Novel niobium and silver toughened hydroxyapatite nanocomposites with enhanced mechanical and biological properties for load-bearing bone implants

Abstract

An ideal load-bearing implant material for hard tissue replacement requires a combination of excellent mechanical properties and biological functions. However, such combination can hardly be achieved by monolithic bioceramics or metals. To this end, by combining the individual characteristic advantages of hydroxyapatite (HA), niobium (Nb) and silver (Ag), we have developed novel Nb and Ag co-reinforced HA nanocomposites by high energy ball milling (HEBM) and spark plasma sintering (SPS). The fabricated HA–20Nb and HA–15Nb–5Ag (wt%) show nanocomposite microstructure with metallic reinforcements uniformly dispersed in the HA matrix. The formation of a nanothick Ca4Nb2O9 transition layer at the interfaces of HA/Nb enables high interface strength between the reinforcements and the HA matrix. Addition of Nb or Nb–Ag could significantly increase the compressive strength and fracture toughness of HA. In vitro and in vivo evaluations further show that addition of Nb could promote osteoblast proliferation, increase the osteogenic differentiation and enhance the osteointegration ability. Incorporation of Ag could remarkably increase the antibacterial activity both against Gram-positive organism Staphylococcus aureus and Gram-negative organism Escherichia coli. Thus, the developed new nanocomposites can bridge the gap between the mechanical and biofunctional requirements for load-bearing bone implants.