| NiTi alloys were active when treating by acid-alkali treatment, and the formation of bone-like apatite on NiTi were accelerated by pre-calcification.The effect of pre-calcification on bone-like apatite formation on acid-alkali treated NiTi and the formation mechanism were investigated in vitro using SEM, EDS, XRD and EIS. The results showed that the typical surface morphology of alkali treatment was stained after pre-calcification and some micro-granule Ca-P particles which facilitated the inhomogeneous nucleation can form in the net-work.β-Ca3(PO4)2 and Ca2P2O7, which are both of precursor phases of HA nucleation, can be detected on chemically treated NiTi with adding pre-calcification for 1d in the simulated body fluid (SBF). SEM results showed that large numbers of uniform granule particles were biomimetic deposited on chemically treated NiTi in the SBF for 3d with adding pre-calcification process, while imperfect coatings with gas hole appeared on the samples without adding pre-calcification process. EIS results confirmed that the proposed electrical equivalent circuit was based on a two-layer model, and circuit description code (CDC) was R(Q(R(QR))). With increasing of immersion time in the SBF, the apatite on chemically treated NiTi surface grew and the resistance of the apatite layer Rp increased continuously. Adding pre-calcification treatment, the rate of growth got faster, which proved that pre-calcification accelerated apatite formation on chemically treated NiTi.TheβTi-Nb-Sn alloys were active when treating by alkali treatment, heat treatment and UV illumination, respectively. The bioactivity of the pre-treated samples was evaluated in the SBF in vitro. The results showed that a large number of etched pits formed after acid corrosion and some porous web-like network appeared on the planar surface boiled in 1mol·l-1 NaOH for 2h. The ball-like apatite particles with ~100 nm scales can be deposited on the surface after soaking in the SBF for 7d, and some micro-cracks had been observed as well. The surface of the samples was fully and uniformly covered by the titanium oxide and niobium oxide after heat-treatedβTi-Nb-Sn at 600℃and 700℃for 3h, respectively. The water contact angle of the surface decreased after UV illumination for 4h and the granule apatite particles were fully and uniformly deposited on the Ti-Nb-Sn in the SBF for 3d. UV illumination can effectively shorten the nucleation periods of the apatite for 2d on heat-treatedβTi-Nb-Sn at 700℃for 3h. A few oxide particles were observed after heat-treatedβTi-Nb-Sn at 400℃for 3h and more oxide particles formed at 400℃for 24h. The water contact angle of the surface also decreased after UV illumination and similar granule apatite particles were deposited on the Ti-Nb-Sn at 400℃for 24h. |
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