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

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.

Oral adverse outcomes associated with the buccal mucosa graft for urethroplasty

OBJECTIVE

The buccal mucosa graft (BMG) is the standard graft for reconstructive urology, but management of the donor site remains under debate. The authors compared postoperative oral adverse outcomes between management methods (closure, nonclosure, or xenograft-assisted closure).

STUDY DESIGN

A retrospective cohort study was conducted, enrolling patients treated at Harborview Medical Center, Seattle, Washington. The patients had a history of urethroplasty using a unilateral BMG, and the primary outcome variables were postoperative oral adverse outcomes, defined as subjective changes in mouth opening, smile, chewing, speech, intraoral bleeding, paresthesia, trismus, and infection. Multivariate and regression analyses were performed.

RESULTS

The sample was composed of 137 patients (95% male; mean age, 48 years). The mean surface areas of the BMG for closure, nonclosure, and xenograft were 1059, 1178, and 1228 mm², respectively. Thirty-four patients completed the survey (7 closure, 17 nonclosure, and 10 xenograft). Multiple linear regression showed a significant difference between the 3 groups with respect to patient-reported chewing ability and trismus favoring xenograft at larger graft sizes (P < .01).

CONCLUSIONS

Xenograft-assisted closure may reduce long-term oral adverse outcomes associated with trismus and subjective changes in chewing, mouth opening, speaking, and smiling with larger grafts. In addition, limited postoperative patient education for oral rehabilitation exercises was noted.

Sources, Selection, and Microenvironmental Preconditioning of Cells for Urethral Tissue Engineering

Urethral stricture is a common urinary tract disorder in men that can be caused by iatrogenic causes, trauma, inflammation, or infection and often requires reconstructive surgery. The current therapeutic approach for complex urethral strictures usually involves reconstruction with autologous tissue from the oral mucosa. With the goal of overcoming the lack of sufficient autologous tissue and donor site morbidity, research over the past two decades has focused on cell-based tissue-engineered substitutes. While the main focus has been on autologous cells from the penile tissue, bladder, and oral cavity, stem cells from sources such as adipose tissue and urine are competing candidates for future urethral regeneration due to their ease of collection, high proliferative capacity, maturation potential, and paracrine function. This review addresses the sources, advantages, and limitations of cells for tissue engineering in the urethra and discusses recent approaches to improve cell survival, growth, and differentiation by mimicking the mechanical and biophysical properties of the extracellular environment.

Tailor-made natural and synthetic grafts for precise urethral reconstruction

Injuries to the urethra can be caused by malformations, trauma, inflammation, or carcinoma, and reconstruction of the injured urethra is still a significant challenge in clinical urology. Implanting grafts for urethroplasty and end-to-end anastomosis are typical clinical interventions for urethral injury. However, complications and high recurrence rates remain unsatisfactory. To address this, urethral tissue engineering provides a promising modality for urethral repair. Additionally, developing tailor-made biomimetic natural and synthetic grafts is of great significance for urethral reconstruction. In this work, tailor-made biomimetic natural and synthetic grafts are divided into scaffold-free and scaffolded grafts according to their structures, and the influence of different graft structures on urethral reconstruction is discussed. In addition, future development and potential clinical application strategies of future urethral reconstruction grafts are predicted.

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.

European Association of Urology Guidelines on Urethral Stricture Disease (Part 1): Management of Male Urethral Stricture Disease

OBJECTIVE

To present a summary of the 2021 version of the European Association of Urology (EAU) guidelines on management of male urethral stricture disease.

EVIDENCE ACQUISITION

The panel performed a literature review on these topics covering a time frame between 2008 and 2018, and used predefined inclusion and exclusion criteria for the literature to be selected. Key papers beyond this time period could be included as per panel consensus. A strength rating for each recommendation was added based on a review of the available literature and after panel discussion.

