Tissue engineering of the urethra: where are we in 2019?

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.

Follow-up and histocompatibility observation of urethral reconstruction with different materials

OBJECTIVE

Our objective is to observe the long-term surgical results of urethral reconstruction using either pedicled penile flaps or lingual mucosa grafts. We also assess the histocompatibility of the reconstructed urethra.

MATERIALS AND METHODS

Clinical data of patients with anterior urethral stenosis undergoing urethra reconstruction by applying different materials were collected from 2014 to 2022 in the Second Hospital of Hebei Medical University. We assessed their efficacy and the occurrence of complications. Patients who required reoperation due to complications were selected. Sections of the reconstructed urethra created with various materials were excised during repair procedures. The excised tissues underwent hematoxylin-eosin staining and immunohistochemistry. Comparison with the original histological morphology was conducted to evaluate histocompatibility.

RESULTS

42 of the 55 patients were cured which showed a surgical success rate of 76.36%. The success rate of urethra reconstruction surgery utilizing lingual mucosa is 71.43% and that of surgeries using pedicled penis flaps is 79.41%. The long-term prognosis of the two groups is similar (P > 0.05). Observations show that the histological morphology of the original epithelium gradually disappeared, leading to adaptive changes to the urinary environment with favorable histocompatibility.

CONCLUSION

The application of lingual mucosal and pedicled penis flaps for urethral reconstruction both have a high surgical success rate. The long-term follow-up results are positive. Both methods are viable for urethral reconstruction and exhibit favorable histocompatibility.

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.

An Update on Female Urethral Stricture Disease

PURPOSE OF REVIEW

To provide an overview of female urethral stricture disease and updates on surgical outcomes.

RECENT FINDINGS

In a large retrospective case series, women reported significant improvements in urinary symptoms and quality of life following treatment of their urethral stricture. Both vaginal flap and buccal mucosal graft urethroplasty have higher short- and long-term success rates than urethral dilation. Female urethral stricture disease is rare and surgical reconstruction has the highest likelihood of long-term success. Due to the complexity of reconstruction, referral to a reconstructive trained urologist should be considered.

Prospects and Challenges of Electrospun Cell and Drug Delivery Vehicles to Correct Urethral Stricture

Current therapeutic modalities to treat urethral strictures are associated with several challenges and shortcomings. Therefore, significant strides have been made to develop strategies with minimal side effects and the highest therapeutic potential. In this framework, electrospun scaffolds incorporated with various cells or bioactive agents have provided promising vistas to repair urethral defects. Due to the biomimetic nature of these constructs, they can efficiently mimic the native cells’ niches and provide essential microenvironmental cues for the safe transplantation of multiple cell types. Furthermore, these scaffolds are versatile platforms for delivering various drug molecules, growth factors, and nucleic acids. This review discusses the recent progress, applications, and challenges of electrospun scaffolds to deliver cells or bioactive agents during the urethral defect repair process. First, the current status of electrospinning in urethral tissue engineering is presented. Then, the principles of electrospinning in drug and cell delivery applications are reviewed. Finally, the recent preclinical studies are summarized and the current challenges are discussed.

Application of regenerative medicine and 3d bioprinting in urology

In the last two decades, a new purpose has collected great efforts from scientists in all branches of medicine. It is about the possibility to make the body regenerate ill tissues and organs by itself with de right artificial stimuli or the construction of new functional organs to replace the damaged ones. This process comprises various interdisciplinary approaches to healthcare, such as tissue engineering, molecular medicine, biotechnology, and three-dimensional printing. Urologists have been remarkably active in this field of medicine called Regenerative Medicine. The searching of the different requirements like suitable and compatible biomaterials, versatile cells, adequate techniques to construct tissues, available biomolecules, and the knowledge of all these minimizing risks, are some of the aims and the approximations until now. Despite many obstacles, in vitro and in vivo studies are already showing encouraging options. We will review the advances related to the bladder, urethra, ureter, and kidneys. Difficulties such as ethical issues, time investment and high costs, have been some of the drawbacks encountered. Further studies are still required for its clinical application in daily life.

