Small intestine submucosa in urethral stricture repair in a consecutive series

The Regenerative Microenvironment of the Tissue Engineering for Urethral Strictures

Urethral stricture caused by various reasons has threatened the quality of life of patients for decades. Traditional reconstruction methods, especially for long-segment injuries, have shown poor outcomes in treating urethral strictures. Tissue engineering for urethral regeneration is an emerging concept in which special designed scaffolds and seed cells are used to promote local urethral regeneration. The scaffolds, seed cells, various factors and the host interact with each other and form the regenerative microenvironment. Among the various interactions involved, vascularization and fibrosis are the most important biological processes during urethral regeneration. Mesenchymal stem cells and induced pluripotent stem cells play special roles in stricture repair and facilitate long-segment urethral regeneration, but they may also induce carcinogenesis and genomic instability during reconstruction. Nevertheless, current technologies, such as genetic engineering, molecular imaging, and exosome extraction, provide us with opportunities to manage seed cell-related regenerative risks. In this review, we described the interactions among seed cells, scaffolds, factors and the host within the regenerative microenvironment, which may help in determining the exact molecular mechanisms involved in urethral stricture regeneration and promoting clinical trials and the application of urethral tissue engineering in patients suffering from urethral stricture.

Small intestinal submucosa graft bulbar urethroplasty is a viable technique: results compared to buccal mucosa graft urethroplasty after propensity score matching

PURPOSE

Small intestinal submucosa (SIS) graft urethroplasty has been employed to decrease buccal mucosa morbidity and facilitate the procedure. The first published series had a short follow-up, inhomogeneous patient selection, and a lack of a control group. Our purpose is to report treatment outcomes at 13 years in a propensity score-matched cohort comparing bulbar urethroplasty with SIS (SISU) or buccal mucosa (BMU).

METHODS

From our institutional database of 1132 bulbar urethroplasties, we used propensity score matching with the nearest-neighbor method without replacement to generate a study sample of 25 BMU and 25 SISU. Failure was defined as any treatment after urethroplasty. Survival analyses were used to analyze treatment failure occurrence with data censored at 156mo.

RESULTS

Matching resulted in a complete correction of bias between the two samples except for the follow-up duration, which was slightly longer in the SIS group. The cumulative treatment success probability of BMU and SISU at 156mo was 83.4% and 68%, respectively. At multivariable Cox regression, SIS graft, previous urethrotomy, stricture length, and lower postoperative Qmax (within 2mo after catheter removal) were predictors of failure. Stricture length had a more remarkable effect in SISU, with estimated survival probabilities from the Cox model lower than 80% in strictures > = 3 cm.

CONCLUSION

SIS has poorer outcomes compared to BM but may still be useful when BM grafting is not possible. The best candidates for SISU, with similar success to BMU, are patients with strictures shorter than 3 cm, preferably without a history of DVIU.

Tissue Engineering for Penile Reconstruction

The penis is a complex organ with a development cycle from the fetal stage to puberty. In addition, it may suffer from either congenital or acquired anomalies. Penile surgical reconstruction has been the center of interest for many researchers but is still challenging due to the complexity of its anatomy and functionality. In this review, penile anatomy, pathologies, and current treatments are described, including surgical techniques and tissue engineering approaches. The self-assembly technique currently applied is emphasized since it is considered promising for an adequate tissue-engineered penile reconstructed substitute.

Biological Macromolecule-Based Scaffolds for Urethra Reconstruction

Urethral reconstruction strategies are limited with many associated drawbacks. In this context, the main challenge is the unavailability of a suitable tissue that can endure urine exposure. However, most of the used tissues in clinical practices are non-specialized grafts that finally fail to prevent urine leakage. Tissue engineering has offered novel solutions to address this dilemma. In this technology, scaffolding biomaterials characteristics are of prime importance. Biological macromolecules are naturally derived polymers that have been extensively studied for various tissue engineering applications. This review discusses the recent advances, applications, and challenges of biological macromolecule-based scaffolds in urethral reconstruction.

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.

Tissue Engineering of the Urethra: From Bench to Bedside

Tissue engineering (TE) is a promising approach for repair/substitution of damaged tissues and organs. Urethral strictures are common and serious health conditions that impair quality of life and may lead to serious organ damage. The search for ideal materials for urethral repair has led to interest of scientists and surgeons in urethral TE. Over the last decades, a significant amount of preclinical studies and considerable progress have been observed. In contrast, urethral TE has made slow progress in clinical practice so far. To address this, we conducted a systematic review of the literature on clinical applications of TE constructs for urethral repair in the last three decades. In summary, the TE approach is promising and effective, but many issues remain that need to be addressed for broader adoption of TE in urethral repair. Better design of trials, better cooperation of research groups and centralization could lead to reduction of costs and slowly proceed to commercialization and routine use of TE products for urethral reconstruction.

