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Two new Ni-free Ti alloys, , have been produced and studied in order to obtain shape memory and low elastic modulus materials for employment in the biomedical field. The new alloys were designed by means of a theoretical molecular orbitals method using nontoxic alloying elements. In the present study, the phases and mechanical properties obtained after solution treatment at 1100°C by 1.5 hours following an ice-water quenching were characterized. Also, special attention on exploring the elastic modulus and shape memory properties via instrumented nanoindentation was given. The microstructural observation revealed b-grain in both alloys with an average size of 268 and 500 lm for Ti-15.7Ta-19.0Nb and Ti-8.8Zr-19.1Nb alloys, respectively. This latter presented also fine and disperse plates inside the grains. X-ray results confirmed the existence of b phase in both alloys and orthorhombic a¢¢ phase on Ti-8.8Zr-19.1Nb alloy. A reversible phase transformation was detected by differential scanning calorimetry in the former alloy, which confirms the presence of shape memory effect. The elastic modulus of the new alloys was smaller than the commercial alloys employed as implant materials. Evidence of phase transformation was detected by nanoindentation, as hysteresis loops between unloading/reloading cycles on the P-h curves obtained at nanometer scale. These results suggest the possibility of using instrumented indentation for shape memory characterization.

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Distraction osteogenesis is a well-established method of endogenous tissue engineering. It is a biological process of bone neo-formation between segments subjected to tension. The concept of this study was to investigate the distraction osteogenesis with a device capable of creating a permanent and constant force during the whole process as if a very large number of small elongations were applied constantly. The mechanical testing of the device used to produce the constant force and the in vivo analysis of the bone growth after it was implanted in rabbits are presented on this work. The device consists of a NiTi coil spring, superelastic at body temperature, in order to have a stress plateau during the austenitic retransformation during the unloading. The in vivo analysis was made on six female rabbits of 12 months old. A segmental mandibulectomy at the horizontal arm of the mandible and a corticotomy at 5mm distant from the gap were made. Next, following a latency period of five days, the SMA springs were implanted to induce the bone neo-formation. The displacement at the unloading plateau shows that it is necessary to have longer springs or to use several (available commercially) in series in order to fulfil the requirements of a human distraction. The temperature variations induced changes in the spring force. However, when the temperature returns to 37 degrees C the distraction force recovers near the initial level and does so completely when the distraction process continues. For the in vivo study, all six rabbits successfully completed the distraction. The radiographies showed the gap as distraction advanced. A continuity in the newly formed bone with similar transversal and horizontal dimensions than the original bone can be observed on the histologies. In conclusion, the application of a constant force on distraction osteogenesis, using SMA springs, may be a successful alternative to the conventional gradual distraction.