A novel inert collagen matrix for hypospadias repair

Organoids of the male reproductive system: Challenges, opportunities, and their potential use in fertility research

Organoids are units of function of a given organ able to reproduce, in culture, a biological structure similar in architecture and function to its counterpart in vivo. Today, it is possible to develop an organoid from a fragment of tissue, a stem cell located in an adult organ, an embryonic stem cell, or an induced pluripotent stem cell. In the past decade, many organoids have been developed which mimic stomach, pancreas, liver and brain tissues, optic cups, among many others. Additionally, different male reproductive system organs have already been developed as organoids, including the prostate and testis. These 3D cultures may be of great importance for urological cancer research and have the potential to be used in fertility research for the study of spermatozoa production and maturation, germ cells-somatic cells interactions, and mechanisms of disease. They also provide an accurate preclinical pipeline for drug testing and discovery, as well as for the study of drug resistance. In this work, we revise the current knowledge on organoid technology and its use in healthcare and research, describe the male reproductive system organoids and other biomaterials already developed, and discuss their current application. Finally, we highlight the research gaps, challenges, and opportunities in the field and propose strategies to improve the use of organoids for the study of male infertility situations. This article is categorized under: Reproductive System Diseases > Stem Cells and Development Reproductive System Diseases > Biomedical Engineering.

Biologic adjuvant urethral coverings for single-stage primary hypospadias repairs: A systematic review and pooled proportional meta-analysis of postoperative urethrocutaneous fistulas

BACKGROUND

The use of barrier layers between the neourethra and skin is associated with lower rates of post-operative urethrocutaneous fistula (UCF) following hypospadias surgery. Recent studies have evaluated the ability of biologic adjuvant urethral coverings (BAUCs) - namely acellular matrix (AM), tissue adhesives (TAs), and autologous platelet-rich plasma or fibrin (PRP/PRF) - to prevent wound complications following hypospadias surgery. In general, however, these studies are small and conducted at single institutions.

OBJECTIVE

To assess the effect of BAUCs on the rate of UCF following single-stage primary hypospadias repair.

METHODS

We conducted a systematic review of studies reporting the rate of postoperative UCF in pediatric patients undergoing single-stage, primary hypospadias repairs using either AM, TA, or PRP/PRF as a layer interposed between the neourethra and skin. We then performed a pooled proportional meta-analysis of post-operative UCF. Patients within each study who underwent comparable surgery but did not receive a BAUC were used as controls.

RESULTS

10 studies were included in our review. The meta-analysis included 280 patients from 7 studies who underwent hypospadias repairs with BAUCs. The pooled incidence of UCF was 10% (95% CI 6-14%). Mean follow-up ranged 5-23.5 months in the 5/7 studies reporting specific durations, and ≥6 month and 14-30 months, respectively, in the other two studies. Patients in whom a BAUC was used had significantly lower odds of UCF than control patients (OR 0.39, 95% CI 0.24-0.64, p = 0.0002). In subgroup analyses, significant superiority held for AM and TA; proximal or penoscrotal cases; transverse preputial island flap (TPIF) technique; when both cases and controls had local flaps; and when neither cases nor controls had flaps.

DISCUSSION

The use of BAUCs was associated with decreased rates of post-operative UCF in single-stage primary hypospadias repairs and may be most beneficial in more severe cases and when used in addition to local flaps or when using a flap is not possible. In 2/3 studies of PRP/PRF and 2/4 studies of tubularized incised plate (TIP) technique, dartos flaps were used in controls but not BAUC patients, which may explain the lack of benefit demonstrated for these subgroups. This meta-analysis is limited by the quality of evidence in the included studies, which are not uniformly randomized. Furthermore, the follow-up durations and methods for assessing complications are not standardized between included studies.

CONCLUSION

The meta-analysis herein suggests that using BAUCs may reduce UCF rates following hypospadias surgery. Rigorous prospective evaluation is needed to validate this benefit.

Tissue Engineering and Regenerative Medicine in Pediatric Urology: Urethral and Urinary Bladder Reconstruction

In the case of pediatric urology there are several congenital conditions, such as hypospadias and neurogenic bladder, which affect, respectively, the urethra and the urinary bladder. In fact, the gold standard consists of a urethroplasty procedure in the case of urethral malformations and enterocystoplasty in the case of urinary bladder disorders. However, both surgical procedures are associated with severe complications, such as fistulas, urethral strictures, and dehiscence of the repair or recurrence of chordee in the case of urethroplasty, and metabolic disturbances, stone formation, urine leakage, and chronic infections in the case of enterocystoplasty. With the aim of overcoming the issue related to the lack of sufficient and appropriate autologous tissue, increasing attention has been focused on tissue engineering. In this review, both the urethral and the urinary bladder reconstruction strategies were summarized, focusing on pediatric applications and evaluating all the biomaterials tested in both animal models and patients. Particular attention was paid to the capability for tissue regeneration in dependence on the eventual presence of seeded cell and growth factor combinations in several types of scaffolds. Moreover, the main critical features needed for urinary tissue engineering have been highlighted and specifically focused on for pediatric application.