Double-Modified Bacterial Cellulose/Soy Protein Isolate Composites by Laser Hole Forming and Selective Oxidation Used for Urethral Repair

In this study, a double-modified bacterial cellulose/soybean protein isolate (DMBC/SPI), a new type of urethral tissue engineering scaffold with good biocompatibility, biodegradability, and cell-oriented growth, was prepared. Bacterial cellulose (BC) was physically and chemically modified by laser hole forming and selective oxidation to obtain the double-modified bacterial cellulose (DMBC). The soybean protein isolate (SPI) was compounded on DMBC to obtain DMBC/SPI with better biocompatibility. DMBC/SPI was used to repair the damaged urethra in rabbits. The results showed that DMBC/SPI was beneficial to heal the damaged urethra and did not cause a milder inflammatory response. The repaired urethra was smooth and continuous. DMBC/SPI has a good urethral repair effect and is expected to be used as a new urethral reconstruction material in clinical applications. In addition, FT-IR spectroscopy, SEM, static contact angle measurements, mechanical property investigation, and cell experiments were also performed to characterize the properties of DMBC/SPI composites.

Reconstruction of Vascular and Urologic Tubular Grafts by Tissue Engineering

Tissue engineering is one of the most promising scientific breakthroughs of the late 20th century. Its objective is to produce in vitro tissues or organs to repair and replace damaged ones using various techniques, biomaterials, and cells. Tissue engineering emerged to substitute the use of native autologous tissues, whose quantities are sometimes insufficient to correct the most severe pathologies. Indeed, the patient’s health status, regulations, or fibrotic scars at the site of the initial biopsy limit their availability, especially to treat recurrence. This new technology relies on the use of biomaterials to create scaffolds on which the patient’s cells can be seeded. This review focuses on the reconstruction, by tissue engineering, of two types of tissue with tubular structures: vascular and urological grafts. The emphasis is on self-assembly methods which allow the production of tissue/organ substitute without the use of exogenous material, with the patient’s cells producing their own scaffold. These continuously improved techniques, which allow rapid graft integration without immune rejection in the treatment of severely burned patients, give hope that similar results will be observed in the vascular and urological fields.

The Clinical Effects of Utilizing Allogeneic Acellular Dermal Matrix in the Surgical Therapy of Anterior Urethral Stricture

OBJECTIVE

The aim of this study was to estimate the clinical effects of allogeneic acellular dermal matrix (ADM) in the surgical therapy of anterior urethral stricture (AUS).

METHODS

We retrospectively collected the clinical data of 49 patients with AUS who underwent urethral repair surgery with ADM in the Department of Urology of the Peking University People's Hospital, and in the First Affiliated Hospital of the People's Liberation Army, from September 2015 to January 2019. The changes in urine flow rate and conditions of urethral mucosal coverage were observed as well as complications and outcomes, and statistical analysis was performed.

RESULTS

The average maximum urine flow rates at the 1st, 6th, and 12th month post-surgery were 16.3 ± 1.5, 15.0 ± 1.9, and 14.6 ± 2.1 mL/s, respectively. These values were significantly higher than the preoperative maximum urine flow rate, 1.3 ± 0.5 mL/s (p < 0.05). Cystoscopy was performed in 11 patients 12 months after surgery, with microscopic assessment revealing good urethral epithelial mucosal coverage. Only 2 patients developed infection 2-4 weeks after surgery, while 7 patients developed noninfective urethral restricture 6-10 months after surgery and 1 patient developed urinary fistula 5 months after surgery. All of these statuses improved after receiving appropriate treatment.

CONCLUSIONS

Use of ADM represents a new option for the surgical management of AUS repair and reconstruction, with positive clinical effects. In addition, it has the advantages of convenient for operation procedures and access, with no need for additional sampling surgery.

Urethroplasty with a bilayered poly-D,L-lactide-co-ε-caprolactone scaffold seeded with allogenic mesenchymal stem cells

Reconstructive surgery for urethral defects employing tissue-engineered scaffolds represents an alternative treatment for urethroplasty. The aim of this study was to compare the therapeutic efficacy of the bilayer poly-D,L-lactide/poly-ε-caprolactone (PL-PC) scaffold seeded with allogenic mesenchymal stem cells (MSCs) for urethra reconstruction in a rabbit model with conventional urethroplasty employing an autologous buccal mucosa graft (BG). The inner layer of the scaffold based on poly-D,L-lactic acid (PL) was seeded with MSCs, while the outer layer, prepared from poly-ε-caprolactone, protected the surrounding tissues from urine. To track the MSCs in vivo, the latter were labeled with superparamagnetic iron oxide nanoparticles. In rabbits, a dorsal penile defect was reconstructed employing a BG or a PL-PC graft seeded with nanoparticle-labeled MSCs. In the 12-week follow-up period, no complications were detected. Subsequent histological analysis demonstrated biointegration of the PL-PC graft with surrounding urethral tissues. Less fibrosis and inflammatory cell infiltration were observed in the experimental group as compared with the BG group. Nanoparticle-labeled MSCs were detected in the urothelium and muscular layer, co-localizing with the urothelium cytokeratin marker AE1/AE3, indicating the possibility of MSC differentiation into neo-urothelium. Our results suggest that a bilayer MSCs-seeded scaffold could be efficiently employed for urethroplasty.

