Acellular matrix in urethral reconstruction

Assessing the effects of bladder decellularization protocols on extracellular matrix (ECM) structure, mechanics, and biology

INTRODUCTION

Acellular matrices have historically been applied as biologic scaffolds in surgery, wound care, and tissue engineering, albeit with inconsistent outcomes. One aspect that varies widely between products is the selection of decellularization protocol, yet few studies assess comparative effectiveness of these protocols in preserving mechanics, and protein content. This study characterizes bladder acellular matrix (BAM) using two different detergent and enzymatic protocols, evaluating effects on nuclei and DNA removal (≥90%), structure, tensile properties, and maintenance of extracellular matrix proteins.

METHODS

Porcine bladders were decellularized with 0.5% Sodium Dodecyl Sulfate (SDS) or 0.25% Trypsin-hypotonic-Triton X-100 hypertonic (TT)-based agitation protocols, followed by DNase/RNase agents. Characterization of BAM included decellularization efficacy (DAPI, DNA quantification), structure (histology and scanning electron microscopy), tensile testing (Instron 345C-1 mechanical tester), and protein presence and diversity (mass spectrometry). SDS and TT data was directly compared to the same native bladder using two-tailed paired t-tests. Native, TT, and SDS cohorts for tensile testing were compared using one-way ANOVA; Tukey's post-hoc tests for among group differences.

RESULTS

Effective nuclei removal was achieved by SDS- and TT-based protocols. However, target DNA removal was achieved with SDS but not TT. SDS more effectively maintained qualitative tissue architecture compared to TT. The tensile modulus of the TT cohort increased, and stretchability decreased after decellularization in both SDS and TT. UTS was unaffected by either protocol. Higher overall diversity and quantity of core matrisome and matrisome-associated proteins was maintained in the SDS vs TT cohort post-decellularization.

CONCLUSION

The results indicated that detergent selection affects multiple aspects of the resultant BAM biologic product. In the selected protocols, SDS was superior to TT efficacy, and maintenance of gross tissue architecture as well as maintenance of ECM proteins. Decellularization increased scaffold resistance to deformation in both cohorts. Future studies applying biologic scaffolds must consider the processing method and agents used to ensure that materials selected are optimized for characteristics that will facilitate effective translational use.

Acellular dermal matrix in urethral reconstruction

The management of severe urethral stricture has always posed a formidable challenge. Traditional approaches such as skin flaps, mucosal grafts, and urethroplasty may not be suitable for lengthy and intricate strictures. In the past two decades, tissue engineering solutions utilizing acellular dermal matrix have emerged as potential alternatives. Acellular dermal matrix (ADM) is a non-immunogenic biological collagen scaffold that has demonstrated its ability to induce layer-by-layer tissue regeneration. The application of ADM in urethral reconstruction through tissue engineering has become a practical endeavor. This article provides an overview of the preparation, characteristics, advantages, and disadvantages of ADM along with its utilization in urethral reconstruction via tissue engineering.

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.

Advances in Biodegradable Polymers and Biomaterials for Medical Applications-A Review

The introduction of new materials for the production of various types of constructs that can connect directly to tissues has enabled the development of such fields of science as medicine, tissue, and regenerative engineering. The implementation of these types of materials, called biomaterials, has contributed to a significant improvement in the quality of human life in terms of health. This is due to the constantly growing availability of new implants, prostheses, tools, and surgical equipment, which, thanks to their specific features such as biocompatibility, appropriate mechanical properties, ease of sterilization, and high porosity, ensure an improvement of living. Biodegradation ensures, among other things, the ideal rate of development for regenerated tissue. Current tissue engineering and regenerative medicine strategies aim to restore the function of damaged tissues. The current gold standard is autografts (using the patient's tissue to accelerate healing), but limitations such as limited procurement of certain tissues, long operative time, and donor site morbidity have warranted the search for alternative options. The use of biomaterials for this purpose is an attractive option and the number of biomaterials being developed and tested is growing rapidly.

Research progress of biomaterials and innovative technologies in urinary tissue engineering

Substantial interests have been attracted to multiple bioactive and biomimetic biomaterials in recent decades because of their ability in presenting a structural and functional reconstruction of urinary tissues. Some innovative technologies have also been surging in urinary tissue engineering and urological regeneration by providing insights into the physiological behavior of the urinary system. As such, the hierarchical structure and tissue function of the bladder, urethra, and ureter can be reproduced similarly to the native urinary tissues. This review aims to summarize recent advances in functional biomaterials and biomimetic technologies toward urological reconstruction. Various nanofirous biomaterials derived from decellularized natural tissues, synthetic biopolymers, and hybrid scaffolds were developed with desired microstructure, surface chemistry, and mechanical properties. Some growth factors, drugs, as well as inorganic nanomaterials were also utilized to enhance the biological activity and functionality of scaffolds. Notably, it is emphasized that advanced approaches, such as 3D (bio) printing and organoids, have also been developed to facilitate structural and functional regeneration of the urological system. So in this review, we discussed the fabrication strategies, physiochemical properties, and biofunctional modification of regenerative biomaterials and their potential clinical application of fast-evolving technologies. In addition, future prospective and commercial products are further proposed and discussed.

