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

Evaluation of Bi-layer Silk Fibroin Grafts for Onlay Urethroplasty in a Female Porcine Model of Long Urethral Strictures

BACKGROUND

Buccal mucosa urethroplasty represents the primary strategy for reconstruction of long urethral strictures (US). However, significant complications including stricture recurrence and donor site morbidity currently hamper this approach. The goal of this study was to determine the efficacy of acellular, bi-layer silk fibroin (BLSF) biomaterials to serve as superior alternatives to buccal mucosal (BM) grafts for repair of 4 cm long US in female swine.

METHODS

Urethral mucosal damage was induced over 4-5 cm long segments via electrocoagulation in adult female swine (N = 10) to promote US over the course of 2-4 weeks. Onlay urethroplasty with BLSF scaffolds or autologous BM grafts (N = 5 per group, ~ 4 cm2) was subsequently performed and animals were maintained for 3 months. Outcome analyses included urethroscopy, retrograde urethrography (RUG), and histological and immunohistochemical (IHC) analyses. Non operated urethral segments served as internal controls (N = 10).

RESULTS

All swine survived the study with no severe complications and exhibited US formation following electrocoagulation with a 43-57% reduction in baseline calibers. At 3 months post-op, imaging modalities revealed both graft cohorts promoted > 80% restoration of native urethral calibers. Histological and IHC evaluations showed BLSF grafts supported the formation of innervated, vascularized urethral-like neotissues with α-smooth muscle actin + and SM22α + smooth muscle bundles as well as pan-cytokeratin + epithelia reminiscent of controls. In contrast, BM grafts primarily retained native oral tissue morphology after urethral transposition exhibiting cytokeratin 1 + stratified, squamous epithelia and scant muscle formation.

CONCLUSIONS

BLSF matrices can promote functional restoration of long US via regeneration of native urethral tissues.

A flexible cystoscopy device prototype for mechanical tissue ablation based on micro-scale hydrodynamic cavitation: Ex vivo and in vivo studies

Minimally invasive methods were sought for faster recovery from benign prostatic hyperplasia (BPH) and lower urinary tract (LUTS) symptoms. For this, the search for effective, low-side-effect methods for tissue ablation, particularly for managing BPH and certain bladder pathologies, has been continued to advance. In this regard, the energy released during the formation of hydrodynamic cavitation bubbles offers an alternative treatment method. In this study, we present the feasibility of the use of hydrodynamic cavitation with a flexible cystoscopy device prototype designed for the treatment of LUTS-related diseases. The developed flexible cystoscopy device prototype allows easy access to the urinary bladder through urethra with minimal pain, demonstrating its suitability as a minimally invasive approach. Precisely targeted cavitation exposure prevents prostatic capsule and bladder perforation. Moreover, an automatic actuating mechanism supports steering for real-time visual feedback. The developed device prototype was first tested on an ex vivo human bladder and then on an in vivo porcine bladder. Histopathological analyses were performed after both species were tested. For both analyses, significant tissue ablation at the targets was observed upon exposure to cavitating flows. Finally, the temperature profile on the device was obtained using a thermal camera. Accordingly, it was observed that the temperature increase during the procedure was not significant. The developed device prototype can thus realize mechanical ablation-based therapy, avoids unintended heat deposition which might appear in laser ablation and leads to fewer side effects such as uncontrolled tissue damage and low target area effectiveness that might occur in minimally invasive tissue ablation methods.

Pediatric bladder tissue engineering: Where have we been and where do we go next?

OBJECTIVES

This review aims to (a) provide a concise overview of early clinical trials in bladder tissue engineering and the associated challenges, (b) evaluate significant advancements over the past 15 years in addressing key limitations in angiogenesis, scaffolding, cell sourcing, and immunomodulation, and (c) explore the individual and synergistic contributions of each domain toward the development of a viable engineered solution.

MATERIALS AND METHODS

Relevant papers for this narrative review were selected through a PubMed search for "bladder tissue engineering" studies published between 01/01/2009 and 12/31/2024, as well as earlier clinical trials that predate this period.

RESULTS

Along with reviewing four major clinical trials, this review highlights nearly 20 distinct studies that showcase progress in the critical domains of angiogenesis, scaffolding, cell sourcing, and immunomodulation.

CONCLUSIONS

Are we close to developing an off-the-shelf bladder substitute? Not yet. Current efforts are focused on addressing two major knowledge gaps: (a) the lack of testing in clinically relevant disease models and (b) the need for a more comprehensive understanding of engineered tissue physiology.

