De novo reconstitution of a functional mammalian urinary bladder by tissue engineering

Drug eluting protein and polysaccharides-based biofunctionalized fabric textiles- pioneering a new frontier in tissue engineering: An extensive review

In the ever-evolving landscape of tissue engineering, medicated biotextiles have emerged as a game-changer. These remarkable textiles have garnered significant attention for their ability to craft tissue scaffolds that closely mimic the properties of natural tissues. This comprehensive review delves into the realm of medicated protein and polysaccharide-based biotextiles, exploring a diverse array of fabric materials. We unravel the intricate web of fabrication methods, ranging from weft/warp knitting to plain/stain weaving and braiding, each lending its unique touch to the world of biotextiles creation. Fibre production techniques, such as melt spinning, wet/gel spinning, and multicomponent spinning, are demystified to shed light on the magic behind these ground-breaking textiles. The biotextiles thus crafted exhibit exceptional physical and chemical properties that hold immense promise in the field of tissue engineering (TE). Our review underscores the myriad applications of drug-eluting protein and polysaccharide-based textiles, including TE, tissue repair, regeneration, and wound healing. Additionally, we delve into commercially available products that harness the potential of medicated biotextiles, paving the way for a brighter future in healthcare and regenerative medicine. Step into the world of innovation with medicated biotextiles-where science meets the art of healing.

Multipotent bone marrow cell-seeded polymeric composites drive long-term, definitive urinary bladder tissue regeneration

To date, there are no efficacious translational solutions for end-stage urinary bladder dysfunction. Current surgical strategies, including urinary diversion and bladder augmentation enterocystoplasty (BAE), utilize autologous intestinal segments (e.g. ileum) to increase bladder capacity to protect renal function. Considered the standard of care, BAE is fraught with numerous short- and long-term clinical complications. Previous clinical trials employing tissue engineering approaches for bladder tissue regeneration have also been unable to translate bench-top findings into clinical practice. Major obstacles still persist that need to be overcome in order to advance tissue-engineered products into the clinical arena. These include scaffold/bladder incongruencies, the acquisition and utility of appropriate cells for anatomic and physiologic tissue recapitulation, and the choice of an appropriate animal model for testing. In this study, we demonstrate that the elastomeric, bladder biomechanocompatible poly(1,8-octamethylene-citrate-co-octanol) (PRS; synthetic) scaffold coseeded with autologous bone marrow-derived mesenchymal stem cells and CD34+ hematopoietic stem/progenitor cells support robust long-term, functional bladder tissue regeneration within the context of a clinically relevant baboon bladder augmentation model simulating bladder trauma. Partially cystectomized baboons were independently augmented with either autologous ileum or stem-cell-seeded small-intestinal submucosa (SIS; a commercially available biological scaffold) or PRS grafts. Stem-cell synergism promoted functional trilayer bladder tissue regeneration, including whole-graft neurovascularization, in both cell-seeded grafts. However, PRS-augmented animals demonstrated fewer clinical complications and more advantageous tissue characterization metrics compared to ileum and SIS-augmented animals. Two-year study data demonstrate that PRS/stem-cell-seeded grafts drive bladder tissue regeneration and are a suitable alternative to BAE.

Autologous Endothelial Progenitor Cells and Bioactive Factors Improve Bladder Regeneration

Insufficient vascularization is still a challenge that impedes bladder tissue engineering and results in unsatisfied smooth muscle regeneration. Since bladder regeneration is a complex articulated process, the aim of this study is to investigate whether combining multiple pathways by exploiting a combination of biomaterials, cells, and bioactive factors, contributes to the improvements of smooth muscle regeneration and vascularization in tissue-engineered bladder. Autologous endothelial progenitor cells (EPCs) and bladder smooth muscle cells (BSMCs) are cultured and incorporated into our previously prepared porcine bladder acellular matrix (BAM) for bladder augmentation in rabbits. Simultaneously, exogenous vascular endothelial growth factor (VEGF) and platelet-derived growth factor BB (PDGF-BB) mixed with Matrigel were injected around the implanted cells-BAM complex. In the results, compared with control rabbits received bladder augmentation with porcine BAM seeded with BSMCs, the experimental animals showed significantly improved smooth muscle regeneration and vascularization, along with more excellent functional recovery of tissue-engineered bladder, due to the additional combination of autologous EPCs and bioactive factors, including VEGF and PDGF-BB. Furthermore, cell tracking suggested that the seeded EPCs could be directly involved in neovascularization. Therefore, it may be an effective method to combine multiple pathways for tissue-engineering urinary bladder.

Preliminary In Vitro Assessment of Decellularized Porcine Descending Aorta for Clinical Purposes

Conduit substitutes are increasingly in demand for cardiovascular and urological applications. In cases of bladder cancer, radical cystectomy is the preferred technique: after removing the bladder, a urinary diversion has to be created using autologous bowel, but several complications are associated with intestinal resection. Thus, alternative urinary substitutes are required to avoid autologous intestinal use, preventing complications and facilitating surgical procedures. In the present paper, we are proposing the exploitation of the decellularized porcine descending aorta as a novel and original conduit substitute. After being decellularized with the use of two alternative detergents (Tergitol and Ecosurf) and sterilized, the porcine descending aorta has been investigated to assess its permeability to detergents through methylene blue dye penetration analysis and to study its composition and structure by means of histomorphometric analyses, including DNA quantification, histology, two-photon microscopy, and hydroxyproline quantification. Biomechanical tests and cytocompatibility assays with human mesenchymal stem cells have been also performed. The results obtained demonstrated that the decellularized porcine descending aorta preserves its major features to be further evaluated as a candidate material for urological applications, even though further studies have to be carried out to demonstrate its suitability for the specific application, by performing in vivo tests in the animal model.