EVIDENCE SYNTHESIS

Management of male urethral strictures has extensively been described in literature. Nevertheless, few well-designed studies providing high level of evidence are available. In well-resourced countries, iatrogenic injury to the urethra is one of the most common causes of strictures. Asymptomatic strictures do not always need active treatment. Endoluminal treatments can be used for short, nonobliterative strictures at the bulbar and posterior urethra as first-line treatment. Repetitive endoluminal treatments are not curative. Urethroplasty encompasses a multitude of techniques, and adaptation of the technique to the local conditions of the stricture is crucial to obtain durable patency rates.

CONCLUSIONS

Management of male urethral strictures is complex, and a multitude of techniques are available. Selection of the appropriate technique is crucial, and these guidelines provide relevant recommendations.

PATIENT SUMMARY

Injury to the urethra by medical interventions is one of the most common reasons of male urethral stricture disease in well-resourced countries. Although different techniques are available to manage urethral strictures, not every technique is appropriate for every type of stricture. These guidelines, developed based on an extensive literature review, aim to guide physicians in the selection of the appropriate technique(s) to treat a specific type of urethral stricture.

Creation of Tissue-Engineered Urethras for Large Urethral Defect Repair in a Rabbit Experimental Model

Introduction: Tissue engineering is a potential source of urethral substitutes to treat severe urethral defects. Our aim was to create tissue-engineered urethras by harvesting autologous cells obtained by bladder washes and then using these cells to create a neourethra in a chronic large urethral defect in a rabbit model. Methods: A large urethral defect was first created in male New Zealand rabbits by resecting an elliptic defect (70 mm²) in the ventral penile urethra and then letting it settle down as a chronic defect for 5-6 weeks. Urothelial cells were harvested noninvasively by washing the bladder with saline and isolating urothelial cells. Neourethras were created by seeding urothelial cells on a commercially available decellularized intestinal submucosa matrix (Biodesign® Cook-Biotech®). Twenty-two rabbits were divided into three groups. Group-A (n = 2) is a control group (urethral defect unrepaired). Group-B (n = 10) and group-C (n = 10) underwent on-lay urethroplasty, with unseeded matrix (group-B) and urothelial cell-seeded matrix (group-C). Macroscopic appearance, radiology, and histology were assessed. Results: The chronic large urethral defect model was successfully created. Stratified urothelial cultures attached to the matrix were obtained. All group-A rabbits kept the urethral defect size unchanged (70 ± 2.5 mm²). All group-B rabbits presented urethroplasty dehiscence, with a median defect of 61 mm² (range 34-70). In group-C, five presented complete correction and five almost total correction with fistula, with a median defect of 0.3 mm² (range 0-12.5), demonstrating a significant better result (p = 7.85 × 10^-5). Urethrography showed more fistulas in group-B (10/10, versus 5/10 in group-C) (p = 0.04). No strictures were found in any of the groups. Group-B histology identified the absence of ventral urethra in unrepaired areas, with squamous cell metaplasia in the edges toward the defect. In group-C repaired areas, ventral multilayer urothelium was identified with cells staining for urothelial cell marker cytokeratin-7. Conclusions: The importance of this study is that we used a chronic large urethral defect animal model and clearly found that cell-seeded transplants were superior to nonseeded. In addition, bladder washing was a feasible method for harvesting viable autologous cells in a noninvasive way. There is a place for considering tissue-engineered transplants in the surgical armamentarium for treating complex urethral defects and hypospadias cases.

Complicated bulbar urethral stricture successfully treated using augmented anastomotic urethroplasty: A case report

Introduction

Management of a complicated urethral stricture is a urological challenge. We present a case of a complicated urethral stricture successfully treated using augmented anastomotic urethroplasty.

Case presentation

A 48‐year‐old man visited our department for the treatment of urethral stricture, for which repeated transurethral procedures had failed. The operative view revealed that the urethral lumen was, in fact, completely obliterated over a 30‐mm segment. We proceeded with augmented anastomotic urethroplasty. After the excision of the obliterated lesion, the ventral half of the bulbar urethral ends was anastomosed and their dorsal half was subsequently augmented via buccal mucosa spread and then fixed to the corpus cavernosa. There has been no indication of recurrence, 4 months after the procedure.

