REGENERATION OF FUNCTIONAL BLADDER SUBSTITUTES USING LARGE SEGMENT ACELLULAR MATRIX ALLOGRAFTS IN A PORCINE MODEL

Human Bronchial Epithelial Cell Growth on Homologous Versus Heterologous Tissue Extracellular Matrix

BACKGROUND

Extracellular matrix (ECM) bioscaffolds produced by decellularization of source tissue have been effectively used for numerous clinical applications. However, decellularized tracheal constructs have been unsuccessful due to the immediate requirement of a functional airway epithelium on surgical implantation. ECM can be solubilized to form hydrogels that have been shown to support growth of many different cell types. The purpose of the present study is to compare the ability of airway epithelial cells to attach, form a confluent monolayer, and differentiate on homologous (trachea) and heterologous (urinary bladder) ECM substrates for potential application in full tracheal replacement.

MATERIALS AND METHODS

Porcine tracheas and urinary bladders were decellularized. Human bronchial epithelial cells (HBECs) were cultured under differentiation conditions on acellular tracheal ECM and urinary bladder matrix (UBM) bioscaffolds and hydrogels and were assessed by histology and immunolabeling for markers of ciliation, goblet cell formation, and basement membrane deposition.

RESULTS

Both trachea and urinary bladder tissues were successfully decellularized. HBEC formed a confluent layer on both trachea and UBM scaffolds and on hydrogels created from these bioscaffolds. Cells grown on tracheal and UBM hydrogels, but not on bioscaffolds, showed positive-acetylated tubulin staining and the presence of mucus-producing goblet cells. Collagen IV immunolabeling showed basement membrane deposition by these cells on the surface of the hydrogels.

CONCLUSIONS

ECM hydrogels supported growth and differentiation of HBEC better than decellularized ECM bioscaffolds and show potential utility as substrates for promotion of a mature respiratory epithelium for regenerative medicine applications in the trachea.

Extracellular Matrix-Based Biomaterials and Their Influence Upon Cell Behavior

Biologic scaffold materials composed of allogeneic or xenogeneic extracellular matrix (ECM) are commonly used for the repair and remodeling of injured tissue. The clinical outcomes associated with implantation of ECM-based materials range from unacceptable to excellent. The variable clinical results are largely due to differences in the preparation of the material, including characteristics of the source tissue, the method and efficacy of decellularization, and post-decellularization processing steps. The mechanisms by which ECM scaffolds promote constructive tissue remodeling include mechanical support, degradation and release of bioactive molecules, recruitment and differentiation of endogenous stem/progenitor cells, and modulation of the immune response toward an anti-inflammatory phenotype. The methods of ECM preparation and the impact of these methods on the quality of the final product are described herein. Examples of favorable cellular responses of immune and stem cells associated with constructive tissue remodeling of ECM bioscaffolds are described.

Injectable Allograft Adipose Matrix Supports Adipogenic Tissue Remodeling in the Nude Mouse and Human

Supplemental Digital Content is available in the text.

Background:

Adipose tissue reaches cellular stasis after puberty, leaving adipocytes unable to significantly expand or renew under normal physiologic conditions. This is problematic in progressive lipodystrophies, in instances of scarring, and in soft-tissue damage resulting from lumpectomy and traumatic deformities, because adipose tissue will not self-renew once damaged. This yields significant clinical necessity for an off-the-shelf de novo soft-tissue replacement mechanism.

Methods:

A process comprising separate steps of removing lipid and cellular materials from adipose tissue has been developed, creating an ambient temperature-stable allograft adipose matrix. Growth factors and matrix proteins relevant to angiogenesis and adipogenesis were identified by enzyme-linked immunosorbent assay and immunohistochemistry, and subcutaneous soft-tissue integration of the allograft adipose matrix was investigated in vivo in both the athymic mouse and the dorsum of the human wrist.

Results:

Allograft adipose matrix maintained structural components and endogenous growth factors. In vitro, adipose-derived stem cells cultured on allograft adipose matrix underwent adipogenesis in the absence of media-based cues. In vivo, animal modeling showed vasculature formation followed by perilipin A–positive tissue segments. Allograft adipose matrix maintained soft-tissue volume in the dorsal wrist in a 4-month investigation with no severe adverse events, becoming palpably consistent with subcutaneous adipose.

Conclusions:

Subcutaneous implantation of allograft adipose matrix laden with retained angiogenic and adipogenic factors served as an inductive scaffold for sustaining adipogenesis. Tissue incorporation assessed histologically from both the subcutaneous injection site of the athymic nude mouse over 6 months and human dorsal wrist presented adipocyte morphology residing within the injected scaffold.

Bioengineering Approaches for Bladder Regeneration

Current clinical strategies for bladder reconstruction or substitution are associated to serious problems. Therefore, new alternative approaches are becoming more and more necessary. The purpose of this work is to review the state of the art of the current bioengineering advances and obstacles reported in bladder regeneration. Tissue bladder engineering requires an ideal engineered bladder scaffold composed of a biocompatible material suitable to sustain the mechanical forces necessary for bladder filling and emptying. In addition, an engineered bladder needs to reconstruct a compliant muscular wall and a highly specialized urothelium, well-orchestrated under control of autonomic and sensory innervations. Bioreactors play a very important role allowing cell growth and specialization into a tissue-engineered vascular construct within a physiological environment. Bioprinting technology is rapidly progressing, achieving the generation of custom-made structural supports using an increasing number of different polymers as ink with a high capacity of reproducibility. Although many promising results have been achieved, few of them have been tested with clinical success. This lack of satisfactory applications is a good reason to discourage researchers in this field and explains, somehow, the limited high-impact scientific production in this area during the last decade, emphasizing that still much more progress is required before bioengineered bladders become a commonplace in the clinical setting.

Autologous granulation tissue tubes for replacement of urethral defects: An experimental study in male rabbits

INTRODUCTION

Tubularized urethroplasty is commonly performed in clinical practice using genital skin flaps, bladder mucosa, and buccal mucosa. However, the long-term effects are not satisfying, and donor site morbidities remain a problem. Besides, those grafts are unavailable with malignant conditions of the urinary tract, a history of lichen sclerosis, or oral disease.

OBJECTIVE

An autologous granulation tissue tube of any required length and diameter can be produced by implanting foreign objects subcutaneously (Summary Fig.). The current study aimed to investigate to what extent of length this fully autologous tissue could be used for tubularized urethroplasty, satisfying urethral patency and tissue regeneration, in male rabbits.

STUDY DESIGN

Twenty-seven New Zealand male rabbits were randomly divided into three groups. Silastic tubes were implanted subcutaneously in Group 1 and Group 2. By 2 weeks the granulation tissue encapsulating the tubes was harvested. In Group 1, pendulous urethral segments of 1 cm were excised, and urethroplasty was performed with the granulation tissue tube in an end-to-end fashion. In Group 2, a pendulous urethral segment of 1.5 cm was replaced with the tissue tube. In Group 3, a pendulous urethral defect of 1 cm was repaired by re-anastomosis as control. Serial urethrograms were performed at 1, 2 and 6 months postoperatively. Meanwhile, the neo-urethra were harvested and analyzed grossly and histologically.

