Shape Memory Effect of Polymer Composites

Shape memory polymers (SMP) are a new class of materials that can recover their shape through an external stimulus and are primarily composed of elastomers, gels, or other soft matter. Reversible one-way shape recovery of these materials for complex geometries can provide control over their dynamic material properties by combining various polymers. Here we present the use of a newly designed and developed 3D printing mechanism, multiphase direct ink writing (MDIW), for the one-step fabrication of layered composite structures with shape memory. The MDIW allows for a combination of a few different polymers and nanoparticles to effectively tune the material properties to precisely control their stimuli responsiveness. The shape memory polymer was composed of thermoplastic polyurethanes (TPUs), biodegradable semi-crystalline polycaprolactone (PCL), and metallic iron oxide (Fe₃O₄) nanoparticles. The composite was designed to respond to thermal and magnetic stimulus with elastomeric TPUs providing the necessary flexibility and strength, while the PCL was used to tune the thermal responsiveness with its low melting temperature and Fe₃O₄ for the magnetic responsiveness. The as-fabricated structures displayed actuation control over a wide temperature range of 40 - 65°C and an efficient recovery rate at higher strain loading. The layered arrangement of the polymers displayed recovery of complex shapes and magnetic maneuverability with 5 degrees of freedom. The dimension-temperature-time relationship of the SMP provides a broad application in bioengineering, microfluidics, energy, and aerospace.