INTRODUCTION: Revascularization of the engineered biomaterial with host vasculature is important for successful implantation.This study aimed to develop pre-vascularized flap bioscaffold to improve the vascularization and survival of engineered tissue after transplantation [1,2].METHODS: A perfusion-decellularization protocol was developed to remove cell components from pig musculofascial flap(DMF)and rat skin/adipose flap(DSAF)[3].hASCs were integrated with DMF and DSAF to test their biocompatibility.DMF and DSAF were implanted in Fisher rats to evaluate implant-host reaction.Re-cellularized and pre-vascularized DMF and DSAF with hASCs and HUVECs were then transplanted as free flap in a nude rat model.RESULTS: H&E,DAPI staining and DNA quantification confirmed cell removal in DMF and DSAF.DMF and DSAF maintained natural extracellular matrix structure with 3D nanofibrous features(SEM imagining),strong mechanical properties,biochemical compositions(collagen+,laminin+,MHC1-e.g.)(IHC staining and Mass Spectrometry),and microcirculatory network with the dominant vascular pedicle structure.DMF and DSAF provide a niche for hASCs and HUVECs proliferation.DMF and DSAF caused little foreign body response in vivo(few CD4+/CD8+; M1-/M2+).Re-cellularized flap constructs were successfully transplanted by microsurgery anastomosis pedicle with recipient femoral artery.Implanted engineered flap was fully survived and remodeled as indicated by pedicle patency and soft tissue formation at 3 months.CONCLUSIONS: Pre-vascularized decellularized flap matrix provides novel promising composite bioscaffold for large-scale soft tissue engineering and reconstruction.