Quantifying the Adhesion of Silicate Glass-Ceramic Coatings onto Alumina for Biomedical Applications

Deposition of bioactive glass or ceramic coatings on the outer surface of joint prostheses is a valuable strategy to improve the osteointegration of implants and is typically produced using biocompatible but non-bioactive materials. Quantifying the coating-implant adhesion in terms of bonding strength and toughness is still a challenge to biomaterials scientists. In this work, wollastonite (CaSiO₃)-containing glass-ceramic coatings were manufactured on alumina tiles by sinter-crystallization of SiO₂-CaO-Na₂O-Al₂O₃ glass powder, and it was observed that the bonding strength decreased from 34 to 10 MPa as the coating thickness increased from 50 to 300 µm. From the viewpoint of bonding strength, the coatings with thickness below 250 µm were considered suitable for biomedical applications according to current international standards. A mechanical model based on quantized fracture mechanics allowed estimating the fracture toughness of the coating on the basis of the experimental data from tensile tests. The critical strain energy release rate was also found to decrease from 1.86 to 0.10 J/m² with the increase of coating thickness, which therefore plays a key role in determining the mechanical properties of the materials.