From Acellular Matrices to Smart Polymers: Degradable Scaffolds that are Transforming the Shape of Urethral Tissue Engineering

Several congenital and acquired conditions may result in severe narrowing of the urethra in men, which represent an ongoing surgical challenge and a significant burden on both health and quality of life. In the field of urethral reconstruction, tissue engineering has emerged as a promising alternative to overcome some of the limitations associated with autologous tissue grafts. In this direction, preclinical as well as clinical studies, have shown that degradable scaffolds are able to restore the normal urethral architecture, supporting neo-vascularization and stratification of the tissue. While a wide variety of degradable biomaterials are under scrutiny, such as decellularized matrices, natural, and synthetic polymers, the search for scaffold materials that could fulfill the clinical performance requirements continues. In this article, we discuss the design requirements of the scaffold that appear to be crucial to better resemble the structural, physical, and biological properties of the native urethra and are expected to support an adequate recovery of the urethral function. In this context, we review the biological performance of the degradable polymers currently applied for urethral reconstruction and outline the perspectives on novel functional polymers, which could find application in the design of customized urethral constructs.

Outcomes of adult urethroplasty with commercially available acellular matrix

Background

Reconstruction for complex urethral strictures may necessitate grafting. Buccal mucosal graft (BMG) harvest involves additional morbidity, making 'off-the-shelf' options attractive. Multiple extracellular matrices (ECMs) have been used with varying degrees of success. We reviewed our experience with MatriStem (ACell, Inc., Columbia, MD, USA) to assess safety and clinical/histologic outcomes.

Methods

All patients undergoing acellular matrix-based reconstruction were included. Data regarding indications for surgery, patient demographics, subsequent procedures, clinical outcomes, and histologic analysis, when present, were collected.

Results

Eight patients undergoing urethral reconstruction with ECM were identified. All repairs were performed as staged procedures. Grafting was performed with either MatriStem alone or MatriStem and concomitant BMG. Seven patients (88%) underwent prior endoscopic intervention and five patients (71%) had failed to respond to one or multiple prior urethroplasties. Length of involved segments ranged from 2.5 to 15 cm. ECM graft placement was feasible and demonstrated excellent graft take. Among patients undergoing second-stage repairs (four of eight, 50%), 50% remained patent without the need for subsequent dilation.

Conclusions

Use of acellular matrix grafts in urethral reconstruction appears safe and feasible. Acellular matrix performs similarly to BMG with respect to graft take and contraction following staged repair. Further study is warranted.

A smart bilayered scaffold supporting keratinocytes and muscle cells in micro/nano-scale for urethral reconstruction

Rationale: In urethral tissue engineering, the currently available reconstructive procedures are insufficient due to a lack of appropriate scaffolds that would support the needs of various cell types. To address this problem, we developed a bilayer scaffold comprising a microporous network of silk fibroin (SF) and a nanoporous bacterial cellulose (BC) scaffold and evaluated its feasibility and potential for long-segment urethral regeneration in a dog model. Methods: The freeze-drying and self-assembling method was used to fabricate the bilayer scaffold by stationary cultivation G. xylinus using SF scaffold as a template. The surface morphology, porosity and mechanical properties of all prepared SF-BC scaffolds were characterized using Scanning electron microscopy (SEM), microcomputed tomography and universal testing machine. To further investigate the suitability of the bilayer scaffolds for tissue engineering applications, biocompatibility was assessed using an MTT assay. The cell distribution, viability and morphology were evaluated by seeding epithelial cells and muscle cells on the scaffolds, using the 3D laser scanning confocal microscopy, and SEM. The effects of urethral reconstruction with SF-BC bilayer scaffold was evaluated in dog urethral defect models. Results: Scanning electron microscopy revealed that SF-BC scaffold had a clear bilayer structure. The SF-BC bilayer scaffold is highly porous with a porosity of 85%. The average pore diameter of the porous layer in the bilayer SF-BC composites was 210.2±117.8 μm. Cultures established with lingual keratinocytes and lingual muscle cells confirmed the suitability of the SF-BC structures to support cell adhesion and proliferation. In addition, SEM demonstrated the ability of cells to attach to scaffold surfaces and the biocompatibility of the matrices with cells. At 3 months after implantation, urethra reconstructed with the SF-BC scaffold seeded with keratinocytes and muscle cells displayed superior structure compared to those with only SF-BC scaffold. Principal Conclusion: These results demonstrate that the bilayer SF-BC scaffold may be a promising biomaterial with good biocompatibility for urethral regeneration and could be used for numerous other types of hollow-organ tissue engineering grafts, including vascular, bladder, ureteral, bowel, and intestinal.

