Feasibility of glass–ceramic coatings on alumina prosthetic implants by airbrush spraying method

This work explores the feasibility of glass-derived coatings (SiO2–CaO–Na2O–Al2O3 system) on bioceramic devices of complex shape by a layer-wise slurry deposition using an airbrush spray gun. Specifically, glass–ceramic coatings with thickness in the 50–500 μm range were prepared on alumina curved substrates by airbrush spraying of glass-based aqueous suspensions followed by sintering. Investigations by scanning electron microscopy and micro-computed tomography revealed that, under appropriate optimization of slurry composition and spraying cycles, this technique is suitable to manufacture homogeneous and continuous coatings on model curved ceramic surfaces. It was observed that neither cracking nor delamination occurred at the interface between coating and substrate. Ad-hoc tensile tests were carried out by properly adapting the relevant ASTM standard to the specific case (curved geometry); the coating adhesion strength was found adequate (about 25 MPa) for biomedical applications. A simple model describing the relationship between coating thickness and number of spraying cycles was also developed and proposed as a useful tool to improve the design and manufacturing of bioceramic coatings.