Interface design and processing of bioactive microporous calcium phosphate coatings on load-bearing zirconia substrate

This study presents the design and processing of interlocked interfaces of graded bioactive calcium phosphate coatings on a load-bearing zirconia substrate. Such interfacial structures can effectively enhance bonding between the coating and substrate, and suppress the residual stress across the interfacial region. Multiple coating layers with graded interconnected micropore structures, and common phases across the layer boundary have been considered to minimize the likelihood of interfacial cracking/delamination. The Focused Ion Beam (FIB) technique was used to reveal microscopic details of the interlocked interface formed by the common calcium phosphate and zirconia phases in both the microporous coating and the dense substrate. The interface microstructure and phase characteristics in the substrate and coatings were confirmed by means of FIB-SEM and X-ray diffraction (XRD) analysis respectively. A preliminary Finite Element Modelling (FEM) study shows that graded and interconnected micropore structures in multiple coating layers and tailored material composition can further reduce the interfacial residual stresses. The flexural and bonding strength of the composite and coating/substrate interface respectively have been characterized. A preliminary and limited in vitro cell test shows that the composite has no cytotoxicity to the fibroblasts. A successful interface design is crucial for bioceramic composite design that combines strength and bioactivity to deliver a potential candidate for load-bearing application.