Constructing artificial urinary conduits: current capabilities and future potential

Evaluation of bi-layer silk fibroin grafts for onlay urethroplasty in a rabbit model of urethral stricture disease

Background: Autologous tissues such as buccal mucosa (BM) are widely used for reconstruction of urethral strictures; however, limitations such as donor site morbidity and scarce tissue supply require the development of alternative biomaterials for urethral repair. The goals of this study were to determine the safety and efficacy of bi-layer silk fibroin (BLSF) matrices for urethral stricture repair and compare histological and functional outcomes to the standard approach, BM urethroplasty under good laboratory practices.Material and methods: A total of 13 rabbits exhibiting urethral stricture formation following electrocoagulation injury were treated with onlay urethroplasty with either acellular BLSF (N = 7) or autologous BM (N = 6) grafts for 3 months. Uninjured control rabbits were maintained in parallel (N = 4).Results and conclusion: Animals receiving BLSF implants were demonstrated to be functionally equivalent to BM grafts in their ability to restored strictured calibers, support micturition and promote tissue regeneration with minimal inflammation.

The Past, Present, and Future of Tubular Melt Electrowritten Constructs to Mimic Small Diameter Blood Vessels - A Stable Process?

Melt Electrowriting (MEW) is a continuously growing manufacturing platform. Its advantage is the consistent production of micro- to nanometer fibers, that stack intricately, forming complex geometrical shapes. MEW allows tuning of the mechanical properties of constructs via the geometry of deposited fibers. Due to this, MEW can create complex mechanics only seen in multi-material compounds and serve as guiding structures for cellular alignment. The advantage of MEW is also shown in combination with other biotechnological manufacturing methods to create multilayered constructs that increase mechanical approximation to native tissues, biocompatibility, and cellular response. These features make MEW constructs a perfect candidate for small-diameter vascular graft structures. Recently, studies have presented fascinating results in this regard, but is this truly the direction that tubular MEW will follow or are there also other options on the horizon? This perspective will explore the origins and developments of tubular MEW and present its growing importance in the field of artificial small-diameter vascular grafts with mechanical modulation and improved biomimicry and the impact of it in convergence with other manufacturing methods and how future technologies like AI may influence its progress.

Evaluation of silk fibroin-based urinary conduits in a porcine model of urinary diversion

Background: The primary strategy for urinary diversion in radical cystectomy patients involves incorporation of autologous gastrointestinal conduits into the urinary tract which leads to deleterious consequences including chronic infections and metabolic abnormalities. This report investigates the efficacy of an acellular, tubular bi-layer silk fibroin (BLSF) graft to function as an alternative urinary conduit in a porcine model of urinary diversion. Materials and methods: Unilateral urinary diversion with stented BLSF conduits was executed in five adult female, Yucatan mini-swine over a 3 month period. Longitudinal imaging analyses including ultrasonography, retrograde ureteropyelography and video-endoscopy were carried out monthly. Histological, immunohistochemical (IHC), and histomorphometric assessments were performed on neoconduits at harvest. Results: All animals survived until scheduled euthanasia and displayed moderate hydronephrosis (Grades 1-3) in reconstructed collecting systems over the course of the study period. Stented BLSF constructs supported formation of vascularized, retroperitoneal tubes capable of facilitating external urinary drainage. By 3 months post-operative, neoconduits contained α-smooth muscle actin+ and SM22α+ smooth muscle as well as uroplakin 3A+ and pan-cytokeratin + urothelium. However, the degree of tissue regeneration in neotissues was significantly lower in comparison to ureteral controls as determined by histomorphometry. In addition, neoconduit stenting was necessary to prevent stomal occlusion. Conclusion: BLSF biomaterials represent emerging platforms for urinary conduit construction and may offer a functional replacement for conventional urinary diversion techniques following further optimization of mechanical properties and regenerative responses.

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.

Decellularized extracellular matrix mediates tissue construction and regeneration

Contributing to organ formation and tissue regeneration, extracellular matrix (ECM) constituents provide tissue with three-dimensional (3D) structural integrity and cellular-function regulation. Containing the crucial traits of the cellular microenvironment, ECM substitutes mediate cell-matrix interactions to prompt stem-cell proliferation and differentiation for 3D organoid construction in vitro or tissue regeneration in vivo. However, these ECMs are often applied generically and have yet to be extensively developed for specific cell types in 3D cultures. Cultured cells also produce rich ECM, particularly stromal cells. Cellular ECM improves 3D culture development in vitro and tissue remodeling during wound healing after implantation into the host as well. Gaining better insight into ECM derived from either tissue or cells that regulate 3D tissue reconstruction or organ regeneration helps us to select, produce, and implant the most suitable ECM and thus promote 3D organoid culture and tissue remodeling for in vivo regeneration. Overall, the decellularization methodologies and tissue/cell-derived ECM as scaffolds or cellular-growth supplements used in cell propagation and differentiation for 3D tissue culture in vitro are discussed. Moreover, current preclinical applications by which ECM components modulate the wound-healing process are reviewed.

The development of marine biomaterial derived from decellularized squid mantle for potential application as tissue engineered urinary conduit

Tissue engineering is focusing research effort on search for new biomaterials that might be applied to create artificial urinary conduit. Nevertheless, the demanding biomechanical characteristics necessary for proper conduit function is difficult to be replicated. In this study, we are introducing novel marine biomaterial obtained by decellularization of squid mantle derived from Loligo vulgaris. Squid mantles underwent decellularization according to developed dynamic flow two-staged procedure. Efficacy of the method was confirmed by computational dynamic flow analysis. Subsequently Decellularized Squid Mantle (DSM) underwent extensive histological analysis and mechanical evaluation. Based on gained biomechanical data the computational modelling using finite element method was utilized to simulate behavior of DSM used as a urinary conduit. Taking into account potential application in reconstructive urology, the DSM was then evaluated as a scaffold for urothelial and smooth muscle cells derived from porcine urinary bladder. Conducted analysis showed that DSM created favorable environment for cells growth. In addition, due to polarized structure and natural external polysaccharide layer, it protected seeded cells from urine.