Thermal Sprayed Biomimetic Nano-Ceramics: Addressing the Processing Issues

There is an ongoing effort to improve the quality and performance of orthopedic implants.  Part of this work involves the development of coatings suitable for use in the human body and having requisite properties and bio-performance characteristics better than those of existing materials.  The present study focused on developing thermal sprayed nano-titania coatings engineered to have a bimodal structure consisting of a major fraction of micron scale dimensions within which were dispersed zones of nanostructured material as well as novel bioactive nano-composites of hydroxyapatite(HA) and nano-zirconia, that have unique fracture toughness behaviour.  The coatings were found to exhibit much higher adhesion to Ti-6Al-4V substrates than conventional coatings and to possess excellent crack propagation resistance characteristics.  The influence of the microstructure near to the coating/substrate interface on the adhesion of the coatings is also investigated. Crack propagation behavior within the coatings was studied through 4-point bend test. Results showed that nanostructures (30-110 nm) within the HA coatings were achieved by high velocity oxy-fuel (HVOF) spraying. The 4-point bend test revealed consistent crack propagation path that the cracks actually grow within the coating with a direction parallel to the interface, and approximately several to 20 microns thick coatings were remained on the substrate.  Cell culture studies indicated that human osteoblasts attached and proliferated well on the coating’s surfaces. The surface nanofeatures and nanostructured zones in the coating are believed to play an important role in the improved bonding, mechanical properties and bioperformance.