Preparation and properties of biomedical segmented polyurethanes based on poly(ether ester) and uniform-size diurethane diisocyanates

This study describes the preparation and properties of a novel aliphatic cost-effective segmented polyurethanes (SPUs) based on poly(ether ester) (poly-(ε-caprolactone-co-l-lactide)-poly(ethylene glycol)-poly-(ε-caprolactone-co-l-lactide), PECLA) and uniform-size diurethane diisocyanates (HDI-BDO-HDI). PECLA was synthesized via bulk ring-opening polymerization with poly(ethylene glycol) (PEG) as an initiator and ε-caprolactone, l-lactide as monomers. By chain extension of PECLA diol with HDI-BDO-HDI, three SPUs with different hydrophilic segments content and hard segments content were obtained. The chemical structures of the chain extender, PECLA and SPUs were confirmed by ¹H NMR, ¹³C NMR, FT-IR, HR-TOF-MS and GPC. The influences of PEG content and uniform-size hard segments on in vitro degradability and mechanical properties of SPU films were researched. Similar thermostability observed in TGA curves of SPU films indicated that the hard segments and PEG content had little influence on the thermostability. The formation of microsphase-separated morphologies, which were demonstrated by the results of DSC and XRD, and physical-linking (H-bonds) network structures led to better mechanical properties of SPU films (ultimate stress: 23.1-17.9 MPa; elongation at break: 840-1130%). The results of water absorption and water contact angle showed that the bulk and surface hydrophilicity were closely related with the hydrophilic PEG content in SPU backbone. And the water absorption being less than 10 wt% indicated that the SPU films had low swelling property. In vitro hydrolytic degradation studies showed that the time of the SPU films becoming fragments was 34-19 days and the degradation rate increased with the increasing content of hydrophilic segments in SPUs, indicating that the degradation rate of SPU films could be controlled by adjusting PEG content. Cytotoxicity test of film extracts were conducted using L929 cells, and the relative growth rate exceeded 90% after incubation for 24, 48 and 72 h, showing excellent cytocompatibility. The acceptable mechanical properties, controllable biodegradability and excellent cytocompatibility of the polyurethanes can make them good candidates for further biomedical applications.