Background:Large-scale muscle tissue engineering remains a major challenge.An axial vascular pedicle and perfusion bioreactor are necessary for the development and maintenance of large-scale engineered muscle to ensure circulation within the construct.We aimed to develop a novel experimental model of a large-scale engineered muscle flap from an existing rat groin fat flap.Methods:A fat flap based on the superficial inferior epigastric vascular pedicle was excised from rats and placed into a perfusion bioreactor.The flaps were kept in the bioreactor for up to 7 weeks,and transdifferentiation of adipose to muscle tissue could have taken place.This system enabled myogenic-differentiation medium flow through the bioreactor at constant pH and oxygen concentration.Assessment of viability was performed by an immunofluorescence assay,histological staining,a calcein-based live/dead test,and through determination of RNA quantity and quality after 1,3,5,and 7 weeks.Results:Immunofluorescence staining showed that smooth muscle around vessels was still intact without signs of necrosis or atrophy.The visual assessment of viability by the calcein-based live/dead test revealed viability of the rat adipose tissue preserved in the bioreactor system with permanent perfusion.RNA samples from different experimental conditions were quantified by spectrophotometry,and intact bands of 18S and 28S rRNA were detected by gel electrophoresis,indicating that degradation of RNA was minimal.Conclusions:Flow perfusion maintains the long-term viability of a rat groin engineered muscle flap in vitro,and a large-scale vascularized muscle could be engineered in a perfusion bioreactor.