Decellularization of the human urethra for tissue engineering applications

Recently, several scaffolds have been introduced for urethral tissue engineering. However, acellular human urethral scaffold harvested from deceased donors may provide significant advantages compared to synthetic, composite, or other biological scaffolds. This study aims to develop the protocol for decellularization of the human urethra that preserves substantial extracellular matrix (ECM) components, which are essential for subsequent recellularization mimicking the natural environment of the native ECM. A total of 12 human urethras were harvested from deceased donors. An equal part of every harvested urethra was used as a control sample for analyses. The protocol design was based on the enzyme-detergent-enzyme method. Trypsin and Triton X-100 were used to remove cells, followed by DNase treatment to remove DNA residues. Subsequently, the specimens were continually rinsed in deionized water for seven days. The efficiency of decellularization was determined by histochemistry, immunohistochemical staining, scanning electron microscopy (SEM), and DNA quantification. Histological analysis confirmed cell removal and preservation of urethral structure after decellularization. The preservation of collagen IV and fibronectin was confirmed by histologic examination and immunohistochemical staining. SEM confirmed the maintenance of the ultrastructural architecture of ECM and fibers. DNA content in decellularized urethra was significantly lower compared to the native sample (P < 0.001), and so the criteria for decellularized tissue were met. Cytotoxicity analysis data showed that the matrix-conditioned medium did not contain soluble toxins and had no significant inhibitory effect on cell proliferation, providing evidence that the decellularized samples are not toxic. This study demonstrates the feasibility of the enzyme-detergent-enzyme-based decellularization protocol for removing cellular components and maintaining urethral ECM and its ultrastructure. Moreover, obtained results provide solid ground for recellularization and urethral tissue engineering, which will follow.

Biomaterials for Testicular Bioengineering: How far have we come and where do we have to go?

Traditional therapeutic interventions aim to restore male fertile potential or preserve sperm viability in severe cases, such as semen cryopreservation, testicular tissue, germ cell transplantation and testicular graft. However, these techniques demonstrate several methodological, clinical, and biological limitations, that impact in their results. In this scenario, reproductive medicine has sought biotechnological alternatives applied for infertility treatment, or to improve gamete preservation and thus increase reproductive rates in vitro and in vivo. One of the main approaches employed is the biomimetic testicular tissue reconstruction, which uses tissue-engineering principles and methodologies. This strategy pursues to mimic the testicular microenvironment, simulating physiological conditions. Such approach allows male gametes maintenance in culture or produce viable grafts that can be transplanted and restore reproductive functions. In this context, the application of several biomaterials have been proposed to be used in artificial biological systems. From synthetic polymers to decellularized matrixes, each biomaterial has advantages and disadvantages regarding its application in cell culture and tissue reconstruction. Therefore, the present review aims to list the progress that has been made and the continued challenges facing testicular regenerative medicine and the preservation of male reproductive capacity, based on the development of tissue bioengineering approaches for testicular tissue microenvironment reconstruction.

Anterior substitutional urethroplasty using a biomimetic poly‐ l ‐lactide nanofiber membrane: Preclinical and clinical outcomes

The aim of this study is to investigate the feasibility and efficacy of a novel biomimetic poly‐l‐lactide (PLLA) nanofiber membrane in repairing anterior urethral strictures from both preclinic and clinic. Biomimetic PLLA membrane was fabricated layer by layer according to the structure of human extracellular matrix. Microstructure, tensile strength, and suture retention strength were fully assessed. Before the clinical application, the safety and toxicology test of the biomimetic PLLA membrane was performed in vitro and in experimental animals. The patients underwent urethroplasty used dorsal onlay or lateral onlay technique. Then, they were followed up for 1 month, 3 months, 6 months, and then annually after the surgery. The mechanical experiments showed well property for application. Biomimetic PLLA membrane was safe according to the in vitro and animal studies. Then, a total of 25 patients (mean age 48.96 years) were included in the study from September 2016 to December 2018. After a mean follow‐up of 33.56 months, 20 patients successfully treated with biomimetic PLLA membrane. Five patients (2 bulbar and 3 penile) suffered postoperational urethral stricture recurrence. None of infection or urinary fistula or any other adverse events related to the use of biomimetic PLLA membrane were observed during the follow‐up period for all patients. The preliminary result confirmed the feasibility and efficacy of the biomimetic PLLA membrane as a novel material for anterior urethral repair. The long‐term effects with more patients should be investigated in further studies.