Conclusion

Augmented anastomotic urethroplasty is a useful technique for repairing a complicated bulbar stricture. Urologists should understand appropriate indications for each treatment method so as to not make cases more complicated to treat.

Urethroplasty performed with an autologous urothelium-vegetated collagen fleece to treat urethral stricture in the minipig model

INTRODUCTION AND OBJECTIVE

Tissue-engineered materials in urethral reconstructive surgeries are a promising field for innovative therapy. Collagen matrices increase stability of cell-based implants and can promote viability and proliferation of urothelial cells. In this study, a collagen type I-based cell carrier (CCC) with stratified multi-layer autologous urothelium was used for urethroplasty after induction of urethral stricture in eight minipigs.

MATERIALS AND METHODS

Minipigs underwent surgical procedures to induce urethral stricture by thermocoagulation. Simultaneously, bladder tissue was harvested. Urothelial cells were expanded, labeled with PKH26 and seeded onto CCC in high density. 3 weeks after strictures were induced and verified by urethrography, minipigs underwent urethroplasty using the seeded CCC. Two animals were euthanized after 1, 2, 4, and 24 weeks. Urethras were histologically examined for integration and survival of seeded CCC. In vivo phenotype of multi-layered urothelium matrix constructs was characterized via immunofluorescence staining with pancytokeratin, CK20, p63, E-cadherin and ZO-1.

RESULTS

Seeded CCCs showed excellent stability and suturability after manipulation and application. Transplanted cells were detected using positive PKH26 fluorescence up to 6 months after labeling. Urothelium matrix implants integrated well into the host tissue without sign of inflammation. Animals showed no sign of rejection or stricture recurrence (urethrography) at any time during experimental period. Immunofluorescence analysis confirmed epithelial phenotype, junction formation and differentiation after 2 weeks.

CONCLUSION

CCC can be suitable for urologic reconstructive surgeries and represents a promising option for clinical application. Longer follow-up results are required to exclude re-occurrence of stricture reformation.

Placental membrane grafts for urethral replacement in a rabbit model: a pilot study

PURPOSE

Several graft materials are available for use in the treatment of urethral stricture disease. Placental membrane is being used in a variety of settings as a graft in wound healing and tissue repair. We aim to evaluate the effect of implanting decellularized human placental membrane into rabbit urethras.

METHODS

Dorsal onlay graft urethroplasty using prepared human placental membrane was performed in 10 New Zealand White rabbits (Oryctolagus cuniculus). After 3 months, the rabbits underwent cystourethroscopy to evaluate urethral patency. The rabbits were then euthanized and the urethras examined for pathological findings.

RESULTS

All urethroplasties were performed without complication. There were no observed episodes of urinary retention, infection, or renal failure. Urethral patency was achieved in all rabbits 3 months postoperatively. Urothelial replacement of the placental membrane graft was observed in all rabbits without malignant transformation.

CONCLUSION

Dorsal onlay urethroplasty using decellularized human placental membrane can safely be performed in a rabbit model. This pilot study demonstrated urothelial replacement of human placental membrane in the rabbit urethra without stricture formation. Placental membrane is a promising biomaterial for urethral reconstruction.

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.

Histopathological changes in oral mucosa in cases of failed augmented urethroplasty

OBJECTIVE

Histopathological changes in oral (buccal or lingual) mucosa after exposure to urine are still not completely understood. We evaluated these changes in free oral mucosal graft integrated in human urethra.

MATERIAL AND METHODS

Total 19 patients with recurrent urethral stricture after oral mucosa urethroplasty (buccal 12 and lingual 7) were prospectively evaluated. Intraoperatively integrated buccal or lingual mucosal graft sample that was previously engrafted to urethra was completely excised along with healthy oral mucosa, and it was sample processed for histopathological evaluation by dedicated pathologist. Preoperative clinical data were properly collected from all the study participants.

