UC San Diego

Unlike many organs, skeletal muscle possesses the ability to naturally regenerate. However, chronic muscle injuries, including ischemia and chronic unloading, interrupt this regenerative process. We sought to investigate the therapeutic potential of a decellularized skeletal muscle extracellular matrix (ECM) hydrogel in ischemia and chronic unloading muscle injury models with a main focus on translating this material into the clinic. A rat hindlimb ischemia model was utilized for a dose optimization study in which three concentrations (4 mg/mL, 6 mg/mL, and 8 mg/mL) were compared to a saline control and non-tissue specific myocardial ECM hydrogel. The 6 mg/mL concentration produced the largest increase in blood perfusion, and efficacy of the 6 mg/mL skeletal muscle ECM hydrogel was then further confirmed in an aged mouse hindlimb ischemia model to more accurately depict patient pathophysiology. Similar to the dose optimization study, significant increases in blood perfusion were observed after 4 weeks. Since the hindlimb ischemia model is an acute model, the skeletal muscle ECM hydrogel was also probed in a more chronic model, specifically a rabbit model of chronic rotator cuff tears. The timing for the ECM hydrogel injection was investigated, and a delayed injection encouraged more muscle regeneration, as demonstrated by upregulation of key muscle transcription factors and the presence of larger diameter arterioles. Although ECM hydrogels possess regenerative capabilities, efficacy may be limited, and, therefore, the material was also evaluated as a delivery vehicle for microRNAs and exosomes. Incorporation of these therapeutics into the hydrogels yielded prolonged release profiles, and the released molecules remained bioactive in vitro. Lastly, several manufacturing considerations were investigated to ensure efficacy of the final product would be maintained during scale-up. Animal-to-animal variability and a bioburden reducing step did not present issues for manufacturing, but the various harvesting conditions yielded differences with the protein content of the final ECM product. All in all, the skeletal muscle ECM hydrogels demonstrated efficacy in multiple skeletal muscle injury models and as a delivery platform for small therapeutics. In addition, the manufacturing of these materials for clinical translation remains feasible amidst additional processing steps.