A biomimetic hyaluronic acid‐silk fibroin nanofiber scaffold promoting regeneration of transected urothelium

This study was designed to investigate the regulatory effect of hyaluronic acid (HA)—coating silk fibroin (SF) nanofibers during epithelialization of urinary tract for urethral regeneration. The obtained electrospun biomimetic tubular HA‐SF nanofiber scaffold is composed of a dense inner layer and a porous outer layer in order to mimic adhesion and cavernous layers of the native tissue, respectively. A thin layer of HA‐gel coating was fixed in the inner wall to provide SF nanofibers with a dense and smooth surface nano‐topography and higher hydrophilicity. Compared with pure SF nanofibers, HA‐SF nanofibers significantly promoted the adhesion, growth, and proliferation of primary urothelial cells, and up‐regulate the expression of uroplakin‐3 (terminal differentiation keratin protein in urothelium). Using the New Zealand male rabbit urethral injury model, the scaffold composed of tubular HA‐SF nanofibers could recruit lumen and myoepithelial cells from the adjacent area of the host, rapidly reconstructing the urothelial barrier in the wound area in order to keep the urinary tract unobstructed, thereby promoting luminal epithelialization, smooth muscle bundle structural remodeling, and capillary formation. Overall, the synergistic effects of nano‐topography and biophysical cues in a biomimetic scaffold design for effective endogenous regeneration.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Mesenchymal Stem Cell-Derived Exosomes Induced by IL-1β Attenuate Urethral Stricture Through Let-7c/PAK1/NF-κB-Regulated Macrophage M2 Polarization

Background

Urethral stricture is a clinical challenge for both patients and clinicians. Post-traumatic urethral stricture is associated with formation of scar tissue caused by excessive inflammation. The aim of this study is exploring potential therapeutic strategies for this condition.

Methods

In vivo experiments on New Zealand rabbits and in vitro experiments on THP-1 monocytes and urethral fibroblasts were performed to investigate the effects on post-traumatic urethral stricture of exosomes isolated from IL-1β-treated mesenchymal stem cells (Exo-MSCs^IL-1β) and the role of macrophage M2 polarization in this process. Additionally, related signaling and mechanism behind were explored.

Results

In a New Zealand rabbit model of post-traumatic urethral stricture, injection of Exo-MSCs^IL-1β significantly reduced urethral stricture and collagen fiber accumulation compared with Exo-MSCs. Addition of Exo-MSCs^IL-1β to THP-1 monocytes in vitro induced M2 macrophage polarization, which, in turn, inhibited activation of urethral fibroblasts and synthesis of collagen. Mechanistically, Exo-MSCs^IL-1β were found to contain high levels of the microRNA let-7c, and luciferase reporter assays showed that let-7c interacted with the 3'UTR of PAK1 mRNA. Transfection of THP-1 cells with a let-7c mimic downregulated PAK1 expression and inhibited activation of the NF-κB signaling pathway.

Conclusion

These results support a role for let-7c-containing Exo-MSCs^IL-1β in reducing urethral stricture via inhibition of PAK1-NF-κB signaling, M2 macrophage polarization, and differentiation of urethral myofibroblasts.

Regeneration of muscular wall of the bladder using a ureter matrix graft as a scaffold

We investigated a method for bladder augmentation in rats using a decellularized ureter graft. We used 16 rats divided into two groups of eight. After partial cystectomy, the bladders in group 1 were grafted with a 1 cm² patch of human decellularized ureter. Rats in group 2 were untreated controls. Biopsies of the graft were taken at 1, 3 and 9 months postoperatively for histological investigation. Total removal of cells and preservation of extracellular matrix (ECM) was confirmed in the decellularized ureter. Histological examination after 1 month revealed few cells at the border of the graft. Three months after the operation, the graft was infiltrated by vessels and smooth muscle and the mucosal lining was complete. All bladder wall components resembled native bladder wall by 9 months after implantation. CD34, CD31, α-smooth muscle actin, S100, cytokeratin AE1/AE3 and vimentin were detected 9 months after the operation. We demonstrated the potential of decellularized biocompatible ureteric grafts for use as a natural collagen scaffold for bladder repair in rats.

Regenerative Medicine Approaches in Bioengineering Female Reproductive Tissues

Diseases, disorders, and dysfunctions of the female reproductive tract tissues can result in either infertility and/or hormonal imbalance. Current treatment options are limited and often do not result in tissue function restoration, requiring alternative therapeutic approaches. Regenerative medicine offers potential new therapies through the bioengineering of female reproductive tissues. This review focuses on some of the current technologies that could address the restoration of functional female reproductive tissues, including the use of stem cells, biomaterial scaffolds, bio-printing, and bio-fabrication of tissues or organoids. The use of these approaches could also be used to address issues in infertility. Strategies such as cell-based hormone replacement therapy could provide a more natural means of restoring normal ovarian physiology. Engineering of reproductive tissues and organs could serve as a powerful tool for correcting developmental anomalies. Organ-on-a-chip technologies could be used to perform drug screening for personalized medicine approaches and scientific investigations of the complex physiological interactions between the female reproductive tissues and other organ systems. While some of these technologies have already been developed, others have not been translated for clinical application. The continuous evolution of biomaterials and techniques, advances in bioprinting, along with emerging ideas for new approaches, shows a promising future for treating female reproductive tract-related disorders and dysfunctions.