Tissue Engineering of the Urethra: From Bench to Bedside

Tissue engineering (TE) is a promising approach for repair/substitution of damaged tissues and organs. Urethral strictures are common and serious health conditions that impair quality of life and may lead to serious organ damage. The search for ideal materials for urethral repair has led to interest of scientists and surgeons in urethral TE. Over the last decades, a significant amount of preclinical studies and considerable progress have been observed. In contrast, urethral TE has made slow progress in clinical practice so far. To address this, we conducted a systematic review of the literature on clinical applications of TE constructs for urethral repair in the last three decades. In summary, the TE approach is promising and effective, but many issues remain that need to be addressed for broader adoption of TE in urethral repair. Better design of trials, better cooperation of research groups and centralization could lead to reduction of costs and slowly proceed to commercialization and routine use of TE products for urethral reconstruction.

Dermal regeneration sheet Integra® in management of recurrent Urethrocutaneous fistula after hypospadias surgery

BACKGROUND

Urethrocutaneous fistula UCF is the most common complication following surgical repair of hypospadias. Currently, the surgical technique mostly used to prevent recurrence employs preputial dartos or testicular tunica vaginalis flaps as a urethral covering. However, autologous tissues are limited in patients with multiple surgeries, and the use of biomaterials as a urethral coverage may represent a good alternative.

OBJECTIVE

The goal of the present study is to assess the results and complications of recurrent UCF correction using a dermal bovine regeneration sheet as a urethral covering.

MATERIALS AND METHOD

From May 2016 to January 2019, all patients with recurrent UCF of the authors center were repaired using this technique. The inclusion criteria were patients who had undergone one or more unsuccessful UCF repair surgeries and the absence of preputial tissue. The informed consent has been signed by all the patients. Patients were examined in outpatient consultations where their urinary stream was evaluated and a physical examination of the penis was conducted.

RESULTS

A total of 12 patients and 13 UCFs were included in the study. The median follow-up was 18 months, (range: 4-26), and only two patients (15%) developed a recurrence of UCF. No complications were observed in the remaining patients (85%) during their evolution. No patient developed a fibrosis increase or loss of elasticity of the tissues in contact with the dermal matrix.

CONCLUSION

The use of an Integra® sheet as a urethral covering during urethral fistula surgery appears to be a safe, effective, and easily reproducible option. However, prospective studies with larger numbers of patients should be performed to corroborate these results.

Tissue Engineering and Stem Cell Therapy in Pediatric Urology

The rapidly expanding field of tissue engineering along with stem cell therapy has a promising future in pediatric urological conditions. The initial struggle seemed difficult in renal regeneration but a functional biounit has been developed. Urine excretion has been demonstrated successfully from stem cell-generated embryonic kidneys. Three-dimensional (3D) stem cell-derived organoids are the new paradigm in research. Techniques to regenerate bladder tissue have reached the clinic, and the urethra is close behind. 3D bioprinted urethras would soon be available. Artificial germ cells produced from mouse pluripotent stem cells have been shown to give rise to live progeny. Myoblast and fibroblast therapy has been safely and effectively used for urinary incontinence. Stress urinary incontinence has been clinically treated with muscle-derived stem cells. Skeletal muscle-derived stem cells have been shown to get converted into smooth muscle cells when implanted into the corpora cavernosa in animal models. This review encompasses the various experimental and clinical developments in this field that can benefit pediatric urological conditions with the contemporary developments in the field.

Aligned Brain Extracellular Matrix Promotes Differentiation and Myelination of Human-Induced Pluripotent Stem Cell-Derived Oligodendrocytes

Myelination by oligodendrocytes (OLs) is a key developmental milestone in terms of the functions of the central nervous system (CNS). Demyelination caused by defects in OLs is a hallmark of several CNS disorders. Although a potential therapeutic strategy involves treatment with the myelin-forming cells, there is no readily available source of these cells. OLs can be differentiated from pluripotent stem cells; however, there is a lack of efficient culture systems that generate functional OLs. Here, we demonstrate biomimetic approaches to promote OL differentiation from human-induced pluripotent stem cells (iPSCs) and to enhance the maturation and myelination capabilities of iPSC-derived OL (iPSC-OL). Functionalization of culture substrates using the brain extracellular matrix (BEM) derived from decellularized human brain tissue enhanced the differentiation of iPSCs into myelin-expressing OLs. Co-culture of iPSC-OL with induced neuronal (iN) cells on BEM substrates, which closely mimics the in vivo brain microenvironment for myelinated neurons, not only enhanced myelination of iPSC-OL but also improved electrophysiological function of iN cells. BEM-functionalized aligned electrospun nanofibrous scaffolds further promoted the maturation of iPSC-OLs, enhanced the production of myelin sheath-like structures by the iPSC-OL, and enhanced the neurogenesis of iN cells. Thus, the biomimetic strategy presented here can generate functional OLs from stem cells and facilitate myelination by providing brain-specific biochemical, biophysical, and structural signals. Our system comprising stem cells and brain tissue from human sources could help in the establishment of human demyelination disease models and the development of regenerative cell therapy for myelin disorders.

Urothelial or oral mucosa cells for tissue-engineered urethroplasty: A critical revision of the clinical outcome

Objective

To report the clinical outcome of urethral reconstruction by cultured urothelial or oral mucosa cells for tissue-engineered urethroplasty.

Methods

We systematically searched for studies reporting the use of tissue-engineered techniques for hypospadias and urethral stricture repair in humans in PubMed and Embase (OvidSP) through January, 1990 to June, 2018. We excluded studies based on titles that clearly were not related to the subject, studies in which tissue-engineered biomaterial were used only in laboratory or experimental animals, and in the absence of autologous cultured epithelial cells. Studies were also excluded if they were not published in English, had no disease background and adequate follow-up. Finally, we search all relevant abstract presented at two of the main urological meetings in the last 10 years: European Association of Urology (EAU) and American Urological Association (AUA).

