Tissue engineering in pediatric urology - a critical appraisal

Pre-vascularisation of the acellular bladder matrix using the omentum in a porcine model prior for bladder reconstruction-a step towards clinical application?

AIM

Research studies with porcine acellular bladder matrix (PABM) showed integration of only small sized stamps in recipient bladders, however for clinical use in bladder augmentation significantly larger patches are needed. We hypothesised pre-vascularisation with omentum may be a step towards clinical translation.

METHOD

Eight domestic pigs were operated three times 8-10 weeks apart: 1-Implantation; PABM with recorded dimensions were sutured around a tissue expanding device, wrapped in omentum and sutured to the anterior abdominal wall. 2-Augmentation; hemi-cystectomy and bladder augmentation was performed with the pre-vascularized PABM using non-absorbable suture 3-Sacrifice; The dimensions of the PABMs were measured macroscopically, the in-vivo microcirculation of the PABMs were assessed using laser speckle contrast imaging. HE staining, uroplakin 3 and CK7 immunohistochemistry was performed.

RESULTS

In seven animals, the bladder augmentation was successful without complication. One animal was lost in bowel obstruction and in two animals enteric fistula was found after the first intervention. The rectangular shape of the initial tissue expander was subsequently changed. All the seven patches were strong, compliant and had integrated with the surrounding native bladder and were 83% (48-100%) of the original patch size. Laser speckle contrast imaging already showed microcirculation at the patch edges at augmentation and this further improved towards the centre of the patches by the end of the study. Histology demonstrated acute inflammatory response with fibroblast infiltration after implantation and full coverage by urothelium was seen with positive staining for CK7 antibodies.

CONCLUSION

Pre-vascularization of PABM in the omentum of healthy porcine models allows larger PABM patches to integrate this may be a step towards clinical application.

Current evidence regarding alternative techniques for enterocystoplasty using regenerative medicine methods: a systematic review

Enterocystoplasty is the most commonly used treatment for bladder reconstruction. However, it has some major complications. In this study, we systematically reviewed the alternative techniques for enterocystoplasty using different scaffolds. A comprehensive search was conducted in PubMed, Embase, and Cochrane Library, and a total of 10 studies were included in this study. Five different scaffolds were evaluated, including small intestinal submucosa (SIS), biodegradable scaffolds seeded with autologous bladder muscle and urothelial cells, dura mater, human cadaveric bladder acellular matrix graft, and bovine pericardium. The overall results revealed that bladder reconstruction using regenerative medicine is an excellent alternative method to enterocystoplasty regarding the improvement of bladder capacity, bladder compliance, and maximum detrusor pressure; however, more large-scale studies are required.

The Healing Effect of Biodegradable Scaffolds Treated with Bone-Marrow Obtained Mesenchymal Stem Cells on Major Tendon Damage in the Dog as a Model

The present study aimed to evaluate the implantation of decellularized small intestinal submucosa- extracellular matrix )SIS-ECM( seeded with bone marrow mesenchymal stem cells (BM-MSCs) to repair full-thickness Achilles tendon defect. For this purpose, 20 healthy adult stray dogs aged 8-12 months old (15±3 kg of weight) were enrolled in this study under an aseptic environment and general anesthesia. A 1.5 cm-long segment-based resection was performed in the mid-substance of the Achilles tendon in the control group (n=10) that did not receive treatment. While, in the experimental group (n=10), regarding the defect of the tendon, the stumps were bridged with decellularized SIS seeded with BM-MSCs (5×106) cells implanted. Afterward, the stumps of the tendon were sutured using the modified Kessler technique (4-0) polypropylene thread. The biomechanical observations of the tendon defect showed an increase in the tensile strength in the experimental group, compared to the control animals. It should be mentioned that this difference was significant (P≤0.05). Histopathological observations of biopsies harvested after the 4th, 8th, and 12th weeks revealed that the implanted graft had seeded with MSCs enhanced high-quality cellular infiltration and the host tissue healing was improved. Similar to the normal tendon, a dense organized collagenous tissue with high cellularity and vascularity was observed due to the presence of the remodeled ECM. However, the arrangement of collagen-fiber-derived connective tissue appeared to be more dominant than that in the experimental group, with less adhesion in the 12th week post-treatment. These findings suggest that the BM-MSCs inoculated with SIS can be employed to repair a damaged Achilles tendon due to the fact that this combination enhances the regeneration of the affected tendon.

Tissue Engineering and Regenerative Medicine in Pediatric Urology: Urethral and Urinary Bladder Reconstruction

In the case of pediatric urology there are several congenital conditions, such as hypospadias and neurogenic bladder, which affect, respectively, the urethra and the urinary bladder. In fact, the gold standard consists of a urethroplasty procedure in the case of urethral malformations and enterocystoplasty in the case of urinary bladder disorders. However, both surgical procedures are associated with severe complications, such as fistulas, urethral strictures, and dehiscence of the repair or recurrence of chordee in the case of urethroplasty, and metabolic disturbances, stone formation, urine leakage, and chronic infections in the case of enterocystoplasty. With the aim of overcoming the issue related to the lack of sufficient and appropriate autologous tissue, increasing attention has been focused on tissue engineering. In this review, both the urethral and the urinary bladder reconstruction strategies were summarized, focusing on pediatric applications and evaluating all the biomaterials tested in both animal models and patients. Particular attention was paid to the capability for tissue regeneration in dependence on the eventual presence of seeded cell and growth factor combinations in several types of scaffolds. Moreover, the main critical features needed for urinary tissue engineering have been highlighted and specifically focused on for pediatric application.