RESULTS

The mean age of the patients was 30 years, and the mean preoperative peak flow rate was 4.2 mL/s. Etiology of initial stricture was idiopathic in 13 (68.42%) patients and traumatic urethral catheterization in 6 (31.58%) patients. Mean interval from previous buccal mucosal urethroplasty to current urethroplasty was 21.9 months (range 12-46 months). On repeat urethroplasty, the mean stricture segment length was 59.2 (38-77) mm [60.08 (38-74.6) mm buccal, and 58.32 (39.6-77) mm lingual]. These integrated oral mucosal grafts maintained their histopathological characteristics in all patients except some kind of changes like submucosal fibrosis in seven (58.33%) cases of buccal and vacuolar degeneration in five (71.42%) cases of lingual mucosal urethroplasty.

CONCLUSION

Histopathological characteristics of integrated oral (buccal and lingual) mucosal grafts were maintained even on exposure to urine except some changes like submucosal fibrosis and vacuolar degeneration. Impact of these changes require further research.

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.

Refractory Urethral Stricture Management: Indications for Alternative Grafts and Flaps

PURPOSE OF REVIEW

Urethral strictures that are refractory to initial management present unique challenges to the reconstructive surgeon. Treatment trends have shifted as new tissue resources are becoming available. There is renewed interest in old methods as skill and technique have improved. We describe the scope of the surgical armamentarium available to develop creative approaches and successful outcomes.

RECENT FINDINGS

We discuss techniques to maximize the availability of oral mucosa, harvest and use of rectal mucosa, and developments in tissue engineering. Evolving methods to assess success of repair are also described. Urethral reconstruction for refractory urethral strictures requires proficiency with multiple methods as these strictures often require combining techniques for successful treatment.

Current Status of Tissue Engineering in the Management of Severe Hypospadias

Hypospadias, characterized by misplacement of the urinary meatus in the lower side of the penis, is a frequent birth defect in male children. Because of the huge variation in the anatomic presentation of hypospadias, no single urethroplasty procedure is suitable for all situations. Hence, many surgical techniques have emerged to address the shortage of tissues required to bridge the gap in the urethra particularly in the severe forms of hypospadias. However, the rate of postoperative complications of currently available surgical procedures reaches up to one-fourth of the patients having severe hypospadias. Moreover, these urethroplasty techniques are technically demanding and require considerable surgical experience. These limitations have fueled the development of novel tissue engineering techniques that aim to simplify the surgical procedures and to reduce the rate of complications. Several types of biomaterials have been considered for urethral repair, including synthetic and natural polymers, which in some cases have been seeded with cells prior to implantation. These methods have been tested in preclinical and clinical studies, with variable degrees of success. This review describes the different urethral tissue engineering methodologies, with focus on the approaches used for the treatment of hypospadias. At present, despite many significant advances, the search for a suitable tissue engineering approach for use in routine clinical applications continues.

Concise Review: Translating Regenerative Biology into Clinically Relevant Therapies: Are We on the Right Path?

Despite approaches in regenerative medicine using stem cells, bio‐engineered scaffolds, and targeted drug delivery to enhance human tissue repair, clinicians remain unable to regenerate large‐scale, multi‐tissue defects in situ. The study of regenerative biology using mammalian models of complex tissue regeneration offers an opportunity to discover key factors that stimulate a regenerative rather than fibrotic response to injury. For example, although primates and rodents can regenerate their distal digit tips, they heal more proximal amputations with scar tissue. Rabbits and African spiny mice re‐grow tissue to fill large musculoskeletal defects through their ear pinna, while other mammals fail to regenerate identical defects and instead heal ear holes through fibrotic repair. This Review explores the utility of these comparative healing models using the spiny mouse ear pinna and the mouse digit tip to consider how mechanistic insight into reparative regeneration might serve to advance regenerative medicine. Specifically, we consider how inflammation and immunity, extracellular matrix composition, and controlled cell proliferation intersect to establish a pro‐regenerative microenvironment in response to injuries. Understanding how some mammals naturally regenerate complex tissue can provide a blueprint for how we might manipulate the injury microenvironment to enhance regenerative abilities in humans. Stem Cells Translational Medicine2018;7:220–231

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.

