TAILORED ONE-WAY AND TWO-WAY SHAPE MEMORY BEHAVIOR OF CROSS-LINKED POLY(ε-CAPROLACTONE) FOR SMART BIOMEDICAL DEVICES

The thermally activated shape memory response of polymeric materials results from a combination of the material molecular architecture with its thermal/deformational history, or “programming”. In this work we investigate the shape memory response of systems based on poly(ε-caprolactone), PCL, so to explore the adoption of proper molecular architectures to tailor their one-way shape memory response, as well as to validate their two-way shape memory capabilities. A series of crosslinked PCL materials were obtained starting from linear, three- and four-arm star PCL functionalized with methacrylate end-groups, allowing to tune the melting temperature (Tm) on a range between 32 and 55°C. The materials' ability to display the one-way and two-way shape memory effect was investigated by the application of proper thermo-mechanical cycles carried out in a DMA machine on cylindric and rectangular specimens. After having “programmed” the cylindric specimens at 50% at a deformation temperature higher than Tm, the materials are seen to fully restore their original shape by heating them on a narrow region close to Tm; further, when the shape memory effect is triggered under fixed strain conditions, the materials are able to exert stress on a range between 0.2 and 7 MPa. The materials also display two-way shape memory features, reversibly moving between two shapes when cooled and heated under a fixed tensile load on a thermal region between melting and crystallization temperatures. Finally, to investigate the application of the biodegradable materials as self-expandable stents, shape memory experiments are currently carried out on tubular specimens.