Penile urethra replacement with autologous cell-seeded tubularized collagen matrices

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.

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.

Global hotspots and emerging trends in 3D bioprinting research

Three-dimensional (3D) bioprinting is an advanced tissue engineering technique that has received a lot of interest in the past years. We aimed to highlight the characteristics of articles on 3D bioprinting, especially in terms of research hotspots and focus. Publications related to 3D bioprinting from 2007 to 2022 were acquired from the Web of Science Core Collection database. We have used VOSviewer, CiteSpace, and R-bibliometrix to perform various analyses on 3,327 published articles. The number of annual publications is increasing globally, a trend expected to continue. The United States and China were the most productive countries with the closest cooperation and the most research and development investment funds in this field. Harvard Medical School and Tsinghua University are the top-ranked institutions in the United States and China, respectively. Dr. Anthony Atala and Dr. Ali Khademhosseini, the most productive researchers in 3D bioprinting, may provide cooperation opportunities for interested researchers. Tissue Engineering Part A contributed the largest publication number, while Frontiers in Bioengineering and Biotechnology was the most attractive journal with the most potential. As for the keywords in 3D bioprinting, Bio-ink, Hydrogels (especially GelMA and Gelatin), Scaffold (especially decellularized extracellular matrix), extrusion-based bioprinting, tissue engineering, and in vitro models (organoids particularly) are research hotspots analyzed in the current study. Specifically, the research topics "new bio-ink investigation," "modification of extrusion-based bioprinting for cell viability and vascularization," "application of 3D bioprinting in organoids and in vitro model" and "research in personalized and regenerative medicine" were predicted to be hotspots for future research.

Ascorbic Acid 2-Phosphate-Releasing Supercritical Carbon Dioxide-Foamed Poly(L-Lactide-Co-epsilon-Caprolactone) Scaffolds Support Urothelial Cell Growth and Enhance Human Adipose-Derived Stromal Cell Proliferation and Collagen Production

Tissue engineering can provide a novel approach for the reconstruction of large urethral defects, which currently lacks optimal repair methods. Cell-seeded scaffolds aim to prevent urethral stricture and scarring, as effective urothelium and stromal tissue regeneration is important in urethral repair. In this study, the aim was to evaluate the effect of the novel porous ascorbic acid 2-phosphate (A2P)-releasing supercritical carbon dioxide-foamed poly(L-lactide-co-ε-caprolactone) (PLCL) scaffolds (scPLCLA2P) on the viability, proliferation, phenotype maintenance, and collagen production of human urothelial cell (hUC) and human adipose-derived stromal cell (hASC) mono- and cocultures. The scPLCLA2P scaffold supported hUC growth and phenotype both in monoculture and in coculture. In monocultures, the proliferation and collagen production of hASCs were significantly increased on the scPLCLA2P compared to scPLCL scaffolds without A2P, on which the hASCs formed nonproliferating cell clusters. Our findings suggest the A2P-releasing scPLCLA2P to be a promising material for urethral tissue engineering.

Therapies Based on Adipose-Derived Stem Cells for Lower Urinary Tract Dysfunction: A Narrative Review

Lower urinary tract dysfunction often requires tissue repair or replacement to restore physiological functions. Current clinical treatments involving autologous tissues or synthetic materials inevitably bring in situ complications and immune rejection. Advances in therapies using stem cells offer new insights into treating lower urinary tract dysfunction. One of the most frequently used stem cell sources is adipose tissue because of its easy access, abundant source, low risk of severe complications, and lack of ethical issues. The regenerative capabilities of adipose-derived stem cells (ASCs) in vivo are primarily orchestrated by their paracrine activities, strong regenerative potential, multi-differentiation potential, and cell–matrix interactions. Moreover, biomaterial scaffolds conjugated with ASCs result in an extremely effective tissue engineering modality for replacing or repairing diseased or damaged tissues. Thus, ASC-based therapy holds promise as having a tremendous impact on reconstructive urology of the lower urinary tract.

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.

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.

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.

