[Tissue engineering in urology. Basic principles and application]

“UroMaix” Scaffolds: Novel Collagen Matrices for Application in Tissue Engineering of the Urinary Tract

Reconstruction of bladder and ureter tissue is indicated in cases of injury, stenosis, infection or tumor. Substitution by ileum, colon or pure synthetic polymers generates a variety of complications. Biohybrid tissue mimicking structural and functional attributes of the multilayered wall architecture of the urinary conduit may be the solution to current problems.

This study reports on porcine urinary tract cells isolated and placed on UroMaix matrices with different degrees of cross-linking produced from highly purified type I collagen from medically approved porcine tissue. A patented procedure revealed membrane structures composed of a dense fibrous side and an open fibrous side. These scaffolds with the porcine urinary tract cells were incubated in a batch culture system for up to 14 days. Cell growth and topographical orientation were examined.

Urothelial cells showed maximum attachment and a significant increase of living cells on the dense fiber layer of UroMaix-1. No attachment of urothelial cells occurred on the other prototypes. Smooth muscle cells showed similar behavior within the open fiber layer of all UroMaix matrices. Both urothelial and smooth muscle cells retained their phenotypes as demonstrated by the immunostaining of epithelial cytokeratin 18 and the smooth muscle myosin heavy chain respectively. Thus we could show that UroMaix scaffolds support the attachment and proliferation of urinary tract cells. The elastomeric properties of the collagenous matrices promise attractive applications in the tissue engineering of the urinary tract with its high mechanical demands.

What's in the Pipeline about Bladder Reconstructive Surgery? Some Remarks on the State of the Art

The fusion of engineering with cell biology and advances in biomaterials may lead to de novo construction of implantable organs. Engineering of neobladder from autologous urothelial and smooth muscle cells cultured on biocompatible, either synthetic or naturally-derived substrates, is now feasible in preclinical studies and may have clinical applicability in the near future. The development of a bioartificial bladder would warrant the prevention of both the metabolic and neoplastic shortcomings of the intestinal neobladder. Two tissue-engineering techniques for bladder reconstruction have been tested on animals: 1) the in vivo technique involves the use of naturally-derived biomaterials for functional native bladder regeneration 2) the in vitro technique involves the establishment of autologous urothelial and smooth muscle cell culture from the host's urinary tract, after which the cells are seeded on the biodegradable matrix-scaffold to create a composite graft that is implanted into the same host for complete histotectonic regeneration. Waiting for the creation of a complete tissue-engineered bladder with a trigone-shaped base, we suggest, in surgical oncology after radical cystectomy, the realization of conduit or continent pouch using tissue-engineered material.

Tissue engineered venous matrices for potential applications in the urogenital tract

Tissue engineering is lacking inexpensive, easily applicable techniques for tissue replacement. We investigated the potential use of native veins for tissue-engineering applications in the urological field. Forty-eight porcine veins, half seeded with urothelial cells and half unseeded, were kept in vitro for 7 days. Four seeded and four unseeded scaffolds were analyzed after 3 and 7 days. The remaining 32 veins were implanted subcutaneously into 16 athymic mice. Four athymic mice were sacrificed after 2, 4, 8, and 12 weeks. Histochemistry, immunohistochemistry (anti-pancytokeratin AE1/AE3, anti-desmin), western blot analyses (CD31), and scanning electron microscopy were performed in the retrieved specimens. The histochemistry of the seeded matrices showed the presence of urothelial cells in vitro and in vivo. After 12 weeks, a multilayer of urothelial cells was present in the hemotoxylin and eosin staining, positive for anti-pancytokeratin AE1/AE3. The western blot analyses showed vascularization of the veins in vivo. The results of scanning electron microscopy revealed a cellular layer on the veins. Native venous matrices may be used as tissue-engineered constructs for reconstructing the urinary tract. The clinical relevance of this approach must be proven in a large-animal model.

Biologische vaskularisierte Matrix (BioVaM)

A new technique is presented to harvest an acellular matrix from a porcine small bowel segment preserving the mesenteric arterial and venous pedicles. Reseeding of this biological vascularized matrix (BioVaM) with functional cells, i.e. smooth muscle and urothelial cells isolated from the urinary tract, and resurfacing of its vascular structures with endothelial precursor cells results in a vascularized tissue engineered graft for reconstruction and augmentation of the urinary bladder. First promising short term implantation experiments using a porcine model for the evaluation of early graft perfusion after vascular anastomosis are presented.