Rodent Model of Masseter Volumetric Muscle Loss for Studying Bioengineering Materials

Craniofacial volumetric muscle loss (VML) injuries can occur as a result of severe trauma, surgical excision, inflammation, and congenital or other acquired conditions. Treatment of craniofacial VML involves surgical, functional muscle transfer. However, these procedures are unable to restore normal function, sensation, or expression, and more commonly, these conditions go untreated. Very little research has been conducted on skeletal muscle regeneration in animal models of craniofacial VML. This manuscript describes a rat model for the study of craniofacial VML injury and a protocol for the histological evaluation of biomaterials in the treatment of these injuries. Liquid hydrogel and freeze-dried scaffolds are applied at the time of surgical VML creation, and masseters are excised at terminal time points up to 12 weeks with high retention rates and negligible complications. Hematoxylin and eosin (HE), Masson's Trichrome, and immunohistochemical analysis are used to evaluate parameters of skeletal muscle regeneration as well as biocompatibility and immunomodulation. While we demonstrate the study of a hyaluronic-acid-based hydrogel, this model provides a means for evaluating subsequent iterations of materials in VML injuries.