Abstract: To obtain an insight to high humidity-caused friction modulation in brake pad-rotor interface, the adhesion phenomenon due to a liquid bridge is simulated using an advanced particle method by varying the shearing speed of the interface. The method, called generalized interpolation material point for fluid-solid interactions (GIMP-FSI), was recently developed from the material point method (MPM) for fluid-solid interactions at small scales where surface tension dominates, thus suitable for studying the partially wet brake friction due to high humidity at a scale of 10 m. Dynamic capillary effects due to surface tension and contact angles are simulated. Adhesion forces calculated by GIMP-FSI are consistent with those from the existing approximate meniscus models. Moreover, the numerical results show that capillary effects induce modulations of adhesion as slip speed changes. In particular, the adhesion modulation could be above 30% at low speed. This finding provides insights into how the high humidity-caused friction could cause modulations of brake, which are unable to be achieved by conventional models. Therefore, the numerical analysis helps to elucidate the complex friction mechanisms associated with brakes that are exposed to high humidity environments.
Abstract: As the gold standard material for artificial joints, ultra-high-molecular-weight polyethylene (UHMWPE) generates wear debris when the material is used in arthroplasty applications. Due to the adverse reactions of UHMWPE wear debris with surrounding tissues, the life time of UHMWPE joints is often limited to 15–20 years. To improve the wear resistance and performance of the material, various attempts have been made in the past decades. This paper reviews existing improvements made to enhance its mechanical properties and wear resistance. They include using gamma irradiation to promote the cross-linked structure and to improve the wear resistance, blending vitamin E to protect the UHMWPE, filler incorporation to improve the mechanical and wear performance, and surface texturing to improve the lubrication condition and to reduce wear. Limitations of existing work and future studies are also identified.
Abstract: The lubrication of the cartilaginous structures in human joints is provided by a fluid from a specialized layer of cells at the surface of a delicate tissue called the synovial lining. Little is known about the characteristics of the fluids produced after a joint arthroplasty procedure. A literature review was carried out to identify papers that characterized the synovial lining and the synovial fluids formed after total hip or knee arthroplasty. Five papers about synovial lining histology and six papers about the lubricating properties of the fluids were identified. The cells making up the re-formed synovial lining, as well as the lining of interface membranes, were similar to the typical Type A and B synoviocytes of normal joints. The synovial fluids around joint replacement devices were typically lower in viscosity than pre-arthroplasty fluids but the protein concentration and phospholipid concentrations tended to be comparable, suggesting that the lining tissue function was preserved after arthroplasty. The widespread, long-term success of joint arthroplasty suggests that the lubricant formed from implanted joint synovium is adequate for good clinical performance in the majority of joints. The role the fluid plays in component wear or failure is a topic for future study.
Abstract: Wear-related complications remain a major issue after unicompartmental arthroplasty. We used a computational model to predict knee wear generated in vitro under diverse conditions. Inverse finite element analysis of 2 different total knee arthroplasty designs was used to determine wear factors of standard and highly crosslinked polyethylene by matching predicted wear rates to measured wear rates. The computed wear factor was used to predict wear in unicompartmental components. The articular surface design and kinematic conditions of the unicompartmental and tricompartmental designs were different. Predicted wear rate (1.77 mg/million cycles) was very close to experimental wear rate (1.84 mg/million cycles) after testing in an AMTI knee wear simulator. Finite element analysis can predict experimental wear and may reduce the cost and time of preclinical testing.
Abstract: Many studies have already considered starved lubrication. However, there have been no reports on the oil film thicknesses under steady starved EHL (elastohydrodynamic lubrication), where the ultra-low volume of oil supplied per unit time is uniform. The present study examined the relationship between the supplied oil flow rate and oil film thickness under steady starved lubrication. A ball-on-disk testing machine was used in experiments to measure the oil film thickness by means of optical interferometry. A microsyringe pump was used to accurately control the supplied oil flow rate. The supplied oil flow rate was kept constant, and the minimum oil film thickness was measured for 1 h after the start of the tests to determine the relationship between the supplied oil flow rate and oil film thickness.
Abstract: Adults suffering from lower back pain often find the cause of pain is degenerative disc disease. While non-surgical treatment is preferred, spinal fusion and total disc replacement remain surgical options for the patient. Total disc replacement is an emerging and improving treatment for degenerative discs. This paper provides a review of lumbar disc replacement for treatment of lower back pain. The mechanics and configuration of the natural disc are first discussed, followed by an introduction of treatment methods that attempt to mimic these mechanics. Total disc replacement types, materials, and failure mechanisms are discussed. Failure mechanisms primarily involve biochemical reactions to implant wear, as well as mechanical incompatibility of the device with natural spine motion. Failure mechanisms include: osteolysis, plastic deformation of polymer components, pitting, fretting, and adjacent level facet and disc degeneration.