Engineering functional bladder tissues

Interlacing biology and engineering: An introduction to textiles and their application in tissue engineering

Tissue engineering (TE) aims to provide personalized solutions for tissue loss caused by trauma, tumors, or congenital defects. While traditional methods like autologous and homologous tissue transplants face challenges such as donor shortages and risk of donor site morbidity, TE provides a viable alternative using scaffolds, cells, and biologically active molecules. Textiles represent a promising scaffold option for both in-vitro and in-situ TE applications. Textile engineering is a broad field and can be divided into fiber-based textiles and yarn-based textiles. In fiber-based textiles the textile fabric is produced in the same step as the fibers (e.g. non-wovens, electrospun mats and 3D-printed). For yarn-based textiles, yarns are produced from fibers or filaments first and then, a textile fabric is produced (e.g. woven, weft-knitted, warp-knitted and braided fabrics). The selection of textile scaffold technology depends on the target tissue, mechanical requirements, and fabrication methods, with each approach offering distinct advantages. Braided scaffolds, with their high tensile strength, are ideal for load-bearing tissues like tendons and ligaments, while their ability to form stable hollow lumens makes them suitable for vascular applications. Weaving, weft-, and warp-knitting provide tunable structural properties, with warp-knitting offering the greatest design flexibility. Spacer fabrics enable complex 3D architecture, benefiting applications such as skin grafts and multilayered tissues. Electrospinning, though highly effective in mimicking the ECM, is structurally limited. The complex interactions between materials, fiber properties, and textile technologies allows for scaffolds with a wide range of morphological and mechanical characteristics (e.g., tensile strength of woven textiles ranging from 0.64 to 180.4 N/mm2). With in-depth knowledge, textiles can be tailored to obtain specific mechanical properties as accurately as possible and aid the formation of functional tissue. However, as textile structures inherently differ from biological tissues, careful optimization is required to enhance cell behavior, mechanical performance, and clinical applicability. This review is intended for TE experts interested in using textiles as scaffolds and provides a detailed analysis of the available options, their characteristics and known applications. For this, first the major fiber formation methods are introduced, then subsequent used automated textile technologies are presented, highlighting their strengths and limitations. Finally, we analyze how these textile and fiber structures are utilized in TE, organized by the use of textiles in TE across major organ systems, including the nervous, skin, cardiovascular, respiratory, urinary, digestive, and musculoskeletal systems.

Bacterial cellulose-based scaffold modified with anti-CD29 antibody to selectively capture urine-derived stem cells for bladder repair

Acellular cellulose-based biomaterials hold promising potential for treating bladder injuries. However, the compromised cellular state surrounding the wound impedes the complete reconstruction of the bladder. This necessitates the development of a bio-instructive cellulose-based biomaterial that actively controls cell behavior to facilitate effective bladder regeneration. To develop such an advanced cell-free scaffold, a bacterial cellulose (BC) substrate is elaborately modified through layer-by-layer assembly of heparin and collagen (H/C), followed by glutaraldehyde crosslinking, resulting in a biomimetic nanofibrous scaffold with optimized mechanical properties and reduced salt crystal deposition. Critically, the scaffold is functionalized with anti-CD29 antibodies, enabling selective in situ capture of urine-derived stem cells (USCs) without compromising their viability. The (H/C)-modified BC scaffold exhibits exceptional swelling and extracellular matrix-like architecture, which mirrors the natural bladder environment. Fluorescent immunostaining confirms uniform antibody grafting, confirming the efficacy of this modified biomaterial in attracting and retaining USCs. Overall, this study introduces a BC-based scaffold that has been innovatively modified with CD29, enabling the selective capture of USCs from urine. This innovative acellular biomaterial represents a promising acellular strategy to address the challenges posed by compromised cellular conditions during bladder reconstruction, offering a novel avenue for regenerative bladder therapies.

Ascorbic Acid 2-Phosphate Releasing Supercritically Foamed Porous Poly-L-Lactide-Co-ε-Caprolactone Scaffold Enhances the Collagen Production of Human Vaginal Stromal Cells: A New Approach for Vaginal Tissue Engineering

BACKGROUND

The reconstructive surgery of vaginal defects is highly demanding and susceptible to complications, especially in larger defects requiring nonvaginal tissue grafts. Thus, tissue engineering-based solutions could provide a potential approach to the reconstruction of vaginal defects.

METHODS

Here, we evaluated a novel porous ascorbic acid 2-phosphate (A2P)-releasing supercritical carbon dioxide foamed poly-L-lactide-co-ε-caprolactone (scPLCLA2P) scaffold for vaginal reconstruction with vaginal epithelial (EC) and stromal (SC) cells. The viability, proliferation, and phenotype of ECs and SCs were evaluated in monocultures and in cocultures on d 1, d 7 and d 14. Furthermore, the collagen production of SCs on scPLCLA2P was compared to that on scPLCL without A2P on d 14.