Comparison of two different methods of establishment of canine urethroplasty model: an experimental trial

Background

Graft substitute urethroplasty is recommended for patients with long segment anterior urethral stricture. The therapeutic effects of the grafts need to be validated on the animal models. Therefore the aim of this study was to compared the operative time, blood loss, intra- and post- operative complications of two different methods of establishment of canine urethroplasty model.

Methods

Twelve Beagle dogs were randomly separated into control and experimental group using a random number table. Six animals in the control group received the conventional urethroplasty, while the other 6 in the experimental group received the modified procedures. Tube cystostomy and urethroplasty were performed in the control group. The cystostomy not the tube cystostomy were performed in the experimental group, and the testes were simultaneously removed with the scrotum. Per- and postoperative outcomes, complications were evaluated.

Results

The urethroplasty were successfully performed for all dogs and all of these procedures were done by the same surgeon. The median operative time in the control and experimental groups was 186.8 min and 188.7 min respectively. The blood loss in the control and experimental groups was 40.8 ml and 45.8 ml respectively. No intraoperative complications occurred. 3 animals in the control group developed acute urinary retention after the accidental removal of suprapubic bladder tube and the cystostomy was done again. There was no occurrence of urinary retention in the experimental group. 4 animals in the control group developed the perineal hematoma, in which one animal had the urine leakage and incision infection. Perineal hematoma occurred in only one animal in the experimental group.

Conclusion

The occurrence of urinary retention and perineal hematoma decreased in the modified group, in which the cystostomy not the tube cystostomy were performed and the testes with the scrotum were simultaneously removed.

Electrospun nanoyarn and exosomes of adipose-derived stem cells for urethral regeneration: Evaluations in vitro and in vivo

Regeneration of urethral defects has been difficult in the clinic. To address it, the collagen/ poly (L-lactide-co-caprolactone) (P(LLA-CL)) nanoyarn scaffold delivering adipose-derived stem cells' exosomes (ADSC-exos) was fabricated. The multipotential differentiation potential of ADSCs were confirmed by Adipogenic, osteogenic, and chondrogenic differentiation. The 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide assay shows that 50% concentration of ADSC-exos nanoyarn scaffold dramatically enhanced the cell viability of fibroblasts. The ADSC-exos nanoyarn scaffold for human foreskin fibroblasts (HFFs) and human urethral scar fibroblasts (HSFs) shows good biocompatibility: theproduction of inflammatory factors IL-6 and Col 1A1 was less, indicating that ADSC-exos had the minimal inflammatory effect of cells. Besides, the cells on the ADSC-exos nanoyarn scaffold did not appear to contribute to DNA damage in the same way as the normal cell's growth did. The HFFs seeding on the ADSC-exos nanoyarn scaffold shows a typical morphology of extending outwards. Urethral repair with ADSC-exos nanoyarn scaffold did not lead to either a sign of urethral stricture or scar formation after 4 weeks post-surgery. The deposition of collagen was less and the epithelial cells formed multiple layer epithelium. The treatment of ADSC-exos stimulated epithelization and vascularization. And the transition from an inflammatory state to a regenerative state was promoted. The ADSC-exos-treated group did not promote the over-proliferation of fibroblasts and the expression of Collagen I. Therefore, the ADSC-exos nanoyarn scaffold has evident, positive effects on wound healing and tissue fibrosis inhibition.

[Which management for anterior urethral stricture in male? 2021 guidelines from the uro-genital reconstruction urologist group (GURU) under the aegis of CAMS-AFU (Committee of Andrology and Sexual Medicine of the French Association of Urology)]

OBJECTIVE

The purpose of this first french guideline is to provide a clinical framework for the diagnosis, treatment and follow-up of anterior urethral strictures. The statements are established by the subgroup working on uro-genital reconstruction surgery (GURU) from the CAMS-AFU (Andrology and Sexual Medicine Committee from the French Association of Urology).

