Biocompatible shape memory polymer actuators with high force capabilities

Abstract

Shape memory polymers (SMP) are a class of stimuli-responsive materials which can change shape upon activation. The objective of this study is to optimize the actuation (or shape recovery) properties of the biocompatible thermoplastic polyurethane (TPU)/polylactic acid (PLA) shape memory polymer (SMP) blend by altering the blend composition and programming temperature. A comprehensive characterization of the shape memory, morphological, and actuation properties of TPU/PLA blends was carried out on 80/20, 65/35, and 50/50 TPU/PLA blends and neat TPU. Three programming temperatures were utilized: 25°C (room temperature), 37°C (body temperature), and 70°C (above the glass transition temperature). The transition temperature (Ttrans) range was characterized by recovering the samples between 30°C and 100°C, at 10°C intervals. The results showed that the shape fixity ratio (Rf) increased significantly with increasing PLA composition and programming temperature, and the shape recovery ratio (Rr) was not dependent on the programming temperature. The Ttrans increased with increasing programming temperature, and its range decreased with increasing PLA composition. The highest shape recovery force was observed in the 80/20 and 65/35 TPU/PLA blends programmed at 70°C, reaching up to 0.6N/cm. These samples were able to lift a 50g weight during the shape recovery process. The actuation forces of the TPU/PLA blends in this study is an order of magnitude higher compared to the currently available biocompatible SMPs. Therefore, these SMP blends can be further developed into actuators for biomedical applications such as artificial muscles.