Biotribology最新文献

Products of densification continue to gain importance in the daily activities due to certain advantages such as reduced cost of logistics, better handling and improved performance with regard to their respective purposes. The durability is a measure of defining the quality of these products thus determining the extent of research and development required to enhance these products. Various methods of determining durability such as the impact tests, tumbling, pneumatics, and high speed dural mechanism have reportedly been utilized. There is sparsity literature on the development of high-speed locally made systems for determining durability of agglomerates. The durability testing apparatus is a locally fabricated device designed as a hybrid of the tumbler and the dural to evaluate agglomerates in a bid to determine their resistance to damages when in dynamic state. The design of this apparatus was carried out putting into consideration various components and fabricated to be used for a wide range of agglomerates. It was evaluated using starch bonded kenaf pellets which was found to have a durability of 98.15–99.72% for trial periods of 60 s per run. The durability testing drum was able to effectively determine the durability of kenaf starch bonded pellets.

Wooden journal bearing is widely used in various applications such as wind turbines and marine bearings. In this paper, the wooden journal bearings is fabricated with teak wood due to their higher strength and durability. Various manufacturing operations such as cutting, turning, etc., are performed during the fabrication process of wooden journal bearings. After fabricating it, the experimental study is performed to analyze the influence of operating parameters on the tribological characteristics of wooden bearings. For this, the operating parameters such as speed and load are considered input variables. Whereas, the tribological characteristics of wooden bearings such as wear resistance and surface roughness are considered the output parameters. The major aim of this study is to analyze and optimize the tribological characteristics of wooden bearings. This can be achieved by increasing its wear resistance and increasing surface roughness. By using the response surface methodology (RSM), the influence of operating parameters (i.e. speed and load) on the tribological characteristics of wooden bearings are analyzed. Furthermore, the desirability function is used to obtain the optimal tribological characteristics of wooden bearings. These results show that speed is the most significant parameter for wear resistance and load for surface roughness of wooden bearings. Due to continuous operation, the wear rate of wooden bearings first increases and then decreases. In addition, the surface roughness of wooden bearings becomes smooth. The regression analysis develops the mathematical relationship between the operating parameters and the tribological characteristics of wooden bearings.

Dry mouth is a troublesome condition linked to lubrication failure and leads to other diseases such as fungal infections and wounds in the oral cavity. There are many commercial salivary substitutes in the market, but none with a long-lasting lubrication effect. Polymer-coated liposomes can be an interesting formulation strategy for retrieving the symptoms of dry mouth by mimicking the micelles of saliva. In the present study, polymer coated-liposomes were prepared by the conventional thin film method and subsequently coated with three different polymers with different charge densities; alginate, chitosan and hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC). The prepared polymer-coated liposomes were studied concerning their lubricating properties using a ball-on-disc tribometer at 2 N load at 37 °C, and their flow behaviours were also measured. Solutions of the pure polymers and dispersions of the uncoated liposomes were also studied to investigate any contributions from the individual components. A commercial dry mouth product based on HEC (hydroxyethyl cellulose) and glycerol was also included. The formulations were measured as soon as possible after preparation and some of them after >4 weeks. Results demonstrated that all the positively-charged formulations (chitosan, positive liposomes and chitosan-coated liposomes) had superior lubricating properties with friction coefficients (μ < 0.1) at orally relevant speeds (50 mm/s) as compared to the neutral or negatively-charged systems. At boundary lubrication conditions (3 mm/s), the chitosan-coated liposomes obtained an even lower friction force than the individual components, thus indicating a synergistic effect between the polymer and the liposome.

Digital Image Correlation (DIC) systems have been used to measure surface displacement fields by tracking a pattern applied to a surface. Offering many benefits in comparison to conventional strain-measurement devices, the use of DIC has been reported in the study of tissue biomechanics and performance of joints underneath. In this study, a new method was developed to apply a quality speckle pattern on the skin of knees. Temporary tattoo paper provided a safe, easy, and quick way for pattern application to the skin without hindering its natural behavior. A pattern was developed for analyzing the knee during a squatting motion in which the field of view, system set up, and curvature of the knee were contributing factors to the development. This research is designed to prove the feasibility of using tattoo papers as patent indicators for DIC measurement. The software was able to map the entire region of the knee and measure the displacement of each area independent of other parts, thus making it easy to identify twisting and bending of the joint. Experimental results indicated that it is an effective method to accurately analyze the motion of the knee without the need of sophisticated equipment. This methodology can be used to understand how strain affects the knee during action and thus will be useful for various sports-related activities such as training and injury management.