Results

A total of six articles, reporting the clinical use of tissue-engineered techniques in humans, were fully reviewed in our review. The epithelial cells were harvested from the urethra (10 patients), the bladder (11 patients) and the mouth (104 patients). The tissue-engineered grafts were used in children for primary hypospadias repair in 16 cases, and in adults for posterior and anterior urethral strictures repair in 109 cases. Tissue-engineered grafts were showed working better in children for primary hypospadias repair than in adults for urethral strictures repair.

Conclusion

One hundred and twenty-five patients received tissue-engineered urethroplasty using cultured epithelial cells for primary hypospadias or urethral strictures repair. The studies demonstrate a high degree of heterogeneity respect to epithelial cells (from urethra, bladder, and mouth), type of scaffold, etiology, site of urethral stricture, number of patients, follow-up and outcomes.

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-Engineered Grafts from Human Decellularized Extracellular Matrices: A Systematic Review and Future Perspectives

Tissue engineering and regenerative medicine involve many different artificial and biologic materials, frequently integrated in composite scaffolds, which can be repopulated with various cell types. One of the most promising scaffolds is decellularized allogeneic extracellular matrix (ECM) then recellularized by autologous or stem cells, in order to develop fully personalized clinical approaches. Decellularization protocols have to efficiently remove immunogenic cellular materials, maintaining the nonimmunogenic ECM, which is endowed with specific inductive/differentiating actions due to its architecture and bioactive factors. In the present paper, we review the available literature about the development of grafts from decellularized human tissues/organs. Human tissues may be obtained not only from surgery but also from cadavers, suggesting possible development of Human Tissue BioBanks from body donation programs. Many human tissues/organs have been decellularized for tissue engineering purposes, such as cartilage, bone, skeletal muscle, tendons, adipose tissue, heart, vessels, lung, dental pulp, intestine, liver, pancreas, kidney, gonads, uterus, childbirth products, cornea, and peripheral nerves. In vitro recellularizations have been reported with various cell types and procedures (seeding, injection, and perfusion). Conversely, studies about in vivo behaviour are poorly represented. Actually, the future challenge will be the development of human grafts to be implanted fully restored in all their structural/functional aspects.

Buccal epithelium Expanded and Encapsulated in Scaffold-Hybrid Approach to Urethral Stricture (BEES-HAUS) procedure: A novel cell therapy-based pilot study

Objectives

To describe the feasibility of a novel cell‐based endoscopic technique using buccal epithelium, expanded and encapsulated in a thermoreversible gelation polymer scaffold for the treatment of urethral stricture.

Methods

Six male patients with bulbar urethral stricture ranging from 2.0 to 3.5 cm in length were included in this pilot study. Autologous buccal epithelial cells from a small buccal mucosal biopsy were isolated, cultured and encapsulated in thermoreversible gelation polymer scaffold, and were implanted at the stricture site after a wide endoscopic urethrotomy.

Results

All the patients voided well, with a mean peak flow rate of 24 mL/s. Urethroscopy carried out at 6 months showed healthy mucosa at the urethrotomy site. However, two of the six patients had recurrence at 18 and 24 months, respectively.

Conclusions

This endoscopic‐based Buccal epithelium Expanded and Encapsulated in Scaffold‐Hybrid Approach to Urethral Stricture (BEES‐HAUS) technique is a promising alternative for the open substitution buccal graft urethroplasty. It is possible to achieve the benefits of open substitution buccal urethroplasty with this endoscopic technique.

Outcomes of adult urethroplasty with commercially available acellular matrix

Background

Reconstruction for complex urethral strictures may necessitate grafting. Buccal mucosal graft (BMG) harvest involves additional morbidity, making 'off-the-shelf' options attractive. Multiple extracellular matrices (ECMs) have been used with varying degrees of success. We reviewed our experience with MatriStem (ACell, Inc., Columbia, MD, USA) to assess safety and clinical/histologic outcomes.

Methods

All patients undergoing acellular matrix-based reconstruction were included. Data regarding indications for surgery, patient demographics, subsequent procedures, clinical outcomes, and histologic analysis, when present, were collected.

Results

Eight patients undergoing urethral reconstruction with ECM were identified. All repairs were performed as staged procedures. Grafting was performed with either MatriStem alone or MatriStem and concomitant BMG. Seven patients (88%) underwent prior endoscopic intervention and five patients (71%) had failed to respond to one or multiple prior urethroplasties. Length of involved segments ranged from 2.5 to 15 cm. ECM graft placement was feasible and demonstrated excellent graft take. Among patients undergoing second-stage repairs (four of eight, 50%), 50% remained patent without the need for subsequent dilation.

Conclusions

Use of acellular matrix grafts in urethral reconstruction appears safe and feasible. Acellular matrix performs similarly to BMG with respect to graft take and contraction following staged repair. Further study is warranted.

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.

Current Status of Tissue Engineering in the Management of Severe Hypospadias

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

A new material to prevent urethral damage after implantation of artificial devices: an experimental study

OBJECTIVE

To validate the application of the bacterial cellulose (BC) membrane as a protecting bar-rier to the urethra.

