Angiogenesis and fibrosis in a volumetric skeletal muscle loss injury using mesenchymal stem cells in a PEGylated fibrin gel on an extracellular matrix

Volumetric Muscle Loss (VML) injury can result from trauma and in military personnel with wound in combat. VML lead to the loss of substantial mass of muscle mass, inherent regenerative capacity, thus can fail to retain functional muscle. Previous work in our lab, has shown partial functional and morphological repair from the injection of PEGylated fibrin gel combined with mesenchymal stem cells (MSC) to skeletal muscle-derived decellularied extracellular matrix (ECM) following fifty-six days after VML injury model. To further investigate the vascularization, innervation, and fibrosis in this model, trichrome, and immunohistochemical analyses were performed in three groups: saline (SAL), mesenchymal stem cell (MSC), and MSCs in PEGylated fibrin gel (PEG+MSC). The PEG+MSC group had as significantly lower percentage of fibrosis than the SAL group in the top, middle and bottom regions within ECM, as well as lower fibrosis only in the middle region when compared to the MSC group (p <0.05). The MSC group had lower fibrosis only in the middle region than SAL group (p <0.05). Similarly, PEG+MSC has higher percentage of cellular area than SAL group in all regions, and the MSC group had as higher percentage of cellular area when compared to SAL group only in the middle region (p <0.05). The only difference in cellular material shown was between the PEG+MSC group and the MSC group in the middle region of ECM (p <0.05). Following a fifty-six day recovery, the blood vessel density of PEG+MSC, and MSC groups were higher than the SAL group (p <0.05) in middle region, with no difference in other regions. The blood vessel ratio of PEG+MSC, and MSC groups were significantly higher than the SAL group (p <0.05) in all regions.