Fracture simulation for zirconia toughened alumina microstructure

Purpose - The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures. Design/methodology/approach - A two-dimensional finite element model is developed with an actual $Al{_2}O{_3}$ - 10 vol% $ZrO{_2}$ microstructure. A bilinear, time-independent cohesive zone law is implemented for describing fracture behaviour of grain boundaries. Simulation conditions are similar to those found at contact between a head and a cup of hip prosthesis. Residual stresses arisen from the mismatch of thermal coefficient between grains are determined. Then, effects of a micro-void and contact stress magnitude are investigated with models containing residual stresses. For the purpose of simulating fatigue behaviour, cyclic loadings are applied to the models. Findings - Results show that crack density is gradually increased with increasing magnitude of contact stress or number of fatigue cycles. It is also identified that a micro-void brings about the increase of crack density rate. Social implications - This paper is the first step for predicting the lifetime of ceramic implants. The social implications would appear in the next few years about health issues. Originality/value - This proposed finite element method allows describing fracture and fatigue behaviours of alumina-zirconia microstructures for hip prosthesis, provided that a microstructure image is available

Degradation of alumina and zirconia toughened alumina (ZTA) hip prostheses tested under microseparation conditions in a shock device

This paper considers the degradation of alumina and zirconia toughened alumina vs. alumina for hip implants. The materials are as assumed to be load bearing surfaces subjected to shocks in wet conditions. The load is a peak of force; 9 kN was applied over 15 ms at 2 Hz for 800,000 cycles. The volumetric wear and roughness are lower for ZTA than for alumina. The long ZTA ageing did not seem to have a direct influence on the roughness. The ageing increased the wear volumes of ZTA and it was found to have a higher wear resistance compared to alumina.Comment: International Conference on BioTribology (ICoBT 2011), Londres, 18 au 21 septembre 2011, Londres : United Kingdom (2011

Predicting the steady state thickness of passive films in order to prevent degradations of implant

Some implants have approximately a lifetime of 15 years. The femoral stem, for example, should be made of 316L/316LN stainless steel. Fretting corrosion, friction under small displacements, should occur during human gait, due to repeated loadings and un-loadings, between stainless steel and bone for instance. Some experimental investigations of fretting corrosion have been practiced. As well known, metallic alloys and especially stainless steels are covered with a passive film that prevents from the corrosion and degradation. This passive layer of few nanometers, at ambient temperature, is the key of our civilization according to some authors. This work is dedicated to predict the passive layer thicknesses of stainless steel under fretting corrosion with a specific emphasis on the role of proteins. The model is based on the Point Defect Model (micro scale) and an update of the model on the friction process (micro-macro scale). Genetic algorithm was used for finding solution of the problem. The major results are, as expected from experimental results, albumin prevents from degradation at the lowest concentration of chlorides; an incubation time is necessary for degrading the passive film; under fretting corrosion and high concentration of chlorides the passive behavior is annihilated

Role of Proteins on the Electrochemical Behavior of Implanted Metallic Alloys, Reproducibility and Time-Frequency Approach from EIS (Electrochemical Impedance Spectroscopy)

Metallic alloys are commonly used in orthopedic implants. Some attempts were investigated for replacing the human organs or joints. Without being exhaustive, some key points of the history of the orthopedic implants could be presented (Callaghan, 2007): - In 1826, the first pseudoarthrosis was practiced by J. Barton with a wood piece of the hip joint; - In 1891, the first femoral head in ivory was implanted by T. Gluck (Gluck, 1890); - In 1923, the "Molded arthroplasty" using hollow hemisphere made of glass was practiced by M.N. Smith-Petersen; - In 1936, the first acrylic femoral stem was implanted by Judet's brothers. One might suggest the implanted materials are close to the organic materials in terms of natural origin. The last one, acrylic polymer, would be a dedicated material because their mechanical properties are close to the ones of bone. However the mechanical and tribological properties are not sufficient for being enough resistants. Thus the metallic implants were investigated because of their better mechanical properties, elastic modulus and tensile strength. Following, few important dates are suggested: - In 1938, M.N. Smith-Petersen used the Vitallium® made of Co-Cr-Mo, Cobalt-Chromium-Molybdenum, alloy for the femoral stem; - In 1949, Judet's brothers implanted the first total hip arthroplasty (Judet, 1949); - Finally, in 1962, Sir J. Charnley imposed the low friction arthroplasty with a femoral stem made of 316L stainless steel (Charnley, Livingstone, 1970; Charnley, Springer, 1970).Finally 3 main materials are implanted as femoral stem or metallic components: the titanium alloy, Ti-6Al-4V, the stainless steel, 316L SS, and the cobalt-chromium alloy (Park, 1992). The first one is dedicated to the femoral stem, the second one is used as material for manufacturing femoral stem, metal back and possibly the head for Metal on Polymer, MoP, contact, the third metal could be investigated as the Head and cup assembly for Metal on Metal, MoM, assembly, the head component for MoP assembly and no frequently the femoral stem. Figure 1 highlights the different assemblies involved in the femoral stem. The ceramic material will not be presented in this work

