Functional grading of pericellular matrix surrounding chondrocytes: potential roles in signaling and fluid transport

The extracellular matrix surrounding chondrocytes within cartilage and fibrocartilage has spatial gradients in mechanical properties. Although the function of these gradients is unknown, the potential exists for cells to tailor their mechanical microenvironment through these gradients. We hypothesized that these gradients enhance fluid transport around the cell during the slow loading cycles that occur over the course of a day, and that this enhancement changes the nature of the mechanical signals received at the surface of the cell. To test this hypothesis, we studied the effect of these gradients on the mechanical environment around a chondrocyte using a closed form, linearized model. Results demonstrated that functional grading of the character observed around chondrocytes in articular cartilage enhances fluid transport, and furthermore inverts compressive radial strains to provide tensile signals at the cell surface. The results point to several potentially important roles for functional grading of the pericellular matrix.