4D Printed Biocompatible Magnetic Composite for Minimally Invasive Deployable Structures

4D printing of shape memory polymers (SMPs) and composites has been realized for a multitude of applications spanning healthcare, soft robotics, environment, space, etc. However, demonstrating such materials for in vivo applications has not been possible to a large extent due to the unavailability of suitable materials with recovery temperatures around physiological levels. Also, direct heating to trigger shape recovery in SMPs is not a practical and elegant approach in many cases. In this study, polylactide-co-trimethylene carbonate (PLMC), an SMP, has been endowed with magnetic iron oxide (Fe3O4) nanoparticles to realize remote heating under alternating magnetic field and at temperatures around 40°C. The PLMC-5% Fe3O4 composite was 3D printed into a variety of shapes, including scaffolds, fixed into pre-programmed temporary shapes to be deployed minimally invasively, and then recovered into original shapes under magnetic actuation. The shape recovery was excellent (>99%) and fast (under 20-30 s). Additionally, these magnetic composites could potentially be guided to the site of deployment through permanent magnets. Both PLMC and its composites were printed in distinct regions of a single structure, deformed, and then recovered by selective and sequential stimulation of magnetic field and heat, respectively. The materials (both PLMC and its nanocomposite) exhibited favorable in vitro and in vivo biocompatibility, thus highlighting their usefulness for being used as deployable tissue scaffolds and medical devices, among other implantable applications.