Synthesis and Evaluation of a Zinc Eluting rGO/Hydroxyapatite Nanocomposite Optimized for Bone Augmentation

Repair of critical size bone defects is a clinical challenge that usually necessitates the use of bone substitutes. For successful bone repair, the substitute should possess osteoconductive, osteoinductive, and vascularization potential, with the ability to control post-implantation infection serving as an additional advantage. With an aim to develop one such substitute, we optimized a zinc-doped hydroxyapatite (HapZ) nanocomposite decorated on reduced graphene oxide (rGO), termed as G3HapZ, and demonstrated its potential to augment the bone repair. The biocompatible composite displayed its osteoconductive potential in biomineralization studies, and its osteoinductive property was confirmed by its ability to induce mesenchymal stem cell (MSC) differentiation to osteogenic lineage assessed by in vitro mineralization (Alizarin red staining) and expression of osteogenic markers including runt-related transcription factor 2 (RUNX-2), alkaline phosphatase (ALP), type 1 collagen (COL1), bone morphogenic protein-2 (BMP-2), osteocalcin (OCN), and osteopontin (OPN). While the potential of G3HapZ to support vascularization was displayed by its ability to induce endothelial cell migration, attachment, and proliferation, its antimicrobial activity was confirmed using S. aureus. Biocompatibility of G3HapZ was demonstrated by its ability to induce bone regeneration and neovascularization in vivo. These results suggest that G3HapZ nanocomposites can be exploited for a range of strategies in developing orthopedic bone grafts to accelerate bone regeneration.