Compostable lignin grafted poly(ε-caprolactone) polyurethane biomedical materials: Shape memory, foaming capabilities, and biocompatibility

Biodegradable shape memory poly(e-caprolactone) (PCL)-based polyurethane (PU) have garnered substantial attention in biomedical applications, due to their unique properties that can recover their original shapes when exposed to temperature stimulus close to body temperature (∼35 °C). This study entails an in situ one-pot synthesis of a compostable shape memory PU system that uses PCL as soft chain segments, 1,4-butanediol (BDO) and glycerol (GLY) as chain extenders, which was then grafted with lignin hard segment and/or crosslinking nodes. The addition of renewable and sustainable lignin not only enhanced the mechanical properties of the PU, but also improved the resulting shape memory effects by increasing the shape fixing and recovery ratio. In PCL system containing BDO (PCL-BDO), 5 wt% lignin loading yields shape fixity and shape recovery ratios of 93.2 % and 81.4 %, respectively. Similarly, 5 wt% lignin in PCL systems containing GLY (PCL-GLY exhibited high shape fixity (64.4 %) and shape recovery ratio (81.4 %), respectively. Rheological characterizations showed strong evidence that the melt strength of both the PCL-BDO and PCL-GLY increased with the presence of lignin, which directly improved the physical foaming capabilities of PCL-based PU. The biocompatibility assessment also showed that the developed shape memory PCL-lignin based PU were not cytotoxic and capable of supporting cell adhesion and cell growth.