“…No adverse immune response was shown after ECM hydrogels were injected in the heart [55, 60, 75–81], fat [43, 45, 47, 50, 67], liver [57], brain [21, 22, 24] skeletal muscle [23, 63, 64, 83], tendon [26, 59, 84], spinal cord [82], lung [49], cartilage [70], or colon [51, 71], and these studies included both homologous and heterologous ECM hydrogels. The findings in vivo are consistent with in vitro studies that have shown the pepsin-digested ECM (“pre-gel”) promotes a regulatory (“M2-like”) macrophage activation state, which is associated with a constructive remodeling response in vivo [71, 90, 91]. For example, macrophages activated toward an M2-like phenotype with solubilized ECM promoted downstream effects such as stimulating the migration and myogenesis of skeletal muscle progenitor cells [90].…”