title: Comparisons of immersion and electrochemical properties of highly biocompatible Ti-15Zr-4Nb-4Ta alloy and other implantable metals for orthopedic implants.
abstract: Metal release from implantable metals and the properties of oxide films formed on alloy surfaces were analyzed, focusing on the highly biocompatible Ti-15Zr-4Nb-4Ta alloy. The thickness and electrical resistance (Rp) of the oxide film on such an alloy were compared with those of other implantable metals. The quantity of metal released during a 1-week immersion test was considerably smaller for the Ti-15Zr-4Nb-4Ta than the Ti-6Al-4V alloy. The potential (E10) indicating a current density of 10μA cm-2estimated from the anodic polarization curve was significantly higher for the Ti-15Zr-4Nb-4Ta than the Ti-6Al-4V alloy and other metals. Moreover, the oxide film (4-7 nm thickness) formed on the Ti-15Zr-4Nb-4Ta surface is electrochemically robust. The oxide film mainly consisted of TiO2with small amounts of ZrO2, Nb2O5and Ta2O5that made the film electrochemically stable. TheRpof Ti-15Zr-4Nb-4Ta was higher than that of Ti-6Al-4V, i.e. 0.9 Ω cm2in 0.9% NaCl and 1.3 Ω cm2in Eagle's medium. ThisRpwas approximately five-fold higher than that of stainless steel, which has a history of more than 40 years of clinical use in the human body. Ti-15Zr-4Nb-4Ta is a potential implant material for long-term clinical use. Moreover,E10andRpwere found to be useful parameters for assessing biological safety.
authors.affiliation: National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba-shi, Ibaraki, 305-8566, Japan.
authors.forename: Yoshimitsu
authors.initials: Y
authors.lastname: Okazaki
authors.affiliation: College of Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki, 316-8511, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nagata
keywords: Ti–15Zr–4Nb–4Ta alloy; angle-resolved x-ray photoelectron spectroscopy; electrochemical stability evaluation; field-emission transmission electron microscopy; implantable metals; passive film