Shape Memory Polymers Based on Naturally-Occurring Bile Acids

Naturally occurring bile acids are ideal building blocks for a new generation of biomaterials displaying low systemic toxicity and engineered properties. Herein we report the synthesis of bile acid-based polyesters using entropy-driven ring-opening metathesis polymerization (ED-ROMP) and characterization of the structure of the resulting polymers. The materials synthesized display high molecular weights (M. above 100000), typical of ED-ROMPs. The mechanical and responsive behavior of these bile acid-based polyesters (BAPs) is studied by dynamic mechanical analysis (DMA) and thermomechanical cycling. Although BAPs are amorphous thermoplastics, they display typical rubber-like elasticity with tunable mechanical behavior, glass transitions close to body temperature, and outstanding shape memory properties. By introducing small changes in the chemical structure of BAPs (amide bonds or additional hydroxyl groups), we were able to correlate the materials stiffness, their T, and shape recovery temperature to their structure. In addition, we show that BAPs call be deformed to high strains even at low temperature and still display shape recovery.