Gracilis muscle flap with a tissue-engineered lining for experimental bladder wall reconstruction

Objective To assess a pedicled gracilis muscle flap pre-laminated with autologous, in vitro-expanded urothelial cells to reconstruct an entire supratrigonal bladder-wall defect in rats. Materials and methods A gracilis muscle flap was harvested from 36 male Wistar rats, transposed into the abdomen and wrapped around a silicon-block space holder. Urothelial cells were harvested and expanded ex vivo. Cells were then suspended in fibrin glue and seeded into the gracilis muscle pocket. One week later this pre-laminated flap was transposed into a surgically created supratrigonal bladder-wall defect. All animals underwent such a pre-laminated gracilis flap bladder reconstruction and were categorized into three experimental groups. All surviving animals with urothelial-culture pre-laminated gracilis flap bladder reconstruction were killed 12 weeks (group 1) later. Control rats had gracilis flaps with no cell seeding and treated only with fibrin glue (group 2) or a standard culture medium (group 3) before reconstruction. Results Specimens stained with haematoxylin and eosin, and a specific immunohistochemical staining (AE1 and AE3-anti-cytokeratin monoclonal antibody stain) showed a continuous, multilayered functioning urothelial lining along the transposed pre-laminated gracilis flap in group 1. All animals in group 1 with an intact urothelial lining on the gracilis muscle survived, in contrast to most animals in groups 2 and 3, where eight and all 12 animals died, respectively. The surviving four animals in group 2 had no detectable urothelial lining. Conclusion Successful urinary reconstruction requires a contractile neo-reservoir resistant to resorption over time and a stable, protective urothelial lining. A gracilis muscle flap can be seeded with autologous cultured urothelial cells suspended in fibrin glue. This pre-laminated flap can be safely transposed on its pedicle and be successfully integrated into the remaining bladder wall, with a urothelial lining and the potential to contract. Further studies in larger animals, with a urodynamic assessment, are warranted to determine if this type of bladder-wall replacement technique is suitable for urinary reconstruction in humans.