MATERIALS AND METHODS

Forty female Wistar rats (four groups of 10): Group 1 (sham), the urethra was dissected as in previous groups and nothing applied around; Group 2, received a 0.7cm strip of the BC applied around the urethra just below the bladder neck; Group 3, received a silicon strip with the same dimensions as in group 2; Group 4, had a combination of 2 and 3 groups being the silicon strip applied over the cellulosic material. Half of the animals in each group were killed at 4 and 8 months. Bladder and urethra were fixed in formalin for histological analysis.

RESULTS

Inflammatory infiltrates were more intense at 4 months at lymphonodes (80% Grade 2), statistically different in the group 2 compared with groups 1 (p=0.0044) and 3 (p=0.0154). At 8 months, all samples were classified as grade 1 indicating a less intense inflammatory reaction in all groups. In group 2, at 8 months, there was a reduction in epithelial thickness (30±1μm) when com-pared to groups 1 (p=0.0001) and 3 (p<0.0001). Angiogenesis was present in groups 2 and 4 and absent in group 3. In BC implant, at 4 and 8 months, it was significant when comparing groups 4 with 1 (p=0.0159).

CONCLUSION

BC membrane was well integrated to the urethral wall promoting tissue remodeling and strengthening based on morphometric and histological results and may be a future option to prevent urethral damage.

Tissue engineered extracellular matrices (ECMs) in urology: Evolution and future directions

Autologous gastrointestinal tissue has remained the gold-standard reconstructive biomaterial in urology for >100 years. Mucus-secreting epithelium is associated with lifelong metabolic and neuromechanical complications when implanted into the urinary tract. Therefore, the availability of biocompatible tissue-engineered biomaterials such as extracellular matrix (ECM) scaffolds may provide an attractive alternative for urologists. ECMs are decellularised, biodegradable membranes that have shown promise for repairing defective urinary tract segments in vitro and in vivo by inducing a host-derived tissue remodelling response after implantation. In urology, porcine small intestinal submucosa (SIS) and porcine urinary bladder matrix (UBM) are commonly selected as ECMs for tissue regeneration. Both ECMs support ingrowth of native tissue and differentiation of multi-layered urothelial and smooth muscle cells layers while providing mechanical support in vivo. In their native acellular state, ECM scaffolds can repair small urinary tract defects. Larger urinary tract segments can be repaired when ECMs are manipulated by seeding them with various cell types prior to in vivo implantation. In the present review, we evaluate and summarise the clinical potential of tissue engineered ECMs in reconstructive urology with emphasis on their long-term outcomes in urological clinical trials.

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.

Urethroplasty using autologous urethral tissue-embedded acellular porcine bladder submucosa matrix grafts for the management of long-segment urethral stricture in a rabbit model

We conducted this study to evaluate the combined effect of acellular bladder submucosa matrix (BSM) and autologous urethral tissue for the treatment of long segment urethral stricture in a rabbit model. To prepare the BSM, porcine bladder submucosa was processed, decellularized, configured into a sheet-like shape, and sterilized. Twenty rabbits were randomized to normal control, urethral stricture, urethroplasty using BSM only or BSM/autologous urethral tissue (n=5 per group). Retrograde urethrography was performed at 4, 8, and 12 weeks postoperatively, and the grafted specimens were harvested at week 12 to evaluate urethral reconstruction through histopathologic and immunohistochemical analysis. The mean urethral width of the control, stricture, BSM, and BSM/autologous urethral tissue groups at week 12 was 10.3±0.80, 3.8±1.35, 8.8±0.84, and 9.1±1.14 mm, respectively. The histopathologic study revealed that the BSM/autologous urethral tissue graft had a normal area of urethral lumen, compact muscular layers, complete epithelialization, and progressive infiltration by vessels in the regenerated urethra. In contrast, the BSM grafts revealed keratinized epithelium, abundant collagenized fibrous connective tissue, and were devoid of bundles of circular smooth muscle. Nontransected ventral onlay-augmented urethroplasty using an acellular BSM scaffold combined with an autologous urethral tissue graft represents a feasible procedure for urethral reconstruction.

[Tissue engineering in reconstructive urology]

The term tissue engineering incorporates various techniques for the production of replacement tissues and organs. In urology tissue engineering offers many promising possibilities for the reconstruction of the urinary tract. Currently, buccal mucosa and urothelial cells are most commonly used for tissue engineering of the urinary tract. Various materials have been tested for their suitability as tissue scaffolds. The ideal scaffold, however, has not yet been found. In addition to material sciences and cell culture methods, surgical techniques play an important role in reconstructive urology for the successful implantation of tissue engineered transplants.

Application of bladder acellular matrix in urinary bladder regeneration: the state of the art and future directions

Construction of the urinary bladder de novo using tissue engineering technologies is the “holy grail” of reconstructive urology. The search for the ideal biomaterial for urinary bladder reconstruction has been ongoing for decades. One of the most promising biomaterials for this purpose seems to be bladder acellular matrix (BAM). In this review we determine the most important factors, which may affect biological and physical properties of BAM and its regeneration potential in tissue engineered urinary bladder. We also point out the directions in modification of BAM, which include incorporation of exogenous growth factors into the BAM structure. Finally, we discuss the results of the urinary bladder regeneration with cell seeded BAM.