Tissue engineering of urethra: Systematic review of recent literature

The purpose of this article was to perform a systematic review of the recent literature on urethral tissue engineering. A total of 31 articles describing the use of tissue engineering for urethra reconstruction were included. The obtained results were discussed in three groups: cells, scaffolds, and clinical results of urethral reconstructions using these components. Stem cells of different origin were used in many experimental studies, but only autologous urothelial cells, fibroblasts, and keratinocytes were applied in clinical trials. Natural and synthetic scaffolds were studied in the context of urethral tissue engineering. The main advantage of synthetic ones is the fact that they can be obtained in unlimited amount and modified by different techniques, but scaffolds of natural origin normally contain chemical groups and bioactive proteins which increase the cell attachment and may promote the cell proliferation and differentiation. The most promising are smart scaffolds delivering different bioactive molecules or those that can be tubularized. In two clinical trials, only onlay-fashioned transplants were used for urethral reconstruction. However, the very promising results were obtained from animal studies where tubularized scaffolds, both non-seeded and cell-seeded, were applied. Impact statement The main goal of this article was to perform a systematic review of the recent literature on urethral tissue engineering. It summarizes the most recent information about cells, seeded or non-seeded scaffolds and clinical application with respect to regeneration of urethra.

Tissue engineered extracellular matrices (ECMs) in urology: Evolution and future directions

Autologous gastrointestinal tissue has remained the gold-standard reconstructive biomaterial in urology for >100 years. Mucus-secreting epithelium is associated with lifelong metabolic and neuromechanical complications when implanted into the urinary tract. Therefore, the availability of biocompatible tissue-engineered biomaterials such as extracellular matrix (ECM) scaffolds may provide an attractive alternative for urologists. ECMs are decellularised, biodegradable membranes that have shown promise for repairing defective urinary tract segments in vitro and in vivo by inducing a host-derived tissue remodelling response after implantation. In urology, porcine small intestinal submucosa (SIS) and porcine urinary bladder matrix (UBM) are commonly selected as ECMs for tissue regeneration. Both ECMs support ingrowth of native tissue and differentiation of multi-layered urothelial and smooth muscle cells layers while providing mechanical support in vivo. In their native acellular state, ECM scaffolds can repair small urinary tract defects. Larger urinary tract segments can be repaired when ECMs are manipulated by seeding them with various cell types prior to in vivo implantation. In the present review, we evaluate and summarise the clinical potential of tissue engineered ECMs in reconstructive urology with emphasis on their long-term outcomes in urological clinical trials.

A systematic review of animal and clinical studies on the use of scaffolds for urethral repair

Replacing urethral tissue with functional scaffolds has been one of the challenging problems in the field of urethra reconstruction or repair over the last several decades. Various scaffold materials have been used in animal studies, but clinical studies on use of scaffolds for urethral repair are scarce. The aim of this study was to review recent animal and clinical studies on the use of different scaffolds for urethral repair, and to evaluate these scaffolds based on the evidence from these studies. PubMed and OVID databases were searched to identify relevant studies, in conjunction with further manual search. Studies that met the inclusion criteria were systematically evaluated. Of 555 identified studies, 38 were included for analysis. It was found that in both animal and clinical studies, scaffolds seeded with cells were used for repair of large segmental defects of the urethra, such as in tubular urethroplasty. When the defect area was small, cell-free scaffolds were more likely to be applied. A lot of pre-clinical and limited clinical evidence showed that natural or artificial materials could be used as scaffolds for urethral repair. Urinary tissue engineering is still in the immature stage, and the safety, efficacy, cost-effectiveness of the scaffolds are needed for further study.

The potential role of tissue-engineered urethral substitution: clinical and preclinical studies

Urethral strictures and anomalies remain among the difficult problems in urology, with urethroplasty procedures being the most effective treatment options. The two major types of urethroplasty are anastomotic urethroplasty and widening the urethral lumen using flaps or grafts (i.e. substitution urethroplasty). However, no ideal material for the latter has been found so far. Designing and selecting such a material is a necessary and challenging endeavour, driving the need for further bioengineered urethral tissue research. This article reviews currently available studies on the potentialities of tissue engineering in urethral reconstruction, in particular those describing the use of both acellular and recellularized tissue-engineered constructs in animal and human models. Possible future developments in this field are also discussed. Copyright © 2015 John Wiley & Sons, Ltd.

Female Urethral Reconstruction

PURPOSE

Female urethral reconstruction can be used successfully to treat a heterogeneous group of urethral disorders through an expanding number of unique approaches. Understanding the diverse etiologies of female urethral stricture and loss is essential in evaluating and diagnosing patients. Although there is an appreciable body of literature addressing female urethral reconstruction individually, there is a paucity of resources that approach this issue holistically. We discuss the relevant female urethral anatomy, pathophysiology, diagnosis and evaluation of female urethral disorders, and current reconstructive techniques, as well as published outcomes data and potential future directions for female urethral reconstruction.

MATERIALS AND METHODS

We reviewed articles published in English and indexed in the PubMed®, Embase® and Google Scholar™ databases, and consulted textbooks. Key search terms used were female, urethra, urethral reconstruction, urethroplasty, pathology, stricture, vaginal flap, bladder flap, graft, dilation, pubovaginal sling, catheterization, imaging, tissue engineering and bioscaffold. We created a synopsis of relevant articles, including original research studies and reviews.