Recurrent Anterior Urethral Stricture: Challenges and Solutions

Recurrent male anterior urethral stricture disease is a complex surgical challenge that should be managed by reconstructive urologists with experience in stricture management. Diagnosis of recurrence requires both anatomic narrowing and patient symptoms identified on validated questionnaires, with limited role for intervention in asymptomatic treatment “failures”. Endoscopic management has a very specific role in recurrence, and the choice of technique for urethroplasty depends on pre-operative urethrography and cystoscopy. Surgical success depends on addressing patient concerns, complete stricture excision, tissue quality optimization, and the use of multi-stage repair when indicated. Augmentation with genital skin flaps and/or grafts is often required, with buccal mucosa as the ideal graft source if local tissue is compromised. Salvage options including urinary diversion and perineal urethrostomy must also be considered in debilitated patients with severe disease or repeated treatment failures. Unique patient populations including patients with hypospadias and lichen sclerosis are among the highest risk for repeated recurrence and require special care in surgical technique, graft selection, and post-operative management.

Sterilization and disinfection methods for decellularized matrix materials: Review, consideration and proposal

Sterilization is the process of killing all microorganisms, while disinfection is the process of killing or removing all kinds of pathogenic microorganisms except bacterial spores. Biomaterials involved in cell experiments, animal experiments, and clinical applications need to be in the aseptic state, but their physical and chemical properties as well as biological activities can be affected by sterilization or disinfection. Decellularized matrix (dECM) is the low immunogenicity material obtained by removing cells from tissues, which retains many inherent components in tissues such as proteins and proteoglycans. But there are few studies concerning the effects of sterilization or disinfection on dECM, and the systematic introduction of sterilization or disinfection for dECM is even less. Therefore, this review systematically introduces and analyzes the mechanism, advantages, disadvantages, and applications of various sterilization and disinfection methods, discusses the factors influencing the selection of sterilization and disinfection methods, summarizes the sterilization and disinfection methods for various common dECM, and finally proposes a graphical route for selecting an appropriate sterilization or disinfection method for dECM and a technical route for validating the selected method, so as to provide the reference and basis for choosing more appropriate sterilization or disinfection methods of various dECM.

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Asepsis is the prerequisite for the experiment and application of biomaterials.

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Sterilization or disinfection affects physic-chemical properties of biomaterials.

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Mechanism, advantages and disadvantages of sterilization or disinfection methods.

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Factors influencing the selection of sterilization or disinfection methods.

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Selection of sterilization or disinfection methods for decellularized matrix.

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

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

Hypoxia-preconditioned adipose-derived stem cells combined with scaffold promote urethral reconstruction by upregulation of angiogenesis and glycolysis

Rationale

Tissue engineering is a promising alternative for urethral reconstruction, and adipose-derived stem cells (ADSCs) are widely used as seeding cells. Hypoxia preconditioning can significantly enhance the therapeutic effects of ADSCs. The low oxygen tension of postoperative wound healing is inevitable and may facilitate the nutritional function of ADSCs. This study aimed to investigate if hypoxia-preconditioned ADSCs, compared to normoxia-preconditioned ADSCs, combined with scaffold could better promote urethral reconstruction and exploring the underlying mechanism.

Methods

In vitro, paracrine cytokines and secretomes that were secreted by hypoxia- or normoxia-preconditioned ADSCs were added to cultures of human umbilical vein endothelial cells (HUVECs) to measure their functions. In vivo, hypoxia- or normoxia-preconditioned ADSCs were seeded on a porous nanofibrous scaffold for urethral repair on a defect model in rabbits.

Results

The in vitro results showed that hypoxia could enhance the secretion of VEGFA by ADSCs, and hypoxia-preconditioned ADSCs could enhance the viability, proliferation, migration, angiogenesis, and glycolysis of HUVECs (p < 0.05). After silencing VEGFA, angiogenesis and glycolysis were significantly inhibited (p < 0.05). The in vivo results showed that compared to normoxia-preconditioned ADSCs, hypoxia-preconditioned ADSCs combined with scaffolds led to a larger urethral lumen diameter, preserved urethral morphology, and enhanced angiogenesis (p < 0.05).

Conclusions

Hypoxia preconditioning of ADSCs combined with scaffold could better promote urethral reconstruction by upregulating angiogenesis and glycolysis. Hypoxia-preconditioned ADSCs combined with novel scaffold may provide a promising alternative treatment for urethral reconstruction.