RESULTS

The urethrograms showed that all animals in Group 1 maintained a wide urethral caliber. In contrast, animals in Group 2 and Group 3 developed progressive strictures. Histologically, an intact urothelium with one to two cell layers lined the graft by 1 month, which was surrounded by increasing organized smooth muscle in Group 1. By 6 months, the grafts were completely integrated into native urethra. Nevertheless, extensive fibrosis occurred in Group 2 and Group 3.

DISCUSSION

The tissue successfully maintained patency and guided urethral regeneration across a distance of 1 cm. As an epithelium-free graft, the tissue showed better results than acellular matrix for tubularized urethroplasty compared with previous studies. Nevertheless, several limitations existed: (1) the urethral defect was created in healthy urethra, which could not fully simulate the clinical situation; (2) as a small animal model, rabbit was less informative for clinical problems; (3) the tissue was inadequate for long segmental urethral replacement. Further study is needed before the procedure is used clinically.

CONCLUSION

An autologous granulation tissue tube grown subcutaneously could be successfully used to repair urethral defects of 1 cm in male rabbits.

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.

Histological Evaluation of Decellularized Skeletal Muscle Tissue Using Two Different Decellularization Agents

The aim of the present study was to determine effect of two decellularized agents, sodium dodecyl sulphate (SDS) and Triton X-100, to the skeletal muscle tissue. Final scaffold was evaluated by several histological techniques to analyse preservation of essential structures including collagen and elastic fibres, basement membranes, glycosaminoglycans and also to confirm elimination of nuclear and cytoplasmic components which are redundant in effectively prepared decellularized scaffolds. Comparison of tissue scaffolds processed with different detergents proved that SDS is superior to Triton X-100 as it can effectively decellularize muscle tissue.

Two differentially structured collagen scaffolds for potential urinary bladder augmentation: proof of concept study in a Göttingen minipig model

Background

The repair of urinary bladder tissue is a necessity for tissue loss due to cancer, trauma, or congenital abnormalities. Use of intestinal tissue is still the gold standard in the urological clinic, which leads to new problems and dysfunctions like mucus production, stone formation, and finally malignancies. Therefore, the use of artificial, biologically derived materials is a promising step towards the augmentation of this specialised tissue. The aim of this study was to investigate potential bladder wall repair by two collagen scaffold prototypes, OptiMaix 2D and 3D, naïve and seeded with autologous vesical cells, as potential bladder wall substitute material in a large animal model.

Methods

Six Göttingen minipigs underwent cystoplastic surgery for tissue biopsy and cell isolation followed by implantation of unseeded scaffolds. Six weeks after the first operation, scaffolds seeded with the tissue cultured autologous urothelial and detrusor smooth muscle cells were implanted into the bladder together with additional unseeded scaffolds for comparison. Cystography and bladder ultrasound were performed to demonstrate structural integrity and as leakage test of the implantation sites. Eighteen, 22, and 32 weeks after the first operation, two minipigs respectively were sacrificed and the urinary tract was examined via different (immunohistochemical) staining procedures and the usage of two-photon laser scanning microscopy.

Results

Both collagen scaffold prototypes in vivo had good ingrowth capacity into the bladder wall including a quick lining with urothelial cells. The ingrowth of detrusor muscle tissue, along with the degradation of the scaffolds, could also be observed throughout the study period.

Conclusions

We could show that the investigated collagen scaffolds OptiMaix 2D and 3D are a potential material for bladder wall substitution. The material has good biocompatible properties, shows a good cell growth of autologous cells in vitro, and a good integration into the present bladder tissue in vivo.

Use of Scaffolding Tissue Biografts To Bolster Vesicourethral Anastomosis During Salvage Robot-assisted Prostatectomy Reduces Leak Rates and Catheter Times

BACKGROUND

One of the key factors contributing to morbidity associated with salvage radical prostatectomy is a significant vesicourethral anastomosis (VUA) disruption or postoperative tissue dehiscence in the region of the distal bladder neck that causes a large prolonged urinary leak, perineal pain, and delayed catheter removal.

OBJECTIVE

To describe our surgical technique using a urinary bladder extracellular matrix (UB-ECM) scaffold incorporated into the base of the VUA and the distal bladder neck during salvage robot-assisted radical prostatectomy (sRARP) and to assess outcomes and safety.

DESIGN, SETTING, AND PARTICIPANTS

From March to July 2015, 15 patients underwent sRARP performed after primary therapy failure by a single surgeon. Two other groups were identified via analysis of propensity score matching. Group 2 (n=45) underwent sRARP with standard suturing without use of the graft. Group 3 (control group; n=45) underwent primary RARP with no graft placement. These two groups were compared group 1 (n=15), in which patients underwent sRARP and received the scaffold in a 1:3:3 match.

SURGICAL PROCEDURE

sRARP with use of a UB-ECM scaffold in the posterior aspect of the VUA and distal bladder neck.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Clinical data were prospectively collected in a customized database and retrospectively analyzed. Analysis of variance and Student's t-test were used to test the equality of means for continuous variables, while the χ² test was used to test categorical variables.

RESULTS AND LIMITATIONS

There were no anastomotic leaks in the control group, with an average catheter time of 6.3 d (5-7 d). However, a clinically significant VUA/bladder neck disruption was observed in 16 patients (35.5%) in group 2, with a median catheterization time of 17.4 d (9-47 d), while in group 1 only one patient (6.66%) had a significant anastomotic leak on cystography (p=0.045), with median catheterization time of 11.2 d (10-52 d) for this group (p<0.05).

CONCLUSIONS

Incorporation of a UB-ECM scaffold into the base of the VUA and distal bladder neck should be considered as an option to decrease morbidity associated with sRARP since it decreased the rate of VUA disruption, enhanced healing, and reduced catheterization time. This technique could be a valuable tool for all surgeons performing sRARP.

PATIENT SUMMARY

We investigated the use of a scaffolding tissue graft when connecting the urethra to the bladder during salvage robot-assisted laparoscopic prostatectomy. This technique was found to be effective and safe.

Silk Fibroin Scaffolds for Urologic Tissue Engineering

Urologic tissue engineering efforts have been largely focused on bladder and urethral defect repair. The current surgical gold standard for treatment of poorly compliant pathological bladders and severe urethral stricture disease is enterocystoplasty and onlay urethroplasty with autologous tissue, respectively. The complications associated with autologous tissue use and harvesting have led to efforts to develop tissue-engineered alternatives. Natural and synthetic materials have been used with varying degrees of success, but none has proved consistently reliable for urologic tissue defect repair in humans. Silk fibroin (SF) scaffolds have been tested in bladder and urethral repair because of their favorable biomechanical properties including structural strength, elasticity, biodegradability, and biocompatibility. SF scaffolds have been used in multiple animal models and have demonstrated robust regeneration of smooth muscle and urothelium. The pre-clinical data involving SF scaffolds in urologic defect repair are encouraging and suggest that they hold potential for future clinical use.

