G A Clavijo-Mejía, M Michálek, F Kurtuldu, L Youssef, E Bussy, A Denoirjean, A Magnaudeix, D Cabrera-German, D Galusek, A R Boccaccini
The study investigates the influence of atmospheric plasma spray (APS) parameters on the structure and chemistry of coatings produced from a bismuth-containing 45S5 bioactive glass (Bi-BG). A melt-derived glass modified with 6.3 wt % Bi2O3 was used as feedstock powder, selected for its previously demonstrated radiopacity, cytocompatibility, angiogenic, and antibacterial activity. Coatings were deposited on titanium alloy substrates using parameter combinations varying arc current intensity, Ar/H2 gas mixture ratio, and stand-off distance (SOD). Phase composition, morphology, and short-range network structure were examined by XRD, SEM, DSC, and Raman spectroscopy. Short SODs combined with high plasma net power reduced deposition efficiency and increased porosity, whereas longer distances favored amorphous phase retention and improved intersplat bonding. A Latin Square design of experiments revealed that SOD was the dominant factor governing hardness, porosity, and thickness, accounting for 31 - 53 % of the total variance, while arc current intensity showed a threshold effect on porosity reduction at elevated current levels. Raman spectroscopy revealed significant changes in phosphate and silicate network units, particularly in symmetric P-O-P and asymmetric Si-O-Si groups. Coatings deposited at moderate plasma net power (24.7 - 29.9 kW) and a long SOD of 120 mm exhibited interfacial hardness values of 296 - 349 HV0.5, porosity below 2.0 %, and thicknesses of 77 - 80 μm, while largely preserving the amorphous network and enhancing mechanical integrity at the coating-substrate interface. This first systematic investigation of APS processing parameters for bismuth-modified 45S5 bioactive glass coatings provides practical guidance for fabricating structurally stable, bioactive, and radiopaque coatings for implantable biomedical devices.