Long-term results of prosthetic ureteral replacement in minipigs

Construction of ureteral grafts by seeding urothelial cells and bone marrow mesenchymal stem cells into polycaprolactone-lecithin electrospun fibers

The aim of the present study was to investigated the construction of polycaprolactone-lecithin (PCL-L) electrospun fibers as a novel scaffold material for a tissue-engineered ureter. The effect of bone marrow mesenchymal stem cells (BM-MSCs) on the neovascularization of the scaffolds and the viability of planted urothelial cells (UCs) on PCL-L were also studied. UCs were obtained from New Zealand rabbit bladders, cultured and then seeded onto the lumen of the tubular scaffolds before being subcutaneously transplanted into the space of nude mice. The cultured UCs showed vacuolar degeneration after 7 days of transplantation and they gradually degraded thereafter. To facilitate the regeneration of the tissue-engineered ureter and the survival of UCs in the implant, MSCs were seeded into the tubular grafts by rolling up the nanofibrous membrane, followed by the seeding of UCs. This facilitated the survival of the UCs, which formed several cellular layers after 30 days. The mean microvessel density was significantly increased in tissues seeded with MSCs. Cell-tracking experiments revealed that the transplanted MSCs did not integrate directly into capillaries for angiogenesis. Our results demonstrated that the PCL-L electrospun fibrous scaffold has a high potential for a tissue-engineered ureter especially when seeded with BM-MSCs, which enhanced angiogenesis.

Constructing a Tissue-Engineered Ureter Using a Decellularized Matrix with Cultured Uroepithelial Cells and Bone Marrow-Derived Mononuclear Cells

This study investigated the efficacy of the ureteral decellularized matrix (UDM) as a scaffold material for a tissue-engineered ureter, and the effect of bone marrow-derived mononuclear cells (BM-MNC) on the neovascularization of the scaffold. Canine ureters were treated with deoxycholic acid to remove all cells. Uroepithelial cells (UEC) were obtained from canine bladders, cultured, and then seeded onto the inner surface of the UDM before transplantation into the subcutaneous space of nude mice or the omentum of nude rats. The cultured UECs began showing vacuolar degeneration 3 days after transplantation and gradually disappeared thereafter. To facilitate neovascularization in the implant, BM-MNCs were seeded around the UDM before transplantation. This facilitated the survival of the UECs, which formed three to five cellular layers after 14 days. The mean microvessel density was significantly increased in tissues seeded with BM-MNCs. However, cell-tracking experiments revealed that the increased number of capillaries in the experimental group was not due to the direct differentiation of transplanted endothelial progenitor cells. Our results demonstrate that the UDM is a useful scaffold for a tissue-engineered ureter, especially when seeded with BM-MNCs to enhance angiogenesis.

Canine ureteral replacement with long acellular matrix tube: is it clinically applicable?

PURPOSE

We evaluated the effectiveness of acellular matrix used as a tube for replacement of a relatively long segment of the canine ureter.

MATERIALS AND METHODS

Acellular matrix was obtained by excision of the whole ureter of donor dogs that were sacrificed and not included in the study group. Retrieved ureters were treated to have complete cell lysis, while maintaining the fiber framework. The study included 10 mongrel dogs in which a 3 cm segment was excised from 1 ureter and replaced by a tube of acellular matrix of the same length and width. The new tube was sutured proximal and distal by watertight interrupted sutures around a 5Fr Double-J stent (Medical Engineering Corp., New York, New York) that remained for 6 weeks. Excretory urography was done 1 and 2 weeks after stent removal and the dogs were then sacrificed. Before sacrifice the ureter was exposed and carefully examined, and the whole specimen was excised for histopathological examination.

RESULTS

All dogs survived surgery except 1, which died 1 week postoperatively of a malpositioned stent and urinary ascites. There was no clinically apparent postoperative complications during the presence or after the removal of the ureteral stents. One week after stent removal excretory urography showed ipsilateral mild to moderate hydroureteronephrosis in 3 dogs and no dye excretion in 6 with a normal contralateral kidney. One week later no dye excretion was detected in all except 1 dog, which showed more radiological deterioration. At the time of sacrifice there was moderate to marked hydroureteronephrosis above the level of the new tube in all dogs. Although the graft was intact in all subjects, marked shrinkage was observed. On ureteral calibration there was significant narrowing of the lumen up to complete occlusion. At 8 weeks histopathological examination showed extensive fibrosis.

CONCLUSIONS

An acellular matrix tube is not able to replace a 3 cm segment of the canine ureter.

Use of reconstructed small intestine submucosa for urinary tract replacement

We used reconstructed SIS (ReSIS), a photocrosslinked biomaterial, to create grafts in various shapes and sizes. Sheets of ReSIS were placed in 14 swine to repair bladder defects, and ReSIS tubes were placed in six swine to replace a segment of excised ureter. Histologic analysis of the bladder repair revealed transitional urothelial cells lining the ReSIS by 1 week. After 2 weeks, fibroblasts and mononuclear cells had infiltrated the ReSIS, neovascularization had occurred, and the urothelial lining was more complex, containing multiple cell layers. After 4 weeks, a definite submucosa was present and the ReSIS was starting to degrade. An initial muscular regeneration was demonstrated at 12 weeks. No foreign body reaction, calcification, or sedimentation was noted in any animal. The ureteral implants showed identical histologic changes, without obstruction or leakage of the replaced segment. The ReSIS allowed rapid urothelial regeneration, ingrowth of new blood vessels, and the orderly deposition and organization of new collagen. Our study demonstrates that the photocrosslinking technique used to create larger sheets and tubes of this biomaterial (ReSIS) does not detract from the positive attributes of the SIS and should improve its usefulness in accomplishing larger bladder augmentations and ureter replacements.

The prosthetic ureter

Ureteral replacement has always been a challenge. Two approaches have been explored: in situ augmentation or replacement and extra-anatomic passage of a conduit. An in-situ prosthetic ureter is basically a simple al. loplastic tube connected to the urinary tract by end-to-end sutures or by intubation and closure. Antireflux devices and peristaltic mechanisms are not necessary. Among the in-situ designs, only those composed of silicone and silicone rubber have performed at all well. Tissue engineering and acellular matrix grafts have produced impressive early results. Subcutaneous ureteral replacement with alloplasts, including a coaxial assembly of an inner silicone and outer expanded polytetrafluoroethylene tube, has produced good results. In the future, we are likely to see bioengineered neotissue combined with highly porous and infection-resistant alloplasts to create better and more functional neo-organs.