Aerosol transfer of bladder urothelial and smooth muscle cells onto demucosalized colonic segments for bladder augmentation: in vivo, long term, and functional pilot study

BACKGROUND

Bladder augmentation technique has changed over the years and the current practice has significant adverse health effects and long-term sequelae. Previously, we reported a novel cell transfer technology for covering demucosalized colonic segments with bladder urothelium and smooth muscle cells through an aerosol spraying of these cells and a fibrin glue mixture.

OBJECTIVE

To determine the long-term durability and functional characteristics of demucosalized segments of colon repopulated with urothelial cells in the bladder of swine for use in augmentation cystoplasty.

STUDY DESIGN

Nine swine were divided into three groups. The first group (control) underwent standard colocystoplasty; the second group underwent colocystoplasty with colonic demucosalization and aerosol application of fibrin glue and urothelial cell mixture; in the third group detrusor cells were added to the mixture described in group two. The animals were kept for 6 months. Absorptive and secretory function was assessed. Bladders were harvested for histological and immunohistochemical evaluation.

RESULTS

All animals but one in the experimental groups showed confluent urothelial coverage of the colonic segment in the bladder without any evidence of fibrosis, inflammation, or regrowth of colonic epithelial cells. Ten percent of the instilled water in the bladder was absorbed within an hour in the control group, but none in experimental groups(p = 0.02). The total urine sediment and protein contents were higher in the control group compared with experimental groups (p < 0.05).

DISCUSSION

Both study groups developed a uniform urothelial lining. Histologically, the group with smooth muscle had an added layer of submucosal smooth muscle. Six months after bladder augmentation the new lining was durable. We were also able to demonstrate that the reconstituted augmented segments secrete and absorb significantly less than the control colocystoplasty group. We used a non-validated simple method to evaluate permeability of the new urothelial lining to water. To determine if the aerosol transfer of bladder cells would have behaved differently in the neurogenic bladder population, this experiment should have been performed in animals with neuropathic bladders.

CONCLUSION

Aerosol spraying of single cell suspension of urothelial and muscular cells with fibrin glue resulted in coverage of the demucosalized intestinal segment with a uniform urothelial layer. This new lining segment was durable without regrowth of colonic mucosa after 6 months. The new reconstituted segment absorbs and secretes significantly less than control colocystoplasty.

Dynamic reciprocity in cell-scaffold interactions

Tissue engineering in urology has shown considerable promise. However, there is still much to understand, particularly regarding the interactions between scaffolds and their host environment, how these interactions regulate regeneration and how they may be enhanced for optimal tissue repair. In this review, we discuss the concept of dynamic reciprocity as applied to tissue engineering, i.e. how bi-directional signaling between implanted scaffolds and host tissues such as the bladder drives the process of constructive remodeling to ensure successful graft integration and tissue repair. The impact of scaffold content and configuration, the contribution of endogenous and exogenous bioactive factors, the influence of the host immune response and the functional interaction with mechanical stimulation are all considered. In addition, the temporal relationships of host tissue ingrowth, bioactive factor mobilization, scaffold degradation and immune cell infiltration, as well as the reciprocal signaling between discrete cell types and scaffolds are discussed. Improved understanding of these aspects of tissue repair will identify opportunities for optimization of repair that could be exploited to enhance regenerative medicine strategies for urology in future studies.

Biomatrices for bladder reconstruction

There is a demand for tissue engineering of the bladder needed by patients who experience a neurogenic bladder or idiopathic detrusor overactivity. To avoid complications from augmentation cystoplasty, the field of tissue engineering seeks optimal scaffolds for bladder reconstruction. Naturally derived biomaterials as well as synthetic and natural polymers have been explored as bladder substitutes. To improve regenerative properties, these biomaterials have been conjugated with functional molecules, combined with nanotechology, or seeded with exogenous cells. Although most studies reported complete and functional bladder regeneration in small-animal models, results from large-animal models and human clinical trials varied. For functional bladder regeneration, procedures for biomaterial fabrication, incorporation of biologically active agents, introduction of nanotechnology, and application of stem-cell technology need to be standardized. Advanced molecular and medical technologies such as next generation sequencing and magnetic resonance imaging can be introduced for mechanistic understanding and non-invasive monitoring of regeneration processes, respectively.

Decellularized tissue and cell-derived extracellular matrices as scaffolds for orthopaedic tissue engineering

The reconstruction of musculoskeletal defects is a constant challenge for orthopaedic surgeons. Musculoskeletal injuries such as fractures, chondral lesions, infections and tumor debulking can often lead to large tissue voids requiring reconstruction with tissue grafts. Autografts are currently the gold standard in orthopaedic tissue reconstruction; however, there is a limit to the amount of tissue that can be harvested before compromising the donor site. Tissue engineering strategies using allogeneic or xenogeneic decellularized bone, cartilage, skeletal muscle, tendon and ligament have emerged as promising potential alternative treatment. The extracellular matrix provides a natural scaffold for cell attachment, proliferation and differentiation. Decellularization of in vitro cell-derived matrices can also enable the generation of autologous constructs from tissue specific cells or progenitor cells. Although decellularized bone tissue is widely used clinically in orthopaedic applications, the exciting potential of decellularized cartilage, skeletal muscle, tendon and ligament cell-derived matrices has only recently begun to be explored for ultimate translation to the orthopaedic clinic.

A dynamic distention protocol for whole-organ bladder decellularization: histological and biomechanical characterization of the acellular matrix

A combined physical-chemical protocol for whole full-thickness bladder decellularization is proposed, based on organ cyclic distention through repeated infusion/withdrawal of the decellularization agents through the urethra. The dynamic decellularization was intended to enhance cell removal efficiency, facilitating the delivery of detergents within the inner layers of the tissue and the removal of cell debris. The use of mild chemical detergents (hypotonic solution and non-ionic detergent) was employed to limit adverse effects upon matrix 3D ultrastructure. Inspection of the presence of residual DNA and RNA was carried out on decellularized matrices to verify effective cell removal. Histological investigation was focused on assessing the retention of adequate structural and functional components that regulate the biomechanical behaviour of the acellular tissue. Biomechanical properties were evaluated through uniaxial tensile loading tests of tissue strips and through ex vivo filling cystometry to evaluate the whole-organ mechanical response to a physiological-like loading state. According to our results, a dynamic decellularization protocol of 17 h duration with a 5 ml/min detergent infusion flow rate revealed higher DNA removal efficiency than standard static decellularization, resulting in residual DNA content < 50 ng/mg dry tissue weight. Furthermore, the collagen network and elastic fibres distribution were preserved in the acellular ECM, which exhibited suitable biomechanical properties in the perspective of its future use as an implant for bladder augmentation.

Tissue-engineered tubular graft for urinary diversion after radical cystectomy in rabbits

BACKGROUND

Clinically, using ileal conduit for urinary diversion often caused many serious complications. Tissue engineering technology may offer an alternative method for urinary diversion after radical cystectomy. In this study, we aimed to make a tissue-engineered tubular graft (TETG) using bladder epithelial cells and bladder acellular matrix (BAM) for urinary diversion in rabbits.

