Mechanical properties of doped Ca-Si based bioceramic coatings for orthopaedic implants

A new generation of Ca-Si based biomaterial has been synthesized by doping trace elements (Sr-Zn) into the CaO-SiO₂ based system to form a novel bioceramic that possesses exceptional bioactivity for bone regeneration; high fracture toughness and compressive strength that are superior to the properties of cortical bone. This work examined mechanical properties of compositional-equivalent coatings processed by atmospheric plasma spray (APS), which have been compared with the currently-accepted commercial hydroxyapatite (HAp: Ca₁₀(PO₄)₆(OH)₂) APS coatings. The Ca-Si based coatings exhibited a uniform distribution of hardness and elastic moduli, higher microhardness, nanohardness and elastic moduli compared to the equivalent properties of a HAp coating with inhomogeneous and significantly anisotropic. This new coating was also subjected to nano-scratch and nano-scanning wear tests where a low volume of wear material was accompanied with low plastic deformation, while the HAp coating revealed ploughing behaviour with material pileup and plastic deformation. The Ca-Si based coating presented significantly higher bond strength that exceeded the requirement for a commercial orthopaedic implant coating. In summary: The Ca-Si based APS coating displayed better mechanical properties than the commercial HAp coating. Hence, the Ca-Si based APS coating offers a potential approach for bioceramic coating applications encountered in orthopaedic implants.