Mechanical induction of bi-directional orientation of primary porcine bladder smooth muscle cells in tubular fibrin-poly(vinylidene fluoride) scaffolds for ureteral and urethral repair using cyclic and focal balloon catheter stimulation

To restore damaged organ function or to investigate organ mechanisms, it is necessary to prepare replicates that follow the biological role model as faithfully as possible. The interdisciplinary field of tissue engineering has great potential in regenerative medicine and might overcome negative side effects in the replacement of damaged organs. In particular, tubular organ structures of the genitourinary tract, such as the ureter and urethra, are challenging because of their complexity and special milieu that gives rise to incrustation, inflammation and stricture formation. Tubular biohybrids were prepared from primary porcine smooth muscle cells embedded in a fibrin gel with a stabilising poly(vinylidene fluoride) mesh. A mechanotransduction was performed automatically with a balloon kyphoplasty catheter. Diffusion of urea and creatinine, as well as the bursting pressure, were measured. Light and electron microscopy were used to visualise cellular distribution and orientation. Histological evaluation revealed a uniform cellular distribution in the fibrin gel. Mechanical stimulation with a stretch of 20% leads to a circumferential orientation of smooth muscle cells inside the matrix and a longitudinal alignment on the outer surface of the tubular structure. Urea and creatinine permeability and bursting pressure showed a non-statistically significant trend towards stimulated tissue constructs. In this proof of concept study, an innovative technique of intraluminal pressure for mechanical stimulation of tubular biohybrids prepared from autologous cells and a composite material induce bi-directional orientation of smooth muscle cells by locally and cyclically applied mechanical tension. Such geometrically driven patterns of cell growth within a scaffold may represent a key stage in the future tissue engineering of implantable ureter replacements that will allow the active transportation of urine from the renal pelvis into the bladder.

Management of penile urethral strictures: Challenges and future directions

The anatomy of the penile urethra presents additional challenges when compared to other urethral segments during open stricture surgery particularly because of its unsuitability for excision and primary anastomosis and its relatively deficient corpus spongiosum. Stricture aetiology, location, length and previous surgical intervention remain the primary factors influencing the choice of penile urethroplasty technique. We have identified what we feel are the most important challenges and controversies in penile urethral stricture reconstruction, namely the use of flaps vs grafts, use of skin or oral mucosal tissue for augmentation/substitution and when a single or a staged approach is indicated to give the best possible outcome. The management of more complex cases such as pan-urethral lichen-sclerosus strictures and hypospadias “cripples” is outlined and potential developments for the future are presented.

New frontiers in urethral reconstruction: injectables and alternative grafts

Contemporary management of anterior urethral strictures requires both endoscopic as well as complex substitution urethroplasty, depending on the nature of the urethral stricture. Recent clinical and experimental studies have explored the possibility of augmenting traditional endoscopic urethral stricture management with anti-fibrotic injectable medications. Additionally, although buccal mucosa remains the gold standard graft for substitution urethroplasty, alternative grafts are necessary for reconstructing particularly complex urethral strictures in which there is insufficient buccal mucosa or in cases where it may be contraindicated. This review summarizes the data of the most promising injectable adjuncts to endoscopic stricture management and explores the alternative grafts available for reconstructing the most challenging urethral strictures. Further research is needed to define which injectable medications and alternative grafts may be best suited for urethral reconstruction in the future.

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.