METHODS

Bladder epithelial cells of rabbit were cultivated and expanded in vitro, which were then seeded on BAM and cultured for 7 d. Then, cell-seeded grafts of 4 cm length and 0.8 cm diameter were used to make TETGs and transferred into the omentum for 2 wk before urinary diversion. In the experimental group, bladders of the rabbits were removed. The proximal ends of TETGs were anastomosed with ureters, and the distal ends were anastomosed with the abdominal stomas. In the control group, TETGs were constructed using unseeded BAM. Newly formed tissue structures were functionally and microscopically evaluated using urography and immunohistochemistry at 1, 2, 4, and 8 wk after operation, respectively. Histologic examination with hematoxylin and eosin staining was conducted to assess tissue regeneration. Immunohistochemistry was performed with AE1/AE3, uroplakin Ⅲa, and zonula occludens 1 (ZO-1) antibodies.

RESULTS

All animals were alive in the experimental group. Hematoxylin and eosin staining showed epithelial coverage in TETG. Immunohistochemistry showed positive stain with AE1/AE3, uroplakin Ⅲa, and ZO-1, which indicated mature and functional epithelial cells on the lumen of TETG. Intravenous urography showed that there were no obstructions in TETGs. In the control group, four rabbits were dead within 2 wk, and scar formation, atresia, and severe hydronephrosis were found.

CONCLUSIONS

It was feasible that TETG constructed using bladder epithelial cells and BAM for urinary diversion after radical cystectomy in rabbits.

Cultured keratinocytes on urinary bladder matrix scaffolds increase angiogenesis and help in rapid healing of wounds

INTRODUCTION

Urinary Bladder Matrix (UBM) is an extracellular matrix (ECM) scaffold. It is now used in wound care management of partial and full-thickness wounds where conventional methods for wound care usually fail to give satisfactory results.

OBJECTIVE

In this study, the authors are comparing the healing of full-thickness excisional wounds in New Zealand rabbits using either UBM scaffolds alone or in combination with cultured keratinocytes. The wounds were compared grossly and histologically.

MATERIALS AND METHODS

It is a comparative controlled study including 40 full-thickness wounds in 2 groups. Group (A) wounds: treated with UBM scaffolds, Group (B) wounds: treated with UBM scaffolds with cultured keratinocytes. The wounds were examined grossly after 1, 2, and 3 weeks, and were examined histologically at the end of the 3rd week using ordinary hematoxylin-eosin staining techniques.

RESULTS

All the wounds healed completely by the end of the 3rd week. Early wound contraction was significantly less in group B. More angiogenic response was evident in all specimens of group B.

CONCLUSION

This study shows that adding cultured keratinocytes to the rough surface of the UBM scaffold may be beneficial in reducing early wound contraction and improving wound vascularity in treatment of full-thickness wounds.

In-vivo autologous bladder muscular wall regeneration: application of tissue-engineered pericardium in a model of bladder as a bioreactor

PURPOSE

Tissue-engineered pericardium (TEP) is a collagen-rich matrix that has previously been shown to promote in vivo and in vitro tissue regeneration. We evaluated the potential of TEP as a source for the in-vivo creation of bladder muscular wall grafts. We used bladder wall as a bioreactor to create a natural environment for cellular growth and differentiation.

MATERIALS AND METHODS

Sixteen rabbits were divided into four groups. A control group underwent classical bladder autoaugmentation. Other groups underwent insertion of TEP between bladder mucosa and muscular layer: group 2 with insertion of TEP, group 3 with TEP over autologous bladder muscular wall fragments, and group 4 with autologous bladder smooth muscle cells (SMCs) seeded on TEP. After 4 and 8 weeks, grafts were biopsied for histopathological evaluations.

RESULTS

Frames from groups 3 and 4 demonstrated more organized muscular wall generation with a significantly higher number of CD34 + endothelial progenitor cells and CD31 + microvessels, and maintenance of α-smooth muscle actin expression through immunohistochemistry. Group 4 showed significant enhancement of SMC penetration to TEP. Although the fragment-seeded group required a simpler procedure, the cell-seeded group showed superior organization of the muscular layer on histopathology. We found a semi-organized muscular layer and new vessels in the margins of TEP in group 3, while there was a homogeneous pattern of SMCs and new vessels in both the margins and center of TEP in group 4.

CONCLUSIONS

This preliminary work has important functional and clinical implications, as it indicates that use of the autologous SMC seeding method may enhance the properties of TEP in terms of bladder wall regeneration.

Bladder tissue engineering: tissue regeneration and neovascularization of HA-VEGF-incorporated bladder acellular constructs in mouse and porcine animal models

Successful tissue engineering requires appropriate recellularization and vascularization. Herein, we assessed the regenerative and angiogenic effects of porcine bladder acellular matrix (ACM) incorporated with hyaluronic acid (HA) and vascular endothelial growth factor (VEGF) in mouse and porcine models. Prepared HA-ACMs were rehydrated in different concentrations of VEGF (1, 2, 3, 10, and 50 ng/g ACM). Grafts were implanted in mice peritoneum in situ for 1 week. Angiogenesis was quantified with CD31 and Factor VIII immunostaining using Simple PCI. Selected optimal VEGF concentration that induced maximum vascularization was then used in porcine bladder augmentation model. Implants were left in for 4 and 10 weeks. Three groups of six pigs each were implanted with ACM alone, HA-ACM, and HA-VEGF-ACM. Histological, immunohistochemical (Uroplakin III, alpha-SMA, Factor VIII), and immunofluorescence (CD31) analysis were performed to assess graft regenerative capacity and angiogenesis. In mouse model, statistically significant increase in microvascular density was demonstrated in the 2 ng/g ACM group. When this concentration was used in porcine model, recellularization increased significantly from weeks 4 to 10 in HA-VEGF-ACM, with progressive decrease in fibrosis. Significantly increased vascularization, coupled with increased urothelium and smooth muscle cell (SMC) regeneration, was observed in HA-VEGF grafts at week 10 in the center and periphery, compared with week 4. HA-VEGF grafts displayed highest in vivo epithelialization, neovascularization, and SMCs regeneration. A total of 2 ng/g tissue VEGF when incorporated with HA proved effective in stimulating robust graft recellularization and vascularization, coordinated with increased urothelial bladder development and SMC augmentation into bundles by week 10.

