Synthesis and characterization of biodegradable linear shape memory polyurethanes with high mechanical performance by incorporating novel long chain diisocyanates†
Biodegradable shape memory polyurethanes (SMPUs) feature microphase separation and shape memory effects. The resulting promotion to bone calcification and capability for minimally invasive implantation make them promising bone repair materials. Unfortunately, insufficient mechanical properties compromise these merits. To get SMPUs with enhanced mechanical properties, we first designed and synthesized two diisocyanates with extended chain length from hexamethylene diisocyanate (HDI) and isosorbide (ISO), which were then employed as a coupling agent to synthesize novel linear SMPUs (ISO-PUs) from poly(DL-lactic acid) (PDLLA)-based macrodiol as the soft segment and ISO as the chain extender. The chemical structure, thermal properties, mechanical properties and shape memory effect of ISO-PUs were carefully investigated by using proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), mechanical test instrument and dynamic thermomechanical analysis (DMA). The results show that the novel diisocyanates increase the content of hard segments and further endow ISO-PUs with excellent mechanical properties both at room temperature (25 °C) and at physiological temperature (37 °C). The shape memory effect is satisfactory as well with a shape fixity ratio of up to 99.8% and a recovery ratio of up to 90.2%. The in vitro degradation experiments in 37 °C phosphate buffer solution (PBS) (pH 7.4), characterized by weight loss and compressive mechanical properties indicate that all ISO-PUs could degrade almost completely within 120 days with a dependence on the content of hard segments. In addition, all ISO-PUs demonstrate good cytocompatibility with osteoblasts. This work solves the critical challenge of the insufficient mechanical properties of linear SMPUs and may facilitate the application of SMPUs in high-value medical devices for bone repair.