Biotribology最新文献

Leonardo da Vinci (1452–1519) was a visionary engineer, scientist, and polymath of the Renaissance era who performed numerous experiments in tribology, including experiments on wear. As discussed by Prof. Dowson, due to the delayed discovery of several caches of his notebook pages (particularly the Codex Madrid I) recognition of Leonardo's immense contributions to the field of tribology was delayed and continues to unfold. Leonardo's illustrations and investigations clearly describe studies and patterns of wear, particularly for loaded shafts and bushings. In this work, we present an attempt to faithfully recreate Leonardo's observations of wear using bushing and shaft systems made from olive wood. Our experiments, performed roughly 500 years after Leonardo's, reproduced his findings and demonstrated shape evolutions during operation as a result of wear. Leonardo's elegant demonstration of a 2-dimensional bushing-and-shaft system in which the shaft is turning inside of the bushing, showed wear to both components and resulted in a tear-dropped shape as the shaft was consumed. Our experiment, which took over 260 days to complete generated a similar tear-drop shape with an acute angle within 5° of the angle in Leonardo's original drawing. This undertaking also revealed the extensive duration of time over which experiments, and mechanisms operated in Leonardo's laboratory and adds to our understanding of the laboratory environment: a dynamic, active, and busy laboratory in motion, with numerous ongoing experiments and moving mechanical assemblies at work. As Prof. Dowson recognized, Leonardo da Vinci was clearly curious and passionate about tribology, as the Codex Madrid I contains thousands of illustrations of tribological components and experiments in friction, wear, and lubrication.

Currently, the artificial hip joint is the best option for total hip arthroplasty, and the demand for this procedure is increasing annually. However, a major deficiency of artificial hip joints is the performance limitation in a wide range of movements, such as those in Muslim prayer (salat), a major religious practice that consists of seven positions representing extreme movements. In this work, a numerical examination is conducted to investigate the performance of artificial hip joints with three texture configurations and with two different ball materials subjected to seven loading conditions of Muslim prayer (salat). Transient non-Newtonian elastohydrodynamic lubrication analyses are solved using the two-way Fluid–Structure Interaction (FSI) method. It is found that the femoral head and the inner liner with a pattern applied to the whole of their contacted surface show a substantial increase in load support when compared with the smooth one; the improvement is approximately 11% and 13%, respectively, for the movement of sitting between two prostrations for left leg, and the bowing position. Furthermore, slight increase in fluid pressure and load support is highlighted compared with the models in which only the liner or head are textured. In addition, the simulation solution shows that for other loading positions, the textured model reveals a reduction in performance. The amount of load support in prostration, sitting between two prostrations (right leg), and sitting (right leg) positions is insufficient, which may lead to direct contact. The simulation results also indicate that the alumina femoral head gives better result compared to the stainless steel one.

Determining a precise contact area between one surface and another surface is essential for understanding tribological tool performance, since this area contributes to the force transmission. Radular teeth are part of the complex molluscan feeding apparatus acting on the ingesta by transmitting muscle-driven forces, in some cases working as a puncturing tool. Various approaches aimed at identifying the contact areas and cutting edges of radular teeth to understand the relationship between both shape and position of teeth and the function. However, most previous studies rely on feeding tracks which are difficult to interpret. To determine load transmitting regions, we here present an easy experimental set-up involving sandpaper that can be applied to a variety of molluscan species. Stylommatophoran gastropods were fed with food paste attached to sandpapers of different roughness for 1 month: subsequently, the radular tooth wear was analysed qualitatively. These feeding experiments under controlled conditions were performed for molluscan radula for the first time revealing distinct sandpaper-induced facets. Comparisons of the tooth material loss led to the determination of the contact areas and the amount of teeth involved in the feeding process, both directly related with the surface roughness. Additionally, the direction of force during feeding was reconstructed. The analyses of wear patterns resulting from the impact of teeth on the sandpaper grains contribute to our knowledge about the underlying mechanisms preventing structural failure in radulae. These mechanisms are based on the biomechanical behaviour of the radular supporting structures.

