Full-thickness loss of articular cartilage will often progress until total destruction of a joint occurs. This in turn is extremely disabling, not only by limitation of function of a joint, but by producing severe pain. Left untreated, articular cartilage is not capable of repairing itself. Therefore, repairs of these lesions will require intervention with an implant that can bring the necessary elements for repair to the site of injury or disease. Work to date has shown that perichondrial tissue, when placed in a full-thickness articular cartilage defect, will proliferate and elaborate matrix that will repair the defect. However, perichondrium has limitations imposed by the amount of the tissue that is available for harvest and, in addition, it is technically challenging to attach to the cartilage defect. On the basis of prior research showing that the perichondrial cells are capable of performing as chondroprogenitor repair cells, the focus of this research has evolved to develop an optimized delivery system for treatment of an osteochondral defect. As conceptualized, this delivery system will consist of a two-layered, anatomically-modeled biodegradable (polylactic acid) scaffold which is seeded with cells cultured from perichondrium. The two-layered polylactic acid scaffold will have a superficial zone that will have a radially-oriented fiber construction, sitting atop a second layer that will have a randomly porous architecture. In addition, this carrier should be capable of delivery of growth factors. Based on the applicants' work, TGFbeta1 will be utilized to augment the cellular response at the repair site. The current proposal has three Specific Aims: 1) to evaluate an anatomic architecture of a polylactic acid biodegradable carrier; 2) to measure the effect of TGFbeta1 on the phenotype of cells grown in culture and its effect on facilitating cartilage repair; and 3) to assess repairs long-term, using an optimized carrier seeded with cultured perichondrial cells in a full-thickness articular cartilage defect in adult rabbits at one and two years post- implantation. The assessment of results will continue to be multidisciplinary, employing: 1) histomorphometric measurement of neocartilage height, area, surface roughness, cell density, subchondral bone restoration, and percent repair; 2) measurement of types I and II collagens by gel filtration HPLC; 3) in situ hybridization of tissue sections using cDNA or riboprobes specific for types I and II collagen mRNAs; 4) RT-PCR of RNA extracted from neocartilage repair tissue for type IX collagen mRNA expression; 5) immunohistochemistry to identify and biochemically characterize cartilage matrix marcomolecules (proteoglycan) at the repair site; 6) biomechanical quantitation of neocartilage and subchondral tissue compressive material properties by confined compression testing with video microscopy; and 7) biomechanical quantitation of neocartilage collagenous matrix function and host tissue integration by tensile testing to determine tissue tensile modulus. The goal is to develop an implant that will consistently and predictably produce repairs of full-thickness articular cartilage defects that will function as well as normal cartilage.
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