Tissue-engineered conduit using urine-derived stem cells seeded bacterial cellulose polymer in urinary reconstruction and diversion

The objective of this study was to generate bacterial cellulose (BC) scaffolds seeded with human urine-derived stem cells (USC) to form a tissue-engineered conduit for use in urinary diversion. Microporous BC scaffolds were synthesized and USC were induced to differentiate into urothelial and smooth muscle cells (SMC). Induced USC (10(6) cells/cm(2)) were seeded onto BC under static and 3D dynamic (10 or 40 RPM) conditions and cultured for 2 weeks. The urothelial cells and SMC derived from USC formed multilayers on the BC scaffold surface, and some cells infiltrated into the scaffold. The urothelium derived from USC differentiation expressed urothelial markers (uroplakin Ia and AE1/AE3) and the SMC expressed SMC markers (α-smooth muscle actin and desmin). In addition, USC/BC scaffold constructs were implanted into athymic mice, and the cells were tracked using immunohistochemical staining for human nuclear antigen. In vivo, the cells appeared to differentiate and express urothelial and SMC markers. In conclusion, porous BC scaffolds allow 3 dimensional growth of USC, leading to formation of a multilayered urothelium and cell-matrix infiltration. Thus, cell-seeded BC scaffolds hold promise for use in tissue-engineered urinary conduits for urinary reconstruction.

Scaffold Characteristics for Functional Hollow Organ Regeneration

Many medical conditions require surgical reconstruction of hollow organs. Tissue engineering of organs and tissues is a promising new technique without harvest site morbidity. An ideal biomaterial should be biocompatible, support tissue formation and provide adequate structural support. It should degrade gradually and provide an environment allowing for cell-cell interaction, adhesion, proliferation, migration, and differentiation. Although tissue formation is feasible, functionality has never been demonstrated. Mainly the lack of proper innervation and vascularisation are hindering contractility and normal function. In this chapter we critically review the current state of engineering hollow organs with a special focus on innervation and vascularisation.

Optimization of a natural collagen scaffold to aid cell-matrix penetration for urologic tissue engineering

The goal of this study was to fabricate a 3-dimensional (3-D) porous scaffold derived from bladder submucosa (BSM) and further recellularize the scaffold with human bladder cells for cell-based urethral tissue engineering. Fresh porcine BSM was soaked with peracetic acid (PAA) at different concentrations (0,1,3,5 and 10%) and then treated with Triton X-100 for decellularization. DNA content analysis showed that nuclear material was removed from the BSM scaffold. Treatment with 5% PAA led to high porosity on the surface of the matrix with retention of less cellular material and maintained about 75% of normal tensile strength. In 3-D dynamic culture, cells formed even multiple layers on the surface of matrix. Cells also penetrated deeper into the lamina propria of the matrix compared to untreated matrix. Immunocytochemical staining indicated that the grafted bladder cells expressed urothelial- and smooth muscle-specific markers both, in vitro and in vivo. This study demonstrates that decellularized/oxidized BSM possesses 3-D porosity for cell infiltration into the matrix. Further, cells seeded on decellularized/oxidized BSM and grown in dynamic culture, significantly promoted cell-matrix penetration in vitro and promoted cell growth in vivo. Scaffolds with such characteristics have potential applications in cell-based urological tissue engineering.

Nerve distribution in rat urinary bladder after incorporation of acellular matrix graft or subtotal cystectomy

OBJECTIVE

In the treatment of reduced bladder capacity, matrix grafts have been used as a scaffold into which cell elements from the native bladder grow, eventually forming a new bladder segment. Functioning motor nerve endings in such segments in the rat have been demonstrated, although little is known about nerve distribution. We compare the pattern of nerve distribution in scaffold-augmented rat bladders with that in bladders regrown after subtotal cystectomy and that in control bladders.

MATERIAL AND METHODS

Female Sprague-Dawley rats were either subtotally cystectomized (n=7) or had a part of the bladder dome replaced by an acellular collagen (small intestinal submucosa) matrix graft (n=10). Fourteen age-matched, unoperated animals were used as controls. Two and a half to 10 months after surgery the bladders were stained for acetylcholinesterase and studied in wholemounts.

RESULTS

No ganglion neurons were observed in any of the bladders. On their ventral side the control bladders showed longitudinal nerve trunks, running in parallel along the longitudinally oriented muscle bundles, while on the lateral and dorsal aspects the nerves were thinner, more irregularly arranged and frequently branched. In the bladders regrown after subtotal cystectomy, the ventral nerves were seen running obliquely to the still longitudinally oriented muscle bundles, resembling the pattern of the normal bladder base; the pattern of the dorsolateral nerves was the same as that in the controls. In the matrix bladders, the muscle and nerve patterns in the native part were the same as those in controls. Muscle bundles were growing into the matrix, accompanied by nerves, which showed limited branching when entering the matrix, usually running in parallel to the muscle, but then branching within the matrix.

CONCLUSIONS

The nerves in the matrix grafts and the regrown parts of the subtotally cystectomized bladders derive from preexisting nerves in the bladder. In neither case does the nerve trunk or muscle bundle arrangement fully attain the pattern found in normal bladders.

Bladder wall grafting in rats using salt-modified and collagen-coated polycaprolactone scaffolds: preliminary report

AIM

A rat model was used for the evaluation of collagen-coated and salt-modified polycaprolactone (PCL) scaffolds for bladder grafting after hemicystectomy.

METHODS

SD rats underwent partial cystectomy and cystoplasty with collagen-coated and salt-modified polycaprolactone scaffolds. The grafts of the regenerated bladder wall were harvested at different intervals and tissue regeneration was evaluated microscopically. Anatomic and functional characters were evaluated by cystography and urodynamics.

RESULTS

At harvesting, after 1 and 2 months, we found good preservation of the bladder shape and volume in all 16 rats receiving PCL cystorrhaphy. No stone formation was observed. Good epithelialization and ingrowth of smooth muscle cells were seen after 2 months grafting. Collagen-coated PCL scaffolds showed considerable encrustation, which appeared to be absorbed and disappear with time. The cystographic and urodynamic examinations revealed intact contour and a well-accommodated bladder with reservoir volume and contractility.

CONCLUSIONS

In the rat model, we have successfully demonstrated the applicability of collagen coated and salt-modified PCL in reconstruction of the partial cystectomized bladder.

Nanofiber technology: designing the next generation of tissue engineering scaffolds

Tissue engineering is an interdisciplinary field that has attempted to utilize a variety of processing methods with synthetic and natural polymers to fabricate scaffolds for the regeneration of tissues and organs. The study of structure-function relationships in both normal and pathological tissues has been coupled with the development of biologically active substitutes or engineered materials. The fibrillar collagens, types I, II, and III, are the most abundant natural polymers in the body and are found throughout the interstitial spaces where they function to impart overall structural integrity and strength to tissues. The collagen structures, referred to as extracellular matrix (ECM), provide the cells with the appropriate biological environment for embryologic development, organogenesis, cell growth, and wound repair. In the native tissues, the structural ECM proteins range in diameter from 50 to 500 nm. In order to create scaffolds or ECM analogues, which are truly biomimicking at this scale, one must employ nanotechnology. Recent advances in nanotechnology have led to a variety of approaches for the development of engineered ECM analogues. To date, three processing techniques (self-assembly, phase separation, and electrospinning) have evolved to allow the fabrication of nanofibrous scaffolds. With these advances, the long-awaited and much anticipated construction of a truly "biomimicking" or "ideal" tissue engineered environment, or scaffold, for a variety of tissues is now highly feasible. This review will discuss the three primary technologies (with a focus on electrospinning) available to create tissue engineering scaffolds that are capable of mimicking native tissue, as well as explore the wide array of materials investigated for use in scaffolds.