Organ bioengineering for the newborn

Regenerative medicine has recently been established as an emerging interdisciplinary field focused on the repair; replacement or regeneration of cells, tissues and organs. It involves various disciplines, which are focused on different aspects of the regeneration process such as cell biology, gene therapy, bioengineering, material science and pharmacology. In this article, we will outline progress on tissue engineering of specific tissues and organs relevant to paediatric surgery.

Regenerative medicine in urology

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

CR, Mauney JR. Acellular bi-layer silk fibroin scaffolds support tissue regeneration in a rabbit model of onlay urethroplasty

Acellular scaffolds derived from Bombyx mori silk fibroin were investigated for their ability to support functional tissue regeneration in a rabbit model of urethra repair. A bi-layer silk fibroin matrix was fabricated by a solvent-casting/salt leaching process in combination with silk fibroin film casting to generate porous foams buttressed by homogeneous silk fibroin films. Ventral onlay urethroplasty was performed with silk fibroin grafts (Group 1, N = 4) (Width×Length, 1×2 cm²) in adult male rabbits for 3 m of implantation. Parallel control groups consisted of animals receiving small intestinal submucosa (SIS) implants (Group 2, N = 4) or urethrotomy alone (Group 3, N = 3). Animals in all groups exhibited 100% survival prior to scheduled euthanasia and achieved voluntary voiding following 7 d of initial catheterization. Retrograde urethrography of each implant group at 3 m post-op revealed wide urethral calibers and preservation of organ continuity similar to pre-operative and urethrotomy controls with no evidence of contrast extravasation, strictures, fistulas, or stone formation. Histological (hematoxylin and eosin and Masson's trichrome), immunohistochemical, and histomorphometric analyses demonstrated that both silk fibroin and SIS scaffolds promoted similar extents of smooth muscle and epithelial tissue regeneration throughout the original defect sites with prominent contractile protein (α-smooth muscle actin and SM22α) and cytokeratin expression, respectively. De novo innervation and vascularization were also evident in all regenerated tissues indicated by synaptophysin-positive neuronal cells and vessels lined with CD31 expressing endothelial cells. Following 3 m post-op, minimal acute inflammatory reactions were elicited by silk fibroin scaffolds characterized by the presence of eosinophil granulocytes while SIS matrices promoted chronic inflammatory responses indicated by mobilization of mononuclear cell infiltrates. The results of this study demonstrate that bi-layer silk fibroin scaffolds represent promising biomaterials for onlay urethroplasty, capable of promoting similar degrees of tissue regeneration in comparison to conventional SIS scaffolds, but with reduced immunogenicity.

Integration of collagen matrices into the urethra when implanted as onlay graft

OBJECTIVE

To assess the integration of decellularized heterologous collagen matrices into the urethra, when implanted with no cells or when seeded with autologous smooth muscle cells.

MATERIALS AND METHODS

Eighteen New Zealand rabbits were randomly assigned to two groups: Group I (n = 9) - animals undergoing urethral segment resection with interposition of a patch of heterologous collagen matrix seeded with autologous smooth muscle cells; Group II (n = 9) - animals undergoing resection of a urethral segment with interposition of a decellularized heterologous collagen matrix patch. Two animals from each group were sacrificed on postoperative days seven, fourteen and twenty-eight; three animals from each group were sacrificed at the end of three postoperative months. At the end of the third month one animal from each group underwent urethroscopy for urethral integrity assessment and one animal from each group had its microcirculation image captured by a SDF device (Side-stream Dark Field - Microscan Analysis Software). One animal from each group in each euthanasia period underwent cystourethrography so as the urethra could be viewed at flow time. The matrices integration was assessed through histological examination using hematoxylin and eosin (H & E), Masson trichrome (MT), Picrosirius red and Von Willebrand staining. In a blind study with two pathologists all the slides were studied.

RESULTS

The matrices whether seeded or not with autologous muscle cells were able to restore the architecture of the urethra, but were eliminated from the first week on, before incorporation. Microcirculation of the neourethra, at the end of the third month, showed the same characteristics as a normal urethra in both groups of animals.

CONCLUSION

Natural heterologous matrices implanted in the urethra as onlay graft were not incorporated into its walls but were able to fully restore the cell architecture of the organ, regardless of being seeded or not with autologous muscle cells.

Applications of tissue engineering in the genitourinary tract

Congenital abnormalities and acquired disorders can lead to organ damage or loss of tissue within the genitourinary tract. For reconstructive purposes, tissue-engineering efforts are currently underway for virtually every type of tissue and organ within the urinary tract. Tissue engineering incorporates the fields of cell transplantation, materials science and engineering for the purpose of creating functional replacement tissue. This article reviews some of the principles of tissue engineering and some of the applications of these principles to the genitourinary tract.

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

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

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

Objective

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

Patients and methods

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

Results

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

Conclusions

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

Spatial patterning of endothelial cells and vascular network formation using ultrasound standing wave fields

The spatial organization of cells is essential for proper tissue assembly and organ function. Thus, successful engineering of complex tissues and organs requires methods to control cell organization in three dimensions. In particular, technologies that facilitate endothelial cell alignment and vascular network formation in three-dimensional tissue constructs would provide a means to supply essential oxygen and nutrients to newly forming tissue. Acoustic radiation forces associated with ultrasound standing wave fields can rapidly and non-invasively organize cells into distinct multicellular planar bands within three-dimensional collagen gels. Results presented herein demonstrate that the spatial pattern of endothelial cells within three-dimensional collagen gels can be controlled by design of acoustic parameters of the sound field. Different ultrasound standing wave field exposure parameters were used to organize endothelial cells into either loosely aggregated or densely packed planar bands. The rate of vessel formation and the morphology of the resulting endothelial cell networks were affected by the initial density of the ultrasound-induced planar bands of cells. Ultrasound standing wave fields provide a rapid, non-invasive approach to pattern cells in three-dimensions and direct vascular network formation and morphology within engineered tissue constructs.

