Tubularized urethral replacement with unseeded matrices: what is the maximum distance for normal tissue regeneration? World J Urol. 2008;26:323-326. [PMID: 18682960 DOI: 10.1007/s00345-008-0316-6]

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.

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.

A perioperative layered autologous tissue expansion graft for hollow organ repair

Tissue engineering has not been widely adopted in clinical settings for several reasons, including technical challenges, high costs, and regulatory complexity. Here, we introduce the Perioperative Layered Autologous Tissue Expansion graft (PLATE graft), a composite biomaterial and collagen-reinforced construct with autologous epithelium on one side and smooth muscle tissue on the other. Designed to mimic the structure and function of natural hollow organs, the PLATE graft is unique in that it can be produced in a standard operating theatre and is cost-effective. In this proof-of-principle study, we test its regenerative performance in eight different organs, present biomechanical and permeability tests, and finally explore its in vivo performance in live rabbits.

Development of male and female models of long urethral strictures in swine

Background

Preclinical animal models which mimic the dimensions of long urethral strictures (>2 cm in length) encountered in the clinic are necessary to evaluate prospective graft designs for urethroplasty. The purpose of this study was to develop both male and female porcine models of long urethral strictures (∼4 cm in length) and characterize histological and functional outcomes of iatrogenic stricture formation between genders.

Methods

Focal, partial thickness urethral injuries were created over 5-6 cm long segments in male and female swine (N = 4 per gender) via electrocoagulation and the degree of stricture formation was monitored for up to 6 weeks by urethroscopy and retrograde urethrography. Animals were sacrificed following stricture confirmation and histological, immunohistochemical, and histomorphometric analyses were performed on strictured and uninjured control urethral segments to profile wound healing responses.

Results

Urethral stricture formation was detected in all female swine by 2 weeks and 100 % of male swine at 3.2 ± 1.8 weeks, post-operatively. The mean length of urethral strictures in both male and female swine was ∼4 cm. Substantial variations in the degree of stricture severity between sexes were observed with males exhibiting significant urethral stenosis and loss of α-smooth muscle actin+ smooth muscle bundles in comparison to controls, while females primarily displayed defects in pan-cytokeratin+ epithelia as well as functional urethral obstruction.

Conclusions

Electrocoagulation injury is sufficient to produce long urethral strictures in male and female swine and the degree of stricture severity and nature of urethral obstruction was observed to be dependent on gender. Animal Protocol: AUP-19-150.

Key message

Novel male and female models of long urethral strictures in swine were created to characterize histological and functional outcomes of iatrogenic stricture formation between genders.

Advancing autologous urothelial micrografting and composite tubular grafts for future single-staged urogenital reconstructions

Urogenital reconstructive surgery can be impeded by lack of tissue. Further developments within the discipline of tissue engineering may be part of a solution to improve clinical outcomes. In this study, we aimed to design an accessible and easily assembled tubular graft with autologous tissue, which could be constructed and implanted as a single-staged surgical procedure within the premises of an ordinary operating room. The ultimate goals would be to optimize current treatment-options for long-term urinary diversion. Therefore, we evaluated the optimal composition of a collagen-based scaffold with urothelial micrografts in vitro, and followingly implanted the construct in vivo as a bladder conduit. The scaffold was evaluated in relation to cell regeneration, permeability, and biomechanical properties. After establishing an optimized scaffold in vitro, consisting of high-density collagen with submerged autologous micrografts and reinforced with a mesh and stent, the construct was successfully implanted in an in vivo minipig model. The construct assemblance and surgical implantation proved feasible within the timeframe of a routine surgical intervention, and the animal quickly recovered postoperatively. Three weeks post-implantation, the conduit demonstrated good host-integration with a multilayered luminal urothelium. Our findings have encouraged us to support its use in more extensive preclinical large-animal studies.

Cell-Based Therapy for Urethral Regeneration: A Narrative Review and Future Perspectives

Urethral stricture is a common urological disease that seriously affects quality of life. Urethroplasty with grafts is the primary treatment, but the autografts used in clinical practice have unavoidable disadvantages, which have contributed to the development of urethral tissue engineering. Using various types of seed cells in combination with biomaterials to construct a tissue-engineered urethra provides a new treatment method to repair long-segment urethral strictures. To date, various cell types have been explored and applied in the field of urethral regeneration. However, no optimal strategy for the source, selection, and application conditions of the cells is available. This review systematically summarizes the use of various cell types in urethral regeneration and their characteristics in recent years and discusses possible future directions of cell-based therapies.

Biodegradable Multi-layered Silk Fibroin-PCL Stent for the Management of Cervical Atresia: In Vitro Cytocompatibility and Extracellular Matrix Remodeling In Vivo

Cervical atresia is a rare congenital Müllerian duct anomaly that manifests as the absence or deformed nonfunctional presence of the cervix. Herein, a multi-layered biodegradable stent is fabricated using a homogeneous blend of silk fibroin with polycaprolactone using hexafluoroisopropanol as a common solution. Briefly, a concentric cylinder of 3D honeycomb layer is sandwiched within electrospun sheets for fixing at the cervico-uterine junction to pave the way of cervical reconstruction. An average length of 40 mm with 3 mm diameter is fabricated for the hybrid stent design. SEM evidences an evenly distributed pore architecture of the electrospun layer, and mechanical characterization of stent reveals a tensile strength of 1.7 ± 0.2 MPa, with a Young's modulus of 5.9 ± 0.1 MPa. Physico-chemical characterization confirms the presence of silk fibroin and poly caprolactone within the engineered stent. Following 14 days of pepsin enzymatic degradation, 18% degradation and a contact angle measurement of 97° are observed. In vitro cytocompatibility studies are performed using site-specific primary human cervical squamous, columnar epithelial cells, and human endometrial stromal cells. The study demonstrates non-cytotoxic cells' viability (no significant toxicity), improved cell anchoring, adherence among the stent layers, and proliferation in the 3D microenvironment. Furthermore, in vivo subcutaneous studies in the rodent model indicate that the implanted stent undergoes constructive remodeling, neo-tissue creation, neo-vasculature formation, and re-epithelialization while maintaining patency for 2 months.