Advances in tissue engineering of peripheral nerve and tissue innervation - a systematic review

Although various options are available to treat injured organs and peripheral nerves, none is without limitations. Auto- and allografts are the first choice of treatment, but tissue survival or functionality is not guaranteed due to often limited vascular and neural networks. In response, tissue-engineered solutions have been developed, yet clinical translations is rare. In this study, a systematic review was performed on tissue-engineered advancements for peripheral nerves and tissues, to aid future developments in bridging the gap toward the clinic by identifying high-potential solutions and unexplored areas. A systematic search was performed in PubMed, Embase, Web of Science, and Scopus until November 9, 2023. Search terms involved "tissue engineering," "guided," "tissue scaffold," and "tissue graft," together with "innervation" and "reinnervation." Original in vivo or in vitro studies meeting the inclusion criteria (tissue-engineered peripheral nerve/innervation of tissue) and no exclusion criteria (no full text available; written in foreign language; nonoriginal article; tissue-engineering of central nervous system; publication before 2012; insufficient study quality or reproducibility) were assessed. A total of 68 out of 3626 original studies were included. Data extraction was based on disease model, cell origin and host species, biomaterial nature and composition, and external stimuli of biological, chemical or physical origin. Although tissue engineering is still in its infancy, explored innervation strategies of today were highlighted with respect to biomaterials, cell types, and external stimuli. The findings emphasize that natural biomaterials, pre-seeding with autologous cell sources, and solutions for reproductive organs are beneficial for future research. Natural biomaterials possess important cues required for cell-material interaction and closely resemble native tissue in terms of biomechanical, geometrical and chemical composition. Autologous cells induce biomaterial functionalization. As these solutions pose no risk of immunorejection and have demonstrated good outcomes, they are most likely to fulfill the clinical demands.

Evaluation of Bi-layer Silk Fibroin Grafts for Inlay Vaginoplasty in a Rat Model

BACKGROUND

Autologous tissues derived from bowel, buccal mucosa and skin are primarily used to repair or replace diseased vaginal segments as well as create neovaginas for male-to-female transgenders. These grafts are often limited by scarce tissue supply, donor site morbidity and post-operative complications. Bi-layer silk fibroin (BLSF) biomaterials represent potential alternatives for vaginoplasty given their structural strength and elasticity, low immunogenicity, and processing flexibility. The goals of the current study were to assess the potential of acellular BLSF scaffolds for vaginal tissue regeneration in respect to conventional small intestinal submucosal (SIS) matrices in a rat model of vaginoplasty.

METHODS

Inlay vaginoplasty was performed with BLSF and SIS scaffolds (N = 21 per graft) in adult female rats for up to 2 months of implantation. Nonsurgical controls (N = 4) were investigated in parallel. Outcome analyses included histologic, immunohistochemical and histomorphometric evaluations of wound healing patterns; µ-computed tomography (CT) of vaginal continuity; and breeding assessments.

RESULTS

Animals in both scaffold cohorts exhibited 100% survival rates with no severe post-operative complications. At 2 months post-op, µ-CT analysis revealed normal vaginal anatomy and continuity in both graft groups similar to controls. In parallel, BLSF and SIS grafts also induced comparable constructive remodeling patterns and were histologically equivalent in their ability to support formation of vascularized vaginal neotissues with native tissue architecture, however with significantly less smooth muscle content. Vaginal tissues reconstructed with both implants were capable of supporting copulation, pregnancy and similar amounts of live births.

CONCLUSIONS

BLSF biomaterials represent potential "off-the-shelf" candidates for vaginoplasty.

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.

Autologous regeneration of blood vessels in urinary bladder matrices provides early perfusion after transplant to the bladder

Large animal testing and clinical trials using bioengineered bladder for augmentation have revealed that large grafts fail due to insufficient blood supply. To address this critical issue, an in vivo staged implant strategy was developed and evaluated to create autologous, vascularized bioengineered bladder tissue with potential for clinical translation. Pig bladders were used to create acellular urinary bladder matrices (UBMs), which were implanted on the rectus abdominus muscles of rats and pigs to generate cellular and vascular grafts. Rectus-regenerated bladder grafts (rrBGs) were highly cellularized and contained an abundance of CD31-positive blood vessels, which were shown to be functional by perfusion studies. Muscle patterns within grafts showed increased smooth muscle formation over time and specifically within the detrusor compartment, with no evidence of striated muscle. Large, autologous rrBGs were transplanted to the pig bladder after partial cystectomy and compared to transplantation of control UBMs at 2 weeks and 3 months post-transplant. Functional, ink-perfused blood vessels were found in the central portion of all rrBGs at 2 weeks, while UBM grafts were significantly deteriorated, contracted and lacked central cellularization and vascularization. By 3 months, rrBGs had mature smooth muscle bundles and were morphologically similar to native bladder. This staged implantation technique allows for regeneration and harvest of large bladder grafts that are morphologically similar to native tissue with functional vessels capable of inosculating with host bladder vessels to provide quick perfusion to the central area of the large graft, thereby preventing early ischemia and contraction.

