Interaction of bone-dental implant with new ultra low modulus alloy using a numerical approach

International audienceAlthough mechanical stress is known as being a significant factor in bone remodeling, most implants are still made using materials that have a higher elastic stiffness than that of bones. Load transfer between the implant and the surrounding bones is much detrimental, and osteoporosis is often a consequence of such mechanical mismatch. The concept of mechanical biocompatibility has now been considered for more than a decade. However, it is limited by the choice of materials, mainly Ti-based alloys whose elastic properties are still too far from cortical bone. We have suggested using a bulk material in relation with the development of a new beta titanium-based alloy. Titanium is a much suitable biocompatible metal, and beta-titanium alloys such as metastable TiNb exhibit a very low apparent elastic modulus related to the presence of an orthorhombic martensite. The purpose of the present work has been to investigate the interaction that occurs between the dental implants and the cortical bone. 3D finite element models have been adopted to analyze the behaviour of the bone-implant system depending on the elastic properties of the implant, different types of implant geometry, friction force, and loading condition. The geometry of the bone has been adopted from a mandibular incisor and the surrounding bone. Occlusal static forces have been applied to the implants, and their effects on the bone-metal implant interface region have been assessed and compared with a cortical bone/ bone implant configuration. This work has shown that the low modulus implant induces a stress distribution closer to the actual physiological phenomenon, together with a better stress jump along the bone implant interface, regardless of the implant design

Microstructure and mechanical behavior of superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N biomedical alloys

International audienceIn this study, the microstructure and the mechanical properties of two new biocompatible superelastic alloys, Ti-24Nb-0.5O and Ti-24Nb-0.5N (at.%), were investigated. Special attention was focused on the role of O and N addition on α″ formation, supereleastic recovery and mechanical strength by comparison with the Ti-24Nb and Ti-26Nb (at.%) alloy compositions taken as references. Microstructures were characterized by optical microscopy, X-ray diffraction and transmission electron microscopy before and after deformation. The mechanical properties and the superelastic behavior were evaluated by conventional and cyclic tensile tests. High tensile strength, low Young's modulus, rather high superelastic recovery and excellent ductility were observed for both superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N alloys. Deformation twinning was shown to accommodate the plastic deformation in these alloys and only the {332}〈113〉 twinning system was observed to be activated by electron backscattered diffraction analyses

Synthesis and characterization of Ti-27.5Nb alloy made by CLAD® additive manufacturing process for biomedical applications

Biocompatible beta-titanium alloys such as Ti-27.5(at.%)Nb are good candidates for implantology and arthroplasty applications as their particular mechanical properties, including low Young’s modulus, could significantly reduce the stress-shielding phenomenon usually occurring after surgery. The CLAD® process is a powder blown additive manufacturing process that allows the manufacture of patient specific (i.e. custom) implants. Thus, the use of Ti-27.5(at.%)Nb alloy formed by CLAD® process for biomedical applications as a mean to increase cytocompatibility and mechanical biocompatibility was investigated in this study. The microstructural properties of the CLAD-deposited alloy were studied with optical microscopy and electron back-scattered diffraction (EBSD) analysis. The conservation of the mechanical properties of the Ti-27.5Nb material after the transformation steps (ingot-powder atomisation-CLAD) were verified with tensile tests and appear to remain close to those of reference material. Cytocompatibility of the material and subsequent cell viability tests showed that no cytotoxic elements are released in the medium and that viable cells proliferated well

Rapport III.1. Propriétés physiques de l’hélium

The principal special physical properties of liquid helium 4 are described, also the characteristics of helium I and II (superfluid ) and the Fontaine effect. These properties are interpreted theoretically with the aid of Tisza’s model and their effect on the use of helium as a cryogenic fluid is discussed.Exposé des principales propriétés physiques singulières de l’hélium 4 liquide ; caractéristiques de l’hélium I et de l’hélium II (superfluide) ; effet Fontaine. Interprétation théorique des propriétés ci-dessus ; modèle de Tisza. Influence des dites propriétés sur le mode d’utilisation de l’hélium comme fluide cryogénique.Laheurte J.-P. Rapport III.1. Propriétés physiques de l’hélium. In: Hydrotechnique des liquides industriels. Compte rendu des douzièmes journées de l'hydraulique. Paris, 6-8 juin 1972. Tome 2, 1973

Topology optimization for the control of load transfer at the bone-implant interface: a preliminary numerical study

International audienceThe numerical approach of topological optimization allows determining the optimal distribution of the material in a given volume in the function of an objective. This approach has recently regained interest thanks to the development of additive manufacturing, which makes it possible to manufacture its resulting parts with complex geometries. In the biomedical field, this numerical approach can also improve the performance of medical devices. Most of the time, the objective of topological optimization is to maximize the stiffness of the considered part while reducing its mass or volume. For example, this criterion has been applied for the optmisation of craniofacial reconstruction prosthesis (Al-tamimi et al. 2017). Some studies have integrated biomechanical considerations in the form of geometrical constraints in taking into account anatomical areas to be avoided (Sutradhar et al. 2016).To our knowledge, no study considers the phenomenon of “stress-shielding” between the bone and the implant in its optimization process. In this work, the originality is the optimization approach which does not only consider the mechanical characteristics of the optimized part (such as its stiffness) but also the mechanical characteristics of the surrounding bone. Thus, it involves specifically taking into account the mechanical behavior of the surrounding bone to topologically optimize the geometry of the medical device and improve the load transfer between the bone and the implant. For that, a numerical simplified Finite Element (FE) model is developed in this paper with a simplified geometry to highlight the possibility of controlling the load transfer bone and implant

NON LINEAR EFFECTS IN THE VICINITY OF A SOLID TRANSDUCER IN AIR

Il a été théoriquement démontré qu'il pouvait exister un nouveau mode hydrodynamique dans un fluide soumis à un bruit acoustique haute fréquence intense et anisotrope (onde de pompe). Dans le but d'observer ce nouvel effet, nous avons étudié les effets non linéaires au voisinage de la surface émettant l'onde de pompe intense. Une onde sonore basse fréquence est réfléchie sur la surface solide du transducteur haute fréquence. L'onde de pompe est émise durant un court intervalle de temps (100 à 500 µs). Le coefficient de réflexion de l'onde basse fréquence est mesuré pour différents angles d'incidence et plusieurs fréquences, avec et sans émission haute fréquence. Les variations de ce coefficient de réflexion sont dues aux effets non linéaires au voisinage du transducteur. Les mesures donnent une bonne description du vent acoustique, mais on n'observe pas la propagation d'un nouveau mode. Une conclusion définitive sur l'existence de ce mode nécessitera des mesures plus précises, et une connaissance approfondie de l'évolution du vent acoustique.It has been theoretically shown that new hydrodynamic modes may exist in fluid submitted to intense anisotropic high frequency sound noise (pump wave). In order to observe this new effect, we have studied the nonlinear effects in the vicinity of the surface emitting the intense high frequency pump wave. A low frequency sound wave is reflected on the solid surface of the high frequency transducer. The pump wave is emitted during a short time interval (100 to 500 µs). The reflection coefficient of the low frequency sound waves is measured for various angles and frequencies with or without the pump wave. The variations of this reflection coefficient are due to the nonlinear effects in the vicinity of the transducer. The measures give a fine description of the acoustic wind but the propagation of new modes is not observed. A definitive conclusion about these new modes needs however more accurate measures and a best knowledge of the evolution of the acoustic wind