A Model to Study Articular Cartilage Mechanical and Biological Responses to Sliding Loads

Abstract

In physiological conditions, joint function involves continuously moving contact areas over the tissue surface. Such moving contacts play an important role for the durability of the tissue. It is known that in pathological joints these motion paths and contact mechanics change. Nevertheless, limited information exists on the impact of such physiological and pathophysiological dynamic loads on cartilage mechanics and its subsequent biological response. We designed and validated a mechanical device capable of applying simultaneous compression and sliding forces onto cartilage explants to simulate moving joint contact. Tests with varying axial loads (1 – 4 kg) and sliding speeds (1 – 20 mm/s) were performed on mature viable bovine femoral condyles to investigate cartilage mechanobiological responses. High loads and slow sliding speeds resulted in highest cartilage deformations. Contact stress and effective cartilage moduli increased with increasing load and increasing speed. In a pilot study, changes in gene expression of extracellular matrix proteins were correlated with strain, contact stress and dynamic effective modulus. This study describes a mechanical test system to study the cartilage response to reciprocating sliding motion and will be helpful in identifying mechanical and biological mechanisms leading to the initiation and development of cartilage degeneration.

Reducing uncertainty when using knee‐specific finite element models by assessing the effect of input parameters

“…To understand the relationship between joint mechanics and the ensuing biological response, a number of in vitro and in vivo models have emerged. In vivo animal models and in vitro tissue explant models have demonstrated that increased joint translation, contact stress, and impact force can lead to cartilage degeneration . In vivo patient‐based studies of joint kinematics and tissue contact have also suggested that changed kinematics during walking can influence changes in joint morphology .…”

“…In vivo animal models and in vitro tissue explant models have demonstrated that increased joint translation, contact stress, and impact force can lead to cartilage degeneration. 8,[27][28][29][30] In vivo patient-based studies of joint kinematics and tissue contact have also suggested that changed kinematics during walking can influence changes in joint morphology. 31 Conceptually, a deeper understanding of a patient's joint mechanics and how those mechanics are affected by injury, could be used to assess the risk of joint tissue degeneration after meniscal injury, and hence the need to surgically intervene.…”

Establishing a live cartilage-on-cartilage interface for tribological testing

“…Even basic tribological models utilizing pin-on-disc or flat-on-flat tribometers lack the rolling and gliding motion seen in vivo[2]. Limited studies have applied more complex mechanical patterns and loads to native cartilage tissue resulting in surface shear stress[17–21]. Second, in tribological testing, the biological cartilage-cartilage interface of a joint is often replaced by an interface of cartilage against glass or other biomaterials[22–26], neglecting the native tissue response to motion and loading against a naturally soft counterface.…”

“…The few studies that do utilize a cartilage-on-cartilage interface do so for studies of friction and/or lubrication[27,28], for comparison against chondroplasty materials[29,30], or for supraphysiological impaction[16]. Third, a final biological concern with many studies is the limited understanding of living cartilage response to tribological stresses as frozen or dead tissue has been typically used[21,31]. Eliminating the biological response from the system provides an incomplete picture of cartilage degradation.…”

Effect of osteochondral graft orientation in a biotribological test system

“…In this context, tribological principles play a significant role and have gained attention over the last decade in elucidating how natural synovial joints function or fail and provide insights into different design principle criteria . The moving contacts between the surfaces are mandatory to produce high fluid pressurization, as well as a low coefficient of friction from a tribological point of view . Important aspects which can affect measurements are friction, wear, and lubrication.…”