Objective: Fibrous tissues of the musculoskeletal system are plagued by their poor healing capacity. Tissue engineering (TE) strategies combine cells and biodegradable scaffolds to fabricate new tissues for implantation. In this proposal, we focus on the knee meniscus, a tissue critical for proper load transfer between the femur and the tibia, and for which current repair strategies do not restore the function. Meniscus damage leads inexorably to cartilage erosion, and in the adult, meniscus healing is limited. The most common surgical procedure is removal of the damaged portion. To address this clinical need, we have devised a novel TE strategy employing anisotropic biodegradable nanofibrous scaffolds to generate constructs for meniscus repair. The objective of this study is to develop and test the efficacy of these novel scaffolds in a large animal meniscus defect model. Research Design: We have developed a novel fabrication process to create dynamic multi-component electrospun scaffolds that promote cellular infiltration while at the same time provide mechanical functionality and direct tissue organization. Here, we introduce three novel features to further their application. First, we include a biomimetic collagen fiber population to enhance cell attachment, invasion, and construct remodeling. Secondly, we improve integration with native tissue via a microsphere-based growth factor delivery system to promote matrix production and angiogenesis. We also employ a new methodology to fabricate scaffolds into the meniscus shape. These scaffolds are tested in a subcutaneous animal model to assess the enhancement of tissue development and vascular invasion. Next, they formed into anatomic shape and tested in a large animal meniscus repair model. In this clinical translation step, we evaluate the construct maturation, as well as their capacity to preserve the underlying articular cartilage. Methodology: Electrospun scaffolds will be fashioned in a novel tri-polymer electrospinning system we recently developed. VEGF and/or TGFbeta will be delivered from co-embedded micropsheres and vascular invasion and matrix development evaluated in a subcutaneous rat model. Next, scaffolds will be formed into anatomic shapes, and used to repair subtotal meniscectomies in a sheep model. We have developed this sheep model over the last two years to evaluate new meniscus formation as well as the mechanical and histological features of the underlying articular cartilage. Findings: Our novel scaffolds are tailored to address the mechanical, biologic, and anatomic requirements of meniscus repair, and will be rigorously evaluated in a large animal defect model. Findings from this study will include degree of vascular invasion, as well as the mechanical properties of the engineered construct and articulating cartilage. Clinical Relationships: This application is focused on the clinical translation of engineered meniscus constructs. We will make significant progress in this translational space, from scaffold production, through to small animal testing, and ultimately to testing of efficacy in a large defect animal model. This work will provide new clinical options for meniscus repair, an otherwise untreatable and prevalent musculoskeletal condition in our active military personnel, and a causative factor for the development of knee osteoarthritis in our aging veteran populations.
This project develops a clinically-relevant approach to fabricate anatomically shaped meniscus constructs that possess several enabling technologies. First, a sacrificial element is engineered into the system to enhance porosity while maintaining fiber alignment critical to meniscus function. Second, a stabilized collagen fiber population is co-electrospun into the network to promote cellular infiltration. Third, a method for placing biodegradable microspheres throughout the fibrous structure is developed to deliver pro-angiogenic growth factors to promote vascular invasion and integration. This highly engineered system provides controlled and direction dependent mechanical properties, tailored degradation to enhance infiltration and integration, and directed neo- vascularization. These enabling technologies culminate in the formation of anatomic shaped implants that are then evaluated in a large animal sub-total meniscus defect model. If successful, this approach would surmount a major hurdle in meniscus tissue engineering to provide an architecturally and biologically relevant template for new tissue formation and with enhanced mechanical properties to support the intense loads found in the joint. This meniscus tissue engineering technique could aid in the treatment of millions of patients afflicted with debilitating joint pathology and degeneration due to trauma or disease, and may be extended for application in other dense fibrous tissues such as tendons and ligaments and the intervertebral disk.