Identification and characterization of bioactive factors in bladder submucosa matrix

In spite of long term clinical use of decellularized bladder submucosa matrix (BSM), little is known about the active factors within this material. In this paper, we analyzed the biological factors from the decellularized BSM using ELISA, Western blotting, and immunohistochemistry for the purpose of effective utilization of this material in the field of regenerative medicine. At least 10 growth factors, including VEGF, BMP4, PDGF-BB, KGF, TGFbeta1, IGF, bFGF, EGF and TGFalpha were found to be preserved in the decellularized BSM. The existence of collagen (type 1, 2, 3, 4), laminin and elastin within the matrix was also demonstrated. The soluble BSM extracts showed a conspicuous effect on cell proliferation when added as a supplement in vitro. These findings demonstrate that growth factors and extracellular matrix in the BSM maintain valuable biological activity even after the decellularization and extraction processes, thus supporting the wide applicability of BSM in tissue regeneration. The identification and characterization of growth factors and extracellular matrix in the BSM is a prerequisite for understanding tissue regeneration using this scaffold.

Changing concepts of bladder regeneration

During the last decade, there has been a dramatic increase in studies aimed at regeneration of the urinary bladder. Many studies employed animal-derived or synthetic materials as grafts for experimental bladder augmentation models, with or without additional measures to promote regeneration, such as autologous cell transplantation or growth factor loading. However, in spite of encouraging results in several reports, few methodologies have shown proven definitive clinical utility. One major problem in these studies is the lack of a clear distinction between native and regenerated bladder in total bladder function after augmentation. Another crucial problem is the absorption and shrinkage of larger grafts, which may result from insufficient vascular supply and smooth muscle regeneration. In contrast, researchers have recently attempted to establish alternative regenerative strategies for treating bladder diseases, and have employed far more diverse approaches according to the various pathological conditions to be treated. For total replacement of the bladder after cystectomy for invasive bladder cancer, urothelium-covered neobladder with non-urinary tract backbone remains a viable choice. In addition, functional bladder diseases such as urinary incontinence, weak detrusor, or non-compliant fibrotic bladder have also been major targets for many leading research groups in this field. These conditions are studied much more from different therapeutic standpoints, aiming at the prevention or reversal of pathological conditions in muscle remodeling or neural control. Such altered research direction would inevitably lead to less surgically based basic biological research, and also would include a far wider spectrum of adult and pediatric bladder diseases, from overactive bladder to dysfunctional voiding.

Cell responses to biomimetic protein scaffolds used in tissue repair and engineering

Basic science research in tissue engineering and regenerative medicine aims to investigate and understand the deposition, growth, and remodeling of tissues by drawing together approaches from a range of disciplines. This review discusses approaches that use biomimetic proteins and cellular therapies, both in the development of clinical products and of model platforms for scientific investigation. Current clinical approaches to repairing skin, bone, nerve, heart valves, blood vessels, ligaments, and tendons are described and their limitations identified. Opportunities and key questions for achieving clinical goals are discussed through commonly used examples of biomimetic scaffolds: collagen, fibrin, fibronectin, and silk. The key questions addressed by three-dimensional culture models, biomimetic materials, surface chemistry, topography, and their interaction with cells in terms of durotaxis, mechano-regulation, and complex spatial cueing are reviewed to give context to future strategies for biomimetic technology.

Quantifying angiogenesis in VEGF-enhanced tissue-engineered bladder constructs by dynamic contrast-enhanced MRI using contrast agents of different molecular weights

PURPOSE

To compare Gadomer, a macromolecular magnetic resonance (MR) contrast agent, and gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) for quantifying angiogenesis in tissue-engineered bladder constructs.

MATERIALS AND METHODS

Constructs enhanced with vascular endothelial growth factor (VEGF) were grafted onto the bladder of 12 rabbits (N= 3/VEGF, VEGF = 0,10,15,20 ng/g tissue). After eight days dynamic contrast-enhanced MRI (DCE-MRI) was performed in each animal using Gadomer and Gd-DTPA, separated by a one-hour interval. DCE-MRI parameters were calculated from two-compartment pharmacokinetics (plasma volume fraction, v(p); transfer constant, K(trans)) and model-free analysis, area under the concentration-time curve (AUC). Histology assessment of microvessel density (MVD) and Evans blue permeability were compared to DCE-MRI.

RESULTS

MVD was elevated (P < 0.05) at the highest VEGF but not among lower levels; permeability differences were absent. Contrast enhancement increased with VEGF and was better resolved with Gadomer than Gd-DTPA. Gadomer was the better assay for estimating plasma volume: v(p) provided the best distinction (P < 0.005), but both v(p) and AUC were correlated to MVD. With Gd-DTPA, only AUC distinguished MVD differences (P< 0.05). Changes in K(trans) were insignificant.

CONCLUSION

Macromolecular contrast agents are valuable for monitoring angiogenesis in tissue-engineered bladder grafts. Compared to Gd-DTPA, Gadomer provides more accurate and precise quantification of microvessel function, and is better suited to pharmacokinetic analysis for accurate physiological quantification.

Dynamic contrast-enhanced MRI to quantify VEGF-enhanced tissue-engineered bladder graft neovascularization: pilot study

Tissue engineered organs require an immediately perfused vascular tree. Currently, neovascularization assessment requires animal sacrifice and graft harvest. In this pilot study we assess whether neovascularization of an engineered urinary bladder construct is enhanced with vascular-derived endothelial growth factor (VEGF) and assessable non-invasively with dynamic contrast-enhanced MRI (DCE-MRI). Rabbit bladder acellular matrix was hybridized with hyaluronic acid (ACM-HA), fortified with one of three concentrations (0 ng, 10 ng, or 20 ng per gram of tissue) of vascular-derived endothelial growth factor (VEGF), and grafted onto bladders in nine rabbits (3 per VEGF concentration). At 1, 2 and 3 weeks, one rabbit from each VEGF group underwent DCE-MRI and graft harvest. Microvasculature was quantified with scrial optical transverse sectioning of CD31 stained whole mounts using PCl software. Masson trichrome and H&E staining were used to assess cellular proliferation and fibrosis. There was a significant difference in mean microvascular area (MVA) between the 10 and 20 ng VEGF groups (230187 vs 477894 microm2, P=0.014) but not between the 0 and 10 ng groups (210497 microm2, P=0.21). Gadolinium uptake increased with MVA and correlated with it on linear regression analysis (Pearson's correlation coefficient r=0.71). At three weeks, stromal cellularity was greatest, and fibrosis was least, in the high VEGF group. This preliminary work demonstrates improved neovascularization of bladder constructs with VEGF fortification of ACM-HA and the feasibility of MRI as a non-invasive method to assume angiogenesis in tissue engineered constructs.

