Effect of HVOF Process Parameters on TiO2 Coatings: An Approach Using DoE and First-Order Process Maps

An experimental approach based on design of experiments, process maps and the analysis of deposition first stages to improve the biocompatibility of High-Velocity Oxygen Fuel (HVOF) hydroxyapatite (HAp) coatings is here presented. A two-level design of three factors (2 3 ) was performed using the stand-off distance (SOD), the fuel-oxygen ratio (F/O) and the powder feed rate (PFR). The effect of these experimental factors on the first stages of the coating formation was investigated to study the physical state of the particles before and after impacting the substrate.This study allowed the selection of the most suitable deposition parameter combinations to obtain HAp coatings with optimal crystallinity (> 45%), Ca/P ratio (approx. 1.67), phase content (> 95% of HAp), which guarantee the coatings mechanical stability and biocompatibility. The behavior of the coating within simulated body fluid (SBF) and cell culture (hFOB) was studied to analyze the apatite layer formation and the extracts cytotoxicity on human osteoblasts, respectively. The results show that the F/O ratio is the most influential factor on temperature and velocity on the in-flight particles and therefore on the coating properties. The SBF results confirmed the formation of an apatite layer after 14 days of immersion. Finally, the mitochondrial activity, measured by the MTS assay, and cell membrane integrity measures by LDH liberation assays, show that the coating released material does not induce toxicity on the exposed cells.

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“…Previous to HAp deposition, substrates were coated with a titanium oxide (TiO 2 ) bond-coat [18,19].…”

Section: Feedstock Powder and Substratesmentioning

confidence: 99%

“…Therefore, the experimental space was limited with a 2 3 factorial design as shown in Figure 2a. The upper and lower limits for each variable were stablished according to literature reports and previous works [18,25,26].…”

Section: Experimental Space and In-flight Particle Conditionsmentioning

confidence: 99%