Biocompatibility Of A Graphene Nanosheet Toughened Hydroxyapatite Ceramic Composite

Hydroxyapatite(HA) is well recognized to be a bioological compatible ceramic with excellent bioactivity and osteoconductivity owing to its chemical composition and crystal structure similar to the apatite in human skeletal system, which are capble of osteoblast adhesion and proliferation, new bone ingrowth and integration with nature bone. Unfortunately, the brittleness in nature associated with HA, and low toughness-induced poor wear resistance still restrict its clinical applications. Therefore, toughening of HA with a second phase has been extensively explored to overcome the deficiencies of pure HA.Graphene with very high specific surface area exhibits excellent performances in mechanical properties, especially, its high specific surface area is expected to improve the efficiency of load transfer from matrix to graphene, and therefore it is widely used as nanofiller in the composites to enhance the mechanical properties of the composites. On the basis of the abovementions, graphene nanosheet(GNS) toughened HA composite was fabricated by spark plasma sintering(SPS), and the mechanical properties of the GNS/HA composite has been assessed in our group’s previous work. Results showed the fracture toughness of a GNS/HA composite increases by up to ~80%. In this study, the biocompatibility(such as osteoblast adhesion, proliferation, differentiation, and mineralization in simulated body fluid) of the GNS/HA composites were evaluated, and the contributions of the added GNS to these properties were also analyzed.Firstly, the biocompatibility of graphene films were evaluated. In-vitro osteoblast results showed that graphene film exhibits much adhesion sites for these osteoblasts and these osteoblasts spread largely, as compared with graphite paper. Moreover, graphene film favorates the proliferation and differentiation of osteoblast on its surface. Simulated body fluid(SBF) mineralization experiments showed that the surface of garphene films is more suitable for mineralization.Secondly osteoblast adhesion, proliferation and differentiation were evaluated on the surfaces of these sintered GNS/HA composites As compared with monolithic HA sample, the amount and spreadability of the adherent osteoblasts are improved on the GNS/HA composites, and focal adhesions is also increased. The proliferation and differentiation of the osteoblasts were observed to be improved with the additive content of GNSs in this research. The wrinkeing texture in nature of these added GNSs is expected to change nanoscale topography of the composites, which in turns provide more suitable sites for adhesion of filopodia and formation of cytoskeleton, and subsequently leading to the improved osteoblast adhesion.The SBF immersion results illustrated that the surface of GNS/HA composite is more suitable for mineralization. The morphology of mineralization-product varies with incorporation of GNSs into HA matrix in the way that short-needle-shaped apatite are formed on pure HA sample whereas curled-sheet-shaped apatite forms on GNS/HA composites. This is likely due to an increased mineralization rate for in the GNS/HA composites, because these added GNSs create more nucleation sites facilitating apatite mineralization.Abovementioned results sufficiently illustrate that the additive GNSs into HA matrix not only impart GNS/HA composites enhanced toughness even at very low GNS content, but also tender them improved biocompatability. Herein,a GNS/HA composite is expected to be a promising material for load-bearing orthopedic implant applications.