Evaluation of Bi-Layer Silk Fibroin Grafts for Penile Tunica Albuginea Repair in a Rabbit Corporoplasty Model

The use of autologous tissue grafts for tunica albuginea repair in Peyronie's disease and congenital chordee is often restricted by limited tissue availability and donor site morbidity, therefore new biomaterial options are needed. In this study, bi-layer silk fibroin (BLSF) scaffolds were investigated to support functional tissue regeneration of tunica albuginea in a rabbit corporoplasty model. Eighteen adult male, New Zealand white rabbits were randomized to nonsurgical controls (NSC, N = 3), or subjected to corporoplasty with BLSF grafts (N = 5); decellularized small intestinal submucosa (SIS) matrices (N = 5); or autologous tunica vaginalis (TV) flaps (N = 5). End-point evaluations were cavernosography, cavernosometry, histological, immunohistochemical, and histomorphometric assessments. Maximum intracorporal pressures (ICP) following papaverine-induced erection were similar between all groups. Eighty percent of rabbits repaired with BLSF scaffolds or TV flaps achieved full rigid erections, compared to 40% of SIS reconstructed animals. Five-minute peak erections were maintained in 60% of BLSF rabbits, compared to 20% of SIS and TV flap reconstructed rabbits. Graft perforation occurred in 60% of TV group at maximum ICP compared to 20% of BLSF cohort. Neotissues supported by SIS and BLSF scaffolds were composed of collagen type I and elastin fibers similar to NSC. SIS and TV flaps showed significantly elevated levels of corporal fibrosis relative to NSC with a corresponding decrease in corporal smooth muscle cells expressing contractile proteins. BLSF biomaterials represent emerging platforms for corporoplasty and produce superior functional and histological outcomes in comparison to TV flaps and SIS matrices for tunica albuginea repair.

Evaluation of Bi-Layer Silk Fibroin Grafts for Tubular Ureteroplasty in a Porcine Defect Model

Ureteral reconstruction with autologous tissue grafts is often limited by tissue availability and donor site morbidity. This study investigates the performance of acellular, bi-layer silk fibroin (BLSF) scaffolds in a porcine model of ureteroplasty. Tubular ureteroplasty with BLSF grafts in combination with transient stenting for 8 weeks was performed in adult female, Yucatan, mini-swine (N = 5). Animals were maintained for 12 weeks post-op with imaging of neoconduits using ultrasonography and retrograde ureteropyelography carried out at 2 and 4 weeks intervals. End-point analyses of ureteral neotissues and unoperated controls included histological, immunohistochemical (IHC), histomorphometric evaluations as well as ex vivo functional assessments of contraction/relaxation. All animals survived until scheduled euthanasia and displayed mild hydronephrosis (Grades 1-2) in reconstructed collecting systems during the 8 weeks stenting period with one animal presenting with a persistent subcutaneous fistula at 2 weeks post-op. By 12 weeks of scaffold implantation, unstented neoconduits led to severe hydronephrosis (Grade 4) and stricture formation in the interior of graft sites in 80% of swine. Bulk scaffold extrusion into the distal ureter was also apparent in 60% of swine contributing to ureteral obstruction. However, histological and IHC analyses revealed the formation of innervated, vascularized neotissues with a-smooth muscle actin+ and SM22α+ smooth muscle bundles as well as uroplakin 3A+ and pan-cytokeratin + urothelium. Ex vivo contractility and relaxation responses of neotissues were similar to unoperated control segments. BLSF biomaterials represent emerging platforms for tubular ureteroplasty, however further optimization is needed to improve in vivo degradation kinetics and mitigate stricture formation.

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

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

Regeneration of muscular wall of the bladder using a ureter matrix graft as a scaffold

We investigated a method for bladder augmentation in rats using a decellularized ureter graft. We used 16 rats divided into two groups of eight. After partial cystectomy, the bladders in group 1 were grafted with a 1 cm² patch of human decellularized ureter. Rats in group 2 were untreated controls. Biopsies of the graft were taken at 1, 3 and 9 months postoperatively for histological investigation. Total removal of cells and preservation of extracellular matrix (ECM) was confirmed in the decellularized ureter. Histological examination after 1 month revealed few cells at the border of the graft. Three months after the operation, the graft was infiltrated by vessels and smooth muscle and the mucosal lining was complete. All bladder wall components resembled native bladder wall by 9 months after implantation. CD34, CD31, α-smooth muscle actin, S100, cytokeratin AE1/AE3 and vimentin were detected 9 months after the operation. We demonstrated the potential of decellularized biocompatible ureteric grafts for use as a natural collagen scaffold for bladder repair in rats.

