesized and used in SPEU formulation. The influences of well-defined hard segment length on the degradability and mechanical properties of SPEU films were researched. The results of differential scanning calorimeter and X-ray powder diffraction showed that the long well-defined hard segments improved the phase separation of soft and hard segments, which led to satisfactory mechanical properties of SPEU films (ultimate stress: 24.8-35.4 MPa; strain at break: 601-669%). And the initial modulus increased from 31.9 MPa (SPEU-II) to 41.7 MPa (SPEU-III) with the increasing length of hard segments. SPEU-III with longer well-defined hard segment containing more urethane groups exhibited slower hydrolytic degradation rate (similar to 67 days) and lower water absorption (similar to 4 wt%) than SPEU-II. The results could be due to the formation of more hydrogen bonds among the hard segments and between the soft and hard segments, which strengthened the interchain attraction and gave a more compact network structure. The SPEU films showed similar thermostability, indicating that the length of hard segments marginally affects the thermostability. Cytotoxicity test of film extracts was conducted using L929 mouse fibroblasts, and the relative growth rate exceeded 90% after incubation for 24, 48, and 72 h, showing excellent cytocompatibility.