In vitro reconstruction of a tissue-engineered endothelialized bladder from a single porcine biopsy

OBJECTIVE

Augmentation of the urinary bladder using a tissue-engineered approach with autologous cells is a very promising technique. To prevent risks of necrosis after transplantation, the graft vascularization process could be markedly enhanced by incorporation of autologous endothelial cells in the tissue-engineered organ. The purpose of this study was to develop a separation technique to extract four bladder cell types from the same biopsy, and to prepare an endothelialized reconstructed bladder.

MATERIALS AND METHODS

Fibroblasts, smooth muscle cells (SMC), urothelial cells (UC) and endothelial cells (EC) were extracted from a small porcine bladder biopsy. The SMC, fibroblasts and EC were seeded on the top of the sponge and cultured for 10 days. Then, the UC were seeded on top of these cells for 15 additional days to produce a three-dimensional bladder wall.

RESULTS

The UC and EC extracts from a single porcine biopsy were 97.2+/-0.6% keratin 8/18-positive and 97.7+/-0.3% PECAM-1-positive pure cells, respectively, as assessed by flow cytometry. The SMC could not be dissociated from fibroblasts, and were present as 37+/-0.5% desmin-positive cells. UC differentiated into a urothelium characterized by umbrella cells and a laminin-positive basal membrane. The EC reorganized in the matrix to form PECAM-1-positive capillary-like tubes.

CONCLUSION

This new model of tissue-engineered bladder has the main advantages of being at least 2mm thick, autologous, and able to promote the formation of capillary-like tubes. It could be a promising alternative to the use of gastrointestinal segments to improve bladder capacity.

Using porcine acellular collagen matrix (Pelvicol®) in bladder augmentation: experimental study

PURPOSE

Evaluate the rabbit augmented bladder with Pelvicol.

MATERIALS AND METHODS

Twenty New Zealand rabbits were divided into 4 groups. Bladder augmentation was performed using a 10 x 10 mm sized porcine acellular collagen matrix. The material was placed on the dome of the bladder wall as a patch with 5-0 polyglycolic sutures. The bladder was resected on the 7th, 14th day, 30th and 90th days, and processed for histological analysis.

RESULTS

No stone formation was found in the first, second and fourth weeks. In the first week, there was inflammatory appearance and roughness in the reconstructed area when compared to other sites on the bladder wall. The material could not be seen in some bladders because of acute inflammatory reaction. The normal bladder epithelium was found on the part of the bladder wall that follows the surface of the eroded material. In the second week, edema was observed through the bladder wall. Perivesical fat tissue increased and it was not easy to distinguish it from the surrounding area. In the fourth week, the bladder wall was thickened and there was a sensation of hardness present. The inner and outer surface of the material was darker than in the other bladders. In the third month, there was no inflammatory reaction; however, there was micro calcification and irregular detrusor regeneration.

CONCLUSIONS

Pelvicol cannot be suitable material for bladder augmentation because of the resultant micro calcification, thickening of the bladder wall and irregular development of detrusor regeneration.

From Molecules to Matrix: Construction and Evaluation of Molecularly Defined Bioscaffolds

In this chapter, we describe the fundamental aspects of the preparation of molecularly-defined scaffolds for soft tissue engineering, including the tissue response to the scaffolds after implantation. In particular, scaffolds prepared from insoluble type I collagen fibres, soluble type II collagen fibres, insoluble elastin fibres, glycosaminoglycans (GAGs) and growth factors are discussed. The general strategy is to prepare tailor-made "smart" biomaterials which will create a specific microenvironment thus enabling cells to generate new tissues. As an initial step, all biomolecules used were purified to homogeneity. Next, porous scaffolds were prepared using freezing and lyophilisation, and these scaffolds were crosslinked using carbodiimides. Crosslinking resulted in mechanically stronger scaffolds and allowed the covalent incorporation of GAGs. Scaffold characteristics were controlled to prepare tailor-made scaffolds by varying e.g. collagen to elastin ratio, freezing rate, degree of crosslinking, and GAGs attachment. The tissue response to scaffolds was evaluated following subcutaneous implantations in rats. Crosslinked scaffolds maintained their integrity and supported the formation of new extracellular matrix. Collagen-GAG scaffolds loaded with basic fibroblast growth factor significantly enhanced neovascularisation and tissue remodelling. Animal studies of two potential applications of these scaffolds were discussed in more detail, i.e. for bladder and cartilage regeneration.

Resorbable extracellular matrix grafts in urologic reconstruction

PURPOSE

There is an increasingly large body of literature concerning tissue-engineering products that may be used in urology. Some of these are quite complex (such as multilayer patient-specific cell-seeded implants) yet the most simple and successful products to date are also the most uncomplicated: resorbable acellular extra-cellular matrices (ECMs) harvested from animals. ECMs have been used in a variety of difficult urologic reconstruction problems, and this review is intended to summarize this complex literature for the practicing urologist.

METHODS

Medline search of related terms such as "SIS, small intestinal submucosa, ECM, extracellular matrix, acellular matrix and urologic reconstruction". Manuscripts missed in the initial search were taken from the bibliographies of the primary references.

RESULTS

Full review of potential clinical uses of resorbable extra-cellular matrices in urologic reconstruction.

CONCLUSIONS

Currently, the "state of the art" in tissue engineering solutions for urologic reconstruction means resorbable acellular xenograft matrices. They show promise when used as a pubovaginal sling or extra bolstering layers in ureteral or urethral repairs, although recent problems with inflammation following 8-ply pubovaginal sling use and failures after 1- and 4-ply SIS repair of Peyronie's disease underscore the need for research before wide adoption. Preliminary data is mixed concerning the potential for ECM urethral patch graft, and more data is needed before extended uses such as bladder augmentation and ureteral replacement are contemplated. The distant future of ECMs in urology likely will include cell-seeded grafts with the eventual hope of producing "off the shelf" replacement materials. Until that day arrives, ECMs only fulfill some of the requirements for the reconstructive urologist.

Tissue Engineering in Urology: Between Basic Research and Clinical Applications

Tissue engineering follows the principles of cell and tissue culture, cloning and stem cell production, and materials science to develop biological substitutes, which could repair and maintain normal function. The biomaterials must be able to control the structure and function of engineered tissue by interacting with both transplanted and host cells. Either natural or synthetic biodegradable materials have been used as cell delivery scaffolds. The stem cell field is also advancing rapidly, opening new options for regenerative medicine. In the genitourinary system, tissue engineering has been applied experimentally for the reconstitution of pelvis, ureter, bladder, urethra, penile corpora cavernosa and testis. This literature review underlines recent advances that have occurred in tissue engineering and describes their clinical repercussions, particularly in offering novel therapies in urogenital pathology.