Bladder muscle regeneration enhanced by sustainable delivery of heparin from bilayer scaffolds carrying stem cells in a rat bladder partial cystectomy model

In bladder tissue engineering, regeneration of muscle is of equal importance to epithelial regeneration. However, as yet there is no effective strategy for promoting bladder muscle regeneration. In this study we aim to promote bladder muscle regeneration by sustainably delivering heparin from a bilayer scaffold carrying stem cells. The bilayer scaffold [heparin-polycaprolactone (PCL)/bladder decellularized matrix (BAM) Hep-PB/PCL] comprises an electrospun layer (Hep-PB electrospun membrane) and a three-dimensional (3D) printed layer (PCL scaffold), fabricated via coaxial-electrospinning and 3D printing, respectively. Heparin was encapsulated into the core of the Hep-PB fibers with a core-shell structure to sustain its release. The morphology of the bilayer scaffold and the microstructure of the electrospun fibers were characterized. The release behavior of heparin from various electrospun membranes was evaluated. The role of Hep-PB in promoting myogenic differentiation of the adipose-derived stem cells (ADSCs) through sustainable release of heparin was also evaluated. After 7 d culture, Hep-PB/PCL scaffolds carrying ADSCs (defined as ASHP) were used for bladder reconstruction in a rat partial cystotomy model. The result shows that the PCL printed scaffold has ordered macropores (∼370 μm), unlike the compact microstructure of electrospun films. The Hep-PB membrane exhibits a sustained release behavior for heparin. This membrane also shows better growth and proliferation of ADSCs than the other membranes. The polymerase chain reaction results show that the expression of smooth muscle cell markers in ADSCs is enhanced by the Hep-PB scaffold. The results of retrograde urethrography and histological staining indicate that the bladder volume in the ASHP group recovers better, and the regenerated bladder muscle bundles are arranged in a more orderly fashion compared with the direct suture and bladder decellularized matrix groups. Therefore, findings from this study show that bladder muscle regeneration could be enhanced by bilayer scaffolds delivering heparin and carrying stem cells, which may provide a new strategy for bladder tissue engineering.

SARS-CoV-2 and tissue damage: current insights and biomaterial-based therapeutic strategies

The effect of SARS-CoV-2 infection on humanity has gained worldwide attention and importance due to the rapid transmission, lack of treatment options and high mortality rate of the virus. While scientists across the world are searching for vaccines/drugs that can control the spread of the virus and/or reduce the risks associated with infection, patients infected with SARS-CoV-2 have been reported to have tissue/organ damage. With most tissues/organs having limited regenerative potential, interventions that prevent further damage or facilitate healing would be helpful. In the past few decades, biomaterials have gained prominence in the field of tissue engineering, in view of their major role in the regenerative process. Here we describe the effect of SARS-CoV-2 on multiple tissues/organs, and provide evidence for the positive role of biomaterials in aiding tissue repair. These findings are further extrapolated to explore their prospects as a therapeutic platform to address the tissue/organ damage that is frequently observed during this viral outbreak. This study suggests that the biomaterial-based approach could be an effective strategy for regenerating tissues/organs damaged by SARS-CoV-2.

Designing a multifaceted bio-interface nanofiber tissue-engineered tubular scaffold graft to promote neo-vascularization for urethral regeneration

Reconstitution of urethral defects through a tissue-engineered autologous urethra is an exciting area of clinical urology research. Despite rapid advances in this field, a tissue-engineered urethra is still inaccessible to clinical applications because of the poor vascularization of the current scaffold materials, especially for the reconstruction of complex urethral defects. In this study, we report the preparation of multifaceted bio-interfacing tissue-engineered autologous scaffolds based on alternating block polyurethane (abbreviated as PU-alt), a kind of tubular scaffold with a hierarchical nanofiber architecture, flexible mechanical properties and a hydrophilic PEGylation interface capable of promoting adhesion, oriented elongation, and proliferation of New Zealand rabbit autologous urethral epithelial cells (ECs) and smooth muscle cells (SMCs) simultaneously, and also upregulating the expression of keratin (AE1/AE3) in ECs and contractile protein (α-SMA) in SMCs as well as the subsequent synthesis of elastin. Three months in vivo scaffold substitution of rabbit urethras displayed that the engineered autologous PU-alt scaffold grafts, with a coating rich in seed cell-matrix, could induce local neo-vascularization, facilitating oriented SMC remodeling and lumen epithelialization as well as patency. Our findings indicate a central role of the synergistic interplay of seed cell-matrix bio-interface and nano-topographic cues in the vascularized urethral reconstruction.