Insights into cellular behavior and micromolecular communication in urothelial micrografts

Autologous micrografting is a technique currently applied within skin wound healing, however, the potential use for surgical correction of other organs with epithelial lining, including the urinary bladder, remains largely unexplored. Currently, little is known about the micrograft expansion potential and the micromolecular events that occur in micrografted urothelial cells. In this study, we aimed to evaluate the proliferative potential of different porcine urothelial micrograft sizes in vitro, and, furthermore, to explore how urothelial micrografts communicate and which microcellular events are triggered. We demonstrated that increased tissue fragmentation subsequently potentiated the yield of proliferative cells and the cellular expansion potential, which confirms, that the micrografting principles of skin epithelium also apply to uroepithelium. Furthermore, we targeted the expression of the extracellular signal-regulated kinase (ERK) pathway and demonstrated that ERK activation occurred predominately at the micrograft borders and that ERK inhibition led to decreased urothelial migration and proliferation. Finally, we successfully isolated extracellular vesicles from the micrograft culture medium and evaluated their contents and relevance within various enriched biological processes. Our findings substantiate the potential of applying urothelial micrografting in future tissue-engineering models for reconstructive urological surgery, and, furthermore, highlights certain mechanisms as potential targets for future wound healing treatments.

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.

A modified biodegradable mesh ureteral stent for treating ureteral stricture disease

Ureteral stricture disease (USD) is a common urologic condition. Patients with ureteral stricture disease may suffer from ipsilateral flank pain, nausea, urinary calculi, infection, and impaired renal function. The treatments of USD include surgery, followed by implantation of the ureteral stent to aid the drainage of the urine. The traditional ureteral stent may sometimes cause urological infection, encrustation, and discomfort. To decrease the complication of the ureteral stent, we modified the structure and material based on the traditional ureteral stent. The traditional nondegradable Double-J shape tubular ureteral stent was turned into the biodegradable mesh ureteral stent. The modified mesh ureteral stent and Double-J ureteral stent were inserted into the ureters of the USD animals, respectively. The results of the gross morphology, serology, urinalysis, histology, microstructure, et al. demonstrated that modified mesh ureteral stent has a favorable ability in supporting the ureter and has no effect on cell proliferation, migration, apoptosis, and cell cycle of the human uroepithelial cells. The mesh ureteral stent could relieve ureter obstruction and can be slowly biodegraded after 3-5 months of implantation without the need for a second surgery to remove the stent. Compared to the Double-J ureteral stent, the modified mesh ureteral stent has a lower rate of urinary tract infection and less encrustation. It is expected to be an alternative treatment approach for USD. However, due to the limited number of animals and clinical data, further study focused on the application value in clinical practice are essential. STATEMENT OF SIGNIFICANCE: This study demonstrates: 1. A modified biodegradable mesh ureteral stent; 2. Without the need for a second surgery to remove the stent; 3. A lower rate of urinary tract infection and less encrustation than a double-J ureteral stent; 4. An alternative treatment approach for USD.

Sensitivity of a two-dimensional biomorphoelastic model for post-burn contraction

We consider a two-dimensional biomorphoelastic model describing post-burn scar contraction. This model describes skin displacement and the development of the effective Eulerian strain in the tissue. Besides these mechanical components, signaling molecules, fibroblasts, myofibroblasts, and collagen also play a significant role in the model. We perform a sensitivity analysis for the independent parameters of the model and focus on the effects on features of the relative surface area and the total strain energy density. We conclude that the most sensitive parameters are the Poisson's ratio, the equilibrium collagen concentration, the contraction inhibitor constant, and the myofibroblast apoptosis rate. Next to these insights, we perform a sensitivity analysis where the proliferation rates of fibroblasts and myofibroblasts are not the same. The impact of this model adaptation is significant.

Exploring the Concept of In Vivo Guided Tissue Engineering by a Single-Stage Surgical Procedure in a Rodent Model

In severe malformations with a lack of native tissues, treatment options are limited. We aimed at expanding tissue in vivo using the body as a bioreactor and developing a sustainable single-staged procedure for autologous tissue reconstruction in malformation surgery. Autologous micro-epithelium from skin was integrated with plastically compressed collagen and a degradable knitted fabric mesh. Sixty-three scaffolds were implanted in nine rats for histological and mechanical analyses, up to 4 weeks after transplantation. Tissue integration, cell expansion, proliferation, inflammation, strength, and elasticity were evaluated over time in vivo and validated in vitro in a bladder wound healing model. After 5 days in vivo, we observed keratinocyte proliferation on top of the transplant, remodeling of the collagen, and neovascularization within the transplant. At 4 weeks, all transplants were fully integrated with the surrounding tissue. Tensile strength and elasticity were retained during the whole study period. In the in vitro models, a multilayered epithelium covered the defect after 4 weeks. Autologous micro-epithelial transplants allowed for cell expansion and reorganization in vivo without conventional pre-operative in vitro cell propagation. The method was easy to perform and did not require handling outside the operating theater.