Molecular, cellular and developmental biology of urothelium as a basis of bladder regeneration

Urinary bladder malfunction and disorders are caused by congenital diseases, trauma, inflammation, radiation, and nerve injuries. Loss of normal bladder function results in urinary tract infection, incontinence, renal failure, and end-stage renal dysfunction. In severe cases, bladder augmentation is required using segments of the gastrointestinal tract. However, use of gastrointestinal mucosa can result in complications such as electrolyte imbalance, stone formation, urinary tract infection, mucous production, and malignancy. Recent tissue engineering techniques use acellular grafts, cultured cells combined with biodegradable scaffolds, and cell sheets. These techniques are not all currently applicable for human bladder reconstruction. However, new avenues for bladder reconstruction maybe facilitated by a better understanding of urogenital development, the cellular and molecular biology of urothelium, and cell-cell interactions, which modulate tissue repair, homeostasis, and disease progression.

Bladder acellular matrix as a substrate for studying in vitro bladder smooth muscle-urothelial cell interactions

The objective of this study was to evaluate the ability of bladder acellular matrix (BAM) to support the individual and combined growth of primary porcine bladder smooth muscle (SMC) and urothelial (UEC) cells. An in vitro co-culture system was devised to evaluate the effect of UEC on (i) SMC-mediated contraction of BAM discs, and (ii) SMC invasiveness into BAM. Cells were seeded onto BAM discs under 4 different culture conditions. Constructs were incubated for 1, 7, 14 and 28 days. Samples were then harvested for evaluation of matrix contraction. Immunohistochemistry (IHC) was utilized to examine cellular organization within the samples and conditioned media supernatants analyzed for net gelatinase activity. BAM contraction was significantly increased with co-culture. The same side co-culture configuration lead to a greater reduction in surface area than opposite side co-culture. IHC revealed enhanced SMC infiltration into BAM when co-culture was utilized. A significant increase in net gelatinase activity was also observed with the co-culture configuration. Enhanced infiltration and contractile ability of bladder SMCs with UEC co-culture may, in part, be due to an increase in gelatinase activity. The influence of bladder UECs on SMC behaviour in vitro indicates that BAM may contain some key inductive factors that serve to promote important bladder cell-cell and cell-matrix interactions.

[Acellular matrix for functional reconstruction of the urogenital tract. Special form of "tissue engineering"?]

Organ substitution and reconstruction of the urogenital system still poses a problem regarding an adequate substitute. Usually non-organ-specific materials are used for reconstruction (bowl, buccal mucosa). This nonspecific tissue can cause side effects that result from the origin and the natural function. Different groups have shown that an acellular matrix graft in the urinary bladder and the urethra served as a scaffold for complete regeneration of all organ wall components and that this organ-specific regeneration simultaneously facilitates functional restitution. New approaches will presumably effect better regeneration after seeding the matrix with organ-specific cells (i.e., urothelial cells). Smaller studies on genital reconstructive surgery could show that vaginal substitution with an acellular matrix might be possible or that there could be a possible substitute for the tunica during surgical treatment of Peyronie's disease.

Ingénierie tissulaire et thérapie cellulaire en urologie

Tissue engineering refers to the techniques that are aimed at regeneration of human tissues and organs. Two elements are necessary for these techniques: matrix and cells. Matrix is the scaffold where tissues may organise. Cells are either autologous cells stimulated to regenerate in vivo, aided by implantation of matrix ("guided tissue regeneration"), or autologous cells cultured outside the body (in vitro) and later returned as auto-transplants. All types of conventional tissue reconstructive surgery need tissue engineering. These techniques have been introduced recently into the clinical practice. One of the main limitations of reconstructive surgery in genitourinary tract is the lack of autologous tissue. Two autotransplants could be distinguished: coherent tissue structure or cell suspensions. The great number of studies published in this area emphasizes the importance of the future clinical implication in urology.

Porosity of porcine bladder acellular matrix: impact of ACM thickness

The objectives of this study are to examine the porosity of bladder acellular matrix (ACM) using deionized (DI) water as the model fluid and dextran as the indicator macromolecule, and to correlate the porosity to the ACM thickness. Porcine urinary bladders from pigs weighing 20-50 kg were sequentially extracted in detergent containing solutions, and to modify the ACM thickness, stretched bladders were acellularized in the same manner. Luminal and abluminal ACM specimens were subjected to fixed static DI water pressure (10 cm); and water passing through the specimens was collected at specific time interval. While for the macromolecule porosity testing, the diffusion rate and direction of 10,000 MW fluoroescein-labeled dextrans across the ACM specimens mounted in Ussing's chambers were measured. Both experiments were repeated on the thin stretched ACM. In both ACM types, the fluid porosity in both directions did not decrease with increased test duration (3 h); in addition, the abluminal surface was more porous to fluid than the luminal surface. On the other hand, when comparing thin to thick ACM, the porosity in either direction was higher in the thick ACM. Macromolecule porosity, as measured by absorbance, was higher for the abluminal thick ACM than the luminal side, but this characteristic was reversed in the thin ACM. Comparing thin to thick ACM, the luminal side in the thin ACM was more porous to dextran than in the thick ACM, but this characteristic was reversed for the abluminal side. The porcine bladder ACM possesses directional porosity and acellularizing stretched urinary bladders may increase structural density and alter fluid and macromolecule porosity.

A rabbit model to tissue engineer the bladder

A rabbit model was used for the evaluation of a collagen-based biomatrix of small intestinal submucosa (SIS, COOK) in comparison to a biochemically reconstructed biomatrix for bladder tissue regeneration. Rabbits underwent partial cystectomy and cystoplasty with SIS patch graft or with a biochemically defined collagen biomatrix. The grafts of the regenerated bladder wall were harvested at different intervals and tissue regeneration was evaluated. The results of the SIS and biochemically defined biomatrix grafts were comparable. At harvesting, we found five bladder stones and encrustation of the biomatrix in 21/56 animals. No stone formation was observed in the control group. The results of the molecularly defined biomatrix are thus far comparable to SIS. Both matrices show good epithelialization and ingrowth of smooth muscle cells. Both biomatrices show considerable encrustation, which appears to disappear in time. The rabbit model is suitable for bladder tissue engineering studies as it is an easy model to use. In this model, besides tissue regeneration, also some of the clinical problems are seen such as encrustation of foreign body material in the bladder. These aspects are subject for further pre-clinical studies in this animal model.

Tissue engineering for the replacement of organ function in the genitourinary system

Acquired and congenital abnormalities may lead to genitourinary organ damage or loss, requiring eventual reconstruction. Tissue engineering follows the principles of cell transplantation, materials science, and engineering toward the development of biological substitutes that would restore and maintain normal function. Tissue engineering may involve matrices alone, wherein the body's natural ability to regenerate is used to orient or direct new tissue growth, or the use of matrices with cells. Both synthetic and natural biodegradable materials have been used, either alone or as cell delivery vehicles. Tissue engineering has been applied experimentally for the reconstitution of several urologic tissues and organs, including bladder, ureter, urethra, kidney, testis, and genitalia. Fetal applications have also been explored. Recently, several tissue engineering technologies have been used clinically including the use of cells as bulking agents for the treatment of vesicoureteral reflux and incontinence and urethral replacement. Recent progress suggests that engineered genitourinary tissues may have clinical applicability in the future.