Friction-corrosion of AISI 316L/bone cement and AISI 316L/PMMA contacts : ionic strength effect on tribological behaviour

International audienceWear phenomena understanding of implants is a challenge: friction-corrosion of biomaterials, which constitute orthopaedic implants, is a significant issue concerning the aseptic loosening. This work aims at studying AISI 316L/bone cement friction which is a tribological problem related to hip joint cemented prostheses. This study focuses on the ionic strength effect on the tribological behaviour of 316L/bone cement and 316L/PMMA contacts. PMMA, poly(methylmethacrylate), can be considered as a model material for bone cement because of vicinity of mechanical properties and PMMA transparency. Pin on disk friction tests were investigated, in different media with NaCl concentration increasing. Friction coefficient and free corrosion potential of 316L sample were monitored. Moreover, SEM-FEG and microraman spectroscopy analyses were investigated on samples surfaces. Friction coefficient evolution according to ionic strength, for 316L/bone cement and 316L/PMMA contacts, are opposite. Indeed, when the ionic strength increases, the friction coefficient growths (decreases), for 316L/PMMA contact (for 316L/bone cement contact). The free corrosion potential decreases in both cases but more drastically for 316L/PMMA contact with ionic strength increasing. One might suggest that ions adsorption on 316L and PMMA surfaces involves attraction between surfaces in contact. On the contrary, ions adsorption on bone cement has no effect in terms of surface attraction forces, the gap between surfaces is too big due to roughness of bone cement. If ions concentration increases, the tribofilm viscosity between 316L and bone cement could increase. Attraction forces between surfaces are the less significant phenomenon compared to lubricant effect of tribofilm, 316L/bone cement contact. SEM-FEG analysis highlighted principally deep grooves on 316L surface, corrosive wear after destruction of passive film by friction. Finally microraman spectroscopy results, on metal surface, show principally Fe3O4 and Cr2O3 oxides deposits. Further investigations are in progress for understanding surfaces interactions during friction

Understanding the dual mobility concept for total hip arthroplasty. Investigations on a multiscale analysis-highlighting the role of arthrofibrosis

International audienceIn hip implants, UHMWPE (ultra high molecular weight polyethylene) liner wear is believed to be a key issue affecting the lifetime of the artificial joint. Dual mobility, a THA (total hip arthroplasty) concept where the liner moves inside the metallic shell, has become popular due to its low dislocation rate. To understand the tribological behavior of this particular implant, especially the role of the second mobility, 12 representative explants were selected from a bank of 250 explants. The implants used were Profil® femoral stem and Novae® metallic shell. The external surface, involved in the second mobility, was examined by 3D profilometry, SEM (scanning electron microscopy) and CMM (coordinate measuring machine). This study highlights a correlation between roughness and CMM evolutions and surgical parameters. A particular wear zone and a wear scenario were identified and validated according to the type of metal-back. A metal transfer between the metal back and the liner was isolated. CMM allowed to measure second mobility wear volume at a macroscopic scale. Thus a realistic wear mechanism has been suggested for this specific implant

Influence of proteins from physiological solutions on the electrochemical behaviour of the Ti-6Al-4V alloy: reproducibility and time-frequency dependence. ---- Influence de la teneur en prot\'eines de solutions physiologiques sur le comportement \'electrochimique du Ti-6Al-4V : reproductibilit\'e et repr\'esentation temps-fr\'equence

The electrochemical behaviour of the biomedical and metallic alloys, especially in the orthopaedic implants fields, raises many questions. This study is dedicated for studying the Ti-6Al-4V alloy, by electrochemical impedance spectroscopy, EIS, in various physiological media,: Ringer solution, phosphate buffered solution (PBS), PBS solution and albumin, PBS solution with calf serum and PBS solution with calf serum and an antioxidant (sodium azide). Moreover, the desionised water was considered as the reference solution. The tests reproducibility was investigated. The time-frequency-Module graphs highlighted that the desionised water is the most protective for the Ti-6Al-4V alloy. This biomedical alloy is the less protected in the solution constituted by PBS and albumin. The time-frequency graph allows pointing out the graphic signatures of adsorption for organic and inorganic species (differences between the modules means in studied solution and the modules mean in the reference solution). --- Le comportement \'electrochimique des alliages m\'etalliques biom\'edicaux, notamment dans le domaine des implants orthop\'ediques, pose encore de nombreuses questions. Ce travail propose d'\'etudier l'alliage de titane Ti-6Al-4V, par spectroscopie d'imp\'edance \'electrochimique, SIE, dans diff\'erents milieux physiologiques : solution de Ringer, solution \`a base d'un tampon phosphate (PBS), solution PBS avec de l'albumine, solution PBS avec du s\'erum bovin et une solution PBS avec du s\'erum bovin et un antioxydant (azoture de sodium). De plus, une solution d'eau ultra-pure servira de r\'ef\'erence. La reproductibilit\'e des tests a \'et\'e \'etudi\'ee. Les repr\'esentations temps-fr\'equence des modules ont mis en \'evidence que l'eau d\'esionis\'ee est la solution qui pr\'esente le caract\`ere le plus protecteur pour le Ti-6Al-4V. Cet alliage de titane est le moins prot\'eg\'e dans la solution de PBS contenant de l'albumine. Cette repr\'esentation permet de mettre en \'evidence des signatures graphiques d'adsorption des esp\`eces inorganiques et organiques (diff\'erences entre les moyennes des modules dans les solutions \'etudi\'ees et la moyenne des modules dans la solution de r\'ef\'erence)

