Suspension plasma spraying of optimized functionally graded coatings of bioactive glass/hydroxyapatite

The innovative suspension plasma spraying (SPS) technique was applied to produce a bioactive glass/hydroxy- apatite (HA) multi-layered functionally graded coating (FGC). The constituent phases were selected to combine the high bone-bonding ability of bioactive glasses (on the surface of the FGC) with the long-term stability of HA (close to the interface with the metal substrate). The fabrication method was optimised using the suspension feed rates which took into account the different deposition efficiencies of bioactive glasses and of HA. During the deposition process, which was carried out with a SG-100 torch an industrial robot was used to realise the torch movement and the spraying parameters were optimised in view of industrial applications of the coatings. A microstructural investigation was performed on the FGC using Raman spectroscopy and environmental scan- ning electron microscopy (ESEM) coupled with X-EDS microanalysis. The analysis confirmed that the obtained compositional gradient met the designed one. The coatings were characterised both in as-sprayed state and after soaking in a simulated body fluid (SBF) for periods ranging from 1 to 14 days. The FGC exhibited a strong reactivity in SBF and a high scratch resistance even after immersion, confirming its potential for biomedical applications.