Bladder Substitution: The Role of Tissue Engineering and Biomaterials

Mechanical characterization of porcine ureter for the evaluation of tissue-engineering applications

Introduction: Clinics increasingly require readily deployable tubular substitutes to restore the functionality of structures like ureters and blood vessels. Despite extensive exploration of various materials, both synthetic and biological, the optimal solution remains elusive. Drawing on abundant literature experiences, there is a pressing demand for a substitute that not only emulates native tissue by providing requisite signals and growth factors but also exhibits appropriate mechanical resilience and behaviour. Methods: This study aims to assess the potential of porcine ureters by characterizing their biomechanical properties in their native configuration through ring and membrane flexion tests. In order to assess the tissue morphology before and after mechanical tests and the eventual alteration of tissue microstructure that would be inserted in material constitutive description, histological staining was performed on samples. Corresponding computational analyses were performed to mimic the experimental campaign to identify the constitutive material parameters. Results: The absence of any damages to muscle and collagen fibres, which only compacted after mechanical tests, was demonstrated. The experimental tests (ring and membrane flexion tests) showed non-linearity for material and geometry and the viscoelastic behaviour of the native porcine ureter. Computational models were descriptive of the mechanical behaviour ureteral tissue, and the material model feasible. Discussion: This analysis will be useful for future comparison with decellularized tissue for the evaluation of the aggression of cell removal and its effect on microstructure. The computational model could lay the basis for a reliable tool for the prediction of solicitation in the case of tubular substitutions in subsequent simulations.

Current evidence regarding alternative techniques for enterocystoplasty using regenerative medicine methods: a systematic review

Enterocystoplasty is the most commonly used treatment for bladder reconstruction. However, it has some major complications. In this study, we systematically reviewed the alternative techniques for enterocystoplasty using different scaffolds. A comprehensive search was conducted in PubMed, Embase, and Cochrane Library, and a total of 10 studies were included in this study. Five different scaffolds were evaluated, including small intestinal submucosa (SIS), biodegradable scaffolds seeded with autologous bladder muscle and urothelial cells, dura mater, human cadaveric bladder acellular matrix graft, and bovine pericardium. The overall results revealed that bladder reconstruction using regenerative medicine is an excellent alternative method to enterocystoplasty regarding the improvement of bladder capacity, bladder compliance, and maximum detrusor pressure; however, more large-scale studies are required.

Decellularized extracellular matrix and silk fibroin-based hybrid biomaterials: A comprehensive review on fabrication techniques and tissue-specific applications

Biomaterials play a fundamental role in tissue engineering by providing biochemical and physical cues that influence cellular fate and matrix development. Decellularized extracellular matrix (dECM) as a biomaterial is distinguished by its abundant composition of matrix proteins, such as collagen, elastin, fibronectin, and laminin, as well as glycosaminoglycans and proteoglycans. However, the mechanical properties of only dECM-based constructs may not always meet tissue-specific requirements. Recent advancements address this challenge by utilizing hybrid biomaterials that harness the strengths of silk fibroin (SF), which contributes the necessary mechanical properties, while dECM provides essential cellular cues for in vitro studies and tissue regeneration. This review discusses emerging trends in developing such biopolymer blends, aiming to synergistically combine the advantages of SF and dECM through optimal concentrations and desired cross-linking density. We focus on different fabrication techniques and cross-linking methods that have been utilized to fabricate various tissue-engineered hybrid constructs. Furthermore, we survey recent applications of such biomaterials for the regeneration of various tissues, including bone, cartilage, trachea, bladder, vascular graft, heart, skin, liver, and other soft tissues. Finally, the trajectory and prospects of the constructs derived from this blend in the tissue engineering field have been summarized, highlighting their potential for clinical translation.

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.

Injectable, stretchable, toughened, bioadhesive composite hydrogel for bladder injury repair†

The bladder is exposed to constant internal and external mechanical forces due to its deformation and the dynamic environment in which it is placed, which can hamper its repair after an injury. Traditional hydrogel materials have limitations regarding their use in the bladder owing to their poor mechanical and tissue adhesion properties. In this study, a composite hydrogel composed of methacrylate gelatine, methacrylated silk fibroin, and Pluronic F127 diacrylate was developed, which combines the characteristics of natural and synthetic polymers. The mechanical properties of the novel hydrogel, such as stretchability, viscoelasticity, and toughness, were improved by virtue of a particular molecular design strategy whereby covalent and non-covalent bond interactions create a cross-linking effect. In addition, the composite hydrogel has important usability properties; it can be injected in liquid format and rapidly transformed into a gel via photo-initiated crosslinking. This was demonstrated on an isolated porcine bladder where the hydrogel closed arbitrarily-shaped tissue defects within 90 s of its application, verifying its effective bioadhesive and sealing properties. This composite hydrogel has great potential for application in bladder injury repair as a tissue-engineering scaffold.

An injectable, stretchable, toughened, bioadhesive composite hydrogel offers a new application strategy for sutureless repair and tissue regeneration of injured bladders.

A Novel Hybrid Membrane for Urinary Conduit Substitutes Based on Small Intestinal Submucosa Coupled with Two Synthetic Polymers

Among the urinary tract's malignancies, bladder cancer is the most frequent one: it is at the tenth position of most common cancers worldwide. Currently, the gold standard therapy consists of radical cystectomy, which results in the need to create a urinary diversion using a bowel segment from the patient. Nevertheless, due to several complications associated with bowel resection and anastomosis, which significantly affect patient quality of life, it is becoming extremely important to find an alternative solution. In our recent work, we proposed the decellularized porcine small intestinal submucosa (SIS) as a candidate material for urinary conduit substitution. In the present study, we create SIS-based hybrid membranes that are obtained by coupling decellularized SIS with two commercially available polycarbonate urethanes (Chronoflex AR and Chronoflex AR-LT) to improve SIS mechanical resistance and impermeability. We evaluated the hybrid membranes by means of immunofluorescence, two-photon microscopy, FTIR analysis, and mechanical and cytocompatibility tests. The realization of hybrid membranes did not deteriorate SIS composition, but the presence of polymers ameliorates the mechanical behavior of the hybrid constructs. Moreover, the cytocompatibility tests demonstrated a significant increase in cell growth compared to decellularized SIS alone. In light of the present results, the hybrid membrane-based urinary conduit can be a suitable candidate to realize a urinary diversion in place of an autologous intestinal segment. Further efforts will be performed in order to create a cylindrical-shaped hybrid membrane and to study its hydraulic behavior.

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.

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.