Electrospun PLGA and PLGA/gelatin scaffolds for tubularized urethral replacement: Studies in vitro and in vivo

To investigate the biocompatibility of polylactic acid-glycolic acid copolymer (PLGA) and PLGA/gelatin scaffolds and their suitability for tubular urethral replacement in a canine model. PLGA and PLGA/gelatin scaffolds was constructed by electrospinning. Microstructural differences between the scaffolds was examined by Scanning electron microscopy (SEM) followed by mechanical properties testing. Biocompatibility of the material was evaluated using SEM 4, 8, 12 and 72 h after PLGA and PLGA/gelatin scaffolds co-culture with urothelial cells. And confocal analysis was also used to showed the cell adhesive and growth at 12 h. Approximately 2 cm of the anterior urethra of twelve dogs were removed and replaced with a scaffold. After the surgery for 1 month performed urethrography and for 3 month perform hematoxylin-eosin (H&E) and Masson. The results indicated that PLGA and PLGA/gelatin scaffolds had a void microfilament structure, similar to that of normal acellular matrix tissue. And the tensile strength was decreased whereas the tensile deformation and suture retention strength was increased in PLGA/gelatin scaffolds compared to that in PLGA scaffolds Urothelial cells grew well on both scaffolds. Postoperatively, animals recovered well and urinated spontaneously. However, urethrography showed varying degrees of urethral strictures in the reconstructed urethras. H&E and Masson showed that multilayer urothelial cells were formed in both the proximal and distal segments of the reconstructed urethras but without continuity. There was a small amount of smooth muscle and blood vessels under the epithelium, but regenerative urothelial cells at the midpoint of the reconstructed segment did not continue. Lots of lymphocyte infiltration was observed under the epithelium, some collagen tissue was deposited under the neo-urethral epithelium were observed. In conclusion, PLGA and PLGA/gelatin scaffolds are not suitable for tubularized urethral replacement in the canine model.

Tissue engineering in reconstructive urology-The current status and critical insights to set future directions-critical review

Advanced techniques of reconstructive urology are gradually reaching their limits in terms of their ability to restore urinary tract function and patients' quality of life. A tissue engineering-based approach to urinary tract reconstruction, utilizing cells and biomaterials, offers an opportunity to overcome current limitations. Although tissue engineering studies have been heralding the imminent introduction of this method into clinics for over a decade, tissue engineering is only marginally applied. In this review, we discuss the role of tissue engineering in reconstructive urology and try to answer the question of why such a promising technology has not proven its clinical usability so far.

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.

Considerations for the clinical use of stem cells in genitourinary regenerative medicine

The genitourinary tract can be affected by several pathologies which require repair or replacement to recover biological functions. Current therapeutic strategies are challenged by a growing shortage of adequate tissues. Therefore, new options must be considered for the treatment of patients, with the use of stem cells (SCs) being attractive. Two different strategies can be derived from stem cell use: Cell therapy and tissue therapy, mainly through tissue engineering. The recent advances using these approaches are described in this review, with a focus on stromal/mesenchymal cells found in adipose tissue. Indeed, the accessibility, high yield at harvest as well as anti-fibrotic, immunomodulatory and proangiogenic properties make adipose-derived stromal/SCs promising alternatives to the therapies currently offered to patients. Finally, an innovative technique allowing tissue reconstruction without exogenous material, the self-assembly approach, will be presented. Despite advances, more studies are needed to translate such approaches from the bench to clinics in urology. For the 21^st century, cell and tissue therapies based on SCs are certainly the future of genitourinary regenerative medicine.

Production and Preparation of Porcine Urinary Bladder Matrix (UBM) for Urinary Bladder Tissue-Engineering Purposes

Surgical repair for the end stage bladder disease utilises vascularised, autogenous and mucus-secreting gastrointestinal tissue to replace the diseased organ or to augment inadequate bladder tissue. Post-operatively, the compliance of the bowel is often enough to restore the basic shape, structure and function of the urinary bladder; however, lifelong post-operative complications are common. Comorbidities that result from interposition of intestinal tissue are metabolic and/or neuromechanical, and their incidence approaches 100%. The debilitating comorbidities and complications associated with such urological procedures may be mitigated by the availability of alternative, tissue-engineered, animal-derived extracellular matrix (ECM) scaffolds such as porcine urinary bladder matrix (UBM). Porcine UBM is a decellularized biocompatible, biodegradable biomaterial derived from the porcine urinary bladder. This chapter aims to describe the production and preparation techniques for porcine UBM for urinary bladder regenerative purposes.

