A co-dispersed nanosystem of strontium-anchored reduced graphene oxide to enhance the bioactivity and mechanical property of polymer scaffolds

Abstract

Poly(L-lactide) (PLLA) is a promising bone repair material owing to its good biocompatibility and natural degradability, but its lack of bioactivity and insufficient mechanical property restrict its further application. Strontium (Sr) nanoparticles can endow materials with bioactivity, while reduced graphene oxide (rGO) nanosheets with excellent strength are commonly used in the strengthening phase. Nevertheless, both Sr nanoparticles and rGO nanosheets are prone to agglomerate in the matrix. In this work, a co-dispersed nanosystem was constructed to solve this issue via synergistic effects. In detail, Sr nanoparticles were anchored on rGO nanosheets via the in situ reduction of strontium chloride and graphene oxide. On the one hand, rGO with large specific surface area provided sufficient space for the uniform anchoring of Sr nanoparticles. On the other hand, Sr nanoparticles formed steric hindrance to block the stacking of rGO nanosheets. Subsequently, the nanosystem was introduced into PLLA scaffolds fabricated via laser additive manufacturing. Results demonstrated that the nanosystem was evenly distributed in the PLLA matrix, which resulted in scaffolds exhibiting a 90% increase in the tensile strength and 117% increase in the compressive strength. More importantly, Sr²⁺ presented a sustained release profile in scaffolds, which is ascribed to the fact that rGO acted as a barrier layer to hinder Sr from reacting with the external solution, preventing its quick release. In vitro experiments revealed that released Sr²⁺ effectively promoted the cell attachment, proliferation and gene expression for a long period.