Bladder Regeneration Using a Smart Acellular Collagen Scaffold with Growth Factors VEGF, FGF2 and HB-EGF.

Tissue engineering may become an alternative to current bladder augmentation techniques. Large scaffolds are needed for clinically significant augmentation, but can result in fibrosis and graft shrinkage. The purpose of this study was to investigate whether smart acellular collagen-heparin scaffolds with growth factors (GFs) VEGF, FGF2, and HB-EGF enhance bladder tissue regeneration and bladder capacity in a large animal model of diseased bladder. Scaffolds of bovine type I collagen with heparin and VEGF, FGF2, and HB-EGF measuring 3.2 cm in diameter were prepared. In 23 fetal sheep, a bladder exstrophy was surgically created at 79 days of gestation. One week after birth (at full term), the bladder was reconstructed by primary closure (PC group) or using a collagen-heparin scaffold with GFs (COLGF group) and compared to a historical group reconstructed with a collagen scaffold without GFs (COL group). Functional (video urodynamics) and histological evaluation was performed 1 and 6 months after bladder repair. The overall survival rate was 57%. Cystograms were normal in all animals, except for low-grade reflux in all groups. Urodynamics showed no statistically significant differences in bladder capacity and compliance between groups. Histological evaluation at 1 month revealed increased urothelium formation, improved angiogenesis, and enhanced ingrowth of smooth muscle cells (SMCs) in the COLGF group compared to the COL group. At 6 months, improved SMC ingrowth was found in the COLGF group compared to the COL group; both scaffold groups showed normal urothelial lining and standard extracellular matrix development. Bladder regeneration using a collagen-heparin scaffold with VEGF, FGF2, and HB-EGF improved bladder tissue regeneration in a large animal model of diseased bladder. Larger GF-loaded constructs need to be tested to reach clinically significant augmentation.

Tissue engineering of diseased bladder using a collagen scaffold in a bladder exstrophy model.

OBJECTIVE: To compare the regenerative capacity of diseased bladder in a large animal model of bladder exstrophy with regeneration in healthy bladder using a highly porous collagen scaffold. MATERIALS AND METHODS: Highly porous bovine type I collagen scaffolds with a diameter of 32 mm were prepared. In 12 fetal sheep a bladder exstrophy was surgically created at 79 days' gestation. Lambs were born at full term (140 days' gestation). After 1 week the bladder lesion was reconstructed and augmented with a collagen scaffold (group 1). In nine normal newborn lambs the bladder was augmented with a collagen scaffold 1 week after birth (group 2). Functional (video-urodynamics) and histological evaluation was performed at 1 and 6 months after surgery. RESULTS: The survival rate was 58% in group 1 and 100% in group 2. Cystograms were normal in all lambs, besides low-grade reflux in both groups. Urodynamics showed comparable capacity between both groups and a trend to lower compliance in group 1. Histological evaluation at 1 month revealed a non-confluent urothelial layer, an immature submucosa, and initial ingrowth of smooth muscle cells. At 6 months both groups showed normal urothelial lining, standard extracellular matrix development, and smooth muscle cell ingrowth. CONCLUSIONS: Bladder tissue regeneration with a collagen scaffold in a diseased bladder model and in healthy bladder resulted in comparable functional and histological outcome, with a good quality of regenerated tissue involving all tissue layers. Improvements may still be needed for larger augmentations or more severely diseased bladders.

Prenatal coverage of experimental gastroschisis with a collagen scaffold to protect the bowel.

BACKGROUND/PURPOSE: In fetuses with gastroschisis, toxic products in the amniotic fluid and constriction at the defect of the abdominal wall are considered causative of damage to the eviscerated bowel. The aim of this study was to cover the eviscerated bowel in gastroschisis with a collagen scaffold to protect the bowel and induce cell growth into the scaffold, which could lead to skin or abdominal wall formation replacing the scaffold. METHODS: In 12 fetal lambs gastroschisis was surgically created at 79 days gestation. A dual-layer type I collagen scaffold was sutured into the skin of the abdominal wall around the defect covering the eviscerated bowel. Lambs were examined after caesarean section at 140 days' gestation. RESULTS: Survival was 67%. In 7 of 8 surviving lambs the bowel was found to be covered after birth. One scaffold had ruptured. The bowel was found repositioned in the abdominal cavity in 5 lambs. In 2 lambs it was still partially outside. Only minor adherence of bowel loops and no fibrous peel formation were seen. Connective tissue and skin tissue replaced the scaffold. CONCLUSIONS: Prenatal coverage of the bowel in experimental gastroschisis with a collagen scaffold is feasible in fetal lambs, significantly diminished damage to the bowel wall, and skin and connective tissue replaced the scaffold. This technique may be promising in the care of fetuses with this congenital anomaly.

Fetal abdominal wall repair with a collagen biomatrix in an experimental sheep model for gastroschisis.

We evaluated the regeneration of the abdominal wall using a dual-layer collagen biomatrix, and the protective effect on the bowel of fetal abdominal wall repair in a fetal sheep model for gastroschisis. In 14 fetal lambs, the abdominal wall was opened at 79 days' gestation, creating a gastroschisis. In group 1, the gastroschisis was left uncovered. In group 2, the bowel was repositioned, and the defect was closed by suturing a collagen biomatrix into the abdominal wall. A cesarean section was performed at 140 days' gestation, and macroscopic and histological evaluation was performed. In the five lambs with a gastroschisis, the eviscerated part of the bowel was coalescent, showed extensive adhesions, and was covered by fibrous peel. In group 2, the abdominal wall had closed, with a firm connection to the native abdominal wall. The biomatrix was largely degraded and replaced by connective tissue with collagen and fibroblasts, neovascularisation, and scattered muscle cells. Minor or no adhesions of the bowel and no peel formation were observed. Abdominal wall tissue replacement using a collagen biomatrix was feasible in fetal lambs, resulting in a closed abdominal wall at birth. Immediate closure of the gastroschisis strongly diminished or prevented bowel adhesions and peel formation.

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.