Bladder Substitution: The Role of Tissue Engineering and Biomaterials

Tissue engineering could play a major role in the setting of urinary diversion. Several conditions cause the functional or anatomic loss of urinary bladder, requiring reconstructive procedures on the urinary tract. Three main approaches are possible: (i) incontinent cutaneous diversion, such as ureterocutaneostomy, colonic or ileal conduit, (ii) continent pouch created using different segments of the gastrointestinal system and a cutaneous stoma, and (iii) orthotopic urinary diversion with an intestinal segment with spherical configuration and anastomosis to the urethra (neobladder, orthotopic bladder substitution). However, urinary diversions are associated with numerous complications, such as mucus production, electrolyte imbalances and increased malignant transformation potential. In this context, tissue engineering would have the fundamental role of creating a suitable material for urinary diversion, avoiding the use of bowel segments, and reducing complications. Materials used for the purpose of urinary substitution are biological in case of acellular tissue matrices and naturally derived materials, or artificial in case of synthetic polymers. However, only limited success has been achieved so far. The aim of this review is to present the ideal properties of a urinary tissue engineered scaffold and to examine the results achieved so far. The most promising studies have been highlighted in order to guide the choice of scaffolds and cells type for further evolutions.

Tissue expander capsule as an induced vascular bed to prefabricate an axial vascularized buccal mucosa-lined flap for tubularized posterior urethral reconstruction: preliminary results in an animal model

Surgical repair of complex posterior urethral disruptions remains one of the most challenging problems in urology. The efficacy of using a tissue expander capsule as an induced vascular bed to prefabricate axial vascularized buccal mucosa-lined flaps for tubularized posterior urethral reconstruction in a rabbit model was tested. The experiments were performed in three stages. First, silicone tissue expanders were inserted into the groin to induce vascularized capsule pouch formation. Next, buccal mucosa grafts were transplanted into the newly formed capsular tissue supplied by axial vessels for buccal mucosa-lined flap prefabrication. Then, circumferential posterior urethral defects were created and repaired with the buccal mucosa graft (Group 1), the capsule flap (Group 2), and the prefabricated capsule buccal mucosa composite flap (Group 3). After surgery, notable contracture of the tubularized buccal mucosa graft was observed in the neourethra, and none of the rabbits in Group 1 maintained a wide urethral caliber. In Group 2, the retrieved neourethra showed little evidence of epithelial lining during the study period, and the lumen caliber was narrowed at the 3-month evaluation. In Group 3, the buccal mucosa formed the lining in the neourethra and maintained a wide urethral caliber for 3 months. The capsule may serve as an induced vascular bed for buccal mucosa-lined flap prefabrication. The prefabricated buccal mucosa-lined flap may serve as a neourethra flap for posterior urethral replacement.

Implant Fibrosis and the Underappreciated Role of Myofibroblasts in the Foreign Body Reaction

Body implants and implantable medical devices have dramatically improved and prolonged the life of countless patients. However, our body repair mechanisms have evolved to isolate, reject, or destroy any object that is recognized as foreign to the organism and inevitably mounts a foreign body reaction (FBR). Depending on its severity and chronicity, the FBR can impair implant performance or create severe clinical complications that will require surgical removal and/or replacement of the faulty device. The number of review articles discussing the FBR seems to be proportional to the number of different implant materials and clinical applications and one wonders, what else is there to tell? We will here take the position of a fibrosis researcher (which, coincidentally, we are) to elaborate similarities and differences between the FBR, normal wound healing, and chronic healing conditions that result in the development of peri-implant fibrosis. After giving credit to macrophages in the inflammatory phase of the FBR, we will mainly focus on the activation of fibroblastic cells into matrix-producing and highly contractile myofibroblasts. While fibrosis has been discussed to be a consequence of the disturbed and chronic inflammatory milieu in the FBR, direct activation of myofibroblasts at the implant surface is less commonly considered. Thus, we will provide a perspective how physical properties of the implant surface control myofibroblast actions and accumulation of stiff scar tissue. Because formation of scar tissue at the surface and around implant materials is a major reason for device failure and extraction surgeries, providing implant surfaces with myofibroblast-suppressing features is a first step to enhance implant acceptance and functional lifetime. Alternative therapeutic targets are elements of the myofibroblast mechanotransduction and contractile machinery and we will end with a brief overview on such targets that are considered for the treatment of other organ fibroses.

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.

Current Applications and Future Directions of Bioengineering Approaches for Bladder Augmentation and Reconstruction

End-stage neurogenic bladder usually results in the insufficiency of upper urinary tract, requiring bladder augmentation with intestinal tissue. To avoid complications of augmentation cystoplasty, tissue-engineering technique could offer a new approach to bladder reconstruction. This work reviews the current state of bioengineering progress and barriers in bladder augmentation or reconstruction and proposes an innovative method to address the obstacles of bladder augmentation. The ideal tissue-engineered bladder has the characteristics of high biocompatibility, compliance, and specialized urothelium to protect the upper urinary tract and prevent extravasation of urine. Despite that many reports have demonstrated that bioengineered bladder possessed a similar structure to native bladder, few large animal experiments, and clinical applications have been performed successfully. The lack of satisfactory outcomes over the past decades may have become an important factor hindering the development in this field. More studies should be warranted to promote the use of tissue-engineered bladders in clinical practice.