Tissue Engineering Neovagina for Vaginoplasty in Mayer-Rokitansky-Küster-Hauser Syndrome and Gender Dysphoria Patients: A Systematic Review

Background: Vaginoplasty is a surgical solution to multiple disorders, including Mayer-Rokitansky-Küster-Hauser syndrome and male-to-female gender dysphoria. Using nonvaginal tissues for these reconstructions is associated with many complications, and autologous vaginal tissue may not be sufficient. The potential of tissue engineering for vaginoplasty was studied through a systematic bibliography search. Cell types, biomaterials, and signaling factors were analyzed by investigating advantages, disadvantages, complications, and research quantity. Search Methods: A systematic search was performed in Medline, EMBASE, Web of Science, and Scopus until March 8, 2022. Term combinations for tissue engineering, guided tissue regeneration, regenerative medicine, and tissue scaffold were applied, together with vaginoplasty and neovagina. The snowball method was performed on references and a Google Scholar search on the first 200 hits. Original research articles on human and/or animal subjects that met the inclusion (reconstruction of vaginal tissue and tissue engineering method) and no exclusion criteria (not available as full text; written in foreign language; nonoriginal study article; genital surgery other than neovaginal reconstruction; and vaginal reconstruction with autologous or allogenic tissue without tissue engineering or scaffold) were assessed. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist, the Newcastle-Ottawa Scale, and the Gold Standard Publication Checklist were used to evaluate article quality and bias. Outcomes: A total of 31 out of 1569 articles were included. Data extraction was based on cell origin and type, biomaterial nature and composition, host species, number of hosts and controls, neovaginal size, replacement fraction, and signaling factors. An overview of used tissue engineering methods for neovaginal formation was created, showing high variance of cell types, biomaterials, and signaling factors and the same topics were rarely covered multiple times. Autologous vaginal cells and extracellular matrix-based biomaterials showed preferential properties, and stem cells carry potential. However, quality confirmation of orthotopic cell-seeded acellular vaginal matrix by clinical trials is needed as well as exploration of signaling factors for vaginoplasty. Impact statement General article quality was weak to sufficient due to unreported cofounders and incomplete animal study descriptions. Article quality and heterogenicity made identification of optimal cell types, biomaterials, or signaling factors unreliable. However, trends showed that autologous cells prevent complications and compatibility issues such as healthy cell destruction, whereas stem cells prevent cross talk (interference of signaling pathways by signals from other cell types) and rejection (but need confirmation testing beyond animal trials). Natural (orthotopic) extracellular matrix biomaterials have great preferential properties that encourage future research, and signaling factors for vascularization are important for tissue engineering of full-sized neovagina.

Remodelling landscape of tissue-engineered bladder with porcine small intestine submucosa using single-cell RNA sequencing

OBJECTIVE

Bioscaffolds are widely used for tissue engineering, but failed and inconsistent preclinical results have hampered the clinical use of bioscaffolds for tissue engineering. We aimed to construct a cellular remodelling landscape and to identify the key cell subpopulations and important genes driving bladder remodelling.

METHODS

Twenty-four reconstructed mouse bladders using porcine small intestinal submucosa (PSIS) were harvested at 1, 3, and 6 weeks to perform single-cell RNA sequencing. Cell types were identified and their differentially expressed genes (DEGs) at each stage were used for functional analysis. Immunofluorescence was used to validate the specific cell type.

RESULTS

The remodelling landscape included 13 cell types. Among them, fibroblasts, smooth muscle cells (SMCs), endothelial cells, and macrophages had the most communications with other cells. In the process of regeneration, DEGs of fibroblasts at 1, 3, and 6 weeks were mainly involved in wound healing, extracellular matrix organization, and regulation of development growth, respectively. Among these cells, Saa3⁺ fibroblasts might mediate tissue remodelling. The DEGs of SMCs at 1, 3, and 6 weeks were mainly involved in the inflammatory response, muscle cell proliferation, and mesenchyme development, respectively. Moreover, we found that Notch3⁺ SMCs potentially modulated contractility. From 1 to 6 weeks, synchronous development of endothelial cells was observed by trajectory analysis.

CONCLUSIONS

A remoulding landscape was successfully constructed and findings might help surficial modifications of PSIS and find a better alternative. However, more in vivo and in vitro studies are needed to further validate these results.

Application of regenerative medicine and 3d bioprinting in urology

In the last two decades, a new purpose has collected great efforts from scientists in all branches of medicine. It is about the possibility to make the body regenerate ill tissues and organs by itself with de right artificial stimuli or the construction of new functional organs to replace the damaged ones. This process comprises various interdisciplinary approaches to healthcare, such as tissue engineering, molecular medicine, biotechnology, and three-dimensional printing. Urologists have been remarkably active in this field of medicine called Regenerative Medicine. The searching of the different requirements like suitable and compatible biomaterials, versatile cells, adequate techniques to construct tissues, available biomolecules, and the knowledge of all these minimizing risks, are some of the aims and the approximations until now. Despite many obstacles, in vitro and in vivo studies are already showing encouraging options. We will review the advances related to the bladder, urethra, ureter, and kidneys. Difficulties such as ethical issues, time investment and high costs, have been some of the drawbacks encountered. Further studies are still required for its clinical application in daily life.

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.

Development of a porcine acellular bladder matrix for tissue-engineered bladder reconstruction

PURPOSE

Enterocystoplasty is adopted for patients requiring bladder augmentation, but significant long-term complications highlight need for alternatives. We established a protocol for creating a natural-derived bladder extracellular matrix (BEM) for developing tissue-engineered bladder, and investigated its structural and functional characteristics.

METHODS

Porcine bladders were de-cellularised with a dynamic detergent-enzymatic treatment using peristaltic infusion. Samples and fresh controls were evaluated using histological staining, ultrastructure (electron microscopy), collagen, glycosaminoglycans and DNA quantification and biomechanical testing. Compliance and angiogenic properties (Chicken chorioallantoic membrane [CAM] assay) were evaluated. T test compared stiffness and glycosaminoglycans, collagen and DNA quantity. p value of < 0.05 was regarded as significant.

RESULTS

Histological evaluation demonstrated absence of cells with preservation of tissue matrix architecture (collagen and elastin). DNA was 0.01 μg/mg, significantly reduced compared to fresh tissue 0.13 μg/mg (p < 0.01). BEM had increased tensile strength (0.259 ± 0.022 vs 0.116 ± 0.006, respectively, p < 0.0001) and stiffness (0.00075 ± 0.00016 vs 0.00726 ± 0.00216, p = 0.011). CAM assay showed significantly increased number of convergent allantoic vessels after 6 days compared to day 1 (p < 0.01). Urodynamic studies showed that BEM maintains or increases capacity and compliance.

CONCLUSION

Dynamic detergent-enzymatic treatment produces a BEM which retains structural characteristics, increases strength and stiffness and is more compliant than native tissue. Furthermore, BEM shows angiogenic potential. These data suggest the use of BEM for development of tissue-engineered bladder for patients requiring bladder augmentation.