RESULTS

Urethral tissue loss and strictures are caused by traumatic injuries, iatrogenic injuries and, rarely, infections and malignancies. A comprehensive patient history and physical examination are critical for diagnosis. Flexible cystoscopy, voiding cystourethrography and endovaginal magnetic resonance imaging can help to determine the surgical method of repair. Minimally invasive approaches to female urethral reconstruction are associated with poor outcomes. Definitive treatment options for repair of female urethral stricture include vaginal flap/wall urethroplasty, graft urethroplasty and distal urethrectomy with advancement meatoplasty. Repair techniques for urethral loss include primary closure, vaginal flap/wall urethroplasty and bladder flap urethroplasty. Vaginal flap approaches with well vascularized grafts and buccal mucosal grafts have high success rates. Tissue engineered grafts are being investigated as a novel treatment modality.

CONCLUSIONS

Female urethral reconstruction is complex, and one must carefully evaluate patients afflicted with urethral disorders. Urethral stricture and urethral loss have different etiologies. Variations of a standard approach might best address the condition of an individual patient. Long-term outcomes data are not available for contemporary techniques of female urethral reconstruction. The highest success rates have been reported with vaginal flap and buccal mucosal graft urethroplasty. Further studies focusing on newer reconstruction techniques and long-term outcomes are warranted.

Tissue engineering in urothelium regeneration

The development of therapeutic treatments to regenerate urothelium, manufacture tissue equivalents or neourethras for in-vivo application is a significant challenge in the field of tissue engineering. Many studies have focused on urethral defects that, in most cases, inadequately address current therapies. This article reviews the primary tissue engineering strategies aimed at the clinical requirements for urothelium regeneration while concentrating on promising investigations in the use of grafts, cellular preparations, as well as seeded or unseeded natural and synthetic materials. Despite significant progress being made in the development of scaffolds and matrices, buccal mucosa transplants have not been replaced. Recently, graft tissues appear to have an advantage over the use of matrices. These therapies depend on cell isolation and propagation in vitro that require, not only substantial laboratory resources, but also subsequent surgical implant procedures. The choice of the correct cell source is crucial when determining an in-vivo application because of the risks of tissue changes and abnormalities that may result in donor site morbidity. Addressing an appropriately-designed animal model and relevant regulatory issues is of fundamental importance for the principal investigators when a therapy using cellular components has been developed for clinical use.

Tissue engineered buccal mucosa for urethroplasty: progress and future directions

PURPOSE

Autologous buccal mucosa is commonly utilized in the surgical treatment of urethral strictures. Extensive strictures require a larger quantity of tissue, which may lead to donor site morbidity. This review assesses progress in producing tissue engineered buccal mucosa as an alternative graft material.

RESULTS

Few clinical studies have introduced cells onto biological or synthetic scaffolds and implanted resulting constructs in patients. The available studies show that buccal mucosa cells on acellular human dermis or on collagen matrix lead to good acute stage tissue integration. Urothelial cells on a synthetic substrate also perform well. However while some patients do well many years post-grafting, others develop stricture recurrence. Acellular biomaterials used to treat long urethral defects in animals commonly lead to fibrosis.

CONCLUSIONS

Tissue engineered buccal mucosa shows promise as a substitute for native tissue. The fibrosis which occurs months post-implantation may reflect the underlying disease process recurring in these patients.

Acellular matrix in urethral reconstruction

The treatment of severe urethral stenosis has always been a challenge even for skilled urologists. Classic urethroplasty, skin flaps and buccal mucosa grafting may not be used for long and complex strictures. In the quest for an ideal urethral substitute, acellular scaffolds have demonstrated the ability to induce tissue regeneration layer by layer. After several experimental studies, the use of acellular matrices for urethral reconstruction has become a clinical reality over the last decade. In this review we analyze advantages and limitations of both biological and polymeric scaffolds that have been reported in experimental and human studies. Important aspects such as graft extension, surgical technique and cell-seeding versus cell-free grafts will be discussed.

Urethral reconstruction with tissue-engineered human amniotic scaffold in rabbit urethral injury models

BACKGROUND

Mitigating urethral injury remains a great challenge for urologists due to lack of ideal biomaterials for urethroplasty. The application of amniotic membranes (AM) over other synthetic materials make it a better potential source for urethral reconstruction. We separated the basement layer of AM to obtain denuded human amniotic scaffold (dHAS) and then inoculated primary rabbit urethral epithelial cells on the surface of dHAS to define whether this strategy minimize potential rejection and maximize the biocompatibility of human AM.

MATERIAL/METHODS

After the successful acquisition of dHAS from AM, cell-seeded dHAS were prepared and characterized. Both cell-seeded dHAS and acellular dHAS were subcutaneously implanted. Immune responses were compared by histological evaluation and CD4 cell and CD8 cell infiltrations. Then they were applied as urethroplastic materials in the rabbit models of urethral injury to fully explore the feasibility and efficacy of tissue-engineered dHAS xenografts in urethral substitution application.