Cell-Seeded Acellular Artery for Reconstruction of Long Urethral Defects in a Canine Model

The management of urethral stricture remains a major therapeutic challenge in clinics. Herein, we explored the feasibility of reconstructing a relatively long segment of the urethra by the cell-seeded acellular artery in a canine model. The acellular arterial matrix was obtained from the excised carotid artery of donor dogs. Autologous adipose-derived stem cells (ADSCs) from 6 male dogs were grown and seeded onto the premade acellular arterial matrix. A 3 cm long segment of the urethra was resected in 12 male dogs. Urethroplasty was performed with the acellular arterial matrix seeded with ADSCs in 6 animals and without cells in 6. Serial urethrography was performed at 1 and 3 months postoperatively. Wide urethral calibers without any signs of strictures were confirmed in all 6 animals in the experimental group. In contrast, urethral stricture was demonstrated in 3 animals in the control group. The graft was highly epithelialized and smooth in the experimental group, while graft contracture and scar formation were showed in the control group. Histologic analysis of the cell-seeded arterial matrix at 1 month confirmed the presence of multilayered urothelium and muscle. The levels of tissue formation developed over time with a progressive increase in muscle content. In contrast, extensive fibrosis and sparse smooth muscle were seen in animals treated with matrix without ADSCs. This study provides preclinical evidence that the ADSC-seeded arterial matrix can be used as a tubularized scaffold in the reconstruction of 3 cm long urethral defect in a male canine model. The ADSC-seeded arterial matrix remodels and regenerates normal-appearing urethral tissue layers over time.

Towards a bioengineered uterus: bioactive sheep uterus scaffolds are effectively recellularized by enzymatic preconditioning

Uterine factor infertility was considered incurable until recently when we reported the first successful live birth after uterus transplantation. However, risky donor surgery and immunosuppressive therapy are factors that may be avoided with bioengineering. For example, transplanted recellularized constructs derived from decellularized tissue restored fertility in rodent models and mandate translational studies. In this study, we decellularized whole sheep uterus with three different protocols using 0.5% sodium dodecyl sulfate, 2% sodium deoxycholate (SDC) or 2% SDC, and 1% Triton X-100. Scaffolds were then assessed for bioactivity using the dorsal root ganglion and chorioallantoic membrane assays, and we found that all the uterus scaffolds exhibited growth factor activity that promoted neurogenesis and angiogenesis. Extensive recellularization optimization was conducted using multipotent sheep fetal stem cells and we report results from the following three in vitro conditions; (a) standard cell culturing conditions, (b) constructs cultured in transwells, and (c) scaffolds preconditioned with matrix metalloproteinase 2 and 9. The recellularization efficiency was improved short-term when transwells were used compared with standard culturing conditions. However, the recellularization efficiency in scaffolds preconditioned with matrix metalloproteinases was 200–300% better than the other strategies evaluated herein, independent of decellularization protocol. Hence, a major recellularization hurdle has been overcome with the improved recellularization strategies and in vitro platforms described herein. These results are an important milestone and should facilitate the production of large bioengineered grafts suitable for future in vivo applications in the sheep, which is an essential step before considering these principles in a clinical setting.

Augmentation of the insufficient tissue bed for surgical repair of hypospadias using acellular matrix grafts: A proof of concept study

Acellular matrices produced by tissue decellularisation are reported to have tissue integrative properties. We examined the potential for incorporating acellular matrix grafts during procedures where there is an inadequate natural tissue bed to support an enduring surgical repair. Hypospadias is a common congenital defect requiring surgery, but associated with long-term complications due to deficiencies in the quality and quantity of the host tissue bed at the repair site. Biomaterials were implanted as single on-lay grafts in a peri-urethral position in male pigs. Two acellular tissue matrices were compared: full-thickness porcine acellular bladder matrix (PABM) and commercially-sourced cross-linked acellular matrix from porcine dermis (Permacol™). Anatomical and immunohistological outcomes were assessed 3 months post-surgery. There were no complications and surgical sites underwent full cosmetic repair. PABM grafts were fully incorporated, whilst Permacol™ grafts remained palpable. Immunohistochemical analysis indicated a non-inflammatory, remodelling-type response to both biomaterials. PABM implants showed extensive stromal cell infiltration and neovascularisation, with a significantly higher density of cells (p < 0.001) than Permacol™, which showed poor cellularisation and partial encapsulation. This study supports the anti-inflammatory and tissue-integrative nature of non-crosslinked acellular matrices and provides proof-of-principle for incorporating acellular matrices during surgical procedures, such as in primary complex hypospadias repair.

Tubularized urethral reconstruction using everted saphenous vein graft in a beagle model

Background

A long segment stricture in the anterior urethra is a challenge in urology. We conducted a study to investigate the efficacy of anterior urethral reconstruction using an everted saphenous vein graft (SVG) in a tubular fashion.

Methods

Twelve male beagles were randomly divided into three groups: experimental group (n = 5), control group (n = 5) and normal group (n = 2). A 3 cm defect in the anterior urethra was created. Autologous SVG was harvested. In the experimental group, urethral defect was replaced by an everted SVG in a tubular fashion. In the control group, urethral reconstruction was performed using an uneverted SVG. Beagles in all groups received retrograde urethrography to evaluate urethral patency and were killed for histological examination 6 months after operation.

Results

Four beagles in the experimental group had no voiding difficulty and the other one could not void spontaneously. Retrograde urethrography showed the four beagles in experimental group had wide urethral lumens. Ether urethral stricture or fistula were detected in all animals in the control group. Histological analysis of the four beagles in the experimental group indicated the everted SVG completely integrated into the urethra. The reconstructed urethra contained a wide lumen and was completely covered by urothelium. The periurethral collagen and muscle fibers formed and were highly organized. Everted SVG showed a high ability of neovascularization. In the control group, the reconstructed segment showed a fibrotic urethral lumen where the urothelium was not intact. Only few new capillaries were formed.

Conclusions

Everted SVG demonstrates for a promising strategy for potential urethral stricture repair.

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.

