Investigator: Eric E. Sabelman, PhD and Peter Johannet, MD Project Staff: Fritz Prinz, PhD and Min Hu, MD, PhD Project Categories: Spinal Cord Injury / Arthritis - 2000 Purpose: Tissue engineering - defined as the combination of living cells with a biomaterial matrix - holds promise for replacing tissues lost to injury, disease and birth defects. Severe pressure sores, ulcers and other wounds with deep tissue loss are now treated by reconstructive surgery, using a muscle flap rotated from an adjacent unaffected site to fill the defect. We are developing a graft for repair of deep or recurring ulcers constructed of several biomaterial matrix layers inoculated with connective tissue and fat cells, nourished either by an external fluid loop through artificial capillaries, or by a microsurgically relocated arteriovenous loop. This proposal will support testing of both approaches in a large animal model, after refinement of the formulation and testing in vitro and in small implants in rats. It is also proposed to advance the state-of-the-art of fabrication of composite tissue-engineered grafts that accurately reproduce complex anatomical structures needed for deep wound repair. Grafts which have entered clinical trials to date have been relatively homogeneous (e.g.: skin, bone, cartilage). Junctions between biomaterial matrices - implicated in scar formation - and restoration of small-scale structures such as sweat glands in skin have been unstudied. Better methods for reconstruction of the bone/cartilage interface are also needed. With the assistance of Prof. Fritz Prinz and colleagues, we are developing a method for aseptically constructing three-dimensional biomaterial structures using CAD-CAM (computer-aided design/manufacturing) technology, using robotic methods which permit de novo fabrication of matrix elements as small as 50 µm from materials specified by a finite element model of the tissue being replaced. The composite artificial/cellular graft is a concept explored by others for skin grafts for burn treatment and cartilage regeneration, and by us for peripheral nerve grafts (Merit Review project B588). Two RR&D pilot projects tested composite collagen/hyaluronic acid grafts for cell compatibility in vitro; (1994-95, #B92-476AP) and microsurgical revascularization in rats (1996-97, #B1839AP). Research Plan: Since grafts thicker than 1 mm require a nutrient source not limited by diffusion from the surface, we will test in animals two approaches: an artificial capillary bed (based on experience with industrial bioreactors for growing cells to near-tissue density), and mobilization and repositioning of arteriovenous pedicles using microsurgical procedures. Extracellular matrices based on Type I collagen and hyaluronic acid reinforced with biodegradable synthetic polymer fiber, tailored to match the properties of the lost tissue, will seeded with autologous cells and implanted into a wound cavity in muscle or connective tissue in a large animal model. Expected Outcomes: Semi-synthetic grafts of all types will eliminate the need for secondary surgery to obtain autograftable tissues, reducing donor site morbidity, risk of infection and loss of function, and time and cost spent during surgery. The range of applications includes not only tissue loss due to pressure sores and overt trauma, but reconstruction of connective tissues following resection for cancer, repair of soft tissues surrounding joints after injury or prosthetic implantation, and, potentially, reconstruction of functional muscle, tendon and bone. Since this proposal culminates in test of grafts for deep wound repair in a large animal model, initial clinical trials in patients whose other options for reconstruction of pressure sores have been exhausted (i.e., previous autografts have failed) could proceed immediately thereafter. Funding Source: VA RR&D Merit Review Funding Status: Approved Letter of Intent |