Correlating Rheological Properties of a Gellan Gum-Based Bioink: A Study of the Impact of Cell Density

Here, for the production of a bioink-based gellan gum, an amino derivative of this polysaccharide was mixed with a mono-functionalized aldehyde polyethyleneglycol in order to improve viscoelastic macroscopic properties and the potential processability by means of bioprinting techniques as confirmed by the printing tests. The dynamic Schiff base linkage between amino and aldehyde groups temporally modulates the rheological properties and allows a reduction of the applied pressure during extrusion followed by the recovery of gellan gum strength. Rheological properties, often related to printing resolution, were extensively investigated confirming pseudoplastic behavior and thermotropic and ionotropic responses. The success of bioprinting is related to different parameters. Among them, cell density must be carefully selected, and in order to quantify their role on printability, murine preostoblastic cells (MC3T3-E1) and human colon tumor cells (HCT-116) were chosen as cell line models. Here, we investigated the effect of their density on the bioink’s rheological properties, showing a more significant difference between cell densities for MC3T3-E1 compared to HCT-116. The results suggest the necessity of not neglecting this aspect and carrying out preliminary studies to choose the best cell densities to have the maximum viability and consequently to set the printing parameters.

Neural Differentiation of Human-Induced Pluripotent Stem Cells (hiPSc) on Surface-Modified Nanofibrous Scaffolds Coated with Platelet-Rich Plasma

The field of tissue engineering exploits living cells in a variety of ways to restore, maintain, or enhance tissues and organs. Between stem cells, human induced pluripotent stem cells (hiPSCs), are very important due to their wide abilities. Growth factors can support proliferation, differentiation, and migration of hiPSCs. Platelet-rich plasma (PRP) could be used as the source of growth factors for hiPSCs. In the present study, proliferation and neural differentiation of hiPSCs on surface-modified nanofibrous Poly-L-lactic acid (PLLA) coated with platelet-rich plasma was investigated. The results of in vitro analysis showed that on the surface, which was modified nanofibrous scaffolds coated with platelet-rich plasma, significantly enhanced hiPSCs proliferation and neural differentiation were observed. Whereas the MTT ([3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide]) results showed biocompatibility of surface-modified nanofibrous scaffolds coated with platelet-rich plasma and the usage of these modified nanoscaffolds in neural tissue engineering in vivo is promising for the future.

Porcine Small Intestinal Submucosa (SIS) as a Suitable Scaffold for the Creation of a Tissue-Engineered Urinary Conduit: Decellularization, Biomechanical and Biocompatibility Characterization Using New Approaches

Bladder cancer (BC) is among the most common malignancies in the world and a relevant cause of cancer mortality. BC is one of the most frequent causes for bladder removal through radical cystectomy, the gold-standard treatment for localized muscle-invasive and some cases of high-risk, non-muscle-invasive bladder cancer. In order to restore urinary functionality, an autologous intestinal segment has to be used to create a urinary diversion. However, several complications are associated with bowel-tract removal, affecting patients' quality of life. The present study project aims to develop a bio-engineered material to simplify this surgical procedure, avoiding related surgical complications and improving patients' quality of life. The main novelty of such a therapeutic approach is the decellularization of a porcine small intestinal submucosa (SIS) conduit to replace the autologous intestinal segment currently used as urinary diversion after radical cystectomy, while avoiding an immune rejection. Here, we performed a preliminary evaluation of this acellular product by developing a novel decellularization process based on an environmentally friendly, mild detergent, i.e., Tergitol, to replace the recently declared toxic Triton X-100. Treatment efficacy was evaluated through histology, DNA, hydroxyproline and elastin quantification, mechanical and insufflation tests, two-photon microscopy, FTIR analysis, and cytocompatibility tests. The optimized decellularization protocol is effective in removing cells, including DNA content, from the porcine SIS, while preserving the integrity of the extracellular matrix despite an increase in stiffness. An effective sterilization protocol was found, and cytocompatibility of treated SIS was demonstrated from day 1 to day 7, during which human fibroblasts were able to increase in number and strongly organize along tissue fibres. Taken together, this in vitro study suggests that SIS is a suitable candidate for use in urinary diversions in place of autologous intestinal segments, considering the optimal results of decellularization and cell proliferation. Further efforts should be undertaken in order to improve SIS conduit patency and impermeability to realize a future viable substitute.

Computer vision-aided bioprinting for bone research

Bioprinting is an emerging additive manufacturing technology that has enormous potential in bone implantation and repair. The insufficient accuracy of the shape of bioprinted parts is a primary clinical barrier that prevents widespread utilization of bioprinting, especially for bone design with high-resolution requirements. During the last five years, the use of computer vision for process control has been widely practiced in the manufacturing field. Computer vision can improve the performance of bioprinting for bone research with respect to various aspects, including accuracy, resolution, and cell survival rate. Hence, computer vision plays a substantial role in addressing the current defect problem in bioprinting for bone research. In this review, recent advances in the application of computer vision in bioprinting for bone research are summarized and categorized into three groups based on different defect types: bone scaffold process control, deep learning, and cell viability models. The collection of printing parameters, data processing, and feedback of bioprinting information, which ultimately improves printing capabilities, are further discussed. We envision that computer vision may offer opportunities to accelerate bioprinting development and provide a new perception for bone research.

Recent Advances in 3D Printing of Biomedical Sensing Devices

Additive manufacturing, also called 3D printing, is a rapidly evolving technique that allows for the fabrication of functional materials with complex architectures, controlled microstructures, and material combinations. This capability has influenced the field of biomedical sensing devices by enabling the trends of device miniaturization, customization, and elasticity (i.e., having mechanical properties that match with the biological tissue). In this paper, the current state-of-the-art knowledge of biomedical sensors with the unique and unusual properties enabled by 3D printing is reviewed. The review encompasses clinically important areas involving the quantification of biomarkers (neurotransmitters, metabolites, and proteins), soft and implantable sensors, microfluidic biosensors, and wearable haptic sensors. In addition, the rapid sensing of pathogens and pathogen biomarkers enabled by 3D printing, an area of significant interest considering the recent worldwide pandemic caused by the novel coronavirus, is also discussed. It is also described how 3D printing enables critical sensor advantages including lower limit-of-detection, sensitivity, greater sensing range, and the ability for point-of-care diagnostics. Further, manufacturing itself benefits from 3D printing via rapid prototyping, improved resolution, and lower cost. This review provides researchers in academia and industry a comprehensive summary of the novel possibilities opened by the progress in 3D printing technology for a variety of biomedical applications.