Effects of Anti-Inflammatory Nanofibers on Urethral Healing

Protracted postsurgical inflammation leading to postoperative complications remains a persistent problem in urethral reconstruction. Nanofibers in the form of peptide amphiphiles expressing anti-inflammatory peptides (AIF-PA) have positively modulated local inflammatory responses. Urethroplasty is performed to repair 5 mm ventral urethral defects with: uncoated small intestinal submucosa (SIS); SIS dip-coated with AIF-PA1 (anti-inflammatory treatment), or SIS dip-coated with AIF-PA6 (control) on 12-week-old male Sprague Dawley rats (n = 6/group/timepoint). Animals are euthanized at 14 and 28 d postsurgery. Hematoxylin-eosin, Masson's Trichrome, and immunohistochemistry with primary antibodies against myeloperoxidase (MPO; neutrophils), CD68, CD86, CD206 (macrophages), and proinflammatory cytokines TNFα and IL-1β are performed. Complete urethral healing occurs in 3/6 uncoated SIS (50%), 2/6 SIS+AIF-PA6 (33.3%), and 5/6 SIS+AIF-PA1 (83.3%) animals at 14 d and all at 28 d. Application of AIF-PA1 to SIS substitution urethroplasty decreases MPO⁺ neutrophils, CD86⁺ M1 proinflammatory macrophages, TNFα, and IL-1β levels while concurrently increasing levels of CD206⁺ M2 proregenerative/anti-inflammatory macrophages at the anastomoses and the regenerated tissue at the wound bed (REGEN). AIF-PA1 treatment enhances the healing process, contributing to earlier, complete urethral healing, and increased angiogenesis. Further studies are needed to elucidate the specific mechanism of inflammatory response modulation on angiogenesis and overall urethral healing.

Frontiers in urethra regeneration: current state and future perspective

Despite the positive achievements attained, the treatment of male urethral strictures and hypospadiases still remains a challenge, particularly in cases of severe urethral defects. Complications and the need for additional interventions in such cases are common. Also, shortage of autologous tissue for graft harvesting and significant morbidity in the location of harvesting present problems and often lead to staged treatment. Tissue engineering provides a promising alternative to the current sources of grafts for urethroplasty. Since the first experiments in urethral substitution with tissue engineered grafts, this topic in regenerative medicine has grown remarkably, as many different types of tissue-engineered grafts and approaches in graft design have been suggested and testedin vivo. However, there have been only a few clinical trials of tissue-engineered grafts in urethral substitution, involving hardly more than a hundred patients overall. This indicates that the topic is still in its inception, and the search for the best graft design is continuing. The current review focuses on the state of the art in urethral regeneration with tissue engineering technology. It gives a comprehensive overview of the components of the tissue-engineered graft and an overview of the steps in graft development. Different cell sources, types of scaffolds, assembling approaches, options for vascularization enhancement and preclinical models are considered.

Towards uterus tissue engineering: a comparative study of sheep uterus decellularisation

Uterus tissue engineering may dismantle limitations in current uterus transplantation protocols. A uterine biomaterial populated with patient-derived cells could potentially serve as a graft to circumvent complicated surgery of live donors, immunosuppressive medication and rejection episodes. Repeated uterine bioengineering studies on rodents have shown promising results using decellularised scaffolds to restore fertility in a partially impaired uterus and now mandate experiments on larger and more human-like animal models. The aim of the presented studies was therefore to establish adequate protocols for scaffold generation and prepare for future in vivo sheep uterus bioengineering experiments. Three decellularisation protocols were developed using vascular perfusion through the uterine artery of whole sheep uteri obtained from slaughterhouse material. Decellularisation solutions used were based on 0.5% sodium dodecyl sulphate (Protocol 1) or 2% sodium deoxycholate (Protocol 2) or with a sequential perfusion of 2% sodium deoxycholate and 1% Triton X-100 (Protocol 3). The scaffolds were examined by histology, extracellular matrix quantification, evaluation of mechanical properties and the ability to support foetal sheep stem cells after recellularisation. We showed that a sheep uterus can successfully be decellularised while maintaining a high integrity of the extracellular components. Uteri perfused with sodium deoxycholate (Protocol 2) were the most favourable treatment in our study based on quantifications. However, all scaffolds supported stem cells for 2 weeks in vitro and showed no cytotoxicity signs. Cells continued to express markers for proliferation and maintained their undifferentiated phenotype. Hence, this study reports three valuable decellularisation protocols for future in vivo sheep uterus bioengineering experiments.

Assessing the potential regeneration ability of corpus spongiosum in rabbit models

Most congenital or acquired urethral diseases are usually accompanied by corpus spongiosum (CS) defects. However, Substitution urethroplasty can only reconstruct urethral lumen, not the CS. Many long-term complications occur due to the lack of protection from CS. Is CS a kind of tissue that cannot be repaired by regeneration and self-healing? In this study, the CS defect with urethral mucosa intact model was established in rabbits by removing the ventral CS tissue. Based on this model, three groups of different CS defect sizes, with lengths of 0.5 cm (Group A), 1.0 cm (Group B) and 1.5 cm (Group C), were then constructed, respectively, to assess the potential regeneration ability of CS. Three months later, the entire urethra, including the CS defect, was assessed by histological staining. Results showed that the vascular sinusoids were completely removed from urethral mucosa. The rabbit model of CS defect was established successfully. Three months post-operatively, the CS defects in all the 3 groups were replaced by disordered collagen instead of regenerating typical sinusoid-like vascular structure, which is significantly different from the normal CS rich in vascular sinusoids. The CS defects could not be repaired through self-healing. The potential regeneration ability of CS is extremely poor.

