Laminin-111-Enriched Fibrin Hydrogels Enhance Functional Muscle Regeneration Following Trauma.

Volumetric muscle loss (VML) is the surgical or traumatic loss of skeletal muscle, which can cause loss of limb function or permanent disability. VML injuries overwhelms the endogenous regenerative capacity of skeletal muscle and results in poor functional healing outcomes. Currently, there are no approved tissue engineering treatments for VML injuries. In this study, fibrin hydrogels enriched with laminin-111 (LM-111; 50-450 µg/mL) were used for the treatment of VML of the tibialis anterior in a rat model. Treatment with fibrin hydrogel containing 450 µg/mL of LM-111 (FBN450) improved muscle regeneration following VML injury. FBN450 hydrogel treatment increased the relative proportion of contractile to fibrotic tissue as indicated by the myosin: collagen ratio on day 28 post-VML injury. FBN450 hydrogels also enhanced myogenic protein expression and increased the quantity of small to medium size myofibers (500-2000 µm2) as well as innervated myofibers. Improved contractile tissue deposition due to FBN450 hydrogel treatment resulted in a significant improvement (∼60%) in torque production at day 28 postinjury. Taken together, these results suggest that the acellular FBN450 hydrogels provide a promising therapeutic strategy for VML that is worthy of further investigation. Impact statement Muscle trauma accounts for 50-70% of total military injuries and complications involving muscle result in ∼80% of delayed amputations. The lack of a clinical standard of care for volumetric muscle loss (VML) injuries presents an opportunity to develop novel regenerative therapies and improve healing outcomes. Laminin-111-enriched fibrin hydrogel may provide a promising therapy for VML that is worthy of further investigation. The acellular nature of these hydrogels will allow for easy off the shelf access to critically injured patients and fewer regulatory hurdles during commercialization.

Co-delivery of fibrin-laminin hydrogel with mesenchymal stem cell spheroids supports skeletal muscle regeneration following trauma.

Volumetric muscle loss (VML) is traumatic or surgical loss of skeletal muscle with resultant functional impairment. Skeletal muscle's innate capacity for regeneration is lost with VML due to a critical loss of stem cells, extracellular matrix, and neuromuscular junctions. Consequences of VML include permanent disability or delayed amputations of the affected limb. Currently, a successful clinical therapy has not been identified. Mesenchymal stem cells (MSCs) possess regenerative and immunomodulatory properties and their three-dimensional aggregation can further enhance therapeutic efficacy. In this study, MSC aggregation into spheroids was optimized in vitro based on cellular viability, spheroid size, and trophic factor secretion. The regenerative potential of the optimized MSC spheroid therapy was then investigated in a murine model of VML injury. Experimental groups included an untreated VML injury control, intramuscular injection of MSC spheroids, and MSC spheroids encapsulated in a fibrin-laminin hydrogel. Compared to the untreated VML group, the spheroid encapsulating hydrogel group enhanced myogenic marker (i.e., MyoD and myogenin) protein expression, improved muscle mass, increased presence of centrally nucleated myofibers as well as small fibers (<500 µm2 ), modulated pro- and anti-inflammatory macrophage marker expression (i.e., iNOS and Arginase), and increased the presence of CD146+ pericytes and CD31+ endothelial cells in the VML injured muscles. Future studies will evaluate the extent of functional recovery with the spheroid encapsulating hydrogel therapy.

Biomimetic sponges improve muscle structure and function following volumetric muscle loss.

Skeletal muscle is inept in regenerating after traumatic injuries such as volumetric muscle loss (VML) due to significant loss of various cellular and acellular components. Currently, there are no approved therapies for the treatment of muscle tissue following trauma. In this study, biomimetic sponges composed of gelatin, collagen, laminin-111, and FK-506 were used for the treatment of VML in a rodent model. We observed that biomimetic sponge treatment improved muscle structure and function while modulating inflammation and limiting the extent of fibrotic tissue deposition. Specifically, sponge treatment increased the total number of myofibers, type 2B fiber cross-sectional area, myosin: collagen ratio, myofibers with central nuclei, and peak isometric torque compared to untreated VML injured muscles. As an acellular scaffold, biomimetic sponges may provide a promising clinical therapy for VML.