Biofabrication of a Functional Tubular Construct from Tissue Spheroids Using Magnetoacoustic Levitational Directed Assembly

In traditional tissue engineering, synthetic or natural scaffolds are usually used as removable temporal support, which involves some biotechnology limitations. The concept of "scaffield" approach utilizing the physical fields instead of biomaterial scaffold has been proposed recently. In particular, a combination of intense magnetic and acoustic fields can enable rapid levitational bioassembly of complex-shaped 3D tissue constructs from tissue spheroids at low concentration of paramagnetic agent (gadolinium salt) in the medium. In the current study, the tissue spheroids from human bladder smooth muscle cells (myospheres) are used as building blocks for assembling the tubular 3D constructs. Levitational assembly is accomplished at low concentrations of gadolinium salts in the high magnetic field at 9.5 T. The biofabricated smooth muscle constructs demonstrate contraction after the addition of vasoconstrictive agent endothelin-1. Thus, hybrid magnetoacoustic levitational bioassembly is considered as a new technology platform in the emerging field of formative biofabrication. This novel technology of scaffold-free, nozzle-free, and label-free bioassembly opens a unique opportunity for rapid biofabrication of 3D tissue and organ constructs with complex geometry.

Complete Human Penile Scaffold for Composite Tissue Engineering: Organ Decellularization and Characterization

Reconstruction for total penile defects presents unique challenges due to its anatomical and functional complexity. Standard methods suffer from high complication rates and poor functional outcomes. In this work we have developed the first protocol for decellularizing whole-organ human penile specimens for total penile tissue engineering. The use of a hybrid decellularization scheme combining micro-arterial perfusion, urethral catheter perfusion and external diffusion enabled the creation of a full-size scaffold with removal of immunogenic components. Decellularization was complete as assessed by H&E and immunohistochemistry, while quantification of residual DNA showed acceptably low levels (<50 ng/mg). An intact ECM was maintained with histologic architecture preservation on H&E and SEM as well as preservation of key proteins such as collagen-1, laminin and fibronectin and retention of growth factors VEGF (45%), EGF (57%) and TGF-beta1 (42%) on ELISA. Post-decellularization patency of the cavernosal arteries for future use in reseeding was demonstrated. Scaffold biocompatibility was evaluated using human adipose-derived stromal vascular cells. Live/Dead stains showed the scaffold successfully supported cell survival and expansion. Influence on cellular behavior was seen with significantly higher expression of VWF, COL1, SM22 and Desmin as compared to cell monolayer. Preliminary evidence for regional tropism was also seen, with formation of microtubules and increased endothelial marker expression in the cavernosa. This report of successful decellularization of the complete human phallus is an initial step towards developing a tissue engineered human penile scaffold with potential for more successfully restoring cosmetic, urinary and sexual function after complete penile loss.

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.

Repair of urethral defects by an adipose mesenchymal stem cell‑porous silk fibroin material

The aim of the present study was to determine whether it was possible to repair urethral defects with a material of adipose mesenchymal stem cells (ADMSCs)-porous silk fibroin (SF). A total of 39 male New Zealand white rabbits were randomly divided into a control group, an SF group and a bromodeoxyuridine (BrdU)-labeled ADMSCs-SF group (SSF group; n=13/group). Defects were made by resecting the posterior urethral wall. The defects in the SF and SSF groups were repaired using SF and BrdU-labeled ADMSCs-SF materials respectively. Then the anterior wall was sutured, and the urethral catheter was retained for 3 weeks following surgery. The catheter was rinsed with nitrofurazone once a day. The cells with positive expressions of factor VIII related antigen (FVIII-RAg), α-smooth muscle actin (α-SMA) and pan-cytokeratin (AE1/AE3) were detected by immunohistochemical assay, and the distributions of BrdU positive cells and macrophages were observed. Urethrography was performed prior to and following surgery. All rabbits had normal urethral morphologies prior to surgery. The incidence rates of postoperative complications in the control, SF and SSF groups were 76.92 (7/13), 23.07 (3/13) and 15.38% (2/13), respectively (P<0.05). The number of positive macrophages in the SSF group was significantly lower than that of the SF group 4 weeks following surgery (P<0.05). In the SSF group, BrdU positive cells were scattered within the SF material following surgery, primarily at the intersection between the SF material and the urethra. The number of FVIII-RAg positive cells in the SSF and SF groups were significantly different (P<0.05), which were also significantly higher than that of control group (P<0.01). The number of α-SMA positive cells in the SSF and SF groups were significantly different (P<0.05), and these values also significantly exceeded those exhibited by the control group (P<0.01). In addition, the SSF and SF groups had positive staining of AE1/AE3. Similar to normal urethral mucosa, the cytoplasm was stained brownish yellow (P<0.05). It is thus feasible to repair urethral defects using ADMSCs-SF material.

