Optimizing Nutrient Supply in Large Engineered Cartilage Tissue Constructs

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DESCRIPTION (provided by applicant): Osteoarthritis (OA) is a debilitating degenerative disease that afflicts an estimated 27 million Americans age 25 and older. This disease leads to the progressive degradation of the articular layers of diarthrodial joints, significantly compromising the main function of cartilage as a load bearing material, leading to pain and limiting activities of daily living. Cartilage functional tissue engineering is a highly promising technology that aims to provide a biological replacement to worn articular layers, as a modality that considerably expands the limited options in the treatment of this disease. Though cartilage degeneration is occasionally limited to small focal areas within articular layers, OA generally becomes symptomatic when degradation has spread over much greater surface areas (such as greater than 25 percent of the articular layer). Unfortunately, functional tissue engineering of large cartilage constructs is significantly constrained by the balance of nutrient transport and consumption. Several studies have shown that matrix deposition and elaboration of functional properties preferentially occurs near the periphery of constructs, where nutrient supply from the surrounding culture medium is most abundant, whereas cells in the interior receive less nutrients and produce less matrix, with poorer functional properties. In this application, an engineering solution is proposed for the technical challenge of supplying plentiful nutrients for large engineered cartilage constructs by optimizing the number and spacing of narrow channels through the full thickness of construct layers, thus recapitulating the nutrient supply provided by cartilage canals during early development. The placement of channels in constructs of various dimensions must be optimized to balance competing needs: Increasing the channel density would logically increase the total nutrient supply, spreading it more evenly across the entire construct. However, an elevated channel density may effectively decrease the cell density and increase the pathways for loss of synthesized matrix products before they bind to the extracellular matrix. This type of optimization analysis, where competing needs must be balanced, is very well suited for an engineering approach that accounts for the dominant mechanisms regulating tissue growth. The development of this engineering technology will proceed through four specific aims: (1) Implement solute diffusion/binding/consumption and tissue growth equations from existing models into custom-written finite element software for the analysis of tissue engineered constructs. (2) Experimentally characterize the parameters needed for modeling nutrient supply and matrix growth in engineered cartilage. (3) Use these computational tools and experimental data to perform the optimization analysis for channel placement in large cylindrical and patella-shaped articular layer constructs. (4) Culture large constructs using theoretically optimal (N) and sub-optimal (N/2 and 2N) number of channels, as well as channel-free controls; compare matrix deposition and functional properties to test that N is the optimal value; refine model if necessary. PUBLIC HEALTH RELEVANCE: Osteoarthritis (OA) of the knee and hip is most often associated with loss of cartilage over relatively large regions of the articular layers. OA patients have limited treatment options: Early interventions mostly address pain management, whereas advanced stages of the disease are generally treated with joint replacement, a treatment constrained by the life expectancy of patients in relation to the survival rate of implants. Cartilage tissue engineering offers an opportunity to provide a biological implant as an intermediate treatment modality that follows conservative pain management but postpones (or possibly eliminates the need for) joint replacement. The technology proposed in this application will facilitate engineering of large cartilage tissue constructs needed to resurface defects in OA joints.