MATERIAL AND METHODS

These guidelines are adapted from the Male Urethral Stricture : American Urological Association Guideline 2016, updated by an additional bibliography from January 2016 to December 2019. Twenty-seven main scenarios seen in clinical practice are identified: from diagnosis, to treatment and follow-up. In addition, this guidelines are powered by anatomical diagrams, treatment algorithms, summaries and follow-up tables.

RESULTS

Anterior urethral strictures are a common condition (0,1 à 1,4 %) in men. The diagnosis is based on a trifecta including an examination with patient reported questionnaires, urethroscopy and retrograde urethrography with voiding cystourethrography. Short meatal stenosis can be treated by dilation or meatotomy, otherwise a urethroplasty can be performed. First line treatment of penile strictures is urethroplasty. Short bulbar strictures (<2cm) may benefit from endourethral treatment (direct visual internal urethrotomy or dilation). In case of recurrence or when the stenosis measures more than 2 cm, a urethroplasty will be proposed. Repeated endourethral treatment management are no longer recommended except in case of palliative option. Urethroplasty is usually done with oral mucosa graft as the primary option, in one or two stages approach depending on the extent of the stenosis and the quality of the tissues. Excision and primary anastomosis or non-transecting techniques are discussed for bulbar urethra strictures. Follow-up by clinical monitoring with urethroscopy, or retrograde urethrography with voiding cystourethrography, is performed at least the first year and then on demand according to symptoms.

CONCLUSION

Anterior urethral strictures need an open surgical approach and should be treated by urethroplasty in most cases. This statement requires a major paradigm shift in practices. Training urologist through reconstructive surgery is the next challenge in order to meet the demand.

A systematic review and meta-analysis of urethral complications and outcomes in transgender men

BACKGROUND

Urologic problems, such as urethral fistulas and strictures, are among the most frequent complications occurring after phalloplasty. Although many studies have reported successful phalloplasty and urethral reconstruction with reliable outcomes in transgender men, no method has become standardized so far. This study aimed to summarize the results of reports on urological complications and outcomes in transgender men with respect to various types of urethral reconstruction.

METHODS

A comprehensive literature search of PubMed, Scopus, and Google Scholar databases was conducted for studies related to phalloplasty in transsexuals. Data on various phallic urethral techniques, urethral complications, and outcomes were collected and analyzed using the random-effects model.

RESULTS

A total of 21 studies (1,566 patients) were included: eight studies (1,061 patients) on "tube-in-tube," nine studies (273 patients) on "prelaminated flap," and six studies (221 patients) on "second flap." Compared with the tube-in-tube technique, the prelaminated flap was associated with a significantly higher urethral stricture/stenosis rate; however, there was no difference between the prelaminated flap and the second flap techniques. For all phalloplasty patients, the pool rate of urethral fistula or stenosis is 48.9%, the rate of the ability to void while standing is 91.5%, occurrence rate of tactile or erogenous sensation is 88%, the prosthesis complication rate is 27.9%, and patient-reported satisfactory outcome rate is 90.5%.

CONCLUSION

Urethral reconstruction with a prelaminated flap was associated with a significantly higher urethral stricture rate and increased need of revision surgery compared with that observed using a skin flap. Overall, most patients were able to void while standing and were satisfied with the outcomes.

A Scarless Healing Tale: Comparing Homeostasis and Wound Healing of Oral Mucosa With Skin and Oesophagus

Epithelial tissues are the most rapidly dividing tissues in the body, holding a natural ability for renewal and regeneration. This ability is crucial for survival as epithelia are essential to provide the ultimate barrier against the external environment, protecting the underlying tissues. Tissue stem and progenitor cells are responsible for self-renewal and repair during homeostasis and following injury. Upon wounding, epithelial tissues undergo different phases of haemostasis, inflammation, proliferation and remodelling, often resulting in fibrosis and scarring. In this review, we explore the phenotypic differences between the skin, the oesophagus and the oral mucosa. We discuss the plasticity of these epithelial stem cells and contribution of different fibroblast subpopulations for tissue regeneration and wound healing. While these epithelial tissues share global mechanisms of stem cell behaviour for tissue renewal and regeneration, the oral mucosa is known for its outstanding healing potential with minimal scarring. We aim to provide an updated review of recent studies that combined cell therapy with bioengineering exporting the unique scarless properties of the oral mucosa to improve skin and oesophageal wound healing and to reduce fibrotic tissue formation. These advances open new avenues toward the ultimate goal of achieving scarless wound healing.