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.

Urinary Tissue Engineering: Challenges and Opportunities

INTRODUCTION

In this review, we discuss major advancements and common challenges in constructing and regenerating a neo-urinary conduit (NUC). First, we focus on the need for regenerating the urothelium, the hallmark the urine barrier, unique to urinary tissues. Second, we focus on clinically feasible scaffolds based on decellularized matrices and molded collagen that are currently of great research interest.

AIM

To discuss the major advancements in constructing a tissue-engineered NUC (TE-NUC) and the challenges involved in their successful clinical translation.

METHODS

A comprehensive search of peer-reviewed literature from PubMed and Google Scholar on subjects related to urothelium regeneration, decellularized tissue matrices, and collagen scaffolds was conducted.

MAIN OUTCOME MEASURE

We evaluated the main biological and mechanical functions of urinary tissues, the need for TE implants to create a urinary diversion, the reasons for their failures in clinical settings, and the applications of decellularized tissue matrices and collagen-based molded scaffolds in their regeneration.

RESULTS

It is necessary to create a urine barrier that prevents urine leakage into the stroma that can cause failure of the graft. Despite the regeneration potential of the urothelium, the limited supply of healthy urothelial cells in patients with bladder cancer remains a major challenge. In this context, alternative strategies, such as transdifferentiation of cells into urothelium or engineered scaffolds based on decellularized tissues and molded collagen with robust urine barrier properties, are active areas of research.

CONCLUSION

There is an immediate need for developing a functional TE-NUC that can improve the quality of life of patients with bladder cancer. It is possible to achieve a TE-NUC by bioengineering an implant that has appropriate biological and mechanical properties to store and transport urine. We anticipate that future advancements in urothelium regeneration and material design will lead us closer to successful neo-urinary tissue constructs. Singh A, Bivalacqua TJ, Sopko N. Urinary Tissue Engineering: Challenges and Opportunities. Sex Med Rev 2018;6:35-44.

"Tissue Papers" from Organ-Specific Decellularized Extracellular Matrices

Using an innovative, tissue-independent approach to decellularized tissue processing and biomaterial fabrication, the development of a series of "tissue papers" derived from native porcine tissues/organs (heart, kidney, liver, muscle), native bovine tissue/organ (ovary and uterus), and purified bovine Achilles tendon collagen as a control from decellularized extracellular matrix particle ink suspensions cast into molds is described. Each tissue paper type has distinct microstructural characteristics as well as physical and mechanical properties, is capable of absorbing up to 300% of its own weight in liquid, and remains mechanically robust (E = 1-18 MPa) when hydrated; permitting it to be cut, rolled, folded, and sutured, as needed. In vitro characterization with human mesenchymal stem cells reveals that all tissue paper types support cell adhesion, viability, and proliferation over four weeks. Ovarian tissue papers support mouse ovarian follicle adhesion, viability, and health in vitro, as well as support, and maintain the viability and hormonal function of nonhuman primate and human follicle-containing, live ovarian cortical tissues ex vivo for eight weeks postmortem. "Tissue papers" can be further augmented with additional synthetic and natural biomaterials, as well as integrated with recently developed, advanced 3D-printable biomaterials, providing a versatile platform for future multi-biomaterial construct manufacturing.