Advanced bioengineering of male germ stem cells to preserve fertility

In modern life, several factors such as genetics, exposure to toxins, and aging have resulted in significant levels of male infertility, estimated to be approximately 18% worldwide. In response, substantial progress has been made to improve in vitro fertilization treatments (e.g. microsurgical testicular sperm extraction (m-TESE), intra-cytoplasmic sperm injection (ICSI), and round spermatid injection (ROSI)). Mimicking the structure of testicular natural extracellular matrices (ECM) outside of the body is one clear route toward complete in vitro spermatogenesis and male fertility preservation. Here, a new wave of technological innovations is underway applying regenerative medicine strategies to cell-tissue culture on natural or synthetic scaffolds supplemented with bioactive factors. The emergence of advanced bioengineered systems suggests new hope for male fertility preservation through development of functional male germ cells. To date, few studies aimed at in vitro spermatogenesis have resulted in relevant numbers of mature gametes. However, a substantial body of knowledge on conditions that are required to maintain and mature male germ cells in vitro is now in place. This review focuses on advanced bioengineering methods such as microfluidic systems, bio-fabricated scaffolds, and 3D organ culture applied to the germline for fertility preservation through in vitro spermatogenesis.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Biodegradable drug-eluting urethral stent in limiting urethral stricture formation after urethral injury: An experimental study in rabbit

In this study, a reproducible urethral injury animal model was developed and the role of the biodegradable drug-eluting urethral stent in limiting urethral stricture formation after urethral injury was evaluated. A total of 22 rabbits were used, and 20 rabbits were randomly chosen to develop urethral injury animal model. Bulbar urethral injury was made by a self-designed explosion device in the 20 rabbits. The urethral injury animal model was then randomly assigned to 2 groups of 10 each, which received a treatment of biodegradable paclitaxel-eluting urethral stent or only end-to-end anastomosis. Other two rabbits served as normal control group. Stents were surgically implanted into the injured urethras of rabbits under direct vision. Reparative effects, including stent degradation, were evaluated by urethroscopy, retrograde urethrography, and histology at different intervals at weeks 4, 8, and 12. In stent-free group, 8 of 10 rabbits developed obvious urethral stricture which was demonstrated by urethroscopy and retrograde urethrography, while in biodegradable paclitaxel-eluting stent group, urethral stricture was absent in all animals (p < 0.05). Histological follow-up indicated that the drug-eluting stents can also minimize the inflammatory reactions and fibrosis formation compared with the stent-free groups. Scanning electron microscope demonstrated that the biodegradable drug-eluting stent can gradually degrade in 12 weeks. The biodegradable paclitaxel-eluting urethral stent is effective in limiting urethral stricture formation after urethral injury.

Tissue engineering in female pelvic floor reconstruction

Pelvic organ prolapse is a common and frequently occurring disease in middle-aged and elderly women. Mesh implantation is an ideal surgical treatment. The polypropylene mesh commonly used in clinical practice has good mechanical properties, but there are long-term complications. The application of tissue engineering technology in the treatment of pelvic organ prolapse disease can not only meet the mechanical requirements of pelvic floor support, but also be more biocompatible than traditional polypropylene mesh, and can promote tissue repair to a certain extent. In this paper, the progress of tissue engineering was summarized to understand the application of tissue engineering in the treatment of pelvic organ prolapse disease and will help in research.

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.

Application of Acellular Tissue Matrix for Enhancement of Weak Abdominal Wall in Animal Model

Background

Abdominal wall weakness occurs when the strength of muscle decreases due to physiological reason or iatrogenic injury. However, the treatment of this disease is complicated.

Aim

To study the therapeutic effect of acellular tissue matrix (ACTM), compared with the polypropylene mesh.

Methods

An abdominal wall weakness model was established in rabbits through motor nerves cutting. The polypropylene mesh and ACTM were implanted in the left and right abdomen sides, respectively. Mechanical testing of abdominal wall muscle and histology and scanning electron microscopy (SEM) evaluation of abdominal tissue explants were performed.

Results

In animal model establishment, the abdominal length of healthy and weakened abdominal wall was 17.0 ± 0.7 cm and 19.0 ± 1.2 cm, respectively (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (

Conclusion

The abdominal wall weakness model in rabbits was successfully established. ACTM is a promising biological material to be possibly further applied in clinical surgery in patients with abdominal wall weakness.

