Tubular Constructs as Artificial Urinary Conduits.

PURPOSE: A readily available artificial urinary conduit might be substituted for autologous bowel in standard urinary diversions and minimize bowel associated complications. However, the use of large constructs remains challenging as host cellular ingrowth and/or vascularization is limited. We investigated large, reinforced, collagen based tubular constructs in a urinary diversion porcine model and compared subcutaneously pre-implanted constructs to cell seeded and basic constructs. MATERIALS AND METHODS: Reinforced tubular constructs were prepared from type I collagen and biodegradable Vicryl® meshes through standard freezing, lyophilization and cross-linking techniques. Artificial urinary conduits were created in 17 female Landrace pigs, including 7 with a basic untreated construct, 5 with a construct seeded with autologous urothelial and smooth muscle cells, and 5 with a free graft formed by subcutaneous pre-implantation of a basic construct. All pigs were evaluated after 1 month. RESULTS: The survival rate was 94%. At evaluation 1 basic and 1 cell seeded conduit were occluded. Urinary flow was maintained in all conduits created with pre-implanted constructs. Pre-implantation of the basic construct resulted in a vascularized tissue tube, which could be used as a free graft to create an artificial conduit. The outcome was favorable compared to that of the other conduits. Urinary drainage was better, hydroureteronephrosis was limited and tissue regeneration was improved. CONCLUSIONS: Subcutaneous pre-implantation of a basic reinforced tubular construct resulted in a vascularized autologous tube, which may potentially replace bowel in standard urinary diversions. To our knowledge we introduce a straightforward 2-step procedure to create artificial urinary conduits in a large animal model.

Fetal bladder wall regeneration with a collagen biomatrix and histological evaluation of bladder exstrophy in a fetal sheep model.

OBJECTIVES: To evaluate histological changes in an animal model for bladder exstrophy and fetal repair of the bladder defect with a molecular-defined dual-layer collagen biomatrix to induce fetal bladder wall regeneration. METHODS: In 12 fetal lambs the abdominal wall and bladder were opened by a midline incision at 79 days' gestation. In 6 of these lambs an uncorrected bladder exstrophy was created by suturing the edges of the opened bladder to the abdominal wall (group 1). The other 6 lambs served as a repair group, where a dual-layer collagen biomatrix was sutured into the bladder wall and the abdominal wall was closed (group 2). A caesarean section was performed at 140 days' gestation, followed by macroscopic and histological examination. RESULTS: Group 1 showed inflammatory and maturational changes in the mucosa, submucosa and detrusor muscle of all the bladders. In group 2, bladder regeneration was observed, with urothelial coverage, ingrowth of fibroblasts and smooth muscle cells, deposition of collagen, neovascularization and nerve fibre formation. This tissue replaced the collagen biomatrix. No structural changes of the bladder were seen in group 2. CONCLUSIONS: The animal model, as in group 1, for bladder exstrophy shows remarkable histological resemblance with the naturally occurring anomaly in humans. This model can be used to develop new methods to salvage or regenerate bladder tissue in bladder exstrophy patients. Fetal bladder wall regeneration with a collagen biomatrix is feasible in this model, resulting in renewed formation of urothelium, blood vessels, nerve fibres, ingrowth of smooth muscle cells and salvage of the native bladder.

Improving the cell distribution in collagen-coated poly-caprolactone knittings.

Adequate cellular in-growth into biomaterials is one of the fundamental requirements of scaffolds used in regenerative medicine. Type I collagen is the most commonly used material for soft tissue engineering, because it is nonimmunogenic and a highly porous network for cellular support can be produced. However, in general, adequate cell in-growth and cell seeding has been suboptimal. In this study we prepared collagen scaffolds of different collagen densities and investigated the cellular distribution. We also prepared a hybrid polymer-collagen scaffold to achieve an optimal cellular distribution as well as sufficient mechanical strength. Collagen scaffolds [ranging from 0.3% to 0.8% (w/v)] with and without a mechanically stable polymer knitting [poly-caprolactone (PCL)] were prepared. The porous structure of collagen scaffolds was characterized using scanning electron microscopy and hematoxylin-eosin staining. The mechanical strength of hybrid scaffolds (collagen with or without PCL) was determined using tensile strength analysis. Cellular in-growth and interconnectivity were evaluated using fluorescent bead distribution and human bladder smooth muscle cells and human urothelium seeding. The lower density collagen scaffolds showed remarkably deeper cellular penetration and by combining it with PCL knitting the tensile strength was enhanced. This study indicated that a hybrid scaffold prepared from 0.4% collagen strengthened with knitting achieved the best cellular distribution.