Effect of processing on microstructure, mechanical properties and dissolution behaviour in SBF of Bioglass (45S5) coatings deposited by Suspension High Velocity Oxy Fuel (SHVOF) thermal spray

Abstract

Bioglass (45S5) is known to react with physiological media and has the unique characteristic of bonding with hard and soft tissues when implanted in the body. 45S5 coatings were deposited by Suspension High Velocity Oxy Fuel (SHVOF) thermal spraying to investigate the effect of combustion conditions on the coating microstructure and surface topography. Bioactive (45S5) coatings were deposited onto 304 stainless steel substrates via SHVOF thermal spray using a water + isopropanol (IPA) based suspension with 8 wt% particle loading. Selected flame powers of 25 kW (low), 50 kW (medium) and 75 kW (high) produced three different coatings of varying microstructure (porosity and thickness) and composition. At 25 kW flame power thin coating of <10 μm thickness was deposited; however, 25 ± 3 μm thick, well bonded coatings to the substrates were deposited at flame powers of 50 and 75 kW. The medium flame power coating was 16 ± 2% porous, while the high flame power coating was 10 ± 1% porous. All the coatings remained amorphous, as confirmed via X-ray diffraction. After immersing the coated samples in simulated body fluid (SBF), 50 and 75 kW coatings revealed hydroxyapatite (HA) deposition after 3 days. Also, no HA deposition was observed on 25 kW coating, even after 7 days of immersion in SBF. EDX analysis of the 50 kW coating after 7 days immersion in SBF showed that the initial coating thickness reduced from 25 μm to 6 μm, it means that this microstructure was highly reactive towards SBF and hence behaved like a resorbable coating. Through SHVOF spraying technique changing the flame power resulted in coatings of varying microstructure. These microstructures behaved differently in SBF, 50 kW coating showed more degradation than the 75 kW coating owing to the porosity.