Biomaterials assisted reconstructive urology: The pursuit of an implantable bioengineered neo-urinary bladder

Urinary bladder is a dynamic organ performing complex physiological activities. Together with ureters and urethra, it forms the lower urinary tract that facilitates urine collection, low-pressure storage, and volitional voiding. However, pathological disorders are often liable to cause irreversible damage and compromise the normal functionality of the bladder, necessitating surgical intervention for a reconstructive procedure. Non-urinary autologous grafts, primarily derived from gastrointestinal tract, have long been the gold standard in clinics to augment or to replace the diseased bladder tissue. Unfortunately, such treatment strategy is commonly associated with several clinical complications. In absence of an optimal autologous therapy, a biomaterial based bioengineered platform is an attractive prospect revolutionizing the modern urology. Predictably, extensive investigative research has been carried out in pursuit of better urological biomaterials, that overcome the limitations of conventional gastrointestinal graft. Against the above backdrop, this review aims to provide a comprehensive and one-stop update on different biomaterial-based strategies that have been proposed and explored over the past 60 years to restore the dynamic function of the otherwise dysfunctional bladder tissue. Broadly, two unique perspectives of bladder tissue engineering and total alloplastic bladder replacement are critically discussed in terms of their status and progress. While the former is pivoted on scaffold mediated regenerative medicine; in contrast, the latter is directed towards the development of a biostable bladder prosthesis. Together, these routes share a common aspiration of designing and creating a functional equivalent of the bladder wall, albeit, using fundamentally different aspects of biocompatibility and clinical needs. Therefore, an attempt has been made to systematically analyze and summarize the evolution of various classes as well as generations of polymeric biomaterials in urology. Considerable emphasis has been laid on explaining the bioengineering methodologies, pre-clinical and clinical outcomes. Some of the unaddressed challenges, including vascularization, innervation, hollow 3D prototype fabrication and urinary encrustation, have been highlighted that currently delay the successful commercial translation. More importantly, the rapidly evolving and expanding concepts of bioelectronic medicine are discussed to inspire future research efforts towards the further advancement of the field. At the closure, crucial insights are provided to forge the biomaterial assisted reconstruction as a long-term therapeutic strategy in urological practice for patients' care.

Regenerative Engineering: Current Applications and Future Perspectives

Many pathologies, congenital defects, and traumatic injuries are untreatable by conventional pharmacologic or surgical interventions. Regenerative engineering represents an ever-growing interdisciplinary field aimed at creating biological replacements for injured tissues and dysfunctional organs. The need for bioengineered replacement parts is ubiquitous among all surgical disciplines. However, to date, clinical translation has been limited to thin, small, and/or acellular structures. Development of thicker tissues continues to be limited by vascularization and other impediments. Nevertheless, currently available materials, methods, and technologies serve as robust platforms for more complex tissue fabrication in the future. This review article highlights the current methodologies, clinical achievements, tenacious barriers, and future perspectives of regenerative engineering.

Mechanical properties of whole-body soft human tissues: a review

The mechanical properties of soft tissues play a key role in studying human injuries and their mitigation strategies. While such properties are indispensable for computational modelling of biological systems, they serve as important references in loading and failure experiments, and also for the development of tissue simulants. To date, experimental studies have measured the mechanical properties of peripheral tissues (e.g. skin)in-vivoand limited internal tissuesex-vivoin cadavers (e.g. brain and the heart). The lack of knowledge on a majority of human tissues inhibit their study for applications ranging from surgical planning, ballistic testing, implantable medical device development, and the assessment of traumatic injuries. The purpose of this work is to overcome such challenges through an extensive review of the literature reporting the mechanical properties of whole-body soft tissues from head to toe. Specifically, the available linear mechanical properties of all human tissues were compiled. Non-linear biomechanical models were also introduced, and the soft human tissues characterized using such models were summarized. The literature gaps identified from this work will help future biomechanical studies on soft human tissue characterization and the development of accurate medical models for the study and mitigation of injuries.

Bladder Substitution: The Role of Tissue Engineering and Biomaterials

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

A Review of Biomaterials and Scaffold Fabrication for Organ-on-a-Chip (OOAC) Systems

Drug and chemical development along with safety tests rely on the use of numerous clinical models. This is a lengthy process where animal testing is used as a standard for pre-clinical trials. However, these models often fail to represent human physiopathology. This may lead to poor correlation with results from later human clinical trials. Organ-on-a-Chip (OOAC) systems are engineered microfluidic systems, which recapitulate the physiochemical environment of a specific organ by emulating the perfusion and shear stress cellular tissue undergoes in vivo and could replace current animal models. The success of culturing cells and cell-derived tissues within these systems is dependent on the scaffold chosen; hence, scaffolds are critical for the success of OOACs in research. A literature review was conducted looking at current OOAC systems to assess the advantages and disadvantages of different materials and manufacturing techniques used for scaffold production; and the alternatives that could be tailored from the macro tissue engineering research field.

Neovascularization of engineered tissues for clinical translation: Where we are, where we should be?

One of the key challenges in engineering three-dimensional tissue constructs is the development of a mature microvascular network capable of supplying sufficient oxygen and nutrients to the tissue. Recent angiogenic therapeutic strategies have focused on vascularization of the constructed tissue, and its integration in vitro; these strategies typically combine regenerative cells, growth factors (GFs) with custom-designed biomaterials. However, the field needs to progress in the clinical translation of tissue engineering strategies. The article first presents a detailed description of the steps in neovascularization and the roles of extracellular matrix elements such as GFs in angiogenesis. It then delves into decellularization, cell, and GF-based strategies employed thus far for therapeutic angiogenesis, with a particularly detailed examination of different methods by which GFs are delivered in biomaterial scaffolds. Finally, interdisciplinary approaches involving advancement in biomaterials science and current state of technological development in fabrication techniques are critically evaluated, and a list of remaining challenges is presented that need to be solved for successful translation to the clinics.

