Acellular bladder matrix allografts in the regeneration of functional bladders: evaluation of large-segment (> 24 cm(2)) substitution in a porcine model

Objectives To evaluate the use of a large-segment (> 24 cm(2)) bladder subs titution with porcine bladder acellular matrix allograft (BAMA) in a large animal model. Materials and methods Bladders were harvested from pigs at the time of necr opsy and subjected to detergent and enzymatic extractions to render them ac ellular. The BAMA produced had the surgical handling and suture-retaining p roperties of normal bladder tissue. Six pigs had BAMA segments implanted un der general anaesthesia, through a low midline abdominal incision and after partial cystectomy. The defect was repaired with a BAMA patch (mean size 4 3.88 cm(2), range 12-72), with no urinary diversion. Two animals each were then killed at 9, 16 and 30 days and the bladders explanted. The native bla dder and BAMA patch were analysed morphometrically to evaluate cellular re- population and matrix re-organization. Results All animals survived surgery; there were no urinary leaks and no st ones detected in any of the bladders. At 9 days there was a diffuse infiltr ation with acute inflammatory cells, but no areas of necrosis. There were i solated areas of smooth muscle cell (SMC) infiltration of the BAMA. At 16 d ays the luminal surface was lined with a single layer of urothelium, there was stromal infiltration with disorganized SMC and angiogenesis, with matur e vessels in the BAMA patch. At 30 days the urothelium was multilayered wit h organizing groups of SMCs and angiogenesis. The highest cell density was at the periphery of the repopulated BAMA patch, decreasing towards the cent re. Conclusions The implantation of large patches of BAMA is technically feasib le and may prove to be a viable surgical alternative to bladder augmentatio n with intestinal segments. The advantages of BAMA include the potential fo r complete and functional regeneration of a bladder substitute. This model provides a tool with which to obtain a better understanding of the cellular and molecular aspects of matrix re-population.