Tissue-engineered PLLA/gelatine nanofibrous scaffold promoting the phenotypic expression of epithelial and smooth muscle cells for urethral reconstruction

The repair and regeneration of tissues using tissue-engineered scaffolds represent the ultimate goal of regenerative medicine. Despite rapid developments in the field, urethral tissue engineering methods are still insufficient to replicate natural urethral tissue because the bioactivity of existing scaffolds is inefficient, especially for large tissue defects, which require large tissue-engineered scaffolds. Here, we describe the efficiency of gelatine-functionalized, tubular nanofibrous scaffolds of poly(l-lactic acid) (PLLA) in regulating the phenotypic expression of epithelial cells (ECs) and smooth muscle cells (SMCs) for urethral reconstruction. Flexible PLLA/gelatine tubular nanofibrous scaffolds with hierarchical architecture were fabricated by electrospinning. The PLLA/gelatine nanofibrous scaffold exhibited enhanced hydrophilicity and significantly promoted the adhesion, oriented elongation, and proliferation of New Zealand rabbit autologous ECs and SMCs simultaneously. Compared with pure PLLA nanofibrous scaffold, PLLA/gelatine nanofibrous scaffolds upregulated the expression of keratin (AE1/AE3) in ECs and actin (α-SMA) in SMCs as well as the synthesis of elastin. Three months of in vivo scaffold replacement of New Zealand rabbit urethras indicated that a tubular cellularized PLLA/gelatine nanofibrous scaffold maintained urethral patency and facilitated oriented SMC remodeling, lumen epithelialization, and angiogenesis. Our observations showed the synergistic effects of nano-morphology and biochemical clues in the design of biomimetic scaffolds, which can effectively promote urethral regeneration.

Urethra-inspired biomimetic scaffold: A therapeutic strategy to promote angiogenesis for urethral regeneration in a rabbit model

Limited angiogenesis and epithelialization make urethral regeneration using conventional tissue-engineered grafts a great challenge. Consequently, inspired from the native urethra, bacterial cellulose (BC) and bladder acellular matrix (BAM) were combined to design a three dimensional (3D) biomimetic scaffold. The developed BC/BAM scaffold was engineered for accelerating urethral regeneration by enhancing angiogenesis and epithelialization. The BC/BAM scaffold reveals the closest mimic of native urethra in terms of the 3D porous nanofibrous structure and component including collagen, glycosaminoglycans, and intrinsic vascular endothelial growth factor (VEGF). In vitro studies showed that the bioinspired BC/BAM scaffold promoted in vitro angiogenesis by facilitating human umbilical vein endothelial cells (HUVECs) growth, expression of endothelial function related proteins and capillary-like tube formation. Effect of the BC/BAM scaffold on angiogenesis and epithelialization was studied by its implantation in a rabbit urethral defect model for 1 and 3 months. Results demonstrated that the improved blood vessels formation in the urethra-inspired BC/BAM scaffold significantly promoted epithelialization and accelerated urethral regeneration. The urethra-inspired BC/BAM scaffold provides us a new design approach to construct grafts for urethral regeneration. STATEMENT OF SIGNIFICANCE: Findings in urethral regeneration demonstrate that an ideal tissue-engineered urethra should have adequate angiogenesis to support epithelialization for urethral regeneration in vivo. In this study, inspired from the native urethra, a bioinspired bacterial cellulose/bladder acellular matrix (BC/BAM) scaffold was developed to promote angiogenesis and epithelialization. The designed scaffold showed the closest physical structure and component to natural urethra, which is beneficial to angiogenesis and regeneration of urethral epithelium. This is the first time to utilize BC and dissolved BAM to develop biomimetic scaffold in urethral tissue engineering. Our biomimetic strategy on urethra graft design provided enhanced angiogenesis and epithelialization to achieve an accelerated and successful rabbit urethral repair. We believe that our urethra-inspired biomimetic scaffold would provide new insights into the design of urethral tissue engineering grafts.

Urethral reconstruction using an amphiphilic tissue-engineered autologous polyurethane nanofiber scaffold with rapid vascularization function

We report the efficient application of a well-layered tubular amphiphilic nanofiber of a polyurethane copolymer (PU-ran) for the regulation the phenotypic expression of epithelial cells (ECs) and smooth muscle cells (SMCs) for vascularized urethral reconstruction.

Recent development and biomedical applications of decellularized extracellular matrix biomaterials

Decellularized matrix (dECM) is isolated extracellular matrix of tissues from its original inhabiting cells, which has emerged as a promising natural biomaterial for tissue engineering, aiming at support, replacement or regeneration of damaged tissues. The dECM can be easily obtained from tissues/organs of various species by adequate decellularization methods, and mimics the structure and composition of the native extracellular matrix, providing a favorable cellular environment. In this review, we summarize the recent developments in the preparation of dECM materials, including decellularization, crosslinking and sterilization. Also, we cover the advances in the utilization of dECM biomaterials in regeneration medicine in pre-clinic and clinical trials. Moreover, we highlight those emerging medical benefits of dECM beyond tissue engineering, such as cell transplantation, in vitro/in vivo model and therapeutic cues delivery. With the advances in the preparation and broader application, the dECM biomaterials could become the gold scaffold and pharmaceutical excipients in medical sciences.

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.

