Biofunctional and Tribomechanical Behavior of Porous Titanium Substrates Coated with a Bioactive Glass Bilayer (45S5–1393)

The porous substrates of commercially pure titanium have been coated with a novel bilayer of bioactive glasses (BGs), 45S5 and 1393, to improve the osseointegration and solve the stress-shielding phenomenon of titanium partial implants. The porosity of the substrates and the scratch resistance and bioactivity of the coating have been evaluated. Results are discussed in terms of stiffness and yield strength of the substrates, as well as the chemical composition, thickness, and design of the bioglass coating (monolithic vs bilayer). The role of the pores was a crucial issue in the anchoring of the coating, both in porosity percentage (30 and 60 vol %) and in pore range size (100-200 and 355-500 μm). The study was focused on the adhesion and infiltration of a 1393 bioglass layer (in contact with a porous titanium substrate), in combination with the biofunctionality of the 45S5 bioglass layer (surrounded by the host bone tissue), as 1393 bioglass enhances the adherence, while 45S5 bioglass promotes higher bioactivity. This bioactivity of the raw powder was initially estimated by nuclear magnetic resonance, through the evaluation of the chemical environments, and confirmed by the formation of hydroxyapatite when immersed in a simulated body fluid. The results revealed that the substrate with 30 vol % of porosity and a range of 355-500 μm pore size, coated with this novel BG bilayer, presented the best combination in terms of mechanical and biofunctional properties.