Biodegradable shape-memory block co-polymers for fast self-expandable stents

Block co-polymers PCTBVs (Mn of 36,300–65,300 g/mol, Tm of 39–40 and 142 °C) containing hyperbranched three-arm poly(ɛ-caprolactone) (PCL) as switching segment and microbial polyester PHBV as crystallizable hard segment were designed as biodegradable shape-memory polymer (SMP) for fast self-expandable stent and synthesized in 96% yield by the reaction of three-arm PCL-triol (Mn of 4200 g/mol, Tm of 47 °C) with methylene diphenyl 4,4′-diisocyanate isocynate (MDI) to form the hyperbrached MDI-linked PCL (PTCM; Mn of 25,400 g/mol and a Tm of 38 °C), followed by further polymerization with PHBV-diol (Mn of 2200 g/mol, Tm of 137 and 148 °C). The polymers were characterized by 1H NMR, GPC, DSC, tensile test, and cyclic thermomechanical tensile test. PCTBVs showed desired thermal properties, mechanical properties, and ductile nature. PCTBV containing 25 wt% PHBV (PCTBV-25) demonstrated excellent shape-memory property at 40 °C, with Rf of 94%, Rr of 98%, and shape recovery within 25s. PCTBV-25 was also shown as a safe material with good biocompatibility by cytotoxicity tests and cell growth experiments. The stent made from PCTBV-25 film showed nearly complete self-expansion at 37 °C within only 25 s, which is much better and faster than the best known self-expandable stents.