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

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

Tissue Engineering in Pediatric Bladder Reconstruction-The Road to Success

Several congenital disorders can cause end stage bladder disease and possibly renal damage in children. The current gold standard therapy is enterocystoplasty, a bladder augmentation using an intestinal segment. However, the use of bowel tissue is associated with numerous complications such as metabolic disturbance, stone formation, urine leakage, chronic infections, and malignancy. Urinary diversions using engineered bladder tissue would obviate the need for bowel for bladder reconstruction. Despite impressive progress in the field of bladder tissue engineering over the past decades, the successful transfer of the approach into clinical routine still represents a major challenge. In this review, we discuss major achievements and challenges in bladder tissue regeneration with a focus on different strategies to overcome the obstacles and to meet the need for living functional tissue replacements with a good growth potential and a long life span matching the pediatric population.

Repair of injured urethras with silk fibroin scaffolds in a rabbit model of onlay urethroplasty

BACKGROUND

Preclinical validation of scaffold-based technologies in animal models of urethral disease is desired to assess wound healing efficacy in scenarios that mimic the target patient population. This study investigates the feasibility of bilayer silk fibroin (BLSF) scaffolds for the repair of previously damaged urethras in a rabbit model of onlay urethroplasty.

MATERIALS AND METHODS

A focal, partial thickness urethral injury was created in adult male rabbits (n = 12) via electrocoagulation and then onlay urethroplasty with 50 mm² BLSF grafts was carried out 2 wk after injury. Animals were randomly divided into three experimental groups and harvested at 2 wk after electrocoagulation (n = 3), and 1 (n = 3) or 3 (n = 6) months after scaffold implantation. Outcome analyses were performed preoperatively and at 2 wk after injury in all groups as well as at 1 or 3 mo after scaffold grafting and included urethroscopy, retrograde urethrography (RUG), and histological and immunohistochemical analyses.

RESULTS

At 2 wk after electrocoagulation, urethroscopic and RUG evaluations confirmed urethral stricture formation in 92% (n = 11/12) of rabbits. Gross tissue assessments at 1 (n = 3) and 3 (n = 6) mo after onlay urethroplasty revealed host tissue ingrowth covering the entire implant site. At 3 mo post-op, RUG analyses of repaired urethral segments demonstrated a 39% reduction in urethral stenosis detected following electrocoagulation injury. Histological and immunohistochemical analyses revealed the formation of innervated, vascularized neotissues with α-smooth muscle actin+ and SM22α+ smooth muscle bundles and pan-cytokeratin + epithelium at graft sites.

CONCLUSIONS

These results demonstrate the feasibility of BLSF matrices to support the repair of previously damaged urethral tissues.

Refractory Urethral Stricture Management: Indications for Alternative Grafts and Flaps

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Tissue engineering for urinary tract reconstruction and repair: Progress and prospect in China

Several urinary tract pathologic conditions, such as strictures, cancer, and obliterations, require reconstructive plastic surgery. Reconstruction of the urinary tract is an intractable task for urologists due to insufficient autologous tissue. Limitations of autologous tissue application prompted urologists to investigate ideal substitutes. Tissue engineering is a new direction in these cases. Advances in tissue engineering over the last 2 decades may offer alternative approaches for the urinary tract reconstruction. The main components of tissue engineering include biomaterials and cells. Biomaterials can be used with or without cultured cells. This paper focuses on cell sources, biomaterials, and existing methods of tissue engineering for urinary tract reconstruction in China. The paper also details challenges and perspectives involved in urinary tract reconstruction.

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.

Biofabrication and biomaterials for urinary tract reconstruction

Reconstructive urologists are constantly facing diverse and complex pathologies that require structural and functional restoration of urinary organs. There is always a demand for a biocompatible material to repair or substitute the urinary tract instead of using patient's autologous tissues with its associated morbidity. Biomimetic approaches are tissue-engineering tactics aiming to tailor the material physical and biological properties to behave physiologically similar to the urinary system. This review highlights the different strategies to mimic urinary tissues including modifications in structure, surface chemistry, and cellular response of a range of biological and synthetic materials. The article also outlines the measures to minimize infectious complications, which might lead to graft failure. Relevant experimental and preclinical studies are discussed, as well as promising biomimetic approaches such as three-dimensional bioprinting.

Two differentially structured collagen scaffolds for potential urinary bladder augmentation: proof of concept study in a Göttingen minipig model

Background

The repair of urinary bladder tissue is a necessity for tissue loss due to cancer, trauma, or congenital abnormalities. Use of intestinal tissue is still the gold standard in the urological clinic, which leads to new problems and dysfunctions like mucus production, stone formation, and finally malignancies. Therefore, the use of artificial, biologically derived materials is a promising step towards the augmentation of this specialised tissue. The aim of this study was to investigate potential bladder wall repair by two collagen scaffold prototypes, OptiMaix 2D and 3D, naïve and seeded with autologous vesical cells, as potential bladder wall substitute material in a large animal model.

