4D printed biocompatible magnetic nanocomposites toward deployable constructs

Abstract

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 at 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 an 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 extent of shape fixity (>95%) and recovery (>99%) was excellent, and the recovery time was short (<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 by a magnetic field and heat, respectively. The materials (both PLMC and its nanocomposites) exhibited excellent in vitro biocompatibility and in vivo biocompatibility. The composite was as efficient as PLMC in supporting osteogenic differentiation of the pre-osteoblasts, as confirmed by mineral deposition in vitro. Thus, the 4D printed shape memory magnetic nanocomposite presented here could be an excellent candidate biomaterial for engineering deployable scaffolds and medical devices, among other implantable applications.