In vitro response of preosteoblastic MG63 cells on Ni-free Ti shape memory substrates.

Ni-free Ti alloys are a potential strategy to overcome the risk of Ni-adverse reactions and rigidity mismatch for implant materials. Here, we report the biological behavior induced for two promising candidate alloys--Ti19.1Nb8.8Zr (M(S) temperature of 46°C and elastic modulus of 74 GPa) and Ti41.2Nb6.1Zr (elastic modulus of 67 GPa)--on cultured MG63 cells, as well as their physical and chemical properties. Contact angle results revealed the hydrophobic character of the former alloy (59.02° ± 2.35°) attributed to the presence of the martensitic phase, while the latter one presented a hydrophilic response (67.77° ± 2.78°). Results showed also that the cell adhesion response (after 4 and 8 h of incubation) in both substrates was not statistically different to that obtained in the cp Ti as control material. These surfaces induced well spread cell morphology with cytoplasmic extension like filopodia of up to 100 μm even at short culture times and presented an uninterrupted proliferation after longer incubation times (9 days). A decrement in the proliferation rate was appreciated from the Ti19.1Nb8.8Zr surface at that time, which was attributed to an earlier activation of the cell differentiation stage, as confirmed by the twofold increment of alkaline phosphatase activity. The results also evidenced that the presence of a 2 nm thick layer of amorphous Nb₂O₅, which was detected on both alloys, has a significant effect on cell behavior favoring the cell adhesion and morphology response of the new alloys studied.