Methods

Six Göttingen minipigs underwent cystoplastic surgery for tissue biopsy and cell isolation followed by implantation of unseeded scaffolds. Six weeks after the first operation, scaffolds seeded with the tissue cultured autologous urothelial and detrusor smooth muscle cells were implanted into the bladder together with additional unseeded scaffolds for comparison. Cystography and bladder ultrasound were performed to demonstrate structural integrity and as leakage test of the implantation sites. Eighteen, 22, and 32 weeks after the first operation, two minipigs respectively were sacrificed and the urinary tract was examined via different (immunohistochemical) staining procedures and the usage of two-photon laser scanning microscopy.

Results

Both collagen scaffold prototypes in vivo had good ingrowth capacity into the bladder wall including a quick lining with urothelial cells. The ingrowth of detrusor muscle tissue, along with the degradation of the scaffolds, could also be observed throughout the study period.

Conclusions

We could show that the investigated collagen scaffolds OptiMaix 2D and 3D are a potential material for bladder wall substitution. The material has good biocompatible properties, shows a good cell growth of autologous cells in vitro, and a good integration into the present bladder tissue in vivo.

Advances in urethral stricture management

Urethral stricture/stenosis is a narrowing of the urethral lumen. These conditions greatly impact the health and quality of life of patients. Management of urethral strictures/stenosis is complex and requires careful evaluation. The treatment options for urethral stricture vary in their success rates. Urethral dilation and internal urethrotomy are the most commonly performed procedures but carry the lowest chance for long-term success (0–9%). Urethroplasty has a much higher chance of success (85–90%) and is considered the gold-standard treatment. The most common urethroplasty techniques are excision and primary anastomosis and graft onlay urethroplasty. Anastomotic urethroplasty and graft urethroplasty have similar long-term success rates, although long-term data have yet to confirm equal efficacy. Anastomotic urethroplasty may have higher rates of sexual dysfunction. Posterior urethral stenosis is typically caused by previous urologic surgery. It is treated endoscopically with radial incisions. The use of mitomycin C may decrease recurrence. An exciting area of research is tissue engineering and scar modulation to augment stricture treatment. These include the use of acellular matrices or tissue-engineered buccal mucosa to produce grafting material for urethroplasty. Other experimental strategies aim to prevent scar formation altogether.

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.

The effects of irradiation on the biological and biomechanical properties of an acellular porcine superflexor tendon graft for cruciate ligament repair

Acellular xenogeneic tissues have the potential to provide ‘off‐the‐shelf’ grafts for anterior cruciate ligament (ACL) repair. To ensure that such grafts are sterile following packaging, it is desirable to use terminal sterilization methods. Here, the effects of gamma and electron beam irradiation on the biological and biomechanical properties of a previously developed acellular porcine superflexor tendon (pSFT) were investigated. Irradiation following treatment with peracetic acid was compared to peracetic acid treatment alone and the stability of grafts following long‐term storage assessed. Irradiation did not affect total collagen content or biocompatibility (determined using a contact cytotoxicity assay) of the grafts, but slightly increased the amount of denatured collagen in and decreased the thermal denaturation temperature of the tissue in a dose dependant fashion. Biomechanical properties of the grafts were altered by irradiation (reduced ultimate tensile strength and Young's modulus, increased failure strain), but remained superior to reported properties of the native human ACL. Long term storage at 4°C had no negative effects on the grafts. Of all the conditions tested, a dose of minimum 25 kGy of gamma irradiation had least effect on the grafts, suggesting that this dose produces a biocompatible pSFT graft with adequate mechanical properties for ACL repair. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2477–2486, 2017.

Current management of urethral stricture disease

Introduction:

Broadly defined, urethral strictures are narrowing of the urethral lumen that is surrounded by corpus spongiosum, i.e., urethral meatus through the bulbar urethra. Urethral stenosis is narrowing of the posterior urethra, i.e., membranous urethra through bladder neck/prostate junction, which is not enveloped by corpus spongiosum. The disease has significant quality of life ramifications because many times younger patients are affected by this compared to many other urological diseases.

Methods:

A review of the scientific literature concerning urethral stricture, stenosis, treatment, and outcomes was performed using Medline and PubMed (U.S. National Library of Medicine and the National Institutes of Health). Abstracts from scientific meetings were included in this review.

Results:

There is level 3 evidence regarding the etiology and epidemiology of urethral strictures, stenoses, and pelvic fracture urethral injuries. Outcomes data from literature regarding intervention for urethral stricture are largely limited to level 3 evidence and expert opinion. There is a single level 1 study comparing urethral dilation and direct vision internal urethrotomy. Urethroplasty outcomes data are limited to level 3 case series.

Conclusions:

Progress is being made toward consistent terminology, and nomenclature which will, in turn, help to standardize treatment within the field of urology. Treatment for urethral stricture and stenosis remains inconsistent between reconstructive and nonreconstructive urologists due to varying treatment algorithms and approaches to disease management. Tissue engineering appears to be future for reconstructive urethral surgery with reports demonstrating feasibility in the use of different tissue substitutes and grafts.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.