Current trends in urethral stricture management

The recent International Consultation on Urological Disease (ICUD) panel 2010 confirmed that a urethral stricture is defined as a narrowing of the urethra consequent upon ischaemic spongiofibrosis, as distinct from sphincter stenoses and a urethral disruption injury. Whenever possible, an anastomotic urethroplasty should be performed because of the higher success rate as compared to augmentation urethroplasty. There is some debate currently regarding the critical stricture length at which an anastomotic procedure can be used, but clearly the extent of the spongiofibrosis and individual anatomical factors (the length of the penis and urethra) are important, the limitation for this being extension of dissection beyond the peno-scrotal junction and the subsequent production of chordee. More recently, there has been interest in whether to excise and anastomose or to carry out a stricturotomy and reanastomosis using a Heineke-Miculicz technique. Augmentation urethroplasty has evolved towards the more extensive use of oral mucosa grafts as compared to penile skin flaps, as both flaps and grafts have similar efficacy and certainly the use of either dorsal or ventral positioning seems to provide comparable results. It is important that the reconstructive surgeon is well versed in the full range of available repair techniques, as no single method is suitable for all cases and will enable the management of any unexpected anatomical findings discovered intra-operatively.

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.

Graft surgery in extensive urethral stricture disease

Surgical treatment of long urethral stricture disease remains one of the most challenging problems in urology. In recent years there has been continuous discussion with regard to the etiology, location, length, and management of extensive urethral stricture disease. Various tissues such as genital and extragenital skin, buccal mucosa, lingual mucosa, small intestinal submucosa, and bladder mucosa have been proposed for urethral reconstruction. The most frequent questions pertain to the optimal technique for urethroplasty and the optimal graft for substitution urethroplasty, as judged by both patient satisfaction and outcome success. We review the recent literature with respect to any new information on graft urethroplasty for extensive urethral stricture.

Histopathological characteristics of buccal mucosa transplants in humans after engraftment to the urethra: a prospective study

PURPOSE

Histopathological changes in buccal mucosa transplants after engraftment to the urethra and exposure to urine remain nebulous. We investigated histopathological changes in buccal mucosa transplants integrated into the urethra in humans.

MATERIALS AND METHODS

We prospectively evaluated 22 patients with recurrent urethral stricture after buccal mucosa urethroplasty between November 2012 and October 2013. All patients underwent repeat buccal mucosa urethroplasty performed by a single surgeon. Intraoperatively we harvested a sample of the integrated buccal mucosa transplant previously engrafted to the urethra, a sample of healthy urethra, a sample of freshly harvested buccal mucosa from the contralateral inner cheek and a sample of fibrotic tissue from the area of the current stricture. A dedicated uropathologist performed meticulous histopathological examination of all tissue samples using hematoxylin and eosin staining. Preoperative clinical data were also collected on all patients.

RESULTS

The mean interval from previous to current buccal mucosa urethroplasty was 22.2 months (range 4.1 to 76.0). Mean stricture length at repeat urethroplasty was 52.7 mm (range 30.0 to 70.0). Histopathological characteristics of the integrated buccal mucosa transplants were completely preserved in all patients, consisting of thick sheets of stratified nonkeratinized squamous epithelium with a stratum spinosum. Transplants were not partially or entirely overgrown with urothelium.

CONCLUSIONS

Buccal mucosa transplants retain their histopathological characteristics and are not overgrown with urothelium after urethral engraftment and urine exposure in humans. These findings may explain the superiority of buccal mucosa transplants on the outcome of substitution urethroplasty compared to that of other materials.

Regenerative medicine in urology

Repair and reconstruction of damaged tissues and organs has been a major issue in the medical field. Regenerative medicine and tissue engineering, as rapid evolving technologies, may offer alternative treatments and hope for patients with serious defects and end-stage diseases. Most urologic diseases could benefit from the development of regenerative medicine and tissue engineering. This article discusses the role of cells and materials in regenerative medicine, as well as the status of current role of regenerative medicine for the generation of specific urologic organs.

