Development of a vascularized graft for skeletal muscle regeneration
While skeletal muscle demonstrates a remarkable ability to heal injuries and strains, there is limited regeneration of severe injuries associated with significant volumetric muscle loss. After injury, as skeletal muscle is regenerating, there is a race between angiogenesis and fibrosis in regards to whether the new muscle will be functional. Angiogenesis of the muscle graft is vital to distributing nutrients and oxygen throughout the defect site. Without adequate vascularization, fibrotic tissue will begin to form and limit the mobility of the newly generated muscle tissue. While various scaffold materials have been used in skeletal muscle regeneration, there remains a need for a graft that will support angiogenesis throughout a defect site in addition to promote skeletal muscle development. Five commonly used substrates (collagen, agarose, alginate, fibrin and collagen chitosan) for grafts were screened down based on their rheological, water absorbtion and tensile characteristics to optimize their myogenic capacity. Collagen and fibrin demonstrated an increased promotion of muscle development, so they were then evaluated at various densities to determine which material supported angiogenesis. Results showed that fibrin at a density of 5 mg/mL demonstrated an increased capacity for myogenesis and angiogenesis in a three dimensional graft model. These results were evaluated with immortalized and primary cells to confirm the findings. With the goal to develop a vascularized graft for skeletal muscle regeneration, two types of grafts were created using a single endothelial cell model and a spheroid cellular model in a fibrin hydrogel. Bioreactor studies with mechanical stretching and perfusion were then used to simulate in vivo like conditions for the grafts to validate the static in vitro results. Overall in this study it was demonstrated that it is possible to create a vascular graft through different angiogenesis models, but there in order to the results to correlate from in vitro to in vivo the grafts should be tested in situ.