Decellularization and recellularization of the ovary for bioengineering applications; studies in the mouse

BACKGROUND

Fertility preservation is particularly challenging in young women diagnosed with hematopoietic cancers, as transplantation of cryopreserved ovarian cortex in these women carries the risk for re-introducing cancer cells. Therefore, the construction of a bioengineered ovary that can accommodate isolated small follicles was proposed as an alternative to minimize the risk of malignancy transmission. Various options for viable bioengineered scaffolds have been reported in the literature. Previously, we reported three protocols for producing mouse ovarian scaffolds with the decellularization technique. The present study examined these scaffolds further, specifically with regards to their extracellular composition, biocompatibility and ability to support recellularization with mesenchymal stem cells.

MATERIAL AND METHODS

Three decellularization protocols based on 0.5% sodium dodecyl sulfate (Protocol 1; P1), or 2% sodium deoxycholate (P2), or a combination of the two detergents (P3) were applied to produce three types of scaffolds. The levels of collagen, elastin and sulfated glycosaminoglycans (sGAGs) were quantified in the remaining extracellular matrix. Detailed immunofluorescence and scanning electron microscopy imaging were conducted to assess the morphology and recellularization efficiency of the constructs after 14 days in vitro utilizing red fluorescent protein-labelled mesenchymal stem cells.

RESULTS

All protocols efficiently removed the DNA while the elastin content was not significantly reduced during the procedures. The SDS-protocol (P1) reduced the sGAG and the collagen content more than the SDC-protocol (P2). All scaffolds were biocompatible and recellularization was successful, particularly in several P2-derived scaffolds. The cells were extensively distributed throughout the constructs, with a denser distribution observed towards the ovarian cortex. The cell density was not significantly different (400 to 550 cells/mm²) between scaffold types. However, there was a tendency towards a higher cell density in the SDC-derived constructs. Scanning electron microscope images showed fibrous scaffolds with a dense repopulated surface structure.

CONCLUSIONS

While there were differences in the key structural macromolecules between protocols, all scaffolds were biocompatible and showed effective recellularization. The results indicate that our SDC-protocol might be better than our SDS-protocol. However, additional studies are necessary to determine their suitability for attachment of small follicles and folliculogenesis.

A tissue-engineered uterus supports live births in rabbits

Bioengineered uterine tissue could provide a treatment option for women with uterine factor infertility. In large-animal models, reconstruction of the uterus has been demonstrated only with xenogeneic tissue grafts. Here we use biodegradable polymer scaffolds seeded with autologous cells to restore uterine structure and function in rabbits. Rabbits underwent a subtotal uterine excision and were reconstructed either with autologous cell-seeded constructs, with non-seeded scaffolds, or by suturing. At 6 months post-implantation, only the cell-seeded engineered uteri developed native tissue-like structures, including organized luminal/glandular epithelium, stroma, vascularized mucosa, and two-layered myometrium. Only rabbits with cell-seeded constructs had normal pregnancies (4/10) within the reconstructed segment of the uterus and supported fetal development to term and live birth. With further development, this approach may provide a regenerative medicine solution to uterine factor infertility.

Sustained release of stromal cell-derived factor-1 alpha from silk fibroin microfiber promotes urethral reconstruction in rabbits

We developed a stromal cell-derived factor-1 alpha (SDF-1α)-aligned silk fibroin (SF)/three-dimensional porous bladder acellular matrix graft (3D-BAMG) composite scaffold for long-section ventral urethral regeneration and repair in vivo. SDF-1α-aligned SF microfiber/3D-BAMG, aligned SF microfiber/3D-BAMG, and nonaligned SF microfiber/3D-BAMG scaffolds were prepared using electrostatic spinning and wet processing. Adipose-derived stem cell (ADSC) and bone marrow stromal cell (BMSC) migration was assessed in the SDF-1α-loaded scaffolds. Sustained SDF-1α release in vitro and vivo was analyzed using enzyme-linked immunosorbent assay (ELISA) and western blotting, respectively. The scaffolds were used to repair a 1.5 × 1 cm² ventral urethral defect in male rabbits in vivo. General observation and retrograde urinary tract contrast assessment were used to examine urethral lumen patency and continuity at 1 and 3 months post-surgery. Postoperative rehabilitation was evaluated using histological detection. The composite scaffolds sustained SDF-1α release for over 16 days in vitro. SDF-1α-aligned SF nanofiber promoted regeneration of urethral mucosa, submucosal smooth muscles, and microvasculature, increased cellular proliferation, and reduced collagen deposition. SDF-1α expression was increased in reconstructed urethra at 3 months post-surgery in SDF-1α-aligned SF group. SDF-1α-aligned SF microfiber/3D-BAMG scaffolds may be used to repair and reconstruct long urethral defects because they accelerate urethral regeneration.

Bioengineered Scaffolds as Substitutes for Grafts for Urethra Reconstruction

Urethral defects originating from congenital malformations, trauma, inflammation or carcinoma still pose a great challenge to modern urology. Recent therapies have failed many times and have not provided the expected results. This negatively affects patients' quality of life. By combining cells, bioactive molecules, and biomaterials, tissue engineering can provide promising treatment options. This review focused on scaffold systems for urethra reconstruction. We also discussed different technologies, such as electrospinning and 3D bioprinting which provide great possibility for the preparation of a hollow structure with well-defined architecture.