RESULTS

Both ECs and SCs maintained their viability on the scPLCLA2P scaffold in mono- and coculture conditions, and the cells maintained their typical morphology during the 14-d culture period. Most importantly, the scPLCLA2P scaffolds supported the collagen production of SCs superior to plain scPLCL based on total collagen amount, collagen I and III gene expression results and collagen immunostaining results.

CONCLUSION

This is the first study evaluating the effect of A2P on vaginal tissue engineering, and the results are highly encouraging, indicating that scPLCLA2P has potential as a scaffold for vaginal tissue engineering.

De- and recellularized urethral reconstruction with autologous buccal mucosal cells implanted in an ovine animal model

OBJECTIVES

Patients with urethral stricture due to any type of trauma, hypospadias or gender dysphoria suffer immensely from impaired capacity to urinate and are in need of a new functional urethra. Tissue engineering with decellularization of a donated organ recellularized with cells from the recipient patient has emerged as a promising alternative of advanced therapy medicinal products. The aim of this pilot study was to develop an ovine model of urethral transplantation and to produce an individualized urethra graft to show proof of function in vivo.

METHODS

Donated urethras from ram abattoir waste were decellularized and further recellularized with autologous buccal mucosa epithelial cells excised from the recipient ram and expanded in vitro. The individualized urethral grafts were implanted by reconstructive surgery in rams replacing 2.5 ± 0.5 cm of the native penile urethra.

RESULTS

After surgery optimization, three ram had the tissue engineered urethra implanted for one month and two out of three showed a partially regenerated epithelium.

CONCLUSIONS

Further adjustments of the model are needed to achieve a satisfactory proof-of-concept; however, we interpret these findings as a proof of principle and a possible path to develop a functional tissue engineered urethral graft with de- and recellularization and regeneration in vivo after transplantation.

A comprehensive review on hydrogel materials in urology: Problems, methods, and new opportunities

Hydrogel materials provide an extremely promising group of materials that can find an increasingly wide range of use in treating urinary system conditions due to their unique properties. The present review describes achievements to date in terms of the use and development prospects of hydrogel materials applications in the treatment and reconstruction of the urinary system organs, which among others include: hydrogel systems of intravesical drug delivery, ureteral stents design, treatment of vesicoureteral reflux, urinary bladder and urethral defects reconstruction, design of modern urinary catheters and also solutions applied in urinary incontinence therapy (Figure 4). In addition, hydrogel materials find increasingly growing applications in the construction of educational simulation models of organs and specific conditions of the urinary system, which enable the education of medical personnel. Numerous research efforts are underway to expand the existing treatment methods and reconstruction of the urinary system based on hydrogel materials. After conducting the further necessary research, many of the innovative solutions developed to date have high application potential.

Application of biomaterials and tissue engineering in bladder regeneration

The primary functions of the bladder are storing urine under low and stable pressure and micturition. Various forms of trauma, tumors, and iatrogenic injuries can cause the loss of or reduce bladder function or capacity. If such damage is not treated in time, it will eventually lead to kidney damage and can even be life-threatening in severe cases. The emergence of tissue engineering technology has led to the development of more possibilities for bladder repair and reconstruction, in which the selection of scaffolds is crucial. In recent years, a growing number of tissue-engineered bladder scaffolds have been constructed. Therefore, this paper will discuss the development of tissue-engineered bladder scaffolds and will further analyze the limitations of and challenges encountered in bladder reconstruction.

Bi-layer silk fibroin skeleton and bladder acellular matrix hydrogel encapsulating adipose-derived stem cells for bladder reconstruction

A scaffold, constructed from a bi-layer silk fibroin skeleton (BSFS) and a bladder acellular matrix hydrogel (BAMH) encapsulated with adipose-derived stem cells (ASCs), was developed for bladder augmentation in a rat model. The BSFS, prepared from silk fibroin (SF), had good mechanical properties that allowed it to maintain the scaffold shape and be used for stitching. The prepared BAM was digested by pepsin and the pH was adjusted to harvest the BAMH that provided an extracellular environment for the ASCs. The constructed BSFS-BAMH-ASCs and BSFS-BAMH scaffolds were wrapped in the omentum to promote neovascularization and then used for bladder augmentation; at the same time, a cystotomy was used as the condition for the control group. Histological staining and immunohistochemical analysis confirmed that the omentum incubation could promote scaffold vascularization. Hematoxylin and eosin and Masson's trichrome staining indicated that the BSFS-BAMH-ASCs scaffold regenerated the bladder wall structure. In addition, immunofluorescence analyses confirmed that the ASCs could promote the regeneration of smooth muscle, neurons and blood vessels and the restoration of physiological function. These results demonstrated that the BSFS-BAMH-ASCs may be a promising scaffold for promoting bladder wall regeneration and the restoration of physiological function of the bladder in a rat bladder augmentation model.

