Encouraging tribomechanical and biological responses of hydroxyapatite coatings reinforced by various levels of niobium pentoxide particles

The development of surface technologies to obtain improved tribomechanical and biological characteristics of synthetic NiTi implants is critical. A suitable match with the mechanical properties of the implanted biomaterial is necessary to reduce the risk of stress-shielding and implantation failure. The present contribution has attempted to assess the influence of the Nb2O5 particle level in an electrolyte, i.e., 0-1 g L-1, on the tribomechanical and biological performance of the HAp layers, which were obtained by galvanostatic pulse electrodeposition on NiTi. The surface characteristics of the electrodeposited layers were analyzed using GIXRD, FESEM, XPS, and contact angle measurements. Nanoindentation, nanoscratch, and pull-off assays were employed to study the tribomechanical properties of the films. The in vitro biocompatibility of the developed specimens was investigated using NIH3T3 fibroblast cells. The results illustrated that a more compact and hydrophilic surface is obtained with the incorporated particles. The Nb content and Ca/P molar ratio are increased from the outermost surface to the subsurface layers of the coatings. The composite coatings showed higher hardness, elastic modulus, bonding strength to the underlying NiTi, and lower COF compared to pure HAp layers. The elastic modulus of the Nb2O5-reinforced HAp films is close to that of cortical bone, reducing stress-shielding risk. The inclusion of Nb2O5 particles in the HAp matrix led to an improvement in cell functions, e.g., viability and proliferation, within the various cell culture durations. The adopted surface modification strategy in this work can create new opportunities for the successful use of NiTi in orthopedic applications. The development of surface technologies to obtain improved tribomechanical and biological characteristics of synthetic NiTi implants is critical.