Future Prospects for Human Tissue Engineered Urethra Transplantation: Decellularization and Recellularization-Based Urethra Regeneration

To evaluate the histological characteristics of decellularized human urethra after transplantation into the rat omentum and compare in vivo cell seeding with perfusion-based and cell sheet urethral regeneration. Eight adult human male urethras accompanied with the surrounding corpus spongiosum were obtained. The tissues were decellularized with detergent-based method. The efficacy of decellularization and extracellular matrix preservation was evaluated by several techniques. Decellularized scaffolds were transplanted into the omentum of 12 male rats and located into the scrotum. Biopsies were taken 1, 3, and 6 months postoperatively to assess the natural recellularization. Mesenchymal stem cells obtained from preputial tissue were seeded with perfusion-based and cell sheet techniques as well. Immunohistochemical staining with α-actin, cytokeratin AE1/AE3, synaptophysin, and CD31 antibodies were performed. Removal of nuclear components and preservation of biomechanical properties was confirmed. In-vivo recellularization revealed promising results in progressive angiogenesis and cell seeding of epithelium-like cells in the lining of the urethra as well as smooth muscle cells in the wall structure. In-vitro urethral regeneration revealed that cell sheet engineering was the technique of choice compared to perfusion-based technique. This study may paw the road for clinical application of acellular urethral matrix with the surrounding corpus spongiosum in urological reconstructive surgery.

Urethral Reconstruction Using Mesothelial Cell-Seeded Autogenous Granulation Tissue Tube: An Experimental Study in Male Rabbits

Objective. This study was to evaluate the utility of the compound graft for tubularized urethroplasty by seeding mesothelial cells onto autogenous granulation tissue. Methods. Silastic tubes were implanted subcutaneously in 18 male rabbits, of which nine underwent omentum biopsies simultaneously for in vitro expansion of mesothelial cells. The granulation tissue covering the tubes was harvested 2 weeks after operation. Mesothelial cells were seeded onto and cocultured with the tissue for 7 days. A pendulous urethral segment of 1.5 cm was totally excised. Urethroplasty was performed with mesothelial cell-seeded tissue tubes in an end-to-end fashion in nine rabbits and with unseeded grafts in others as controls. Serial urethrograms were performed at 1, 2, and 6 months postoperatively. Meanwhile, the neourethra was harvested and analyzed grossly and histologically. Results. Urethrograms showed cell-seeded grafts maintained wide at each time point, while strictures formation was found in unseeded grafts. Histologically, layers of urothelium surrounded by increasingly organized smooth muscles were observed in seeded grafts. In contrast, myofibroblasts accumulation and extensive scarring occurred in unseeded grafts. Conclusions. Mesothelial cell-seeded granulation tissue tube can be successfully used for tubularized urethroplasty in male rabbits.

Acellular Urethra Bioscaffold: Decellularization of Whole Urethras for Tissue Engineering Applications

Patients with stress urinary incontinence mainly suffer from malfunction of the urethra closure mechanism. We established the decellularization of porcine urethras to produce acellular urethra bioscaffolds for future tissue engineering applications, using bioscaffolds or bioscaffold-derived soluble products. Cellular removal was evaluated by H&E, DAPI and DNA quantification. The presence of specific ECM proteins was assessed through immunofluorescence staining and colorimetric assay kits. Human skeletal muscle myoblasts, muscle progenitor cells and adipose-derived stromal vascular fractions were used to evaluate the recellularization of the acellular urethra bioscaffolds. The mechanochemical decellularization system removed ~93% of tissue's DNA, generally preserving ECM's components and microarchitecture. Recellularization was achieved, though methodological advances are required regarding cell seeding strategies and functional assessment. Through microdissection and partial digestion, different urethra ECM-derived coating substrates were formulated (i.e. containing smooth or skeletal muscle ECM) and used to culture MPCs in vitro. The skeletal muscle ECM substrates enhanced fiber formation leading to the expression of the main skeletal muscle-related proteins and genes, as confirmed by immunofluorescence and RT-qPCR. The described methodology produced a urethra bioscaffold that retained vital ECM proteins and was liable to cell repopulation, a crucial first step towards the generation of urethra bioscaffold-based Tissue Engineering products.