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

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

Biofabrication of a Tubular Model of Human Urothelial Mucosa Using Human Wharton Jelly Mesenchymal Stromal Cells

Several models of bioartificial human urothelial mucosa (UM) have been described recently. In this study, we generated novel tubularized UM substitutes using alternative sources of cells. Nanostructured fibrin-agarose biomaterials containing fibroblasts isolated from the human ureter were used as stroma substitutes. Then, human Wharton jelly mesenchymal stromal cells (HWJSC) were used to generate an epithelial-like layer on top. Three differentiation media were used for 7 and 14 days. Results showed that the biofabrication methods used here succeeded in generating a tubular structure consisting of a stromal substitute with a stratified epithelial-like layer on top, especially using a medium containing epithelial growth and differentiation factors (EM), although differentiation was not complete. At the functional level, UM substitutes were able to synthesize collagen fibers, proteoglycans and glycosaminoglycans, although the levels of control UM were not reached ex vivo. Epithelial differentiation was partially achieved, especially with EM after 14 days of development, with expression of keratins 7, 8, and 13 and pancytokeratin, desmoplakin, tight-junction protein-1, and uroplakin 2, although at lower levels than controls. These results confirm the partial urothelial differentiative potential of HWJSC and suggest that the biofabrication methods explored here were able to generate a potential substitute of the human UM for future clinical use.

Review of clinical experience on biomaterials and tissue engineering of urinary bladder

PURPOSE

In recent pre-clinical studies, biomaterials and bladder tissue engineering have shown promising outcomes when addressing the need for bladder tissue replacement. To date, multiple clinical experiences have been reported. Herein, we aim to review and summarize the reported clinical experience of biomaterial usage and tissue engineering of the urinary bladder.

METHODS

A systematic literature search was performed on Feb 2019 to identify clinical reports on biomaterials for urinary bladder replacement or augmentation and clinical experiences with bladder tissue engineering. We identified and reviewed human studies using biomaterials and tissue-engineered bladder as bladder substitutes or augmentation implants. The studies were then summarized for each respective procedure indication, technique, follow-up period, outcome, and important findings of the studies.

RESULTS

An extensive literature search identified 25 studies of case reports and case series with a cumulative clinical experience of 222 patients. Various biomaterials and tissue-engineered bladder were used, including plastic/polyethylene mold, preserved dog bladder, gelatine sponge, Japanese paper with Nobecutane, lypholized human dura, bovine pericardium, amniotic membrane, small intestinal mucosa, and bladder tissue engineering with autologous cell-seeded biodegradable scaffolds. However, overall clinical experiences including the outcomes and safety reports were not satisfactory enough to replace enterocystoplasty.

CONCLUSION

To date, several clinical experiences of biomaterials and tissue-engineered bladder have been reported; however, various studies have reported non-satisfactory outcomes. Further technological advancements and a better understanding is needed to advance bladder tissue engineering as a future promising management option for patients requiring bladder drainage.

Augmentation Cystoplasty of Diseased Porcine Bladders with Bi-Layer Silk Fibroin Grafts

IMPACT STATEMENT

The search for an ideal "off-the-shelf" biomaterial for augmentation cystoplasty remains elusive and current scaffold configurations are hampered by mechanical and biocompatibility restrictions. In addition, preclinical evaluations of potential scaffold designs for bladder repair are limited by the lack of tractable large animal models of obstructive bladder disease that can mimic clinical pathology. The results of this study describe a novel, minimally invasive, porcine model of partial bladder outlet obstruction that simulates clinically relevant phenotypes. Utilizing this model, we demonstrate that acellular, bi-layer silk fibroin grafts can support the formation of vascularized, innervated bladder tissues with functional properties.

Bioengineering Approaches for Bladder Regeneration

Current clinical strategies for bladder reconstruction or substitution are associated to serious problems. Therefore, new alternative approaches are becoming more and more necessary. The purpose of this work is to review the state of the art of the current bioengineering advances and obstacles reported in bladder regeneration. Tissue bladder engineering requires an ideal engineered bladder scaffold composed of a biocompatible material suitable to sustain the mechanical forces necessary for bladder filling and emptying. In addition, an engineered bladder needs to reconstruct a compliant muscular wall and a highly specialized urothelium, well-orchestrated under control of autonomic and sensory innervations. Bioreactors play a very important role allowing cell growth and specialization into a tissue-engineered vascular construct within a physiological environment. Bioprinting technology is rapidly progressing, achieving the generation of custom-made structural supports using an increasing number of different polymers as ink with a high capacity of reproducibility. Although many promising results have been achieved, few of them have been tested with clinical success. This lack of satisfactory applications is a good reason to discourage researchers in this field and explains, somehow, the limited high-impact scientific production in this area during the last decade, emphasizing that still much more progress is required before bioengineered bladders become a commonplace in the clinical setting.

