Search for: All records

Abstract Temporomandibular joint (TMJ) diseases such as osteoarthritis and disc displacement have no permanent treatment options, but lubrication therapies, used in other joints, could be an effective alternative. However, the healthy TMJ contains fibrocartilage, not hyaline cartilage as is found in other joints. As such, the effect of lubrication therapies in the TMJ is unknown. Additionally, only a few studies have characterized the friction coefficient of the healthy TMJ. Like other cartilaginous tissues, the mandibular condyles and discs are subject to changes in friction coefficient due to fluid pressurization. In addition, the friction coefficients of the inferior joint space of the TMJ are affected by the sliding direction and anatomic location. However, these previous findings have not been able to identify how all three of these parameters (anatomic location, sliding direction, and fluid pressurization) influence changes in friction coefficient. This study used Stribeck curves to identify differences in the friction coefficients of mandibular condyles and discs based on anatomic location, sliding direction, and amount of fluid pressurization (friction mode). Friction coefficients were measured using a cartilage on glass tribometer. Both mandibular condyle and disc friction coefficients were well described by Stribeck curves (R2 range 0.87–0.97; p < 0.0001). These curves changed based on anatomic location (Δμ ∼ 0.05), but very few differences in friction coefficients were observed based on sliding direction. Mandibular condyles had similar boundary mode and elastoviscous mode friction coefficients to the TMJ disc (μmin ∼ 0.009 to 0.19) and both were lower than hyaline cartilage in other joints (e.g., knee, ankle, etc.). The observed differences here indicate that the surface characteristics of each anatomic region cause differences in friction coefficients. 

Tissue‐engineered cartilage has shown promising results in the repair of focal cartilage defects. However, current clinical techniques rely on an extra surgical procedure to biopsy healthy cartilage to obtain human chondrocytes. Alternatively, induced pluripotent stem cells (iPSCs) have the ability to differentiate into chondrocytes and produce cartilaginous matrix without the need to biopsy healthy cartilage. However, the mechanical properties of tissue‐engineered cartilage with iPSCs are unknown and might be critical to long‐term tissue function and health. This study used confined compression, cartilage on glass tribology, and shear testing on a confocal microscope to assess the macroscale and microscale mechanical properties of two constructs seeded with either chondrocyte‐derived iPSCs (Ch‐iPSCs) or native human chondrocytes. Macroscale properties of Ch‐iPSC constructs provided similar or better mechanical properties than chondrocyte constructs. Under compression, Ch‐iPSC constructs had an aggregate modulus that was two times larger than chondrocyte constructs and was closer to native tissue. No differences in the shear modulus and friction coefficients were observed between Ch‐iPSC and chondrocyte constructs. On the microscale, Ch‐iPSC and chondrocyte constructs had different depth‐dependent mechanical properties, neither of which matches native tissue. These observed depth‐dependent differences may be important to the function of the implant. Overall, this comparison of multiple mechanical properties of Ch‐iPSC and chondrocyte constructs shows that using Ch‐iPSCs can produce equivalent or better global mechanical properties to chondrocytes. Therefore, iPSC‐seeded cartilage constructs could be a promising solution to repair focal cartilage defects. The chondrocyte constructs used in this study have been implanted into humans for clinical trials. Therefore, Ch‐iPSC constructs could also be used clinically in place of the current chondrocyte construct.