Fretting-corrosion between 316L SS and PMMA: Influence of ionic strength, protein and electrochemical conditions on material wear. Application to orthopaedic implants

International audienceIn biomedical field, fretting-corrosion between 316L SS femoral stem and bone cement is one of the significant causes of the hip prosthesis loosening. This article investigates wear by fretting-corrosion at the contact between 316L and PMMA. The influences of the ionic strength (NaCl solutions from 10−3 to 1 mol L−1), a model protein (albumin) and electrochemical conditions on contact behaviour are studied. At OCP (open circuit potential) conditions, the chlorides concentration, i.e. the ionic strength, increases the 316L wear; and albumin, concentration of 1 g L−1, does not play a significant role in total 316L wear. At cathodic applied potential E = −400 mV(SCE), a threshold concentration of 10−1 mol L−1 (NaCl solution), Cth, indicates two behaviours: a protective effect below Cth, and an additional anodic dissolution above Cth. One might suggest that, beyond Cth, the passive layer is not efficient for protecting against the corrosion. At this potential, albumin reduces wear due to corrosion and amplifies mechanical wear induced by corrosion. Albumin seems to act as an anodic inhibitor. To determine the mechanisms of synergism, a "more cathodic" potential is applied, E = −800 mV(SCE), during fretting-corrosion experiments. Consequently, the corrosive wear can be neglected and the mechanical wear can be only measured

Concept de double mobilité pour les prothèses totales de hanche : analyses multi-échelles de son fonctionnement

National audience120000 prothèses de hanche sont implantées chaque année, en France, 800000 en Europe. Cet acte chirurgical représente un enjeu de santé publique majeur, dans les années à venir. Dans l'optique d'augmenter la durée de vie des implants, un concept original de l'articulation d'une prothèse de hanche, le concept de double mobilité, représente maintenant 30 % des implants de hanche en France. 250 explants ont été conservés avec leurs caractéristiques complètes, ainsi que celles des patients. Une population homogène d'explants de LIP sans descellement acétabulaire, à même embase fémorale Profil ® a été ciblée. Puis, une première analyse visuelle et les données opératoires ont dégagé 12 explants caractéristiques. Une analyse de rugosimétrie de surface de la convexité a été menée (profilométries 2D et 3D) sur 5 zones de 1 mm² pour 2 latitudes choisies ainsi que le sommet (11 surfaces) [1,2]. La cartographie intégrale, relevés tridimensionnels macroscopiques, a été réalisée. La microscopie électronique à balayage munie d'une sonde EDS a permis de caractériser les transferts métalliques, insert sur metal back, dus à la 2 e mobilité. L'évolution de paramètres particuliers de rugosité 3D a permis de mettre en évidence les différents mécanismes d'usure de la 2 ème mobilité. Les metal backs en alliage de titane, ainsi que les échecs par fibrose capsulaire ont montré un fluage du UHMWPE (Ultra High Molecular Weight PolyEthylen) sans usure significative, ce qui explique une LIP précoce par un contact plus fréquent sur la collerette de rétentivité. Les surfaces de metal-back en acier présentent une phase de fluage puis une phase de frottement sur une bande caractéristique. L'usure du metal back en miroir corrèle cette observation. Le dessin prothétique et la balance de Pauwels permettent d'expliquer finement cette bande d'usure. De plus, il a été mis en évidence que l'usure n'est pas liée à l'âge ou au diamètre de l'insert. Il a été possible d'établir un scénario du mouvement de la deuxième mobilité, à partir des explants étudiés, en tenant compte des matériaux, de la taille des éléments prothétiques et de toutes les données disponibles

Wear behavior of PAEK, poly(aryl-ether-ketone), under physiological conditions, outlooks for performing these materials in the field of hip prosthesis

International audienceThis study is focused on performing tribological tests on new materials for orthopaedic implants applications, PAEK (poly aryl ether ketone) polymer group. The experiments were performed in physiological liquid, at 37 °C, for simulating the human body fluid. PAEK's tribological properties that are wear rate of polymers and wear mechanisms on common metallic alloys used as orthopaedic implants: Co-Cr, 316L SS and Ti-6Al-4V are compared to the gold standard used for hip joint prosthesis, the UHMWPE (ultra high molecular weight polyethylene) on the same metal alloys. PEEK (poly ether ether ketone) and PEKK (poly ether ketone ketone)/CF (carbon fibers) show the lowest wear rate on every counter metallic material; the system UHMWPE on any metal alloys exhibit the highest wear rate although having the lowest friction coefficient. From microscopic images and the evolution of the friction coefficient, a wear mechanism was suggested for each polymeric material