Three dimensional printed nanostructure biomaterials for bone tissue engineering

The suffering from organ dysfunction due to damaged or diseased tissue/bone has been globally on the rise. Current treatment strategies for non-union bone defects include: the use of autografts, allografts, synthetic grafts and free vascularized fibular grafts. Bone tissue engineering has emerged as an alternative for fracture repair to satisfy the current unmet need of bone grafts and to alleviate the problems associated with autografts and allografts. The technology offers the possibility to induce new functional bone regeneration using synergistic combination of functional biomaterials (scaffolds), cells, and growth factors. Bone scaffolds are typically made of porous biodegradable materials that provide the mechanical support during repair and regeneration of damaged or diseased bone. Significant progress has been made towards scaffold materials for structural support, desired osteogenesis and angiogenesis abilities. Thanks for innovative scaffolds fabrication technologies, bioresorbable scaffolds with controlled porosity and tailored properties are possible today. Despite the presence of different bone scaffold fabrication methods, pore size, shape and interconnectivity have not yet been fully controlled in most of the methods. Moreover, scaffolds with tailored porosity for specific defects are still difficult to manufacture. Nevertheless, such scaffolds can be designed and fabricated using three dimensional (3D) printing approaches. 3D printing technology, as an advanced tissue scaffold fabrication method, offers the opportunity to produce complex geometries with distinct advantages. The technology has been used for the production of various types of bodily constructs such as blood vessels, vascular networks, bones, cartilages, exoskeletons, eyeglasses, cell cultures, tissues, organs and novel drug delivery devices. This review focuses on 3D printed scaffolds and their application in bone repair and regeneration. In addition, different classes of biomaterials commonly employed for the fabrication of 3D nano scaffolds for bone tissue engineering application so far are briefly discussed.

A dual nozzle 3D printing system for super soft composite hydrogels

Due to their inability to sustain their own weight, 3D printing materials as soft as human tissues is challenging. Hereby we describe the development of an extrusion additive manufacturing (AM) machine able to 3D print super soft hydrogels with micro-scale precision. By designing and integrating new subsystems into a conventional extrusion-based 3D printer, we obtained hardware that encompasses a range of new capabilities. In particular, we integrated a heated dual nozzle extrusion system and a cooling platform in the new system. In addition, we altered the electronics and software of the 3D printer to ensure fully automatized procedures are delivered by the 3D printing device, and super-soft tissue mimicking parts are produced. With regards to the electronics, we added new devices to control the temperature of the extrusion system. As for the software, the firmware of the conventional 3D printer was changed and modified to allow for the flow rate control of the ink, thus eliminating overflows in sections of the printing path where the direction/speed changes sharply.

Combating COVID-19 with tissue engineering: a review

The ongoing COVID-19 pandemic triggered by SARS-CoV-2 emerged from Wuhan, China, firstly in December 2019, as well spread to almost all around the world rapidly. The main reason why this disease spreads so many people in a short time is that the virus could be transmitted from an infected person to another by infected droplets. The new emergence of diseases usually may affect multiple organs; moreover, this disease is such an example. Numerous reported studies focus on acute or chronic organ damage caused by the virus. At this point, tissue engineering (TE) strategies can be used to treat the damages with its interdisciplinary approaches. Tissue engineers could design drug delivery systems, scaffolds, and especially biomaterials for the damaged tissue and organs. In this review, brief information about SARS-CoV-2, COVID-19, and epidemiology of the disease will be given at first. After that, the symptoms, the tissue damages in specific organs, and cytokine effect caused by COVID-19 will be described in detail. Finally, it will be attempted to summarize and suggest the appropriate treatments with suitable biomaterials for the damages via TE approaches. The aim of this review is to serve as a summary of currently available tissue damage treatments after COVID-19.

Bilayer Scaffolds for Interface Tissue Engineering and Regenerative Medicine: A Systematic Reviews

PURPOSE

This systematic review focus on the application of bilayer scaffolds as an engaging structure for the engineering of multilayered tissues, including vascular and osteochondral tissues, skin, nerve, and urinary bladder. This article provides a concise literature review of different types of bilayer scaffolds to understand their efficacy in targeted tissue engineering.

METHODS

To this aim, electronic search in the English language was performed in PMC, NBCI, and PubMed from April 2008 to December 2019 based on the PRISMA guidelines. Animal studies, including the "bilayer scaffold" and at least one of the following items were examined: osteochondral tissue, bone, skin, neural tissue, urinary bladder, vascular system. The articles which didn't include "tissue engineering" and just in vitro studies were excluded.

RESULTS

Totally, 600 articles were evaluated; related articles were 145, and 35 full-text English articles met all the criteria. Fifteen articles in soft tissue engineering and twenty items in hard tissue engineering were the results of this exploration. Based on selected papers, it was revealed that the bilayer scaffolds were used in the regeneration of the multilayered tissues. The highest multilayered tissue regeneration has been achieved when bilayer scaffolds were used with mesenchymal stem cells and differentiation medium before implanting. Among the studies being reported in this review, bone marrow mesenchymal stem cells are the most studied mesenchymal stem cells. Among different kinds of multilayer tissue, the bilayer scaffold has been most used in osteochondral tissue engineering in which collagen and PLGA have been the most frequently used biomaterials. After osteochondral tissue engineering, bilayer scaffolds were widely used in skin tissue engineering.

CONCLUSION

The current review aimed to manifest the researcher and surgeons to use a more sophisticated bilayer scaffold in combinations of appropriate stem cells, and different can improve multilayer tissue regeneration. This systematic review can pave a way to design a suitable bilayer scaffold for a specific target tissue and conjunction with proper stem cells.

Electrospinning: Application and Prospects for Urologic Tissue Engineering

Functional disorders and injuries of urinary bladder, urethra, and ureter may necessitate the application of urologic reconstructive surgeries to recover normal urine passage, prevent progressive damages of these organs and upstream structures, and improve the quality of life of patients. Reconstructive surgeries are generally very invasive procedures that utilize autologous tissues. In addition to imperfect functional outcomes, these procedures are associated with significant complications owing to long-term contact of urine with unspecific tissues, donor site morbidity, and lack of sufficient tissue for vast reconstructions. Thanks to the extensive advancements in tissue engineering strategies, reconstruction of the diseased urologic organs through tissue engineering have provided promising vistas during the last two decades. Several biomaterials and fabrication methods have been utilized for reconstruction of the urinary tract in animal models and human subjects; however, limited success has been reported, which inspires the application of new methods and biomaterials. Electrospinning is the primary method for the production of nanofibers from a broad array of natural and synthetic biomaterials. The biomimetic structure of electrospun scaffolds provides an ECM-like matrix that can modulate cells' function. In addition, electrospinning is a versatile technique for the incorporation of drugs, biomolecules, and living cells into the constructed scaffolds. This method can also be integrated with other fabrication procedures to achieve hybrid smart constructs with improved performance. Herein, we reviewed the application and outcomes of electrospun scaffolds in tissue engineering of bladder, urethra, and ureter. First, we presented the current status of tissue engineering in each organ, then reviewed electrospun scaffolds from the simplest to the most intricate designs, and summarized the outcomes of preclinical (animal) studies in this area.