RESULTS

Mild inflammatory infiltration was observed in cell-seeded dHAS grafts, as revealed by fewer accumulations of CD4 cells and CD8 cells (or neutrophils or other immune cells). Urethral defects of rabbits in the urethroplastic group with dHAS implantation (n=6) were completely resolved in one month, while there were one infection and one fistula in the control group with acellular dHAS patches (n=6). Histopathological analysis revealed mild immune response in cell-seeded dHAS group (P<0.05).

CONCLUSIONS

Tissue-engineered dHAS minimize potential rejection and maximize the biocompatibility of AM, which makes it a potential ideal xenograft for urethral reconstruction.

CR, Mauney JR. Acellular bi-layer silk fibroin scaffolds support tissue regeneration in a rabbit model of onlay urethroplasty

Acellular scaffolds derived from Bombyx mori silk fibroin were investigated for their ability to support functional tissue regeneration in a rabbit model of urethra repair. A bi-layer silk fibroin matrix was fabricated by a solvent-casting/salt leaching process in combination with silk fibroin film casting to generate porous foams buttressed by homogeneous silk fibroin films. Ventral onlay urethroplasty was performed with silk fibroin grafts (Group 1, N = 4) (Width×Length, 1×2 cm²) in adult male rabbits for 3 m of implantation. Parallel control groups consisted of animals receiving small intestinal submucosa (SIS) implants (Group 2, N = 4) or urethrotomy alone (Group 3, N = 3). Animals in all groups exhibited 100% survival prior to scheduled euthanasia and achieved voluntary voiding following 7 d of initial catheterization. Retrograde urethrography of each implant group at 3 m post-op revealed wide urethral calibers and preservation of organ continuity similar to pre-operative and urethrotomy controls with no evidence of contrast extravasation, strictures, fistulas, or stone formation. Histological (hematoxylin and eosin and Masson's trichrome), immunohistochemical, and histomorphometric analyses demonstrated that both silk fibroin and SIS scaffolds promoted similar extents of smooth muscle and epithelial tissue regeneration throughout the original defect sites with prominent contractile protein (α-smooth muscle actin and SM22α) and cytokeratin expression, respectively. De novo innervation and vascularization were also evident in all regenerated tissues indicated by synaptophysin-positive neuronal cells and vessels lined with CD31 expressing endothelial cells. Following 3 m post-op, minimal acute inflammatory reactions were elicited by silk fibroin scaffolds characterized by the presence of eosinophil granulocytes while SIS matrices promoted chronic inflammatory responses indicated by mobilization of mononuclear cell infiltrates. The results of this study demonstrate that bi-layer silk fibroin scaffolds represent promising biomaterials for onlay urethroplasty, capable of promoting similar degrees of tissue regeneration in comparison to conventional SIS scaffolds, but with reduced immunogenicity.

Epithelial-differentiated adipose-derived stem cells seeded bladder acellular matrix grafts for urethral reconstruction: an animal model

The limited amount of available epithelial tissue is considered a main cause of the high rate of urethral reconstruction failures. The aim of this study was to investigate whether epithelial-differentiated rabbit adipose-derived stem cells (Epith-rASCs) could play a role of epithelium in vivo functionally and be a potential substitute of urothelium. Substitution urethroplasty was performed to repair an anterior urethral defect in male New Zealand rabbits using Epith-rASCs seeded bladder acellular matrix grafts (BAMGs) after 5-bromo-2'-deoxyuridine (BrdU) labeling, based on the in vitro epithelial induction system we previously described. Urethroplasty with cell-free BAMGs and with undifferentiated rASCs (Und-rASCs) seeded BAMGs were performed as controls. After surgery, a notable amelioration of graft contracture and recovery of urethral continuity were observed in the Epith-rASCs/BAMG group by retrograde urethrograms and macroscopic inspection. Immunofluorescence revealed that the BrdU-labeled Epith-rASCs/Und-rASCs colocalized with cytokeratin 13 or myosin. Consistent with the results of western blotting, at early postimplantation stage, the continuous epithelial layer with local multilayered structure was observed in the Epith-rASCs/BAMG group, whereas no significant growth and local monolayer growth profile of epithelial cells were observed in the BAMG and Und-rASCs/BAMG group, respectively. The results showed that Epith-rASCs could serve as a potential substitute of urothelium for urethral tissue engineering and be available to prevent lumen contracture and subsequent complications including recurrent stricture.

