Surface modification of TiTa alloy and its <italic>in vitro</italic> osteogenic biological activity

Surface modification of biomedical metal materials is an effective strategy to enhance its osteogenic biological activity， which can greatly reduce the time for forming a strong chemical bonding between the implant and the human hard tissue. This has great significance to ensure the rapid recovery of patients after implantation surgery. In this work， a facile two-step modification method of alkali heat coupled with pre-calcification is carried out to treat the biomedical titanium tantalum alloy （Ti∶Ta=43∶57， mass ratio）， and its osteogenic bioactivity is evaluated by simulated body fluid （SBF） immersion tests. The results show that no bone-like apatite coating is deposited on the surface of TiTa with alkali-heat treatment after soaking in SBF even for 18 days. While the TiTa alloy treated with alkali-heat and pre-calcification exhibits excellent in vitro osteogenic bioactivity. When the modified TiTa alloy is incubated in SBF for only 3 days， its surface is entirely coated with a newly formed spherical clusters of the hydroxyapatite （HA） coating. The boosted osteogenic bioactivity of TiTa alloy modified with alkali-heat followed by pre-calcification is a synergistic result of multiple factors. That is， after hydrothermal treatment of TiTa alloy in NaOH， a porous， coarse and super-hydrophilic surface， with a static water contact angle from initial （54.9±2.1）° to （11.2±2.4）°， is formed， which is beneficial to the adsorption and spreading of SBF. After further pre-calcification treatment， initial crystal nuclei of calcium and phosphorus compounds are successfully introduced into the surface of TiTa， which can rapidly induce calcium and phosphate ions to precipitate and grow into HA during the SBF immersion process.