Biofabrication of cell-laden allografts of goat urinary bladder scaffold for organ reconstruction/regeneration

INTRODUCTION

Bladder dysfunction has been considered as one of the most critical health conditions with no proper treatment. Current therapeutic approaches including enterocystoplasty have several limitations. Hence, biofabrication of cell-laden biological allografts using decellularized Goat urinary bladder scaffolds for organ reconstruction/regeneration was major objective of this study.

MATERIALS AND METHODS

An efficient method for decellularization of Goat urinary bladder (N = 3) was developed by perfusion of gradient change of detergents through ureter. The retention of organ architecture, extracellular matrix composition, mechanical properties and removal of cellular components was characterized using histological, cellular and molecular analysis. Further, mesenchymal stem cells (MSCs) from human umbilical cord blood (UCB) were used for preparing biological construct of decellularized urinary bladder (DUB) scaffolds to augment the urinary bladder reconstruction/regeneration.

RESULTS

The decellularization method adopted in this study generated completely DUB scaffolds within 10 h at 100 mm Hg pressure and constant flow rate of 1 mL/min. The DUB scaffold retains organ architecture, ECM composition, and mechanical strength. No significant amount of residual nucleic acid was observed post-decellularization. Furthermore, MSCs derived from human UCB engrafted and proliferated well on DUB scaffolds in highly aligned manner under xeno-free condition.

CONCLUSION

Biofabricated humanized urinary bladder constructs provides xeno-free allografts for future application in augmenting urinary bladder reconstruction/regeneration with further development.

A tissue-engineered uterus supports live births in rabbits

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

Pre-innervated tissue-engineered muscle promotes a pro-regenerative microenvironment following volumetric muscle loss

Volumetric muscle loss (VML) is the traumatic or surgical loss of skeletal muscle beyond the inherent regenerative capacity of the body, generally leading to severe functional deficit. Formation of appropriate somato-motor innervations remains one of the biggest challenges for both autologous grafts as well as tissue-engineered muscle constructs. We aim to address this challenge by developing pre-innervated tissue-engineered muscle comprised of long aligned networks of spinal motor neurons and skeletal myocytes on aligned nanofibrous scaffolds. Motor neurons led to enhanced differentiation and maturation of skeletal myocytes in vitro. These pre-innervated tissue-engineered muscle constructs when implanted in a rat VML model significantly increased satellite cell density, neuromuscular junction maintenance, graft revascularization, and muscle volume over three weeks as compared to myocyte-only constructs and nanofiber scaffolds alone. These pro-regenerative effects may enhance functional neuromuscular regeneration following VML, thereby improving the levels of functional recovery following these devastating injuries.

Whole Organ Engineering: Approaches, Challenges, and Future Directions

End-stage organ failure remains a leading cause of morbidity and mortality across the globe. The only curative treatment option currently available for patients diagnosed with end-stage organ failure is organ transplantation. However, due to a critical shortage of organs, only a fraction of these patients are able to receive a viable organ transplantation. Those patients fortunate enough to receive a transplant must then be subjected to a lifelong regimen of immunosuppressant drugs. The concept of whole organ engineering offers a promising alternative to organ transplantation that overcomes these limitations. Organ engineering is a discipline that merges developmental biology, anatomy, physiology, and cellular interactions with enabling technologies such as advanced biomaterials and biofabrication to create bioartificial organs that recapitulate native organs in vivo. There have been numerous developments in bioengineering of whole organs over the past two decades. Key technological advancements include (1) methods of whole organ decellularization and recellularization, (2) three-dimensional bioprinting, (3) advanced stem cell technologies, and (4) the ability to genetically modify tissues and cells. These advancements give hope that organ engineering will become a commercial reality in the next decade. In this review article, we describe the foundational principles of whole organ engineering, discuss key technological advances, and provide an overview of current limitations and future directions.

Innervation: the missing link for biofabricated tissues and organs

Innervation plays a pivotal role as a driver of tissue and organ development as well as a means for their functional control and modulation. Therefore, innervation should be carefully considered throughout the process of biofabrication of engineered tissues and organs. Unfortunately, innervation has generally been overlooked in most non-neural tissue engineering applications, in part due to the intrinsic complexity of building organs containing heterogeneous native cell types and structures. To achieve proper innervation of engineered tissues and organs, specific host axon populations typically need to be precisely driven to appropriate location(s) within the construct, often over long distances. As such, neural tissue engineering and/or axon guidance strategies should be a necessary adjunct to most organogenesis endeavors across multiple tissue and organ systems. To address this challenge, our team is actively building axon-based "living scaffolds" that may physically wire in during organ development in bioreactors and/or serve as a substrate to effectively drive targeted long-distance growth and integration of host axons after implantation. This article reviews the neuroanatomy and the role of innervation in the functional regulation of cardiac, skeletal, and smooth muscle tissue and highlights potential strategies to promote innervation of biofabricated engineered muscles, as well as the use of "living scaffolds" in this endeavor for both in vitro and in vivo applications. We assert that innervation should be included as a necessary component for tissue and organ biofabrication, and that strategies to orchestrate host axonal integration are advantageous to ensure proper function, tolerance, assimilation, and bio-regulation with the recipient post-implant.

The promise of regenerative medicine in the treatment of urogenital disorders

Polymers and scaffolds are the most significant tools in regenerative medicine. Urogenital disorders are an important group of diseases that greatly affect the patient's life expectancy and quality. Reconstruction of urogenital defects is one of the current challenges in regenerative medicine. Regenerative medicine, as well as tissue engineering, may offer suitable approaches, while the tools needed are appropriate materials and cells. Autologous urothelial cells obtained from biopsy, bone marrow-derived stem cells, adipose stem cells and urine-derived stem cells that expressed mesenchymal cell markers are the cells that mainly used. In addition, two main types of biomaterials mainly exist; synthetic polymers and composite scaffolds that are biodegradable polymers with controllable properties and naturally derived biomaterials such as extracellular matrix components and acellular tissue matrices. In this review, we present and evaluate the most appropriate and suitable scaffolds (naturally derived and synthetic polymers) and cells applied in urogenital reconstruction.