Regenerative medicine as a new therapeutic strategy for lower urinary tract dysfunction

The use of regenerative medicine for the treatment of organic and functional disorders intractable to conventional treatment has increased worldwide. This innovative medical field might particularly hold promise for the treatment of life-threatening diseases or healing of irreplaceable organs, such as the heart, liver and brain. Dysfunction of the urogenital tract and associated organs other than the kidney might not have immediate life-threatening implications; furthermore, the effectiveness of alternative therapy, such as enterocystoplasty for bladder cancer, has been shown. Therefore, most physicians or scientists do not give much importance to these disorders. However, urological disease has increased in developed societies in recent years. Furthermore, medical costs have also escalated. Disorders of the lower urinary tract, such as urinary disturbance or incontinence, can lead to other complications, impairing quality of life and ultimately increasing short- and long-term medical expenses. Regenerative medicine might hold potential solutions to these problems. Recent advances in urogenital regenerative medicine are reviewed in the present article, with particular reference to lower urinary tract reconstruction. The potential of regenerative medicine for the treatment of intractable lower urinary tract dysfunction compared with conventional treatment is also discussed.

Cell-seeded tubularized scaffolds for reconstruction of long urethral defects: a preclinical study

BACKGROUND

The treatment options for patients requiring repair of a long segment of the urethra are limited by the availability of autologous tissues. We previously reported that acellular collagen-based tubularized constructs seeded with cells are able to repair small urethral defects in a rabbit model.

OBJECTIVE

We explored the feasibility of engineering clinically relevant long urethras for surgical reconstruction in a canine preclinical model.

DESIGN, SETTING, AND PARTICIPANTS

Autologous bladder epithelial and smooth muscle cells from 15 male dogs were grown and seeded onto preconfigured collagen-based tubular matrices (6 cm in length). The perineal urethral segment was removed in 21 male dogs. Urethroplasties were performed with tubularized collagen scaffolds seeded with cells in 15 animals. Tubularized constructs without cells were implanted in six animals. Serial urethrography and three-dimensional computed tomography (CT) scans were performed pre- and postoperatively at 1, 3, 6, and 12 mo. The animals were euthanized at their predetermined time points (three animals at 1 mo, and four at 3, 6, and 12 mo) for analyses.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Statistical analysis of CT imaging and histology was not needed.

RESULTS AND LIMITATIONS

CT urethrograms showed wide-caliber urethras without strictures in animals implanted with cell-seeded matrices. The urethral segments replaced with acellular scaffolds collapsed. Gross examination of the urethral implants seeded with cells showed normal-appearing tissue without evidence of fibrosis. Histologically, an epithelial cell layer surrounded by muscle fiber bundles was observed on the cell-seeded constructs, and cellular organization increased over time. The epithelial and smooth muscle phenotypes were confirmed using antibodies to pancytokeratins AE1/AE3 and smooth muscle-specific desmin. Formation of an epithelial cell layer occurred in the unseeded constructs, but few muscle fibers formed.

CONCLUSIONS

Cell-seeded tubularized collagen scaffolds can be used to repair long urethral defects, whereas scaffolds without cells lead to poor tissue development and strictures. This study demonstrates that long tissue-engineered tubularized urethral segments may be used for urethroplasty in patients.

Esophageal tissue engineering: A new approach for esophageal replacement

A number of congenital and acquired disorders require esophageal tissue replacement. Various surgical techniques, such as gastric and colonic interposition, are standards of treatment, but frequently complicated by stenosis and other problems. Regenerative medicine approaches facilitate the use of biological constructs to replace or regenerate normal tissue function. We review the literature of esophageal tissue engineering, discuss its implications, compare the methodologies that have been employed and suggest possible directions for the future. Medline, Embase, the Cochrane Library, National Research Register and ClinicalTrials.gov databases were searched with the following search terms: stem cell and esophagus, esophageal replacement, esophageal tissue engineering, esophageal substitution. Reference lists of papers identified were also examined and experts in this field contacted for further information. All full-text articles in English of all potentially relevant abstracts were reviewed. Tissue engineering has involved acellular scaffolds that were either transplanted with the aim of being repopulated by host cells or seeded prior to transplantation. When acellular scaffolds were used to replace patch and short tubular defects they allowed epithelial and partial muscular migration whereas when employed for long tubular defects the results were poor leading to an increased rate of stenosis and mortality. Stenting has been shown as an effective means to reduce stenotic changes and promote cell migration, whilst omental wrapping to induce vascularization of the construct has an uncertain benefit. Decellularized matrices have been recently suggested as the optimal choice for scaffolds, but smart polymers that will incorporate signalling to promote cell-scaffold interaction may provide a more reproducible and available solution. Results in animal models that have used seeded scaffolds strongly sug- gest that seeding of both muscle and epithelial cells on scaffolds prior to implantation is a prerequisite for complete esophageal replacement. Novel approaches need to be designed to allow for peristalsis and vascularization in the engineered esophagus. Although esophageal tissue engineering potentially offers a real alternative to conventional treatments for severe esophageal disease, important barriers remain that need to be addressed.