Genitourinary Tissue Engineering: Reconstruction and Research Models

Tissue engineering is an emerging field of research that initially aimed to produce 3D tissues to bypass the lack of adequate tissues for the repair or replacement of deficient organs. The basis of tissue engineering protocols is to create scaffolds, which can have a synthetic or natural origin, seeded or not with cells. At the same time, more and more studies have indicated the low clinic translation rate of research realised using standard cell culture conditions, i.e., cells on plastic surfaces or using animal models that are too different from humans. New models are needed to mimic the 3D organisation of tissue and the cells themselves and the interaction between cells and the extracellular matrix. In this regard, urology and gynaecology fields are of particular interest. The urethra and vagina can be sites suffering from many pathologies without currently adequate treatment options. Due to the specific organisation of the human urethral/bladder and vaginal epithelium, current research models remain poorly representative. In this review, the anatomy, the current pathologies, and the treatments will be described before focusing on producing tissues and research models using tissue engineering. An emphasis is made on the self-assembly approach, which allows tissue production without the need for biomaterials.

Tissue engineering: recent advances and review of clinical outcome for urethral strictures

PURPOSE OF REVIEW

Urethrotomy remains the first-line therapy in the treatment of a urethral stricture despite data showing no real chance of a cure after repeated urethrotomies. An anastomotic or an augmentation urethroplasty using oral mucosa can be offered to patients following failed urethrotomy. The potential for a tissue engineered solution as an alternative to native tissue has been explored in recent years and is reviewed in this article.

RECENT FINDINGS

More than 80 preclinical studies have investigated a tissue-engineered approach for urethral reconstruction mostly using decellularized natural scaffolds derived from natural extracellular matrix with or without cell seeding. The animal models used in preclinical testing are not representative of disease processes seen with strictures in man. The available clinical studies are based on small noncontrolled series.

SUMMARY

There is a potential role for tissue engineering to provide a material for substitution urethroplasty and work has demonstrated this. Further work will require a rigorous basic science programme and adequate evaluation of the material prior to its introduction into clinical practice. The research with tissue engineering applied to the urethra has not yet been resulted in a widely available material for clinical use that approaches the efficacy seen with the use of autologous grafts.

Potential strategies to prevent encrustations on urinary stents and catheters - thinking outside the box: a European network of multidisciplinary research to improve urinary stents (ENIUS) initiative

Introduction: Urinary stents have been around for the last 4 decades, urinary catheters even longer. They are associated with infections, encrustation, migration, and patient discomfort. Research efforts to improve them have shifted onto molecular and cellular levels. ENIUS brought together translational scientists to improve urinary implants and reduce morbidity.Methods & materials: A working group within the ENIUS network was tasked with assessing future research lines for the improvement of urinary implants.Topics were researched systematically using Embase and PubMed databases. Clinicaltrials.gov was consulted for ongoing trials.Areas covered: Relevant topics were coatings with antibodies, enzymes, biomimetics, bioactive nano-coats, antisense molecules, and engineered tissue. Further, pH sensors, biodegradable metals, bactericidal bacteriophages, nonpathogenic uropathogens, enhanced ureteric peristalsis, electrical charges, and ultrasound to prevent stent encrustations were addressed.Expert opinion: All research lines addressed in this paper seem viable and promising. Some of them have been around for decades but are yet to proceed to clinical application (i.e. tissue engineering). Others are very recent and, at least in urology, still only conceptual (i.e. antisense molecules). Perhaps the most important learning point resulting from this pan-European multidisciplinary effort is that collaboration between all stakeholders is not only fruitful but also truly essential.

