In-vitro engineering of implantable human urinary tract tissue matrices.

Due to lack or destruction of functional tissues, congenital and acquired diseases of the genitourinary tract may need, for the engineering of these tissues, biomaterials as cell carriers. Cell cultures of human urothelial and bladder smooth muscle cells were established and growth of the latter, also under mechanical stimulation was analysed. Collagen and polyesterurethane foam scaffolds were evaluated for their aptitude as cell carriers. Scaffolds made of collagens, naturally occurring extracellular matrix proteins, are biocompatible and can induce tissue regeneration and are therefore apt for tissue engineering. The attachment of serum proteins to their surfaces does further improve these characteristics, mimicking an almost natural cell environment. We investigated the aptitude of equine collagen scaffolds (Tissue Fleece) modified by coating foetal bovine serum proteins, for human bladder smooth muscle cell attachment and growth. Furthermore we evaluated a highly porous biodegradable polyesterurethane foam (DegraPol), as scaffold for smooth muscle tissue engineering. These cell-polymer constructs were characterised by histology, scanning electron microscopy, immunohistochemistry and proliferation assays. Cell attachment and growth on collagen scaffolds improved when pre-coated with serum proteins. Cell penetration assessed by histology showed similar results on modified and native scaffolds. Further these cell-scaffold constructs were implanted in the dorsal subcutaneous space of athymic mice. In vivo studies showed the presence of the transplanted smooth muscle cells until day 3. Thereafter angiogenesis was induced and infiltration of mouse fibroblasts and polymorphonuclear cells was observed. Smooth muscle cells grown on DegraPol showed the same morphology as when grown on a control polystyrene surface. Positive immunostaining with anti-alpha smooth muscle actin indicated the preservation of the specific cell phenotype. Micrographs from scanning electron microscopy showed that the cells grew on the foam surface as well as inside the pores. The smooth muscle cells proliferated well on DegraPol, however, proliferation rate decreased due to apoptosis with time in culture. Although the above scaffolds provide an adequate milieu for cell attachment, their ability for cell penetration and growth is reduced. For this reason we are now evaluating a biodegradable poly (ethylene glycol) (PEG) hydrogel, which allows integration of cells within the matrix and also provides an excellent scaffold for the controlled incorporation of biological signals.