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.

Tissue engineering of urinary bladder and urethra: advances from bench to patients

Urinary tract is subjected to many varieties of pathologies since birth including congenital anomalies, trauma, inflammatory lesions, and malignancy. These diseases necessitate the replacement of involved organs and tissues. Shortage of organ donation, problems of immunosuppression, and complications associated with the use of nonnative tissues have urged clinicians and scientists to investigate new therapies, namely, tissue engineering. Tissue engineering follows principles of cell transplantation, materials science, and engineering. Epithelial and muscle cells can be harvested and used for reconstruction of the engineered grafts. These cells must be delivered in a well-organized and differentiated condition because water-seal epithelium and well-oriented muscle layer are needed for proper function of the substitute tissues. Synthetic or natural scaffolds have been used for engineering lower urinary tract. Harnessing autologous cells to produce their own matrix and form scaffolds is a new strategy for engineering bladder and urethra. This self-assembly technique avoids the biosafety and immunological reactions related to the use of biodegradable scaffolds. Autologous equivalents have already been produced for pigs (bladder) and human (urethra and bladder). The purpose of this paper is to present a review for the existing methods of engineering bladder and urethra and to point toward perspectives for their replacement.

The use of small intestinal submucosa graft for hypospadias repair: Pilot study

Objective

To evaluate the outcome of using commercially available (SIS) grafts for repairing hypospadias. Collagen-based acellular matrices, including SIS and bladder submucosa matrix, have been used to repair urethral strictures, with varying success, and patients with hypospadias and with inadequate or no genital skin need a substitute tissue for urethroplasty.

Patients and methods

This pilot study included 12 patients (mean age 8 years, range 1.5–15) with hypospadias (distal in six, mid-shaft in four and proximal in two). They underwent a repair with four layers of prefabricated SIS as an onlay graft. The outcome was assessed for cosmetic appearance, urinary stream and the postvoid residual volume. The chi-squared and Mann–Whitney U-tests were used to assess the relationship between preoperative factors and the outcome of the repair with SIS grafting.

Results

The mean (range) follow-up was 23 (6–36) months. Nine patients ultimately voided normally, with a good cosmetic appearance and no postvoid residual urine. Six patients had a successful repair with no further intervention, whilst three had small fistulae that were treated by simple closure. In three patients the graft failed, by complete disruption or stricture. Graft infection adversely affected the outcome of SIS grafting.

Conclusions

The prefabricated SIS graft can be used as an alternative substitute for urethral reconstruction when genital skin is insufficient or lacking, as in circumcised patients or a repeat hypospadias repair. Graft infection is the chief reason for graft failure and should be prevented. Further studies with more patients are needed to confirm these preliminary results.

Design of 3D scaffolds for tissue engineering testing a tough polylactide-based graft copolymer

The aim of this research was to investigate a tough polymer to develop 3D scaffolds and 2D films for tissue engineering applications, in particular to repair urethral strictures or defects. The polymer tested was a graft copolymer of polylactic acid (PLA) synthesized with the rationale to improve the toughness of the related PLA homopolymer. The LMP-3055 graft copolymer (in bulk) demonstrated to have negligible cytotoxicity (bioavailability >85%, MTT test). Moreover, the LMP-3055 sterilized through gamma rays resulted to be cytocompatible and non-toxic, and it has a positive effect on cell biofunctionality, promoting the cell growth. 3D scaffolds and 2D film were prepared using different LMP-3055 polymer concentrations (7.5, 10, 12.5 and 15%, w/v), and the effect of polymer concentration on pore size, porosity and interconnectivity of the 3D scaffolds and 2D film was investigated. 3D scaffolds got better results for fulfilling structural and biofunctional requirements: porosity, pore size and interconnectivity, cell attachment and proliferation. 3D scaffolds obtained with 10 and 12.5% polymer solutions (3D-2 and 3D-3, respectively) were identified as the most suitable construct for the cell attachment and proliferation presenting pore size ranged between 100 and 400μm, high porosity (77-78%) and well interconnected pores. In vitro cell studies demonstrated that all the selected scaffolds were able to support the cell proliferation, the cell attachment and growth resulting to their dependency on the polymer concentration and structural features. The degradation test revealed that the degradation of polymer matrix (ΔMw) and water uptake of 3D scaffolds exceed those of 2D film and raw polymer (used as control reference), while the mass loss of samples (3D scaffold and 2D film) resulted to be controlled, they showed good stability and capacity to maintain the physical integrity during the incubation time.