In Situ Precipitation of Cluster and Acicular Hydroxyapatite onto Porous Poly(γ-benzyl-l-glutamate) Microcarriers for Bone Tissue Engineering

Bone tissue engineering scaffold based on microcarriers provides an effective approach for the repair of irregular bone defects. The implantation of microcarriers by injection can reduce surgical trauma and fill various irregular shaped bone defects. Microcarriers with porous structure and osteogenic properties have shown great potential in promoting the repair of bone defects. In this study, two kinds of hydroxyapatite/poly-(γ-benzyl-l-glutamate) (HA/PBLG) microcarriers were constructed by emulsion/in situ precipitation method and their structures and properties were studied. First, PBLG porous microcarriers were prepared by an emulsion method. Surface carboxylation of PBLG microcarriers was performed to promote the deposition of HA on PBLG microcarriers. Next, the modified porous PBLG microcarriers were used as the matrix, combined with the in situ precipitation method; the cluster HA and acicular HA were precipitated onto the surface of porous microcarriers in the presence of ammonia water and tri(hydroxymethyl)aminomethane (Tris) solution, respectively. The micromorphology, composition, and element distribution of the two kinds of microcarriers were characterized by TEM, SEM, and AFM. Adipose stem cells (ADSCs) were cultured on the cluster HA/PBLG and acicular HA/PBLG microcarriers, respectively. ADSCs could grow and proliferate normally on both kinds of microcarriers wherein the acicular HA/PBLG microcarriers were more favorable for early cell adhesion and showed a beneficial effect on mineralization and osteogenic differentiation of ADSCs. Successful healing of a rabbit femur defect verified the bone regeneration ability of acicular HA/PBLG microcarriers.

Molecular and histological studies of bladder wound healing in a rodent model

The field of regenerative medicine encounters different challenges. The success of tissue-engineered implants is dependent on proper wound healing. Today, the process of normal urinary bladder wound healing is poorly characterized. We aspired to explore and elucidate the natural response to injury in an in vivo model in order to further optimize tissue regeneration in future studies. In this study, we aimed to characterize histological and molecular changes during normal healing in a rat model by performing a standardized incisional wound followed by surgical closure. We used a rodent model (n = 40) to follow the healing process in the urinary bladder for 28 days. Surgical exposure of the bladder without incision (n = 40) was performed in controls. Histological characterization and western blot analyses of proteins was carried out using specific staining and markers for inflammation, proliferation, angiogenesis, and tissue maturation. For the molecular characterization of gene expression total RNA was collected for RT² -PCR in wound healing pathway arrays. Analysis of histology revealed distinct, but overlapping, phases of healing with a local inflammatory response (days 1-8) simultaneous with a rapid formation of granulation tissue and proliferation (days 2-8). We also identified significant changes in gene expression related to inflammation, proliferation, and extracellular matrix formation. Healing of an incisional wound in a rodent urinary bladder demonstrated that all the classical phases of wound healing: hemostasis, inflammation, proliferation followed by tissue maturation were present. Our data suggest that the bladder and the skin share similar molecular signaling during wound healing, although we noted differences in the duration of each phase compared to previous studies in rat skin. Further studies will address whether our findings can be extrapolated to the human bladder.

Recent advances in biomaterials for 3D scaffolds: A review

Considering the advantages and disadvantages of biomaterials used for the production of 3D scaffolds for tissue engineering, new strategies for designing advanced functional biomimetic structures have been reviewed. We offer a comprehensive summary of recent trends in development of single- (metal, ceramics and polymers), composite-type and cell-laden scaffolds that in addition to mechanical support, promote simultaneous tissue growth, and deliver different molecules (growth factors, cytokines, bioactive ions, genes, drugs, antibiotics, etc.) or cells with therapeutic or facilitating regeneration effect. The paper briefly focuses on divers 3D bioprinting constructs and the challenges they face. Based on their application in hard and soft tissue engineering, in vitro and in vivo effects triggered by the structural and biological functionalized biomaterials are underlined. The authors discuss the future outlook for the development of bioactive scaffolds that could pave the way for their successful imposing in clinical therapy.

Tissue Engineering in Pediatric Bladder Reconstruction-The Road to Success

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

Regenerative Medicine Therapies for Equine Wound Management

Wound management in horses can strike fear in some and passion in others. Wounds are common injuries in horses of all descriptions and requires exceptional knowledge and care to achieve a successful outcome. New treatments to overcome the critical challenges with equine wounds are always desired: managing dehisced and/or nonhealing wounds, managing exuberant granulation tissue, and ultimately achieving a functional tissue coverage. Regenerative medicine represents a broad set of tools with great promise to manipulate the deficiencies recognized in equine wound healing and improve the outcome.

Bioengineered bladder patches constructed from multilayered adipose-derived stem cell sheets for bladder regeneration

Cell-seeded scaffolds are a common route of cell transplantation for bladder repair and reconstruction. However, when cell suspensions are harvested, proteolytic enzymes often cause extracellular matrix damage and loss of intercellular junctions. To overcome this problem, we developed a bioengineered three-dimensional bladder patch comprising porous scaffolds and multilayered adipose-derived stem cell (ASC) sheets, and evaluated its feasibility for bladder regeneration in a rat model. Adipose-derived stem cells (ASCs) were labeled with ultrasmall super-paramagnetic iron oxide (USPIO) nanoparticles. ASC patches were constructed using multilayered USPIO-labeled ASC sheets and porous polyglycolic acid scaffolds. To monitor the distribution and localization of bioengineered bladder patches in live animals, magnetic resonance imaging (MRI) was performed 2 weeks, 4 weeks and 8 weeks after transplantation. The bladder regenerative potential of ASC patches was further evaluated by urodynamic and histological analysis. Scanning electron microscopy indicated that cell sheets adhered tightly to the scaffold. MRI showed hypointense signals that lasted up to 8 weeks at the site of USPIO-labeled ASC sheet transplants. Immunofluorescence demonstrated that these tissue-engineered bladder patches promoted regeneration of urothelium, smooth muscle, neural cells and blood vessels. Urodynamic testing revealed that the ASC patch restored bladder function with augmented capacity. The USPIO-labeled ASC patch provides a promising perspective on image-guided tissue engineering and holds great promise as a safe and effective therapeutic strategy for bladder regeneration. STATEMENT OF SIGNIFICANCE: Adipose-derived stem cell (ASC) sheets avoid enzymatic dissociation and preserve the cell-to-cell interactions and extracellular matrix (ECM) proteins, which exhibit great potential for tissue regeneration. In this study, we developed a bioengineered three-dimensional bladder patch comprising porous scaffolds and multilayered ASC sheets, and evaluated its feasibility for bladder regeneration in a rat model. Tissue-engineered bladder patches restored bladder function and promoted regeneration of urothelium, smooth muscle, neural cells and blood vessels. Moreover, ultrasmall super-paramagnetic iron oxide (USPIO)-labeled bladder patches can be dynamically monitored in vivo by noninvasive MRI for long periods of time. Therefore, The USPIO-labeled bladder patch provides a promising image-guided therapeutic strategy for bladder regeneration.

