Improvement of the balance between a reduced stress shielding and bone ingrowth by bioactive coatings onto porous titanium substrates

Commercial pure titanium is known as good substitute for cortical bone tissue. Nevertheless, stress-shielding and the lack of osseointegration are still some limitations to solve. In this study, porous titanium substrates were manufactured by space-holder technique (50 vol% of NH4HCO3 with particle size between 250 and 355 μm). The obtained stiffness and yield strength of specimens were compatible with cortical bone tissue. The substrates were coated with three layers of Bioglass® 45S5 (BG) by dripping sedimentation, a new and economic technique. The porosity and surface characterization were performed by Archimedes' method, image analysis, X-ray micro computed tomography and confocal laser microscopy, while the mechanical behavior was analyzed by ultrasound technique, uniaxial compression and micro-mechanical testing. Homogeneity, infiltration efficiency and coating integrity were evaluated. The adhesion of the coating was better on porous titanium substrates than on full dense ones. Finally, the bioactivity of the BG coating was determined via immersion in Simulated Body Fluid. The formation and growth of hydroxyapatite on the substrate were studied by scanning electron microscopy and X-ray diffraction analysis. The results showed hydroxyapatite formation in both coated full dense and porous samples. These features indicate the improvement of osseointegration for this sort of load bearing Ti implants.