Penile urethra replacement with autologous cell-seeded tubularized collagen matrices

Acellular collagen matrices have been used as an onlay material for urethral reconstruction. However, cell-seeded matrices have been recommended for tubularized urethral repairs. In this study we investigated whether long segmental penile urethral replacement using autologous cell-seeded tubularized collagen-based matrix is feasible. Autologous bladder epithelial and smooth muscle cells from nine male rabbits were grown and seeded onto preconfigured tubular matrices constructed from decellularized bladder matrices obtained from lamina propria. The entire anterior penile urethra was resected in 15 rabbits. Urethroplasties were performed with tubularized matrices seeded with cells in nine animals, and with matrices without cells in six. Serial urethrograms were performed at 1, 3 and 6 months. Retrieved urethral tissues were analysed using histo- and immunohistochemistry, western blot analyses and organ bath studies. The urethrograms showed that animals implanted with cell-seeded matrices maintained a wide urethral calibre without strictures. In contrast, the urethras with unseeded scaffolds collapsed and developed strictures. Histologically, a transitional cell layer surrounded by muscle was observed in the cell-seeded constructs. The epithelial and smooth muscle phenotypes were confirmed with AE1/AE3 and α-actin antibodies. Organ bath studies of the neourethras confirmed both physiological contractility and the presence of neurotransmitters. Tubularized collagen matrices seeded with autologous cells can be used successfully for long segmental penile urethra replacement, while implantation of tubularized collagen matrices without cells leads to poor tissue development and stricture formation. The cell-seeded collagen matrices are able to form new tissue, which is histologically similar to native urethra.

Outcome of small intestinal submucosa graft for repair of anterior urethral strictures

OBJECTIVES

To investigate the feasibility of small intestinal submucosa graft for the repair of selected anterior urethral strictures.

METHODS

From June 2009 to May 2011, 28 men (mean age 39 years) with anterior urethral strictures underwent urethroplasty using a four-layer small intestinal submucosa patch graft in an onlay or inlay fashion. The stricture was localized to the bulbar urethra in eight patients, the bulbopenile area in nine patients and the distal penile urethra in 10 patients. Failed hypospadias was observed in one patient. The mean stricture length was 4.6 cm (range 3.5-7.0 cm).

RESULTS

The mean follow-up period was 24.8 months (range 12-30 months). No postoperative complications, such as infection or rejection, were related to the use of heterologous graft material. The patients voided well postoperatively, with peak flows between 16 and 44 mL/s (mean 25.4 mL/s) in 26 patients. Two patients (7.1%) developed a urethral narrowing; this occurred at 5 months in one patient and 6 months in the other, and cystoscopy, which was carried out at 20 and 24 weeks, respectively, showed clear cicatricial tissue at the proximal anastomotic site. Dilation was carried out once every 4-6 months for recurrent stricture in one patient and lingual mucosal graft urethroplasty was carried out in the other patient at 18 months postoperatively. Biopsies were obtained in four patients at 18, 24, 36 and 42 weeks, respectively. Squamous epithelium with or without hyperkeratosis was observed on histological examination of the small intestinal submucosa-grafted areas.

CONCLUSIONS

The small intestinal submucosa matrix appears to be a safe and effective reconstructive material for selective use in urethral reconstructive surgery.

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.