Articular hyaline cartilage is a highly specialized tissue with complex biomechanical and biochemical properties designed to meet the demands of daily joint loading. Focal defects in articular cartilage can lead to changes of these properties over time, causing degeneration of the tissue and eventually pathologies like osteoarthritis. Although current cartilage repair strategies are capable of providing a short-term solution, fibrocartilaginous repair tissue is often formed. Due to the presence of collagen type I, decreased collagen type II and aggrecan content, and the loss of structural organization, the biomechanical properties are insufficient to meet the demands of daily joint loading.
The composition of the extracellular matrix (ECM) is determined by the synthesis of matrix components (e.g. collagens and proteoglycans) by chondrocytes. The expression of these matrix components is regulated by a complex network of intracellular signaling pathways sensitive to extracellular stimuli (e.g. mechanical stress and strain, fluid flow, and osmotic pressure). These stimuli are thought to be transduced by the pericellular matrix (PCM), a narrow region of matrix surrounding chondrocytes. The chondrocyte and its PCM together are called a chondron. The PCM has significantly different biochemical and biomechanical properties when compared to the ECM. This discrepancy is thought to create the optimal microenvironment for chondrocytes and could be essential to the phenotypic stability of chondrocytes.
Current cartilage tissue engineering approaches often involve the use of (fiber-reinforced) hydrogels. When assessing the quality of such constructs, the mechanical properties of the complete construct are often considered. However, to our knowledge, there are little to no studies dedicated to optimizing the cell microenvironment within these structures. Additionally, hydrogels which have properties favorable to the chondrogenic phenotype have lacking mechanical properties and vice versa.
Within this project we aim to first investigate the effect of the native PCM on the chondrogenic phenotype in a 3D culture system. This culture system consists of a hydrogel in which chondrocyte naturally lose their chondrogenic phenotype. Secondly, we aim to develop a multi-component cartilage construct where multiple kinds of hydrogels will mimic the properties of both the ECM and PCM. To do this we aim to create an artificial chondron by encapsulating chondrocytes in microgels. This approach could create an artificial microenvironment favorable to the chondrogenic phenotype, while the mechanical properties of the complete construct are sufficient to withstand joint loading.