SIU/ICUD Consultation on Urethral Strictures: The management of anterior urethral stricture disease using substitution urethroplasty

In this systematic review of the literature, a search of the PubMed database was conducted to identify articles dealing with augmentation/substitution urethral reconstruction of the anterior urethral stricture. The evidence was categorized by stricture site, surgical technique, and the type of tissue used. The committee appointed by the International Consultation on Urological Disease reviewed this data and produced a consensus statement relating to the augmentation and substitution of the anterior urethra. In this review article, the background pathophysiology is discussed. Most cases of urethral stricture disease in the anterior urethra are consequent on an ischemic spongiofibrosis. The choice of technique and the surgical approach are discussed along with the potential pros and cons of the use of a graft vs a flap. There is research potential for tissue engineering. The efficacy of the surgical approach to the urethra is reviewed. Whenever possible, a 1-stage approach is preferable from the patient's perspective. In some cases, with complex penile urethral strictures, a 2-stage procedure might be appropriate, and there is an important potential role for the use of a perineal urethrostomy in cases where there is an extensive anterior urethral stricture or where the patient does not wish to undergo complex surgery, or medical contraindications make this hazardous. It is important to have accurate outcome measures for the follow-up of patients, and in this context, a full account needs to be taken of patients' perspectives by the use of appropriate patient-reported outcome measures. The use of symptoms and a flow rate can be misleading. It is well established that with a normally functioning bladder, the flow rate does not diminish until the caliber of the urethra falls below 10F. The most accurate means of following up patients after stricture surgery are by the use of endoscopy or visualization by urethrography. Careful consideration needs to be made of the outcomes reported in the world literature, bearing in mind these aforementioned points. The article concludes with an overview of the key recommendations provided by the committee.

Tissue engineering in urethral reconstruction--an update

The field of tissue engineering is rapidly progressing. Much work has gone into developing a tissue engineered urethral graft. Current grafts, when long, can create initial donor site morbidity. In this article, we evaluate the progress made in finding a tissue engineered substitute for the human urethra. Researchers have investigated cell-free and cell-seeded grafts. We discuss different approaches to developing these grafts and review their reported successes in human studies. With further work, tissue engineered grafts may facilitate the management of lengthy urethral strictures requiring oral mucosa substitution urethroplasty.

Long-term results of small intestinal submucosa graft in bulbar urethral reconstruction

OBJECTIVE

To retrospectively report the long-term results of the use of a small intestinal submucosa (SIS) graft in bulbar urethral repair.

METHODS

From 2003 to 2007, 25 men (mean age 40.5 years) with bulbar strictures underwent patch graft urethroplasty using SIS placed on the dorsal or ventral or dorsal plus ventral surface of the urethra. The mean follow-up period was 71 months (range 52-100). The clinical outcome was considered a failure when any postoperative instrumentation, including dilation, was needed.

RESULTS

Of the 25 cases, 19 (76%) were successful and 6 (24%) were failures. No postoperative complications were related to the use of heterologous graft material, such as infection or rejection. The failure rate was 14% for strictures <4 cm and 100% for strictures >4 cm.

CONCLUSION

At long-term follow-up, in bulbar stricture repair, SIS grafts showed similar results to penile skin grafts but were less effective than buccal mucosa grafts. The use of SIS as graft material should not be the first choice but represents an alternative option for patients with bulbar strictures that are not long and who refuse the harvesting or are not ideal candidates for buccal mucosa or penile skin grafts. Larger series of patients with longer follow-up are needed before widespread use can be advocated.

Mechanical stimuli-induced urothelial differentiation in a human tissue-engineered tubular genitourinary graft

BACKGROUND

A challenge in urologic tissue engineering is to obtain well-differentiated urothelium to overcome the complications related to other sources of tissues used in ureteral and urethral substitution.

OBJECTIVE

We investigated the effects of in vitro mechanical stimuli on functional and morphologic properties of a human tissue-engineered tubular genitourinary graft (TTGG).

DESIGN, SETTING, AND PARTICIPANTS

Using the self-assembly technique, we developed a TTGG composed of human dermal fibroblasts and human urothelial cells without exogenous scaffolding. Eight substitutes were subjected to dynamic flow and hydrostatic pressure for up to 2 wk compared to static conditions (n=8).

MEASUREMENTS

Stratification and cell differentiation were assessed by histology, electron microscopy, immunostaining, and uroplakin gene expression. Barrier function was determined by permeation studies with carbon 14-urea.

RESULTS AND LIMITATIONS

Dynamic conditions showed well-established stratified urothelium and basement membrane formation, whereas no stratification was observed in static culture. The first signs of cell differentiation were perceived after 7 d of perfusion and were fully expressed at day 14. Superficial cells under perfusion displayed discoidal and fusiform vesicles and positive staining for uroplakin 2, cytokeratine 20, and tight junction protein ZO-1, similar to native urothelium. Mechanical stimuli induced expression of the major uroplakin transcripts, whereas expression was low or undetectable in static culture. Permeation studies showed that mechanical constraints significantly improved the barrier function compared to static conditions (p<0.01 at 14 d, p<0.05 at 7 d) and were comparable to native urothelium.

CONCLUSIONS

Mechanical stimuli induced in vitro terminal urothelium differentiation in a human genitourinary substitute displaying morphologic and functional properties equivalent to a native urologic conduit.

