Microstructural and in vitro characterisation of high-velocity suspension flame sprayed (HVSFS) bioactive glass coatings

The paper reports the first attempt at employing the innovative high-velocity suspension flame spraying (HVSFS) technique in order to deposit bioactive glass coatings. Fine (micrometric) glass particles having a composition similar to that of the A–W (apatite–wollastonite) bioactive glass–ceramic as proposed by Kokubo were dispersed into a 50% water + 50% isopropanol solvent mixture and the resulting suspension (containing 20 wt.% glass powder) was thermally sprayed onto Ti plates using a modified high velocity oxy-fuel torch.Each torch pass produces a dense coating layer, featuring strong cohesion between lamellae thanks to viscous flow sintering along the interlamellar boundary. However, some porosity exists between different layers deposited during successive torch passes.In vitro bioactivity tests indicate that the coatings interact remarkably with the simulated body fluid (SBF), developing a thick silica-rich layer containing hydroxyapatite crystals.