Study Of Transport Behavior For Cartilage Under Rolling-compressing Load

Articular cartilage is white, compact connective tissue that covers the bony articulating ends inside the joint, where there is no nerves, vessels, or lymph. It relies on external mechanical environment to acquire nutritional ingredient and discharge metabolic waste, and changes chondrocyte biological activities through external loads, especially to cartilage defect caused by injuries or diseases, applying external loads can change biological metabolic process in tissue, and accelerate cartilage repair.This paper proposes a rolling–compressing load method based on the movement character of knee joint, and studies solute transport behavior within articular cartilage through experiments and finite element simulation.Fluorescein isothiocyanate–Dextran(4k Da) and Tetramethylrhodamine isothiocyanate– Dextran(0.43 k Da) were used to mark fresh articular cartilage of a mature pig in our experiments. Solute fluorescence intensity changing with time and depth of cartilage layer was measured under rolling–compressing load and static state respectively, the distribution of corresponding relative concentration was calculated, and changing laws of solute diffusivity were acquired based on the fluorescence microscope imaging method. Results show comparing with the sample under static state, solute relative concentration and diffusivity of articular cartilage under rolling–compressing load increase significantly, especially in transitional and deep layers, whereas the diffusivity in superficial layer changes unconspicuous. In the initial period, relative concentration of superficial layer and diffusivity of deep layer increase distinctly. With rolling times increasing, relative concentration of transitional and deep layer increasing distinctly, as well as diffusivity of transitional layer. Smaller molecular weight solute is easier to transport relative to larger molecular weight solute. Therefore, rolling–compressing load can promote solute transport of articular cartilage and improve solute diffusivity.2D finite element model was established using ANSYS in numerical modeling. The distributions of stress field and concentration field under load were discussed, and the curves that concentration changed with time and cartilage depth were acquired. The relationship between solute concentration and time as well as that between solute concentration and cartilage depth were explored under different velocities, friction coefficients and amounts of compression respectively. Results show that solute transport affected by the amount of compression is obvious, especially in the transitional and deep layer, while that affected by the rate of rolling–compressing and friction coefficient are not evident. Rolling–compressing load provides an important and new method to repairing injured cartilage clinically and tissue engineering.