A Review of Composition–Structure–Function Properties and Tissue Engineering Strategies of Articular Cartilage: Compare Condyle Process and Knee Joint

Abstract

Temporomandibular joint (TMJ) and knee joint are two of the most important joints in human body. The TMJ, connecting mandible and skull, regulates mandibular movement. The movable circular upper end of the mandible is called condyle, and the upper concave part above the condyle is called articular fossa. Between condyle and articular fossa is a disc composed of fibrocartilage, which is called articular disc. The articular disc has a buffering effect of absorbing pressure, which makes the condyle easy to move in opening, closing, and chewing movement. [1][2][3] Knee joint is the largest and most complex joint in human body, composed of lower tibia, upper femur, and patella. Placed between the articular surfaces of the medial and lateral condyles of the femur and tibia, the semilunar fibrocartilage structure, called meniscus, can buffer the vibration of the joint and avoid direct bone friction. [4] The condylar cartilage of TMJ and the tibial cartilage of knee joint are highly comparable because they are in similar positions and mechanical environment. The superficial layer of condylar cartilage is fibrocartilage, and its deeper layer is hyaline-like cartilage. The hyaline cartilage rich in proteoglycan is covered with surface fibrocartilage layer rich in collagen. [5] However, the tibial artilage is consistent with most articular cartilage and belongs to hyaline cartilage.In terms of biomechanics, there are differences and similarities in the test methods of condylar cartilage and tibial plateau cartilage. Both use dynamic thermomechanical analysis (DMA) and nanoindentation technology to analyze the modulus of cartilage under dynamic compression, and establish finite element models to simulate the biomechanical state of real cartilage. [6,7] For condylar cartilage, indentation creep test is often used to test its compressive properties, which is a way to extract the data of aggregate modulus, Poisson's ratio, and solid matrix permeability by fitting creep data with curves. [8] Other research methods, such as dynamic small strain shear test using automatic dynamic viscoelastometer, have also been applied to measuring the biomechanical properties of condylar cartilage. Almost all biomechanical experiments of condylar cartilage are in vitro. [9] However, for the tibial cartilage, the stress force applied in the test is mostly the stress under the natural motion state, such as walking and jumping. And most of the experiments are in vivo. After a certain motion stimulus is applied, the specific strain response is measured by magnetic resonance imaging (MRI)