This study presents an improvement of an existing tribocorrosion model developed for passive CoCrMo alloys. This model is based on an empirical formalism established by Duncan Dowson in his pioneering works on the relation between wear and elasto-hydrodynamic lubrication. The improvement consists in introducing surface topography features allowing for a mechanistic relation between lubrication and wear. The effective normal force accounting for the plastic deformation of passive metals during lubricated tribocorrosion was described through the real contact area, which in turn was related to the worn surface topography (roughness) and the elasto-hydrodynamic film thickness. The modified model was applied to results from dedicated tribocorrosion experiments obtained by varying the lubricant viscosity and the contacting surface roughness. Good correlations were found between the mechanical and chemical wear rates and corresponding variables, which validated the model. Further development of the model should include boundary film effects, third bodies build-up and time dependent evolution of the worn surface.

Due to the known osteolytic potential of polyethylene, pre-clinical testing of total hip replacements (THR) has been much focused on articulating wear in the past. However, friction related effects (e.g. taper wear or mechanical implant loosening) are reported for modern THR. Established material combinations made of cross-linked polyethylene, ceramics and metals are measured in a modified hip simulator to investigate friction for two different walking profiles: ISO 14242-1 and data from patient measurements. In addition, the patient profile was adapted for different loads during the swing phase, a variation in patient weight and walking speed. Ceramic-on-Ceramic bearings show the lowest overall frictional torques over a gait cycle for all investigated testing profiles while there is no difference between the head material (metal, ceramics) when combined with polyethylene. Taper torques of under 2 Nm are reported for continuous walking. Friction increases with higher patient weight and lower walking speed. In addition, the swing phase load only seems to have an influence on polyethylene bearings while hard-on-hard (combinations of ceramics and metal only) are less sensitive to a variation of load in the last 40% of the gait cycle. Friction measurements offer a powerful tool to increase the performance of pre-clinical testing. Beside the continuous “ideal” conditions presented here, more challenging profiles are proposed.

Biomechanical influences play a fundamental role in the structural, functional, and biosynthetic properties of articular cartilage. During physiologic joint loading, the contact area between two surfaces migrates due to the primary and secondary motions of the joint. It has been demonstrated that a migratory contact area plays a critical role in reducing the coefficient of friction at the cartilage surface. However, a detailed analysis of the influences that a migratory contact area plays on the structural, functional, and biosynthetic properties remain to be explored. In this study, bovine cartilage explants were placed in a biotribometer. Explants were subjected to compression and shear forces of migratory contact area, namely moving contact (MC) articulation, or stationary contact area, namely stationary contact (SC) articulation. Free swelling explants were used as control. In a separate study, bovine cartilage-bone grafts were used for frictional testing. On histologic analysis, the SC group had evidence of surface fibrillations, which was not evident in the MC group. Compared to the SC group, the MC group cartilage explants had increased chondrocyte viability, increased lubricin synthesis, and comparable proteoglycan synthesis and release. MC articulation had reduced coefficient of friction as compared to SC articulation. MC articulation led to reduced surface roughness as compared to SC articulation. In conclusion, a migratory contact area can play an important role in maintaining the structural, function, and biosynthetic properties of articular cartilage. This study provides further evidence of the importance of migratory contact area and in vitro assessment of natural joint movement, which can be further evaluated in the context of cartilage homeostasis and disease.

Various hydrogels have been developed to use as artificial cartilage. Poly(vinyl alcohol) (PVA) hydrogel cross-linked by hydrogen bonds is biocompatible and has similar properties to natural articular cartilage. For clinical use as artificial cartilage, superior tribological performance with low friction and minimal wear are required. In our previous study, three kinds of preparation methods for PVA hydrogels with high water content, i.e., the repeated freeze-thawing (FT) method, the cast-drying (CD) method and the layered hybrid method composed of FT and CD layers were applied. As hybrid gel specimens, (CD on FT) and (FT on CD) gels were prepared. The comparison between experiment and biphasic finite element analysis showed that the frictional behaviors of these PVA hydrogels at slow speed are controlled by their biphasic lubrication mechanism. After that, it was found that the biphasic properties of FT gel with heterogeneous network structure was largely changed after immersion in water for more than 6 years. In this paper, the influence of changes in permeability with aging of FT gel on friction and biphasic behaviors of PVA hydrogels was evaluated by biphasic finite element analysis. As aged FT specimens with lower permeability, four kinds of aged FT specimens with different elastic properties were evaluated. As a result, it is suggested that frictional behavior of PVA FT gels with aging can be improved by lowering of permeability in aged FT gel. Furthermore, it is expected that hybrid gel as CD on aged FT with appropriate elastic modulus can sustain superior low friction.