Biomaterial Scaffolds for Reproductive Tissue Engineering

The reproductive system usually involves gamete producing gonads, a series of specialized ducts, accessory glands and the external genitalia. Despite there are many traditional methods such as hormonal and surgical approaches, at present no effective treatments exist to help patients suffering from serious diseases of reproductive system, including congenital and acquired abnormalities, malignant tumor, traumatic, infectious etiologies, inflammation and iatrogenic injuries. Tissue engineering holds promise for reproductive medicine through the development of biological alternative. Till now, a diverse range of biomaterials have been utilized as suitable substrates to match both the mechanical and biological context of reproductive tissues. The current review will focus mainly on the applications of biomaterial scaffolds and their major achievements in each region of reproductive systems.

Seeding cell approach for tissue-engineered urethral reconstruction in animal study: A systematic review and meta-analysis

We systematically reviewed published preclinical studies to evaluate the effectiveness of cell-seeded tissue engineering approach for urethral reconstruction in an animal model. The outcomes were summarized by success factors in the animal experiments, which evaluate the possibility and feasibility of a clinical application in the future. Preclinical studies of tissue engineering approaches for urethral reconstruction were identified through a systematic search in PubMed, Embase, and Biosis Previews (web of science SP) databases for studies published from 1 January 1980 to 23 November 2014. Primary studies were included if urethral reconstruction was performed using a tissue-engineered biomaterial in any animal species (with the experiment group being a cell-seeded scaffold and the control group being a cell-free scaffold) with histology and urethrography as the outcome measure. A total of 15 preclinical studies were included in our meta-analysis. The histology and urethrography outcome between the experimental and control groups were considered to be the most clinically relevant. Through this systematic approach, our outcomes suggested that applying the cell-seeded biomaterial in creating a neo-urethra was stable and effective. And multi-type cells including epithelial cells as well as smooth muscle cells or fibroblasts seemed to be a better strategy. Stem cells, especially after epithelial differentiation, could be a promising choice for future researches.

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

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

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

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

Urovision 2020: The future of urology

Urology, as a specialty, has always been at the forefront of innovation and research. Newer technologies have been rapidly embraced and, in many cases, improved upon in order to achieve better patient outcomes. This review addresses the possible future directions that technological advances in urology may take. The role of further miniaturization of urolithiasis treatment, robotic surgery and other minimally invasive techniques is addressed. The potential for enhanced imaging and diagnostic techniques like magnetic resonance imaging and ultrasonography modifications, as well as the potential applications of nanotechnology and tissue engineering, are reviewed.

This article is based on the Dr. Sitharaman Best Essay award of the Urological Society of India for 2013.

Regenerative medicine in urology

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

Fibroblast engraftment in the decellularized mouse lung occurs via a β1-integrin-dependent, FAK-dependent pathway that is mediated by ERK and opposed by AKT

Creation of bioartificial organs has been enhanced by the development of strategies involving decellularized mammalian lung. Because fibroblasts critically support lung function through a number of mechanisms, study of these cells in the context of the decellularized lung has the potential to improve the structure and function of tissue-engineered lungs. We characterized the engraftment and survival of a mouse fibroblast cell line in decellularized rat lung slices and found a time-dependent increase in cell numbers assessed by hematoxylin and eosin staining, cell proliferation assessed by Ki67 staining, and minimal cell death assessed by TUNEL staining. We developed a repopulation index to allow quantification of cell survival that accounts for variation in cell density throughout the seeded scaffold. We then applied this method to the study of mouse lung scaffolds and found that decellularization of presliced mouse lungs produced matrices with preserved alveolar architecture and proteinaceous components including fibronectin, collagens I and IV, laminin, and elastin. Treatment with a β1-integrin-neutralizing antibody significantly reduced the repopulation index after 24 h of culture. Treatment with focal adhesion kinase (FAK) inhibitor and extracellular signal-regulated kinase (ERK) inhibitor further reduced initial repopulation scores while treatment with AKT inhibitor increased initial scores. Rho-associated kinase inhibitor had no discernible effect. These data indicate that initial adhesion and survival of mouse fibroblasts in the decellularized mouse lung occur in a β1-integrin-dependent, FAK/ERK-dependent manner that is opposed by AKT.