This Translational Research Partnership Award proposal addresses the Fiscal Year 2011 Peer Reviewed Orthopaedic Research Program congressionally directed topic area of treatment of post-traumatic osteoarthritis. Osteoarthritis (OA) is a degenerative disease of the articular cartilage affecting millions of people worldwide. Articular cartilage is a smooth tissue that covers the ends of bones where they come together at a joint. This cartilage helps support body weight and allows the bones to glide over one another without painful friction. When this cartilage is damaged, OA can often result, with cartilage degradation causing the bones to rub against each other painfully. Of all OA cases, about 10%-15% of them are post-traumatic OA resulting from an acute injury. Post-traumatic OA is a common problem among soldiers, who can suffer traumatic joint injuries during combat. Articular cartilage, a tissue with few cells and without a blood supply, is not naturally able to repair itself when it is damaged. Current techniques used in the clinic to treat damaged articular cartilage do not typically restore total function, and thus an alternative therapy is needed, which is the focus of this proposal.

Cartilage tissue engineering, in which a method is devised for promoting the regeneration of this tissue, may provide a much-needed alternative, as it could be a way to create new functional articular cartilage. Stem cells, such as human adipose-derived stem cells (hASCs) and human mesenchymal stem cells (hMSCs) harvested from fat tissue and bone marrow, respectively, have been shown to be a promising cell source for cartilage tissue engineering strategies, as they can be grown in culture to produce many cells, and these cells are able to change into many different cell types including the cells that make up cartilage, known as chondrocytes. Two important factors that can promote these stem cells to change into chondrocytes are a high initial density of cells and exposure to soluble bioactive factors. One method to form cartilage tissue is to use self-assembling cell sheets; these show promise for cartilage tissue engineering as they may form large constructs with high surface areas and volumes. These large constructs may be more practical for use in the clinic.

In our lab, a technology has been developed comprised of self-assembling stem cell sheets incorporated with bioactive factor-releasing hydrogel microspheres. This system of self-assembled, microsphere-incorporated stem cell sheets is capable of forming cartilage in the presence of chondrogenic growth factors, either supplied in the culture media or incorporated into and released from the microspheres. There is currently extensive literature demonstrating that delivery of genetic material, such as siRNAs and miRNAs, can also direct these stem cells to become chondrocytes and form cartilage. Our lab has recently developed novel biomaterials permitting the controlled, sustained, and localized delivery of siRNA. Therefore, the proposed work seeks to present specific siRNAs and/or miRNAs to block the expression of genes that inhibit chondrogenesis or promote chondrocyte hypertrophy, which is undesirable. In addition, hydrostatic pressure or pulsatile fluid flow will also be applied to the engineered cartilage sheets. The goal is to maximize the quality and quantity of cartilage formed through the defined presentation of these specific signals and to demonstrate the system's potential in repairing full thickness articular cartilage defects in vivo. Benefits of this technology include (1) decreased time to surgical treatment compared to other tissue engineering approaches that rely on in vitro chondrogenic differentiation of stem cells, (2) the ease of access to these stem cells, and (3) the directed regeneration approach that leads to functional, uniform cartilage formation and decreased healing time. The clinical goal is the pursuit of Phase I clinical trials in articular cartilage defects in 3 years. This project will identify important design parameters for enhancing cartilage formation and provide critical proof of principle in a larger animal model of a clinically relevant full thickness cartilage defect. This would be a very promising technology for advancing the treatment of patients suffering from post-traumatic OA and could significantly improve the health and lives of military service members and veterans suffering from such injuries.