Microstructural and in vitro characterisation of 45S5 bioactive glass coatings deposited by Solution Precursor Plasma Spraying (SPPS)

Abstract

The present work focused on the development of bioactive glass coatings employing Solution Precursor Plasma Spraying. Precursors of SiO2, CaO, Na2O and P2O5 were mixed in distilled water to prepare concentrated solutions with a composition close to the 45S5 bioactive glass. Solutions were rheologically characterised to assess their stability with time and deposited onto AISI type 304 stainless steel to develop coatings under different parameters related to the thermal spraying technique. The effect of these parameters on coatings microstructure was studied by scanning electron microscopy. Coatings were also analysed by X–ray diffraction and scratch test to complete the microstructural characterization. Moreover, coatings bioactivity was evaluated by immersing them in Simulated Body Fluid. The study showed that using short spraying distances and low argon flow rates, gave rise to the typical microstructure derived from liquid feedstocks whereas some crystallization associated to the long spray distance used occurred. Scratch test revealed that the resulting coating possessed good mechanical properties when compared with similar coatings obtained by other plasma spraying techniques. Moreover, the obtained coating could develop an hydroxycarbonate apatite layer when in contact with Simulated Body Fluid as demonstrated by scanning electron microscopy, X–ray diffraction and Fourier transform infrared spectroscopy.