Tissue-Engineered Neo-Urinary Conduit from Decellularized Trachea

Decellularized tissues have been increasingly popular for constructing scaffolds for tissue engineering applications due to their beneficial biological compositions and mechanical properties. It is therefore natural to consider decellularized trachea for construction of tissue-engineered trachea, as well as other tubular organs. A Neo-Urinary Conduit (NUC) is such a tubular organ that works as a passage for urine removal in bladder cancer patients who need a urinary diversion after their diseased bladder is removed. In this study, we report our findings on the feasibility of using a decellularized trachea for NUC applications. As a NUC scaffold, decellularized trachea provides benefits of having not only naturally occurring biological components but also having sufficient mechanical properties and structural integrity. We, therefore, decellularized rabbit trachea, evaluated its mechanical performance, and investigated its ability to support in vitro growth of human smooth muscle cells (hSMCs) and human urothelial cells (hUCs). The decellularized trachea had appropriate biomechanical properties with ultimate tensile strength of ∼0.34 MPa in longitudinal direction and ∼1.0 MPa in circumferential direction and resisted a radial burst pressure of >155 mm Hg. Cell morphology study by scanning electron microscopy further showed that hUCs grown on decellularized trachea adopted a typical flatten and interconnected network structure in the lumen of the scaffold, while they formed a round spherical shape and did not spread on the outer surfaces. SMCs, on the other hand, spread well throughout the scaffold. The gene expression analysis by real time quantitative polymerase chain reaction (RT-qPCR) and immunofluorescence studies further confirmed scaffold's ability to support long-term growth of hSMCs. Since uroepithelium has been shown to regenerate itself over time in vivo, these findings suggest that it is possible to construct a NUC from decellularized trachea without any preseeding of UCs. In future, we plan to translate decellularized trachea in a preclinical animal model and evaluate its biological performance.

Redefining medicine from an anticipatory perspective

The meaning of the concept of anticipation escapes the majority of those concerned with change, in particular those who study health. To characterize only genetic disorders, such as conditions with progressively earlier symptoms and higher intensity of disease from generation to generation, in terms of anticipatory expression is rather limited and limiting. Practitioners of medical care could benefit from understanding anticipation as definitory of the living. This view explains why diminished anticipatory expression, in all forms of the living, results in conditions calling for medical attention. So far, medicine has opted for a deterministic-reductionist perspective that reduces the living to a machine. Medical care, stuck in the grey zone between success and failure, should overcome its reactive obsession. From an almost exclusively mechanistic activity, it should evolve into a holistic proactive practice of well-being that reflects awareness of anticipation.

Current concepts of the acontractile bladder

The acontractile bladder (AcB) is a urodynamic-based diagnosis wherein the bladder is unable to demonstrate any contraction during a pressure flow study. Although it is often grouped with underactive bladder, it is a unique phenomenon and should be investigated independently. The purpose of the present review was to examine the current literature on AcB regarding its pathology, diagnosis, current management guidelines, and future developments. We performed a review of the PubMed database, classifying the evidence for AcB pathology, diagnosis, treatment, and potential future treatments. Over the 67 years covered in our review period, 42 studies were identified that met our criteria. Studies were largely poor quality and mainly consisted of retrospective review or animal models. The underlying pathology of AcB is variable with both neurological and myogenic aetiologies. Treatment is largely tailored for renal preservation and reduction of infection. Although future developments may allow more functional restorative treatments, current treatments mainly focus on bladder drainage. AcB is a unique and understudied bladder phenomenon. Treatment is largely based on symptoms and presentation. While cellular therapy and neuromodulation may hold promise, further research is needed into the underlying neuro-urological pathophysiology of this disease so that we may better develop future treatments.

In Vitro Differentiation and Propagation of Urothelium from Pluripotent Stem Cell Lines

Bioengineering of bladder tissue, particularly for those patients who have advanced bladder disease, requires a source of urothelium that is healthy, capable of significant proliferation in vitro and immunologically tolerated upon transplant. As pluripotent stem cells have the potential to fulfill such criteria, they provide a critical cell source from which urothelium might be derived in vitro and used clinically. Herein, we describe the in vitro differentiation of urothelium from the H9 human embryonic stem cell (hESC) line through the definitive endoderm (DE) phase via selective culture techniques. The protocol can be used to derive urothelium from other hESCs or human-induced pluripotent stem cells.

