Sintering and plasma spray deposition of bioactive glass-Matrix composites for medical applications

Three different bioactive glass-matrix composites were obtained by a viscous flow sintering process: the green samples were prepared by uniaxial cold pressing of powdered glasses (labelled as AP40, TAP and RKKP in this paper), mixed with 15% (volume) of titanium particles. The viscous flow sintering process was optimised by thermal analysis (DTA) and by heating microscopy to obtain high density bulk composites. The glasses and the sintered composites were also powdered and deposited by Vacuum Plasma Spray (VPS) on a Ti-6Al-4V alloy, to obtain bioactive glass and composite coatings. Each coating was characterised by means of optical and electron microscopy, X-ray diffraction (XRD), energy dispersion spectroscopy (EDS), Vickers indentations and shear tests. The bioactivity of the coatings was tested by soaking the coated samples into a simulated body fluid (SBF) at 37°C: the growth of a Ca and P rich silica-gel layer was observed on their surface after 30 days. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses were performed on the SBF in order to observe the Si, Ca and P leaching versus the time. Each coating showed a good adherence to the metallic substrate, comparable with that of the VPS hydroxyapatite coatings and a remarkable bioactivity. Moreover the intrinsic toughness of the composite coatings was found to be higher than that of the pure glass coatings.