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.

Regenerative and engineered options for urethroplasty

Surgical correction of urethral strictures by substitution urethroplasty - the use of grafts or flaps to correct the urethral narrowing - remains one of the most challenging procedures in urology and is frequently associated with complications, restenosis and poor quality of life for the affected individual. Tissue engineering using different cell types and tissue scaffolds offers a promising alternative for tissue repair and replacement. The past 30 years of tissue engineering has resulted in the development of several therapies that are now in use in the clinic, especially in treating cutaneous, bone and cartilage defects. Advances in tissue engineering for urethral replacement have resulted in several clinical applications that have shown promise but have not yet become the standard of care.

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

Purpose

The purpose of this review is to assess the potential role of tissue engineering for urethral reconstruction. It is well- recognised that urethrotomy remains the first-line therapy in the treatment of urethral stricture. Following on from the randomised study which recommended no difference between urethrotomy and urethral dilation, Steenkamp et al. reported long-term success rates of only 20%. Patients with longer strictures, penile or distal urethral strictures, and extensive periurethral spongiofibrosis typically do not respond well to repeated incisions. This report reviews the potential role of tissue engineering as applied to augmentation urethroplasty, which is the treatment of choice following failed urethrotomy.

Methods

A review of the literature was carried out. The principal emphasis was on tissue engineering as applied to augmentation urethroplasty, but an introductory section reviews the use of urethrotomy and the background to contemporary practise with augmentation urethroplasty using oral mucosa.

Results

It is evident that a cellular matrix which requires the ingrowth of cells is unlikely to be successful except for very short strictures. Other approaches such as injection of stem cells have not been adequately trialled in humans to date. Tissue-engineered substitute for autologous oral mucosa has been used and the results relating to this are reviewed.

Conclusions

Tissue engineering of autologous tissue for urethroplasty is expensive. It is unnecessary for the majority of cases, but could be potentially useful for very lengthy strictures, for instance, relating to lichen sclerosis. Whilst tissue-engineered oral mucosa has been successfully used, a great deal more work would be necessary to develop an appropriate matrix. Another study has looked at a larger series using an alternative tissue-engineered substitute, but the results have been very disappointing. At present, it has to be concluded that there is no effective and validated tissue engineering solution for the management of urethral stricture disease.

Regenerative collagen biomembrane: Interim results of a Phase I veterinary clinical trial for skin repair

Background: The availability of commercial tissue engineering skin repair products for veterinary use is scarce or non-existent. To assess features of novel veterinary tissue engineered medical devices, it is therefore reasonable to compare with currently available human devices. During the development and regulatory approval phases, human medical devices that may have been identified as comparable to a novel veterinary device, may serve as predicate devices and accelerate approval in the veterinary domain. The purpose of the study was to evaluate safety and efficacy of the biomembrane for use in skin repair indications. Methods: In the study as a whole (3 year total length), 15 patients (animals), dogs and cats (male/female, <8 years) with skin lesions of different etiologies considered difficult to heal (size, >2 cm), with a wound depth equivalent to 2nd/3rd degree burns are to be studied from Day 0 to Day 120-240, post-application of the biomembrane. This interim report covers the 5 patients assessed to date and deemed eligible, of which 3 enrolled, and 2 have completed the treatment. Wound beds were prepared and acellular collagen biomembranes (Eva Scientific Ltd, São Paulo, Brazil) applied directly onto the wounds, and sutured at the margins to the patient's adjacent tissue. Wound size over time, healing rate, general skin quality and suppleness were assessed as outcomes. Qualitative (appearance and palpation) and quantitative (based on Image Analysis of photographs) wound assessment techniques were used. Results: Both patients' wounds healed fully, with no adverse effects, and the healing rate was comparable in both, maxing out at approximately 1 cm 2/day. Conclusions: Early results on the biomembrane's safety and efficacy indicate suitability for skin repair usage in veterinary patients.

Tissue engineering in pediatric urology - a critical appraisal

Tissue engineering is defined as the combination of biomaterials and bioengineering principles together with cell transplantation or directed growth of host cells to develop a biological replacement tissue or organ that can be a substitute for normal tissue both in structure and function. Despite early promising preclinical studies, clinical translation of tissue engineering in pediatric urology into humans has been unsuccessful both for cell-seeded and acellular scaffolds. This can be ascribed to various factors, including the use of only non-diseased models that inaccurately describe the structural and functional modifications of diseased tissue. The paper addresses potential future strategies to overcome the limitations experienced in clinical applications so far. This includes the use of stem cells of various origins (mesenchymal stem cells, hematopoietic stem/progenitor cells, urine-derived stem cells, and progenitor cells of the urothelium) as well as the need for a deeper understanding of signaling pathways and directing tissue ingrowth and differentiation through the concept of dynamic reciprocity. The development of smart scaffolds that release trophic factors in a set and timely manner will probably improve regeneration. Modulation of innate immune response as a major contributor to tissue regeneration outcome is also addressed. It is unlikely that only one of these strategies alone will lead to clinically applicable tissue engineering strategies in pediatric urology. In the meanwhile, the fundamental new insights into regenerative processes already obtained in the attempts of tissue engineering of the lower urogenital tract remain our greatest gain.

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.

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

INTRODUCTION

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

DISCUSSION

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

CONCLUSION

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

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.