Abstract
Titania-based films on selective laser melted Ti13Zr13Nb have been formed by micro-arc oxidation (MAO) at different process parameters (voltage, current, processing time) in order to evaluate the impact of MAO process parameters in calcium and phosphate (Ca + P) containing electrolyte on surface characteristic, early-stage bioactivity, nanomechanical properties, and adhesion between the oxide coatings and substrate. The surface topography, surface roughness, pore diameter, elemental composition, crystal structure, surface wettability, and the early stage-bioactivity in Hank’s solution were evaluated for all coatings. Hardness, maximum indent depth, Young’s modulus, and Ecoating/Esubstrate, H/E, H3/E2 ratios were determined in the case of nanomechanical evaluation while the MAO coating adhesion properties were estimated by the scratch test. The study indicated that the most important parameter of MAO process influencing the coating characteristic is voltage. Due to the good ratio of structural and nanomechanical properties of the coatings, the optimal conditions of MAO process were found at 300 V during 15 min, at 32 mA or 50 mA of current, which resulted in the predictable structure, high Ca/P ratio, high hydrophilicity, the highest demonstrated early-stage bioactivity, better nanomechanical properties, the elastic modulus and hardness well close to the values characteristic for bones, as compared to specimens treated at a lower voltage (200 V) and uncoated substrate, as well as a higher critical load of adhesion and total delamination.
Highlights
Titanium and its alloys are widely used for medical applications
The curve characteristic is typical for the micro-arc oxidation (MAO) process, where the variation of voltage can be divided into three stages [39]
The voltage increases slowly, which corresponds to the beginning of the micro-arc oxidation process, where the oxide layer is broken down to form a discharge channel
Summary
Pure Ti (cp-Ti) or Ti with Al, V, and Mo alloying elements are still among the most common materials used for implantation. Due to the reported mismatch in mechanical properties between bones and those materials, leading to the stress-shielding and implant loosening, as well as the toxicity of Al and V, new solutions are considered. Among the perspective materials are β-type titanium alloys [1,2,3] known as low modulus and bioinert metals containing Ti, Zr, Nb, Hf, Ta alloying elements [4,5]. The material ensures preferable mechanical properties, which has been proved as an effective factor in inhibiting bone atrophy [6] there is still a problem with its bioactivity.
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