Penile urethra replacement with autologous cell-seeded tubularized collagen matrices

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

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Tissue engineering of reproductive tissues and organs

Regenerative medicine and tissue engineering technology may soon offer new hope for patients with serious injuries and end-stage reproductive organ failure. Scientists are now applying the principles of cell transplantation, material science, and bioengineering to construct biological substitutes that can restore and maintain normal function in diseased and injured reproductive tissues. In addition, the stem cell field is advancing, and new discoveries in this field will lead to new therapeutic strategies. For example, newly discovered types of stem cells have been retrieved from uterine tissues such as amniotic fluid and placental stem cells. The process of therapeutic cloning and the creation of induced pluripotent cells provide still other potential sources of stem cells for cell-based tissue engineering applications. Although stem cells are still in the research phase, some therapies arising from tissue engineering endeavors that make use of autologous adult cells have already entered the clinic. This article discusses these tissue engineering strategies for various organs in the male and female reproductive tract.

Overcoming hypoxia to improve tissue-engineering approaches to regenerative medicine

The current clinical successes of tissue engineering are limited primarily to low-metabolism, acellular, pre-vascularized or thin tissues. Mass transport has been identified as the primary culprit, limiting the delivery of nutrients (such as oxygen and glucose) and removal of wastes, from tissues deep within a cellular scaffold. While strategies to develop sufficient vasculature to overcome hypoxia in vitro are promising, inconsistencies between the in vitro and the in vivo environments may still negate the effectiveness of large-volume tissue-engineered scaffolds. While a common theme in tissue engineering is to maximize oxygen supply, studies suggest that moderate oxygenation of cellular scaffolds during in vitro conditioning is preferable to high oxygen levels. Aiming for moderate oxygen values to prevent hypoxia while still promoting angiogenesis may be obtained by tailoring in vitro culture conditions to the oxygen environment the scaffold will experience upon implantation. This review discusses the causes and effects of tissue-engineering hypoxia and the optimization of oxygenation for the minimization of in vivo hypoxia.

Prepubertal follow-up after hypospadias repair with autologous in vitro cultured urothelial cells

AIM

To evaluate the long-term effects on hypospadias repair with cultured autologous urothelial cells.

METHODS

From 2000 to 2002, six patients with scrotal or perineal hypospadias and pronounced chordee were treated surgically with cultured autologous urothelial cell transplants. All patients were evaluated at 6-8 years postoperatively, that is, in the prepubertal period. The outcome was assessed with respect to cosmetic appearance, voiding function, urinary flow, artificial erection, urethroscopy and biopsies.

RESULTS

Median follow-up time was 7.25 years. Up to date, all patients present with a good cosmetic appearance. One of the boys prefers a sitting voiding position. Urinary flow curves are bell-shaped in all but one. All have straight erections, urethroscopy reveals an even, non-hair-bearing surface on the transplanted side and 2/6 present with urothelial cells in biopsies. Limitations of this follow-up study include a small group of patients and lack of controls. However, patients with severe hypospadias have high complication rates, and our results are equal or better than expected for the phenotype.

CONCLUSION

Tissue engineering for severe hypospadias repair can be performed in a safe manner. The method is feasible for treatment of a selected group of hypospadias, where pronounced chordee and shortage of preputial and penile skin complicates the creation of a neourethra.

Regenerative medicine as applied to general surgery

The present review illustrates the state of the art of regenerative medicine (RM) as applied to surgical diseases and demonstrates that this field has the potential to address some of the unmet needs in surgery. RM is a multidisciplinary field whose purpose is to regenerate in vivo or ex vivo human cells, tissues, or organs to restore or establish normal function through exploitation of the potential to regenerate, which is intrinsic to human cells, tissues, and organs. RM uses cells and/or specially designed biomaterials to reach its goals and RM-based therapies are already in use in several clinical trials in most fields of surgery. The main challenges for investigators are threefold: Creation of an appropriate microenvironment ex vivo that is able to sustain cell physiology and function in order to generate the desired cells or body parts; identification and appropriate manipulation of cells that have the potential to generate parenchymal, stromal and vascular components on demand, both in vivo and ex vivo; and production of smart materials that are able to drive cell fate.

Cell-seeded tubular acellular matrix for replacing a long circumferential urethral defect in a canine model: Is it clinically applicable?

Objective

To evaluate the feasibility of replacing a relatively long segment of the canine urethra by a tube of cell-seeded acellular collagen bladder matrix.

Materials and methods

The study included 14 female mongrel dogs in which a 3-cm segment of the whole urethral circumference was excised and replaced by a tube of acellular matrix seeded with autologous urothelial cells. The acellular matrix was obtained from the excised bladder of female donor dogs that were not included in the study. Autologous cells were obtained from the study dogs by open bladder biopsy, with subsequent in vitro expansion and cultivation. Urethroplasty was performed over a 16 F urethral catheter that was kept for 4 weeks. The dogs were killed humanely (one every week for 4 weeks and then one monthly for 10 months). After stent removal, retrograde urethrography was used each month in the living dogs. If retention occurred a urethrogram was taken and then the dog was killed humanely. All grafts from dogs were harvested and sent for histopathological examination.