Urinary Tissue Engineering: Challenges and Opportunities

INTRODUCTION

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

AIM

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

METHODS

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

MAIN OUTCOME MEASURE

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

RESULTS

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

CONCLUSION

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

Tissue 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.

Biomanufacturing Seamless Tubular and Hollow Collagen Scaffolds with Unique Design Features and Biomechanical Properties

A versatile process to develop designer collagen scaffolds for hollow and tubular tissue engineering applications is presented. This process creates seamless and biomechanically tunable scaffolds ranging from ureter-like microsized tubings to structures with highly customized lumens that resemble intestinal villi, fluid bladders, and alveolar sacs that together with stem cells can potentially be used in preclinical and clinical settings.

Whyever bladder tissue engineering clinical applications still remain unusual even though many intriguing technological advances have been reached?

To prevent problematic outcomes of bowel-based bladder reconstructive surgery, such as prosthetic tumors and systemic metabolic complications, research works, to either regenerate and strengthen failing organ or build organ replacement biosubstitute, have been turned, from 90s of the last century, to both regenerative medicine and tissue engineering.Various types of acellular matrices, naturally-derived materials, synthetic polymers have been used for either "unseeded" (cell free) or autologous "cell seeded" tissue engineering scaffolds. Different categories of cell sources - from autologous differentiated urothelial and smooth muscle cells to natural or laboratory procedure-derived stem cells - have been taken into consideration to reach the construction of suitable "cell seeded" templates. Current clinically validated bladder tissue engineering approaches essentially consist of augmentation cystoplasty in patients suffering from poorly compliant neuropathic bladder. No clinical applications of wholly tissue engineered neobladder have been carried out to radical-reconstructive surgical treatment of bladder malignancies or chronic inflammation-due vesical coarctation. Reliable reasons why bladder tissue engineering clinical applications so far remain unusual, particularly imply the risk of graft ischemia, hence its both fibrous contraction and even worse perforation. Therefore, the achievement of graft vascular network (vasculogenesis) could allow, together with the promotion of host surrounding vessel sprouting (angiogenesis), an effective graft blood supply, so avoiding the ischemia-related serious complications.

Bladder Reconstruction with Human Amniotic Membrane in a Xenograft Rat Model: A Preclinical Study

Background: Human amniotic membranes (HAMs) are assumed to have a number of unique characteristics including durability, hypoallergenic and anti-inflammatory properties. Materials and Methods: Multilayer HAMs from caesarian sections were applied to repair defined bladder defects in male Sprague-Dawley rats. The animals were sacrificed at 7, 21 and 42 days after implantation. Bladder volume capacity after grafting was measured. Histological analyses were performed to asses a number of parameters including HAM degradation, inflammatory reaction, graft rejection and smooth muscle ingrowth. Results: One rat died from sepsis in the treated group. No severe complications or signs of leakage were observed. Bladder capacity did not change over time. The initially increased inflammation in the HAM group diminished significantly over time (p<0.05). No signs of HAM degradation were observed and smooth muscle staining increased over time. Conclusions: HAMs appear to be durable and hypoallergenic grafts. The assumed suitability for the reconstruction of urinary tract justifies further research on detailed immunological process in larger grafts.

Linearized texture of three-dimensional extracellular matrix is mandatory for bladder cancer cell invasion

In the fields of biomaterials and tissue engineering simulating the native microenvironment is of utmost importance. As a major component of the microenvironment, the extracellular matrix (ECM) contributes to tissue homeostasis, whereas modifications of native features are associated with pathological conditions. Furthermore, three-dimensional (3D) geometry is an important feature of synthetic scaffolds favoring cell stemness, maintenance and differentiation. We analyzed the 3D structure, geometrical measurements and anisotropy of the ECM isolated from (i) human bladder mucosa (basal lamina and lamina propria) and muscularis propria; and, (ii) bladder carcinoma (BC). Next, binding and invasion of bladder metastatic cell line was observed on synthetic scaffold recapitulating anisotropy of tumoral ECM, but not on scaffold with disorganized texture typical of non-neoplastic lamina propria. This study provided information regarding the ultrastructure and geometry of healthy human bladder and BC ECMs. Likewise, using synthetic scaffolds we identified linearization of the texture as a mandatory feature for BC cell invasion. Integrating microstructure and geometry with biochemical and mechanical factors could support the development of an innovative synthetic bladder substitute or a tumoral scaffold predictive of chemotherapy outcomes.

