Electrochemically formed passive layers on titanium — Preparation and biocompatibility assessment in Hank's balanced salt solution

Abstract

Uniform and crack-free passive layers on Ti are prepared using AC voltage in 7.5 wt.% aq. NH₄·BF₄ at 25 °C. The passive layers possess coloration (wide spectrum of colors) that depends on the experimental conditions. The biocompatibility of such prepared passive layers is evaluated using corrosion science and analytical techniques. Their corrosion behavior, Ti-ion release, surface roughness, and wettability in Hank's Balanced Salt Solution (HBSS) at 37 °C are the main focus of this work. Open-circuit potential and polarization measurements demonstrate that the corrosion potential (E_corr) of the passive layers becomes more positive than that of the untreated Ti. The value of E_corr increases as we increase the AC voltage (V_AC). Their corrosion rate (CR) is lower than that of the untreated Ti, and they reduced the Ti-ion release level from 230 to 15 ppb. An increase in the AC voltage frequency (f) leads to a slightly higher level of the Ti-ion release (~50 ppb). Surface profilometry, optical microscopy, and scanning electron microscopy (SEM) analyses show that prolonged exposure of the passive layers to HBSS results in changes to their surface topography. The passive layers prepared by the application of AC voltage are rougher and more hydrophilic than the untreated Ti. Our methodology of preparing biocompatible passive layers on Ti might be applied as a new surface treatment procedure for Ti implants.Key words: titanium, metal surface treatment, surface roughness, corrosion, metal ion release, contact angle.