Tissue engineering in urethral reconstruction

Tissue engineering is an exciting and rapidly evolving technology. In this review, we discuss the recent progress made in the field of urethral reconstruction and consider the clinical implications and further advancement of these endeavours.

Urethral reconstruction of critical defects in rabbits using molecularly defined tubular type I collagen biomatrices: key issues in growth factor addition

Tubular type I collagen biomatrices with and without growth factors (GFs) were constructed and evaluated in a rabbit model for critical urethral defects. Porous tubular biomatrices with an inner diameter of 3  mm were prepared using highly purified collagen fibrils and were crosslinked with or without heparin. Heparinized biomatrices were supplemented with the heparin-binding GFs vascular endothelial GF, fibroblast GF-2, and heparin-binding epidermal GF. Biomatrices with and without GFs were used to replace a critical 1 cm urethral segment in rabbits (n = 32). All animals showed normal urination without urinary retention. General histology and immunohistology of graft areas (2, 4, 12, and 24 weeks after implantation) indicated that all biomatrices were replaced by urethra-like structures with normal appearing cytokeratin-positive urothelium surrounded by vascularized tissue. The GF-containing biomatrices showed an increase in extracellular matrix deposition, neovascularization, urothelium, glands, granulocytes, and fibroblasts, compared with biomatrices without GF. GFs substantially improved molecular features of healing but failed to be superior in functional outcome. Retrograde urethrography indicated a normal urethral caliber in case of biomatrices without GF, but a relative narrowing of the urethra at 2 weeks postsurgery and diverticula after 4 weeks in case of biomatrices with GF. In conclusion, tubular acellular type I collagen biomatrices were successful in repairing urethral lesions in artificial urethral defects, and inclusion of GF has a profound effect on regenerative processes.

[Urethral reconstructive surgery]

There is no technique which can be used in all types and localizations of urethral strictures. Urethral strictures occur in the majority of cases in the bulbar urethra. The success rate of urethroplasty is above 80% and results are much better compared to DVIU. Dorsal onlay shows a significantly better success rate than ventral onlay. If the graft bed has poor vascularization a flap should be used or a staged approach should be considered.

Tissue Engineering for the Lower Urinary Tract: A Review of a State of the Art Approach

OBJECTIVES

Tissue engineering (TE) has become synonymous with physiological and functional reconstructive approaches in medicine. Although the goals of TE are ambitious and have not yet been attained, significant milestones have been achieved and future possibilities are great. To examine these possibilities with a special emphasis on the lower urinary tract, we provide a review of the development of TE techniques and a high-level overview of related regulatory and legal issues.

METHODS

Current trends in the field of TE, including the use of stem cells, scaffold optimization, and acellular tissue and growth factors, were reviewed and critically assessed through a comprehensive literature review using the PubMed database. Because of the rapid development of new TE approaches, recent abstracts from international urology conventions were included. A review of 2007 European Medicines Agency and Commission for Advanced Therapies legal regulations was also performed.

RESULTS

Although several clinical TE approaches have been developed, most lack objective validation. A variety of TE techniques are currently under development or investigation, but thus far, no one approach is clearly superior on the basis of significant long-term studies. A medical product based on TE and stem cells can be successfully developed only with careful consideration of legal and ethical regulations.

CONCLUSIONS

TE holds the promise for a tremendous impact on reconstructive urology. However, research must be focused and intensified for the full potential clinical benefits to be made widely available. Because the product development is affected by legal regulations, consensus must be achieved.

Small intestinal submucosa (SIS) graft urethroplasty: short-term results

OBJECTIVE

We evaluated the use of small intestinal submucosa (SIS) graft in penile and bulbar urethroplasties.

METHODS

From 2003 to 2004, 20 men (mean age, 41 yr) with anterior urethral strictures underwent urethroplasty using SIS (COOK) as an inlay or onlay patch graft. Stricture location was penile in 1 patient, bulbar in 16, and penile-bulbar in 3. Average stricture and graft lengths were 3 and 5.7 cm, respectively. A dorsal inlay graft was performed in 14 cases, ventral onlay graft in 1, and dorsal inlay plus ventral onlay in 5. Clinical outcome was considered successful if no postoperative procedure was needed.

RESULTS

Mean follow-up period was 21 mo (range: 13-35 mo). Seventeen cases (85%) were successful and 3 (15%) were failures. No postoperative complications were related to the use of heterologous graft material, such as infection or rejection. Sixteen successes (94%) were bulbar repairs and one a penile-bulbar repair, with stricture and graft average lengths 2.6 and 5.35 cm, respectively. Cystoscopy at 3 mo revealed adequate calibre lumens, but SIS grafted areas were not completely replaced by urothelium. The three failures were penile and penile-bulbar urethral repairs with stricture and graft average lengths of 5.7 and 7.7 cm, respectively. Recurrences showed fibrous tissue involving the grafted area with extension into the penile and bulbar urethra.

CONCLUSIONS

In our short-term results, SIS seems to be a versatile material that may have a role in select urethral reconstructions. Longer follow-up and further investigations in select patients are needed before widespread use is advocated.