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The Effects of Material Properties of Hydrogels for Cartilage Tissue Engineering

Kara L. Spiller and Anthony Lowman. Chemical and Biological Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104

Currently no clinical successful technique exists to halt the degeneration of articular cartilage due to a cartilage defect. Despite extensive research into the use of hydrogels as scaffolds for cartilage repair, controversy exists regarding optimal material properties. Poly (vinyl alcohol) hydrogels have been modified to improve cellular adhesion by the physical or covalent addition of extracellular matrix proteins like fibronectin. The porosity of these hydrogels has also been controlled up to 65%, with pore sizes ranging from 50 to 100 um, and the effects of porosity on the migration of bone marrow stromal cells (BMSCs) throughout the hydrogels are being investigated. In order to examine the effects of mechanical properties on the response of BMSCs, it was important to ensure that the initial distribution of cells throughout the hydrogels was homogenous. Therefore, hydrogels based on poly(n-isopropylacrylamide) have been developed, which are thermally responsive in that they are liquid below body temperature and form stiff gels above body temperature. Cells can be incorporated into the hydrogels by stirring at room temperature and subsequently raising the temperature of this cell-hydrogel mixture, so that cells are physically entrapped and uniformly distributed throughout the matrix. The mechanical properties of this hydrogel system can be varied by the addition of methacrylic acid. The elastic modulus of the gels has been controlled from 100 to 500 kPa, depending on the relative amounts of monomers. The effects of mechanical properties on the behavior of BMSCs, in terms of gene expression and deposition of extracellular matrix proteins, is currently being investigated in both static cell culture and under dynamic loading conditions.