Results

Exploration at 1, 2, 3 and 4 weeks showed progressive shrinkage in length, together with relative narrowing of the lumen. Three dogs developed retention within a week after stent removal and the other seven developed retention within 4 months. Retrograde urethrograms showed evidence of stricture and/or fistula at the graft site in all dogs. On exploration, grafts showed marked shrinkage (0.6–1.2 cm in length) with complete obliteration of their lumens. Histopathological examination showed extensive fibrosis of the matrix with no evident urothelial architecture.

Conclusion

Cell-seeded acellular matrix tube is insufficient to replace a 3-cm circumferential urethral defect in dogs.

Regenerative medicine strategies

Applications of regenerative medicine technology may offer novel therapies for patients with injuries, end-stage organ failure, or other clinical problems. Currently, patients suffering from diseased and injured organs can be treated with transplanted organs. However, there is a severe shortage of donor organs that is worsening yearly as the population ages and new cases of organ failure increase. Scientists in the field of regenerative medicine and tissue engineering are now applying the principles of cell transplantation, material science, and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. The stem cell field is also advancing rapidly, opening new avenues for this type of therapy. For example, therapeutic cloning and cellular reprogramming may one day provide a potentially limitless source of cells for tissue engineering applications. While stem cells are still in the research phase, some therapies arising from tissue engineering endeavors have already entered the clinical setting successfully, indicating the promise regenerative medicine holds for the future.

Tissue engineering of the penis

Congenital disorders, cancer, trauma, or other conditions of the genitourinary tract can lead to significant organ damage or loss of function, necessitating eventual reconstruction or replacement of the damaged structures. However, current reconstructive techniques are limited by issues of tissue availability and compatibility. Physicians and scientists have begun to explore tissue engineering and regenerative medicine strategies for repair and reconstruction of the genitourinary tract. Tissue engineering allows the development of biological substitutes which could potentially restore normal function. Tissue engineering efforts designed to treat or replace most organs are currently being undertaken. Most of these efforts have occurred within the past decade. However, before these engineering techniques can be applied to humans, further studies are needed to ensure the safety and efficacy of these new materials. Recent progress suggests that engineered urologic tissues and cell therapy may soon have clinical applicability.

[Reconstructive urethroplasty using porcine acellular matrix (SIS): evolution of the grafting technique and results of 10-year experience]

INTRODUCTION

Long tract urethral reconstruction still has no other resolution than two-stage techniques or graft and flap procedures, that are neither simple nor trouble-free. Tissue engineering simplifies this surgery using porcine acellular matrix, obtained from small intestine submucosa (SIS): thin but strong, ready for grafting, it is not immunogenic, being deprived of cells. It is a biological bridge for reconstruction, promoting the regeneration of surrounding tissue. We report our experience using SIS for urethroplasty.

MATERIALS AND METHODS

After coronal or perineal-scrotal incision and penile degloving, the urethra is rotated of 180° and opened through the entire restricted tract. The graft is sutured dorsally and reinforced by the contact with the cavernous bodies to prevent pouching. From 1999 to 2005 we performed this grafting procedure in 36 men and 4 women. Afterwards, 16 more surgeries performed were with direct ventral graft procedure, without urethra isolation and rotation, with worthy simplification.

RESULTS

A 10-year follow-up shows satisfactory urodynamic and subjective outcomes for both procedures, assessed by voiding urethrography, uroflowmetry, International Prostate Symptom Score, and Quality of Life perception. At urethroscopy the graft appears completely homogeneous to the native tissue, as confirmed by the histological examination. The ventral direct graft represents the more consistent innovation: we did not observe pouching and the results remained effective. For penile urethra, in a few patients, periodic dilatations were necessary.

CONCLUSIONS

SIS can be considered as an alternative to more difficult grafting procedures, which are probably no more indispensable in urethral enlargement, even for critical strictures

Regenerative medicine strategies for treating neurogenic bladder

Neurogenic bladder is a general term encompassing various neurologic dysfunctions of the bladder and the external urethral sphincter. These can be caused by damage or disease. Therapeutic management options can be conservative, minimally invasive, or surgical. The current standard for surgical management is bladder augmentation using intestinal segments. However, because intestinal tissue possesses different functional characteristics than bladder tissue, numerous complications can ensue, including excess mucus production, urinary stone formation, and malignancy. As a result, investigators have sought after alternative solutions. Tissue engineering is a scientific field that uses combinations of cells and biomaterials to encourage regeneration of new, healthy tissue and offers an alternative approach for the replacement of lost or deficient organs, including the bladder. Promising results using tissue-engineered bladder have already been obtained in children with neurogenic bladder caused by myelomeningocele. Human clinical trials, governed by the Food and Drug Administration, are ongoing in the United States in both children and adults to further evaluate the safety and efficacy of this technology. This review will introduce the principles of tissue engineering and discuss how it can be used to treat refractory cases of neurogenic bladder.

Regenerative medicine in urology

The term 'regenerative medicine' encompasses strategies for restoring or renewing tissue or organ function by: (i) in vivo tissue repair by in-growth of host cells into an acellular natural or synthetic biomaterial, (ii) implantation of tissue 'engineered'in vitro by seeding cultured cells into a biomaterial scaffold, and (iii) therapeutic cloning and stem cell-based tissue regeneration. In this article, we review recent developments underpinning the emerging science of regenerative medicine and critically assess where successful implementation of novel regenerative medicine approaches into urology practice might genuinely transform the quality of life of affected individuals. We advocate the need for an evidence-based approach supported by strong science and clinical objectivity.