Stem Cells in Functional Bladder Engineering

Conditions impairing bladder function in children and adults, such as myelomeningocele, posterior urethral valves, bladder exstrophy or spinal cord injury, often need urinary diversion or augmentation cystoplasty as when untreated they may cause severe bladder dysfunction and kidney failure. Currently, the gold standard therapy of end-stage bladder disease refractory to conservative management is enterocystoplasty, a surgical enlargement of the bladder with intestinal tissue. Despite providing functional improvement, enterocystoplasty is associated with significant long-term complications, such as recurrent urinary tract infections, metabolic abnormalities, stone formation, and malignancies. Therefore, there is a strong clinical need for alternative therapies for these reconstructive procedures, of which stem cell-based tissue engineering (TE) is considered to be the most promising future strategy. This review is focused on the recent progress in bladder stem cell research and therapy and the challenges that remain for the development of a functional bladder wall.

In vivo regeneration of bladder muscular wall using decellularized colon matrix: an experimental study

BACKGROUND

Finding a proper scaffold for augmentation is a serious challenge in bladder tissue engineering. We hereby aimed to determine the histological aspects of a decellularized colon graft for bladder augmentation in healthy rats.

METHODS

Rat colon tissues were decellularized using perfusion-based method. After partial cystectomy, bladders were grafted with a patch of decellularized colon. Bladder specimens were investigated in 12 rats at 1, 3, and 9 months postoperatively for further histological changes and immunohistochemistry analyses were also performed.

RESULTS

One month after implantation, partial seeding of new cells was observed. After 3 months continuity of transitional epithelium of natural bladder on the decellularized grafted colon tissue was confirmed with histological and immunohistochemical examinations. All augmented bladders demonstrated a spherical shape without stone formation, necrosis or graft rejection. The presence of urothelium with similar morphology to the natural urothelium and visible blood vessels were found within 3 months of operation. All immunohistochemical markers (except markers of colonic stem cells) were expressed in biopsies obtained 3 months after surgery demonstrating a progressive vascular and smooth muscle cell infiltration into the graft after implantation.

CONCLUSION

This study suggests that decellularized colon may provide a viable material for bladder augmentation in rats to pave the road for future applications of this natural collagen scaffold.

Tissue-engineered tubular substitutions for urinary diversion in a rabbit model

Clinically, autologous gastrointestinal segments are traditionally used for urinary diversion. However, this procedure often causes many serious complications. Tissue engineering may provide an alternative treatment method in urinary diversion. This research aims to produce tissue-engineered tubular substitutions by using homologous adipose-derived stem cells, smooth muscle cells, and bladder acellular matrix in developing urinary diversion in a rabbit model. Adipose-derived stem cells and smooth muscle cells of rabbit were obtained and cultured in vitro. These cultured adipose-derived stem cells and smooth muscle cells were seeded onto the two sides of the bladder acellular matrix and then incubated for seven days. The cell-seeded matrix was used to build tissue-engineered tubular substitutions, which were then implanted and wrapped into the omentum in vivo for two weeks to promote angiogenesis. In the experimental group, the bladder of 20 rabbits was totally resected, and the above tissue-engineered tubular substitutions were used for urinary diversion. In the control group, bladder acellular matrix tubular substitutions with unseeded cells were implanted into the omentum and were used as urinary diversion on another five rabbits with the same process. The implants were harvested, and histological examination was conducted at 2, 4, 8, and 16 weeks after operation. Intravenous urography assessment was performed at 16 weeks postoperatively. All the rabbits were alive in the experimental group until they were sacrificed. Histological analysis of the construct displayed the presence of multilayer urothelial cells on the luminal side and organized smooth muscle tissue on the other side, and different diameters of neovascularization were clearly identified in the substitutions obtained. No leakage, stricture, or obstructions were noted with intravenous urography assessment. All the animals in the control group died within two weeks, and urine leakage, scar formation, and inflammation were detected through autopsy. This study demonstrates the feasibility of tissue-engineered tubular substitutions constructed using homologous adipose-derived stem cells, smooth muscle cells, and bladder acellular matrix for urinary diversion in a rabbit model.

Future Perspectives in Bladder Tissue Engineering

Substantial clinical need persists for improved autologous tissues to augment or replace the urinary bladder and research has begun to address this using tissue engineering techniques. The implantation of both tissue scaffolds which allow for native bladder tissue ingrowth and autologous bladder grafts created from in vitro cellularization of such scaffolds have been tested clinically; however, successful outcomes in both scenarios have been challenged by insufficient vascularity resulting from large graft sizes, which subsequently limits tissue ingrowth and leads to central graft ischemia. Consequently, recent research has focused on developing better methods to produce scaffolds with increased tissue ingrowth and vascularity. This review provides an update on bladder tissue engineering and outlines the challenges that remain to clinical implementation.

