An ab initio study of the structural and mechanical alterations of Ti-Nb alloys

This article describes a systematic theoretical investigation of the role of Nb substitution on the structural and mechanical properties of Ti-Nb alloys. The aim is to understand the origin of the low-rigidity of some of these materials. This quality makes these materials suitable for metallic implants. The mechanical stability conditions in conjunction with the calculated elastic constants of Ti-Nb predict the destabilization of α′ and ω structures, while the β-phase can be stabilized for Nb content above 10 at. %. The evaluated Young's moduli (E) follow the sequence of Eω > Eα′ > Εα″ > Εβ, revealing high Eω and Eα′ values (greater than 120 GPa), while the Eβ value converges to approximately 87 GPa. The averaged E, estimated from a weighted average of Eω, Eα′, Εα″, and Εβ ab initio values, reproduces the experimental Ti-Nb Young's modulus w-shaped curve. Young's modulus surface reveals highly anisotropic E values for all Ti-Nb phases. Eβ exhibits values under 30 GPa along the [100] direction for Nb compositions larger than 12 at. %, suggesting that the orientational growth of a Ti-Nb alloy is important for the design of low-rigidity alloys, especially at small Nb concentrations. These results can be used as a guide for the design of novel low-rigidity alloys for biomedical applications

Atomic Force Microscopy of height fluctuations of fibroblast cells

We investigated the nanometer scale height fluctuations of 3T3 fibroblast cells with the atomic force microscope (AFM) under physiological conditions. Correlation between these fluctuations and lateral cellular motility can be observed. Fluctuations measured on leading edges appear to be predominantly related to actin polymerization-depolymerization processes. We found fast (5 Hz) pulsatory behavior with 1--2 nm amplitude on a cell with low motility showing emphasized structure of stress fibres. Myosin driven contractions of stress fibres are thought to induce this pulsation.Comment: 6 pages, 5 figures, 1 tabl

Ab-initio and experimental study of phase stability of Ti-Nb alloys

A systematic theoretical and experimental study concerning the crystallographic structure and electronic properties of Ti-xNb (x 18.75 at% the β-phase is favoured against all other crystallographic structures in line with the experimental results. Interestingly, at high Nb content the α′ and ω hexagonal phases become unstable due to the electronic band filling close to the Fermi level EF, which is mainly due to Nb-p and Ti-d antibonding hybridizations. On the contrary, in the cubic β-Ti-25Nb (at%) the depletion of the occupied electronic states at the EF occurs mainly due to Nb-d and Ti-d bonding interactions, resulting in a stable β-TiNb structure. These data could enlighten the electronic origin of the Ti-Nb phase stability, thus, may contribute to the design of β stabilized low moduli Ti-based alloys suitable for load-bearing biomedical applications

Ab-initio and experimental study of phase stability of Ti-Nb alloys

International audienceA systematic theoretical and experimental study concerning the crystallographic structure and electronic properties of Ti-xNb (x 18.75 at% the beta-phase is favoured against all other crystallographic structures in line with the experimental results. Interestingly, at high Nb content the alpha' and omega hexagonal phases become unstable due to the electronic band filling close to the Fermi level E-F, which is mainly due to Nb-p and Ti-d antibonding hybridizations. On the contrary, in the cubic beta-Ti-25Nb (at%) the depletion of the occupied electronic states at the EF occurs mainly due to Nbd and Ti-d bonding interactions, resulting in a stable beta-TiNb structure. These data could enlighten the electronic origin of the Ti-Nb phase stability, thus, may contribute to the design of beta stabilized low moduli Ti-based alloys suitable for load-bearing biomedical applications. (C) 2016 Elsevier B. V. All rights reserved