Healthy articular cartilage supports load bearing and frictional properties unmatched among biological tissues and man-made bearing materials. Balancing fluid exudation and recovery under loaded and articulated conditions is essential to the tissue’s biological and mechanical longevity. Our prior tribological investigations, which leveraged the convergent stationary contact area (cSCA) configuration, revealed that sliding alone can modulate cartilage interstitial fluid pressurization and the recovery and maintenance of lubrication under load through a mechanism termed ‘tribological rehydration.’ Our recent comparative assessment of tribological rehydration revealed remarkably consistent sliding speed-dependent fluid recovery and lubrication behaviors across femoral condyle cartilage from five mammalian species (equine/horse, bovine/cow, porcine/pig, ovine/sheep, and caprine/goat). In the present study, we identified and characterized key predictive relationships among tissue properties, sliding-induced tribological rehydration, and the modulation/recovery of lubrication within healthy articular cartilage. Using correlational analysis, we linked observed speed-dependent tribological rehydration behaviors to cartilage’s geometry and biphasic properties (tensile and compressive moduli, permeability). Together, these findings demonstrate that easily measurable tissue characteristics (e.g., bulk tissue material properties, compressive strain magnitude, and strain rates) can be used to predict cartilage’s rehydration and lubricating abilities, and ultimately its function in vivo.
Listed In: Biomechanical Engineering, Biotribology

As a treatment for end-stage elbow joint arthritis, total elbow replacement (TER) results in joint motions similar to the intact joint; however, bearing wear, excessive deformations and/or early fracture may necessitate early revision of failed implant components. A finite element model of a TER assembly was developed based on measurements from a Coonrad-Morrey implant (Zimmer, Inc., Warsaw, IN) using nonlinear elasto-plastic UHMWPE material properties and a frictional penalty contact formulation. The loading scenario applied to the model includes a flexion-extension motion, a joint force reaction with variable magnitude and direction and a time varying varus-valgus (VV) moment with a maximum magnitude of 13 N.m, simulating a chair-rise scenario as an extreme loading condition. Model results were compared directly with corresponding experimental data. Experimental wear tests were performed on the abovementioned implants using a VIVO (AMTI, Watertown, MA) six degree-of-freedom (6-DOF) joint motion simulator apparatus. The worn TER bushings were scanned after the test using micro computed tomography (μCT) imaging techniques, and reconstructed as 3D models. Contact pressure distributions on the humeral and ulnar bushings correlate with the sites of damage as represented by the μCT data and gross observation of clinical retrievals. The results demonstrate UHMWPE bushing damage due to different loading protocols. Numerical results demonstrate strong agreement with experimental data based on the location of deformation and creep on bushings and exhibit promising capabilities for predicting the damage and failure mechanisms of TER implants.
Listed In: Biomechanical Engineering, Biomechanics, Biotribology, Mechanical Engineering, Orthopedic Research

During osteoarthritis (OA), the lubricity of synovial fluid (SF) decreases. Therefore, we synthesized a novel, 2MDa polymer biolubricant (“2M TEG”) designed to augment the lubricating properties of SF in OA. This study’s aims were 1) to compare the abilities of 2M TEG and bovine synovial fluid (BSF) to reduce the coefficient of friction (COF) for previously “worn” cartilage specimens during a long-duration, torsional, wear test, and 2) using the same regimen, examine the “reversibility” of 2M TEG’s lubricity relative to BSF. For both aims, each wear test consisted of subjecting mated, bovine osteochondral plug pairs to 10,080 rotations. To accomplish Aim 1, plug pairs were subjected to three sequential wear regimens (Wear 1-3). Wear 1&2 were used to progressively “wear” the cartilage, and Wear 3 was used to test the efficacy of either BSF (n=4) or 2M TEG (n=4) on “worn” cartilage. For Aim 2, three pairs were subjected to four sequential wear regimens, where the lubricants were BSF, BSF, 2M TEG, and BSF, respectively. The relative percent reduction in COF between Wear 3 and Wear 2 in Aim 1 was greatest for 2M TEG, followed by BSF. For Aim 2, the mean percent reduction in COF for Wear 3 relative to Wear 2 was almost exactly the same as the mean increase in COF for Wear 4 relative to Wear 3. By reducing the COF for worn cartilage in OA joints, synthetic biolubricants such as 2M TEG could help minimize further cartilage wear and ameliorate the progression of OA.
Listed In: Biomechanical Engineering, Biomechanics, Biotribology, Orthopedic Research