Biomatrices for bladder reconstruction

There is a demand for tissue engineering of the bladder needed by patients who experience a neurogenic bladder or idiopathic detrusor overactivity. To avoid complications from augmentation cystoplasty, the field of tissue engineering seeks optimal scaffolds for bladder reconstruction. Naturally derived biomaterials as well as synthetic and natural polymers have been explored as bladder substitutes. To improve regenerative properties, these biomaterials have been conjugated with functional molecules, combined with nanotechology, or seeded with exogenous cells. Although most studies reported complete and functional bladder regeneration in small-animal models, results from large-animal models and human clinical trials varied. For functional bladder regeneration, procedures for biomaterial fabrication, incorporation of biologically active agents, introduction of nanotechnology, and application of stem-cell technology need to be standardized. Advanced molecular and medical technologies such as next generation sequencing and magnetic resonance imaging can be introduced for mechanistic understanding and non-invasive monitoring of regeneration processes, respectively.

Potential of stem cell treatment in detrusor dysfunction

The current treatments of bladder dysfunctions, such as bladder overactivity and impaired ability to empty, have limitations, and new treatment alternatives are needed. Stem cell transplantation and tissue engineering have shown promising results in preclinical studies. Stem cells were originally thought to act by differentiating into various cell types, thereby replacing damaged cells and restoring functional deficits. Even if such a mechanism cannot be excluded, the current belief is that a main action is exerted by the stem cells secreting bioactive factors that direct other stem cells to the target organ. In addition, stem cells may exert a number of other effects that can improve bladder dysfunction, since they may have antiapoptotic, antifibrotic, and immunomodulatory properties, and can induce neovascularization. Tissue engineering for bladder replacement, which has had varying success in different animal species, has reached the proof-of-concept state in humans, but recent research suggests that the present approaches may not be optimal. Further studies on new approaches, using animal models with translational predictability, seem necessary for further progress.

In vitro evaluation of endothelial progenitor cells from adipose tissue as potential angiogenic cell sources for bladder angiogenesis

Autologous endothelial progenitor cells (EPCs) might be alternative angiogenic cell sources for vascularization of tissue-engineered bladder, while isolation and culture of EPCs from peripheral blood in adult are usually time-consuming and highly inefficient. Recent evidence has shown that EPCs also exist in the adipose tissue. As adipose tissue is plentiful in the human body and can be easily harvested through a minimally invasive method, the aim of this study was to culture and characterize EPCs from adipose tissue (ADEPCs) and investigate their potential for the neovascularization of tissue-engineered bladder. Adipose stromal vascular fraction (SVF) was isolated and used for the culture of ADEPCs and adipose derived stem cells (ADSCs). After SVF was cultured for one week, ADEPCs with typical cobblestone morphology emerged and could be isolated from ADSCs according to their different responses to trypsinization. Rat bladder smooth muscle cells (RBSMCs) were isolated and cultured from rat bladder. RBSMCs exhibited typical spindle-shaped morphology. ADEPCs had higher proliferative potential than ADSCs and RBSMCs. ADEPCs stained positive for CD34, Stro-1, VEGFR-2, eNOS and CD31 but negative for α-SMA, CD14 and CD45. ADSCs stained positive for CD34, Stro-1 and α-SMA but negative for VEGFR-2, eNOS, CD31, CD14 and CD45. RBSMCs stained only positive for α-SMA. ADEPCs could be expanded from a single cell at an early passage to a cell cluster containing more than 10,000 cells. ADEPCs were able to uptake DiI-Ac-LDL, bind UEA-1 and form capillary-like structures in three-dimensional scaffolds (Matrigel and bladder acellular matrix). ADEPCs were also able to enhance the human umbilical vein endothelial cells’ capability of capillary-like tube formation on Matrigel. Additionally, significantly higher levels of mRNA and protein of vascular endothelial growth factor were found in ADEPCs than in RBSMCs. These results suggest the potential use of ADEPCs as angiogenic cell sources for engineering bladder tissue.

Three-dimensional printing of nanomaterial scaffolds for complex tissue regeneration

Three-dimensional (3D) printing has recently expanded in popularity, and become the cutting edge of tissue engineering research. A growing emphasis from clinicians on patient-specific care, coupled with an increasing knowledge of cellular and biomaterial interaction, has led researchers to explore new methods that enable the greatest possible control over the arrangement of cells and bioactive nanomaterials in defined scaffold geometries. In this light, the cutting edge technology of 3D printing also enables researchers to more effectively compose multi-material and cell-laden scaffolds with less effort. In this review, we explore the current state of 3D printing with a focus on printing of nanomaterials and their effect on various complex tissue regeneration applications.

Regenerative rehabilitation: a new future?