During archaeological fieldwork wedge-shaped quartz stones that show clearly visible "glossy patches" composed of high quartz have been found. It is generally accepted that these tools have been used to cleave or punch wood and bone materials. For the transformation from quartz to high-quartz to occur, the temperature should exceed 574 °C. The hypothesis tested in this manuscript is that the phase change in the stone tool results from frictional heating during the cleaving action. Dry sliding friction measurements were carried out on a reciprocating tribometer using four types of stone, representing the punch tool, and pine, oak and bovine bone, representing the work piece. Measured coefficients of friction were approximately 0.1 on oak, 0.2 on pine and up to 0.35 on bovine bone, with some minor fluctuations for the different types of stone. These coefficients of friction were inserted into a computational model describing the flash temperatures in a moving contact, from which it was shown that the hypothesis might hold in the case of lydite-bone contact. This means that the glossy patches on the stone tools may have been caused by frictional heating during the cleaving of bone.

In recent years tribology tests have been used to measure friction properties of oral consumables such as semi-solid foods and medicines. The tests aim to simulate thin-film mastication conditions and are intended to correlate with mouth feel or food texture properties. In this paper a new approach is proposed to better simulate shear conditions, fluid supply and friction data capture associated with mastication and swallowing. Two primary changes are suggested: these are the reduction of the inlet influence on lubricant film properties and the ability to measure transient and time-dependent friction. The new test was used to measure friction for a range of oral medicines including a viscous solution (cough syrup) and particulate suspensions (paediatric, calcium carbonate) in combination with an artificial saliva (mucin solution), The tongue-palate was replicated by a PCX glass lens loaded and reciprocating against a textured silicone surface. A short stroke length, comparable to the Hertzian diameter of the contact, was used so the contact operated in a partially replenished lubrication condition. This ensured the film in the contact region has the same composition as the bulk fluid. Friction was measured continuously during reciprocation for up to 5 cycles (comparable to mastication time) and data was sampled at 100 Hz to capture transient friction. Tests were run with and without a mucin layer present. The results showed that tests performed after 20 min adsorption of an artificial saliva solution reduced the friction coefficient from μ = 1 to μ = 0.2–0.3. Tests with the paracetamol suspensions, which contain hard particles, recorded transient friction spikes which were not recorded for the softer calcium carbonate suspensions. Key conclusions for the design of pertinent simulation tests are that the film properties in the oral cavity are not determined by the inlet as for classical lubrication. The (bulk) oral sample is captured in the tongue-palate contact and not continually replenished. When sheared it will exhibit time (transient, longer-term) and speed dependent friction responses which contribute to sensory and texture perception.

Metal wear and corrosion debris remain a limiting factor for long-term durability of total hip replacement (THR). Common wear particle production techniques for research differ from the actual tribocorrosion processes at the implant site, potentially causing loss of valuable information. The aim of this study was to investigate reactions to freshly generated and time-stabilized particles and ions released from CoCrMo-alloy using a bio-tribometer, which mimics conditions of the periprosthetic environment.

THP-1 macrophages were challenged with freshly produced or time-stabilized wear debris. Wear generation took place in a custom-built bio-tribometer inside a CO₂ incubator operating with a reciprocating rotation of an Al₂O₃ ball against a CoCrMo disc. Two different electrochemical conditions with increasingly forced corrosion rates were tested: +0.45 V (passive domain) and +0.67 V (transition to transpassive domain). Cell viability, proinflammatory cytokines, electrochemical measurements and ICP-MS metal ion content analyses were performed.

Cobalt/ chromium concentrations were 6.6/ 1.6 ppm in the passive domain and almost doubled to 11.4/ 3.0 ppm in the passive-transpassive domain. Under those electrochemical conditions, freshly produced and time-stabilized CoCrMo wear decreased cell viability to the same extent. Secretion of proinflammatory cytokines were not significantly different for freshly produced and time-stabilized debris.

This study suggests that freshly generated and time-stabilized metal particles/ions cause similar toxicity and inflammatory reactions in macrophages, indicating that standard practices for generating wear debris are valid methods to evaluate wear particle disease. Other cell types, materials, and corrosion potentials need to be studied in the future to solidify the conclusion.

