Dynamic Hydrostatic Pressurization Increases Matrix Gene Expression by Chondrocytes in 3D Culture

Articular cartilage is the load-bearing substance that covers the bony surfaces of articulating bones. With its high water content and small pore size, deformation of cartilage induces a very high hydrostatic pressure within the cartilage. This hydrostatic pressure has been shown both theoretically and experimentally to support upwards of 90% of the applied load (1), and can be on the order of 6–12 MPa. Chondrocytes, the cells within cartilage respond to this pressure by altering their rates of biosynthesis. Studies utilizing radionucleotide incorporation in both explant and monolayer cultures (2–4) have shown that in general dynamic pressurization increases synthesis, while static pressurization decreases synthesis. More recently, Smith et al have shown that dynamic pressurization (10MPa, 1 Hz) of cells in monolayer culture can upregulate matrix gene expression (5,6). Further, a study in PGA constructs has shown that long term application of dynamic pressure can increase matrix deposition (7). In this study, we seek to expand on these findings by examining the response in gene expression of articular chondrocytes encapsulated in alginate, a charged, 3D hydrogel.