Wear of cobalt chromium molybdenum alloy in a reciprocating ball-on-plate test was measured for a series of model synovial fluid samples, where the effect of protein and phospholipid content was examined. The protein content (albumin and γ-globulin) was varied to replicate a range of healthy and diseased SF pathologies. The results showed reduced wear was strongly correlated with increasing protein content. The effect of phospholipid addition on wear was more complex. Limited evidence suggested phospholipids reduced wear for a high albumin/γ-globulin ratio (A/G) but increased wear for low A/G ratios. Post-test examination showed thick (~μm) insoluble “gel-like” films were deposited in, and around, the wear scar. Micro Infrared Reflection Absorption Spectroscopy analysis indicated the films were predominately denatured β-sheet proteins although in some cases lipids were also present. Similar films were found in tests with human synovial fluid samples. Scanning Electron Microscopy imaging showed an aggregated fibril “rope” structure typical of non-native β-sheet proteins. The gel film is a protein-rich viscous phase which is entrained intermittently to form a lubrication film which contributes to surface protection and reduction of wear. We also suggest the formation of gel deposits is comparable to the “boosted” lubrication model of proposed by Professor Duncan Dowson for articular cartilage. In the boosted model high-viscosity, concentrated protein films are formed in depressions on the cartilage surface. The tests indicate the chemistry of human synovial fluid, particularly the protein content, could affect CoCrMo wear and therefore the risk of implant failure.

Tribocorrosion of implants has been widely addressed in the orthopedic and dental research fields. This study is a systematic scoping review about research methods that combine tribocorrosion tests with cells/tissues cultures, aimed to identify related current problems and future challenges.

We used 4 different databases to identify 1022 records responding to an articulated keywords search-strategy. After removing the duplicates and the articles that didn't meet the search-criteria, we assessed 20 full-text articles for eligibility. Of the 20 eligible articles, we charted 8 records on cell cultures combined with tribocorrosion tests on implant materials (titanium, CoCrMo, and/or stainless steel). The year of publication ranged from 1991 to 2019. The cell line used was mostly murine. Two records used fretting tests, while 6 used reciprocating sliding with pin-on-disc tribometers. An electrochemical three-electrode setup was used in 4 records. We identified overall two experimental approaches: cells cultured on the metal (5 records), and cells cultured near the metal (3 records).

Research activities on tribocorrosion processes in the presence of cells have been undertaken worldwide by a few groups. After a limited initial interest on this topic in the 1990's, research activities have restarted in the last decade, renewing the topic with technologically more advanced setups and analytical tools. We identified the main problems to be the lack of test reproducibility and wear particle characterization. We believe that the main challenges lay in the interdisciplinary approach, the inter-laboratory validation of experiments, and the interpretation of results, particularly in relation to potential clinical significance.

Current hip prostheses make extensive use of Ti-6Al-4 V alloy. This material was originally designed for aerospace applications. Moreover, its poor tribological properties are well known. However, beta, or near beta Ti alloys are known to have superior properties in that its elastic modulus is closer to that of bone coupled with a good fatigue resistance. Therefore, this work aims to analyse the tribocorrosion behaviour of 4 different titanium alloys (Ti-13Nb-13Zr, Ti-12Mo-6Zr-2Fe and Ti–29Nb–13Ta–4.6Zr aged at 300 °C and at 400 °C) at anodic potential, OCP and cathodic potential at 0.5 N, 1 N and 2 N in bovine serum to identify the main cause of material degradation, effect of microstructure and the synergism between corrosion and wear. The results show the alloys become more active when subjected to sliding in all conditions, but the material loss is lower at anodic potential. Finally, at anodic potential wear is lower than at cathodic potential which is explained by increase in the mechanical wear at cathodic potential.