Evaluation of Poly (Carbonate-Urethane) Urea (PCUU) Scaffolds for Urinary Bladder Tissue Engineering

Although the previous success of bladder tissue engineering demonstrated the feasibility of this technology, most polyester based scaffolds used in previous studies possess inadequate mechanical properties for organs that exhibit large deformation. The present study explored the use of various biodegradable elastomers as scaffolds for bladder tissue engineering and poly (carbonate-urethane) urea (PCUU) scaffolds mimicked urinary bladder mechanics more closely than polyglycerol sebacate-polycaprolactone (PGS-PCL) and poly (ether-urethane) urea (PEUU). The PCUU scaffolds also showed cyto-compatibility as well as increased porosity with increasing stretch indicating its ability to aid in infiltration of smooth muscle cells. Moreover, a bladder outlet obstruction (BOO) rat model was used to test the safety and efficacy of the PCUU scaffolds in treating a voiding dysfunction. Bladder augmentation with PCUU scaffolds led to enhanced survival of the rats and an increase in the bladder capacity and voiding volume over a 3 week period, indicating that the high-pressure bladder symptom common to BOO was alleviated. The histological analysis of the explanted scaffold demonstrated smooth muscle cell and connective tissue infiltration. The knowledge gained in the present study should contribute towards future improvement of bladder tissue engineering technology to ultimately aide in the treatment of bladder disorders.

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 engineering in pediatric urology - a critical appraisal

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

TGFβ-1 and epithelial-mesenchymal interactions promote smooth muscle gene expression in bone marrow stromal cells: Possible application in therapies for urological defects

Purpose

For regenerative and cellular therapies of the urinary tract system, autologous bladder smooth muscle cells (SMCs) have several limitations, including constricted in vitro proliferation capacity and, more importantly, inability to be used in malignant conditions. The use of in vitro (pre-)differentiated multipotential adult progenitor cells may help to overcome the shortcomings associated with primary cells.

Methods

By mimicking environmental conditions of the bladder wall, we investigated in vitro effects of growth factor applications and epithelial-mesenchymal interactions on smooth muscle gene expression and on the morphological appearance of adherent bone marrow stromal cells (BMSCs).

Results

Transcription growth factor beta-1 (TGFβ-1) upregulated the transcription of myogenic gene desmin and smooth muscle actin-γ2 in cultured BMSCs. Stimulatory effects were significantly increased by coculture with urothelial cells. Prolonged stimulation times and epigenetic modifications further enhanced transcription levels, indicating a dose-response relationship. Immunocytochemical staining of in vitro-differentiated BMSCs revealed expression of myogenic protein α-smooth muscle actin and desmin, and changes in morphological appearance from a fusiform convex shape to a laminar flattened shape with filamentous inclusions similar to the appearance of bladder SMCs. In contrast to the TGFβ-1 action, application of vascular endothelial growth factor (VEGF) did not affect the cells.

Conclusions

The combined application of TGFβ-1 and epithelial-mesenchymal interactions promoted in vitro outgrowth of cells with a smooth muscle-like phenotype from a selected adherent murine bone marrow-derived cell population.

“UroMaix” Scaffolds: Novel Collagen Matrices for Application in Tissue Engineering of the Urinary Tract

Reconstruction of bladder and ureter tissue is indicated in cases of injury, stenosis, infection or tumor. Substitution by ileum, colon or pure synthetic polymers generates a variety of complications. Biohybrid tissue mimicking structural and functional attributes of the multilayered wall architecture of the urinary conduit may be the solution to current problems.

This study reports on porcine urinary tract cells isolated and placed on UroMaix matrices with different degrees of cross-linking produced from highly purified type I collagen from medically approved porcine tissue. A patented procedure revealed membrane structures composed of a dense fibrous side and an open fibrous side. These scaffolds with the porcine urinary tract cells were incubated in a batch culture system for up to 14 days. Cell growth and topographical orientation were examined.

Urothelial cells showed maximum attachment and a significant increase of living cells on the dense fiber layer of UroMaix-1. No attachment of urothelial cells occurred on the other prototypes. Smooth muscle cells showed similar behavior within the open fiber layer of all UroMaix matrices. Both urothelial and smooth muscle cells retained their phenotypes as demonstrated by the immunostaining of epithelial cytokeratin 18 and the smooth muscle myosin heavy chain respectively. Thus we could show that UroMaix scaffolds support the attachment and proliferation of urinary tract cells. The elastomeric properties of the collagenous matrices promise attractive applications in the tissue engineering of the urinary tract with its high mechanical demands.

In Vitro Construction of Urinary Bladder Wall using Porcine Primary Cells Reseeded on Acellularized Bladder Matrix and Small Intestinal Submucosa

BACKGROUND

Partial or radical cystectomy requires replacement of the urinary reservoir normally achieved by using small or large bowel segments. Our aim was to establish tissue engineering of an bioartificial bladder wall using primary cultures of porcine urothelial (pUC) and bladder smooth muscle cells (pSMC) to be reseeded on different acellular biological matrices.

METHODS

Primary porcine cultures of pUC and pSMC were established from open bladder biopsy material 25 mm2 in size. Acellular matrix was generated either from a) porcine bladder wall segments or b) tubular small intestinal submucosa with the still attached decellularized muscularis layer. Reseeding of these matrices with primary cells was done in a two-dimensional static model and in a three-dimensional rotating bioreactor perfused with cell culture medium for a period of 6 weeks.

RESULTS

Prior to reseeding the cultured cells were characterized as pUC and pSMC by immunohistochemical staining with either anti-keratin 7 or anti-alpha actin. For both matrices a reseeded double layer cell system of pUC and pSMC could be identified after incubation in the described systems for 6 weeks.

CONCLUSIONS

Our results document successful generation of tissue engineered urinary bladder wall, which can be used in further large animal transplantation experiments.