Modern rehabilitation medicine is propelled by newfound knowledge aimed at offering solutions for an increasingly aging population afflicted by chronic debilitating conditions. Considered a core component of future health care, the rollout of regenerative medicine underscores a paradigm shift in patient management targeted at restoring physiologic function and restituting normative impact. Nascent regenerative technologies offer unprecedented prospects in achieving repair of degenerated, diseased, or damaged tissues. In this context, principles of regenerative science are increasingly integrated in rehabilitation practices as illustrated in the present Supplement. Encompassing a growing multidisciplinary domain, the emergent era of "regenerative rehabilitation" brings radical innovations at the forefront of healthcare blueprints.

Induction of human embryonic and induced pluripotent stem cells into urothelium

In vitro generation of human urothelium from stem cells would be a major advancement in the regenerative medicine field, providing alternate nonurologic and/or nonautologous tissue sources for bladder grafts. Such a model would also help decipher the mechanisms of urothelial differentiation and would facilitate investigation of deviated differentiation of normal progenitors into urothelial cancer stem cells, perhaps elucidating areas of intervention for improved treatments. Thus far, in vitro derivation of urothelium from human embryonic stem cells (hESCs) or human induced pluripotent stem (hiPS) cells has not been reported. The goal of this work was to develop an efficient in vitro protocol for the induction of hESCs into urothelium through an intermediary definitive endoderm step and free of matrices and cell contact. During directed differentiation in a urothelial-specific medium ("Uromedium"), hESCs produced up to 60% urothelium, as determined by uroplakin expression; subsequent propagation selected for 90% urothelium. Alteration of the epithelial and mesenchymal cell signaling contribution through noncell contact coculture or conditioned media did not enhance the production of urothelium. Temporospatial evaluation of transcription factors known to be involved in urothelial specification showed association of IRF1, GET1, and GATA4 with uroplakin expression. Additional hESC and hiPS cell lines could also be induced into urothelium using this in vitro system. These results demonstrate that derivation and propagation of urothelium from hESCs and hiPS cells can be efficiently accomplished in vitro in the absence of matrices, cell contact, or adult cell signaling and that the induction process appears to mimic normal differentiation.

Liver support strategies: cutting-edge technologies

The treatment of end-stage liver disease and acute liver failure remains a clinically relevant issue. Although orthotopic liver transplantation is a well-established procedure, whole-organ transplantation is invasive and increasingly limited by the unavailability of suitable donor organs. Artificial and bioartificial liver support systems have been developed to provide an alternative to whole organ transplantation, but despite three decades of scientific efforts, the results are still not convincing with respect to clinical outcome. In this Review, conceptual limitations of clinically available liver support therapy systems are discussed. Furthermore, alternative concepts, such as hepatocyte transplantation, and cutting-edge developments in the field of liver support strategies, including the repopulation of decellularized organs and the biofabrication of entirely new organs by printing techniques or induced organogenesis are analysed with respect to clinical relevance. Whereas hepatocyte transplantation shows promising clinical results, at least for the temporary treatment of inborn metabolic diseases, so far data regarding implantation of engineered hepatic tissue have only emerged from preclinical experiments. However, the evolving techniques presented here raise hope for bioengineered liver support therapies in the future.

Alternatives to conventional enterocystoplasty in children: a critical review of urodynamic outcomes

Alternatives to conventional enterocystoplasty have been developed in order to avoid the most common complications derived from contact of the urine with intestinal mucosa. In this article critically we review the literature on the topics: ureterocystoplasty, detrusorectomy, detrusorotomy, seromuscular gastroenterocystoplasty, use of off the shelf biomaterials, and bladder augmentation by bioengineering. Recognizing the difficulty of deciding when a child with a history of posterior urethral valves requires and augmentation and that the development of a large megaureter in cases of neurogenic dysfunction represents a failure of initial treatment, we conclude that ureterocystoplasty can be useful in selected cases when a large dilated ureter is available. Seromuscular colocystoplasty lined with urothelium (SCLU) has been urodynamically effective in several series when the outlet resistance is high and no additional intravesical procedures are necessary. Seromuscular gastrocystoplasty lined with urothelium seems to offer no distinct advantages and involves a much more involved operation. The use of seromuscular segments without urothelial preservation, with or without the use of an intravesical balloon has been reported as successful in two centers but strict urodynamic evidence of its effectiveness is lacking. The published evidence argues strongly against the use of detrusorectomy or detrusorotomy alone because of the lack of significant urodynamic benefits. Two recent reports discourage the use of small intestinal submucosa patches because of a high failure rate. Finally, research into the development of a bioengineered bladder constructed with cell harvested from the same patient continues but is fraught with technical and conceptual problems. In conclusion of the methods reviewed, only ureterocystoplasty and SCLU have been proven urodynamically effective and reproducible.