Mass transfer studies of tissue engineered cartilage

Tissue engineered cartilage can be grown in vitro using isolated cartilage cells and biodegradable polyglycolic acid scaffolds. In the present study, the kinetics of mass transfer and the regeneration of tissue components (i.e., cells, glycosaminoglycan, and collagen) were studied for cell-polymer constructs cultured in orbitally mixed petri dishes. Over 6 weeks of cultivation, the composition and morphology of the constructs changed toward an increasingly compact tissue structure as a result of cell proliferation, regeneration of the cartilaginous matrix, and scaffold degradation. Overall rates of mass transfer were determined for disk shaped constructs (10 mm in diameter x 5 mm thick) exposed to a small volume of a well mixed solution of tracer molecules, i.e., glucose and dextran with molecular weights of 180 Da and 4400 Da, respectively. The kinetics of mass transfer between the construct and the solution was assessed from measured time profiles of tracer concentration in the solution and physical construct properties. Mass transfer parameters (e.g., kinetic constants of tracer uptake, partition coefficients) were calculated numerically by solving the material balance equations over the time of tracer diffusion. Mass transfer rates of glucose and dextran decreased over cultivation time in parallel with the accumulation of tissue components in cell-polymer constructs.