Successful engraftment of epithelial cells derived from autologous rabbit buccal mucosal tissue, encapsulated in a polymer scaffold in a rabbit model of a urethral stricture, transplanted using the transurethral approach

Background

A pilot study reported an autologous buccal mucosal cell transplant in humans through the trans-urethral route using the buccal epithelium expanded and encapsulated in scaffold-hybrid approach to urethral stricture (BEES-HAUS), a minimally invasive approach to treat urethral stricture. Although successful outcomes were achieved in that study, for further validation, it is essential to prove that the transplanted buccal epithelium was engrafted over the urothelium through histological examination of the urethra, harvested post-transplant, which is infeasible in humans. Herein, we report the successful creation of an animal model of urethral stricture and the engraftment of epithelial cells derived from autologous buccal mucosal tissue, encapsulated in a thermo-reversible gelation polymer (TGP) scaffold, transplanted by trans-urethral route.

Methods

An animal model of urethral stricture was created in Japanese white male rabbits using electro-coagulation. Buccal tissue was harvested from the rabbits and subjected to enzyme digestion, followed by 5-7 days of in vitro culture in conventional two-dimensional (2D) culture and in a 3D platform of thermo-reversible gelation polymer (3D-TGP) culture. The cells harvested from the groups were mixed and encapsulated and transplanted with TGP, by transurethral catheterization. Fourteen days later, the urethra was harvested and subjected to histological examination. The buccal biopsy tissue, cells after digestion and cells post-culture were also subjected to histological examination. Urethrogram and endoscopy images were recorded at different time points.

Results

The stricture was successfully created, with the coagulated area markedly stenosed. Histological staining of the cells after in vitro processing showed that the cells grew with native epithelial and rounded cell morphology in 3D-TGP while they differentiated into fibroblast like-cells in 2D culture. Histological staining of the urethral tissue after transplantation revealed the engraftment of the transplanted buccal mucosal cells, with stratified squamous epithelium over the specialized stratified urothelium in the urethrotomy site.

Conclusion

We used histology to prove the successful engraftment of TGP-encapsulated buccal mucosal epithelial cells in an animal model of urethral injury with healing of the injured tissue. The model of urethral stricture and cell therapy, using a transurethral approach, recapitulates the previously reported BEES-HAUS approach and lays the foundation for larger multi-centric translational clinical studies.

Patient-reported outcomes for typical single cheek harvesting vs atypical lingual, labial or bilateral cheeks harvesting: a single-center analysis of more than 800 patients

PURPOSE

The optimal harvesting site for oral grafting in patients with urethral strictures remain controversial, with no study investigating morbidity on large scale. We aimed to compare typical single cheek harvesting vs atypical lingual, labial or bilateral cheeks harvesting in terms of complications and patient-reported outcomes.

METHODS

Within 827 patients treated at our referral center with oral graft urethroplasty, we compared typical vs atypical harvesting techniques. A self-administered, semiquantitative, non-validated questionnaire assessed early (10 days) and late (4 months) postoperative complications and patient-reported outcomes. A semiquantitative score was calculated according to patient responses, and it was used to assess early (6 questions) and late (13 questions) patient dissatisfaction status. Patients were defined early and/or late dissatisfied when they scored ≥ 7 and ≥ 10 at the early or late questionnaires, respectively.

RESULTS

Between 1998 and 2019, our patients predominantly received typical single cheek harvesting (89% vs 11%), with + 1.5% increase rate per year (p < 0.001). Early and late dissatisfied patients were, respectively, 170 (23%) vs 39 (44%) and 59 (8%) vs 16 (18%) in the typical vs atypical groups. Atypical harvesting was associated with higher rates of early (Odds ratio [OR]: 2.34; 95% Confidence interval [CI] 1.44-3.75; p = 0.001) and late (OR: 2.37; 95%CI 1.22-4.42; p = 0.008) postoperative dissatisfaction.

CONCLUSIONS

Typical single cheek harvesting was the preferred surgical option at our center and it was associated with negligible early and late rates of complications and patient's dissatisfaction. Conversely, atypical lingual, labial or bilateral cheeks harvesting was associated with higher complications and frequent patient dissatisfaction.