Adult articular cartilage has biomechanical, compositional, structural, and biological properties that can provide effective load-bearing function for decades. Developmental mechanisms create such mature articular cartilage, of a particular size and shape, through growth and remodeling of immature tissue under biochemical and biomechanical regulation. The fabrication of cartilaginous tissue grafts, of an analogously stable function and form, underlies a number of existing surgical treatments for restoring damaged joints as well as emerging tissue engineering therapies. The long-term goal of this project is to establish integrative scientific principles that allow the bioengineering fabrication of articular cartilage grafts of increasingly precise properties (maturity, size, shape), effective for surgical treatment of damaged diarthrodial joints. In the initial funding period, we established (1) the baseline mechanical and compositional properties of articular cartilage at various stages of growth, and their correlative relationships, (2) the ability of biological and biomechanical stimuli to modulate cell functions and in vitro growth during up to six weeks of culture, (3) the effects of targeted matrix manipulations on in vitro growth, implicating a critical role for matrix remodeling and in particular a balance between swelling mediated by fixed charge and restraint by the collagen network, and (4) methods to determine chondrocyte organization in three dimensions within cartilage tissue. These results evoked the current working hypothesis, that the maturity, size, and shape of live articular cartilage grafts can be prescribed by a combination of biological and biomechanical stimuli and chemical manipulations that modulate the remodeling of selected components of the tissue matrix. To test this hypothesis, studies are proposed to determine if in vitro remodeling of articular cartilage tissue can be manipulated to achieve (1) adult-like maturity, i.e., to undergo functional maturation of the load-bearing tissue matrix, (2) increased size, i.e., to undergo axial and radial expansion, and (3) desired shapes, i.e., to become convex or concave. Experiments will manipulate (a) matrix composition and assembly, (b) cell metabolism, and (c) the internal growth stress, and analyze kinematic growth. Relevance to Public Health. The proposed research will establish new scientific concepts and engineering methods to create a next generation of therapeutic cartilage tissue. The resultant tissue grafts would be especially useful for replacement of articular cartilage for large and advanced defects.
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