Shape memory composites composed of polyurethane/ZnO nanoparticles as potential smart biomaterials

Polyurethanes are commonly used as shape memory materials due to their micro-phase separation structure. The degree of micro-phase separation is the key factor in the shape memory properties of materials. In this study, the shape memory polyurethane (SMPU) elastomer was prepared based on polycaprolactone diols, isophorone diisocyanate, and 1, 4-butanediol. And the branched structure is introduced by glycerol and hexamethylene diisocyanate to increase the degree of micro-phase separation. Moreover, nano-ZnO is also used to enhance micro-phase separation. Atomic force microscopy images clearly show that the nano-ZnO disperses uniformly in the polymer matrix and leads to significant change in the phase structure of SMPU. Dynamic mechanical analysis results indicate that the SMPU/ZnO nanocomposites possess two phase transition above 0°C, one is the melting transition of the soft segments, which is near the body temperature, and the other is the glass transition of hard segments. And with the addition of nano-ZnO, the difference in transition temperature between the hard and the soft segments is significantly increased. The relationship between shape memory properties and the micro-phase separation is explored and discussed. In vitro biocompatibility studies show that the SMPU/ZnO nanocomposites have good biosafety. Therefore, the obtained bionanocomposites have the potential application prospect as smart biomaterials.