Pyrolytic carbon (PyC) is a common material used in mechanical heart valves. This investigation studies the effects of surface finish on the the sliding wear between two PyC surfaces. The primary application being, the prediction of wear at articulating surfaces within bileaflet mechanical heart valves. An experimental apparatus is designed which allows a cylinder to rotate on a flat plate at a constant frequency and load. The cylinder is harder (greater modulus of elasticity) than the flat surface. Two surface finishes of a single (hard) cylinder and two flat surfaces of different hardnesses (single surface finish) are investigated, for a total of four cases. These four cases are studied at four sliding distances. The exerimental data is used to develop theoretical load and stress-dependent models for sliding abrasive wear. For the boron alloyed PyC material used in this investigation, the load-dependent wear model is most applicable for unpolished cylinders and the stress-dependent model is most applicable for polished cylinders. These two models are used to make theoretical predictions of pivot wear in a bileaflet mechanical valve of the same material. The predictions from the stress-dependent wear model was found to be quite accurate with actual wear measurements. The methods developed in this paper are generalized and applied to other valve designs and materials.

A custom-built tribometer was employed to investigate the impact of the roughness of deformable tongue mimicking surfaces (TMS) on friction mechanisms occurring under the effect of lubrication with Newtonian solutions of glycerol. TMSs with modulated roughness (range of asperity heights Ra: 20–140 μm) were manufactured from gels of polyvinyl alcohol (PVA). Newtonian aqueous solutions of glycerol covering a wide range of viscosity (1–1400 mPa.s) were used as simple food models spread on the TMSs. The tribological behavior of the system was studied during shear back and forth movements. The ratio between tangential and normal forces was analyzed both in terms of average values and of fluctuations, over specific time periods set at the end of motion and rest steps. The average values of friction level were reported to increase when (i) the roughness of the TMSs increased and when (ii) the viscosity of glycerol solutions decreased. These trends could be consistent with mixed lubrication. The fluctuations of friction level during motion steps were for their part generally of higher amplitude as the roughness of the surface increased, with main frequencies ranging from 10 to 20 Hz. The study demonstrates the importance (i) of the biological relevance of tongue properties (contact areas, rigidity, and asperity heights) and (ii) of the thorough analysis of tangential to normal force ratio to better understand the complex mechanisms of friction occurring in the mouth during food consumption.

Despite the clinical success of hip joint replacement, the risk of revision, particularly in younger and more active patients, still remains a concern. To identify conditions of high wear, fatigue and potential failure modes, there is need to be able to replicate a range of in vivo conditions with pre-clinical testing methods in order to predict the range of clinical wear. In particular, edge loading of metal-on-polyethylene hip replacements has the potential to have impact on both surface wear and fatigue failure. The mode of edge loading explored in this study involves separation of the centres of the femoral head and acetabular cup during a portion of the gait cycle. Such edge loading can occur due to variations in translational and/or rotational positioning of the hip replacement. In this study, the influence of translational positioning along the medial-lateral axis (medial-lateral translational mismatch) combined with rotational positioning of the acetabular cup about the anterior-posterior axis (cup inclination angle) on the occurrence and severity of edge loading, and wear and plastic deformation, was investigated for size 36 mm metal-on-polyethylene total hip replacements on a ProSim EM13 electromechanical hip joint simulator. A two phase approach was used; a short term study where the mechanics of the hip bearing were assessed under a wide range of input conditions (45° and 65° cup inclination angle and 1, 2, 3, 4 mm medial-lateral translational mismatch); followed by wear simulation for a lower number of conditions.

Larger medial-lateral translational mismatch conditions led to increased levels of dynamic separation between the femoral head and acetabular cup with the largest dynamic separation (2.4 ± 0.2 mm, mean ± 95% confidence limits) measured under 4 mm translational mismatch with the 65° cup inclination angle conditions. The load at the rim at 0.5 mm of separation was also highest at this condition, as was the mean wear rate (23.0 ± 2.4 mm³ / million cycles).

Dynamic separation, load at the rim and wear was consistently greater with the steeper cup inclination angle of 65° compared to 45° for all translational mismatch conditions. Translational mismatch conditions of 3 mm and 4 mm resulted in dynamic separation displacements >0.5 mm. At a 45° cup inclination angle under standard concentric conditions (zero translational mismatch) minimal wear and plastic deformation occurred at the rim of the cup, however at a 65° cup inclination edge contact at the rim was identified.

Variations in rotational (cup inclination angle) and translational (medial-lateral) positioning influenced the magnitude of dynamic separation, severity of edge loading, and wear of metal – on - moderately cross-linked polyethylene hip replacements, demonstrating the importance of surgical component positioning.