Silk-Reinforced Collagen Hydrogels with Raised Multiscale Stiffness for Mesenchymal Cells 3D Culture

Type I collagen hydrogels are of high interest in tissue engineering. With the evolution of 3D bioprinting technologies, a high number of collagen-based scaffolds have been reported for the development of 3D cell cultures. A recent proposal was to mix collagen with silk fibroin derived from Bombyx mori silkworm. Nevertheless, due to the difficulties in the preparation and the characteristics of the protein, several problems such as phase separation and collagen denaturation appear during the procedure. Therefore, the common solution is to diminish the concentration of collagen although in that way the most biologically relevant component is reduced. In this study, we present a new, simple, and effective method to develop a collagen-silk hybrid hydrogel with high collagen concentration and with increased stiffness approaching that of natural tissues, which could be of high interest for the development of cardiac patches for myocardial regeneration and for preconditioning of mesenchymal stem cells (MSCs) to improve their therapeutic potential. Sericin in the silk was preserved by using a physical solubilizing procedure that results in a preserved fibrous structure of type I collagen, as shown by ultrastructural imaging. The macro- and micromechanical properties of the hybrid hydrogels measured by tensile stretch and atomic force microscopy, respectively, showed a more than twofold stiffening than the collagen-only hydrogels. Rheological measurements showed improved printability properties for the developed biomaterial. The suitability of the hydrogels for 3D cell culture was assessed by 3D bioprinting bone marrow-derived MSCs cultured within the scaffolds. The result was a biomaterial with improved printability characteristics that better resembled the mechanical properties of natural soft tissues while preserving biocompatibility owing to the high concentration of collagen. Impact statement In this study, we report the development of silk microfiber-reinforced type I collagen hydrogels for 3D bioprinting and cell culture. In contrast with previously reported studies, a novel physical method allowed the preservation of the silk sericin protein. Hydrogels were stable, showed no phase separation between the biomaterials, and they presented improved printability. An increase between two- and threefold of the multiscale stiffness of the scaffolds was achieved with no need of using additional crosslinkers or complex methods, which could be of high relevance for cardiac patches development and for preconditioning mesenchymal stem cells (MSCs) for therapeutic applications. We demonstrate that bone marrow-derived MSCs can be effectively bioprinted and 3D cultured within the stiffened structures.

Evaluation of Bilayer Silk Fibroin Grafts for Tubular Esophagoplasty in a Porcine Defect Model

Surgical reconstruction of tubular esophageal defects with autologous gastrointestinal segments is the gold standard treatment to replace damaged or diseased esophageal tissues. Unfortunately, this approach is associated with adverse complications, including dysphagia, donor-site morbidity, and in some cases patient death. Bilayer silk fibroin (BLSF) scaffolds were investigated as alternative, acellular grafts for tubular esophagoplasty in a porcine defect model for 3 months of implantation. Adult Yucatan mini-swine (n = 5) were subjected to esophageal reconstruction with tubular BLSF grafts (2 cm in length) in combination with transient esophageal stenting for 2 months followed by a 1-month period, where the graft site was unstented. All animals receiving BLSF grafts survived and were capable of solid food consumption, however strictures were noted at graft regions in 60% of the experimental cohort between 2 and 3 months postop and required balloon dilation. In addition, fluoroscopic analysis showed peristaltic function in only 1/5 neotissues. Following swine harvest at 3 months, ex vivo tissue bath evaluations revealed that neoconduits exhibited contractile responses to carbachol, electric field stimulation, and KCl, whereas sodium nitroprusside and isoproterenol induced relaxation effects. Histological (Masson's Trichrome) and immunohistochemical analyses of regenerated tissue conduits showed a stratified, squamous epithelium expressing pan-cytokeratins buttressed by a vascularized lamina propria containing a smooth muscle-rich muscularis mucosa surrounded by a muscularis externa. Neuronal density, characterized by the presence of synaptophysin-positive boutons, was significantly lower in neotissues in comparison to nonsurgical controls. BLSF scaffolds represent a promising platform for the repair of tubular esophageal defects, however improvements in scaffold design are needed to reduce the rate of complications and improve the extent of constructive tissue remodeling. Impact statement The search for a superior "off-the-shelf" scaffold capable of repairing tubularesophageal defects as well as overcoming limitations associated with conventional autologous gastrointestinal segments remains elusive. The purpose of this study was to investigate the performance of an acellular, bilayer silk fibroin graft (BLSF) for tubular esophagoplasty in a porcine model. Our results demonstrated that BLSF scaffolds supported the formation of tubular neotissues with innervated, vascularized epithelial and muscular components capable of contractile and relaxation responses. BLSF scaffolds represent a promising platform for esophageal tissue engineering.

Roles of Silk Fibroin on Characteristics of Hyaluronic Acid/Silk Fibroin Hydrogels for Tissue Engineering of Nucleus Pulposus

Silk fibroin (SF) and hyaluronic acid (HA) were crosslinked by horseradish peroxidase (HRP)/H₂O₂, and 1,4-Butanediol di-glycidyl ether (BDDE), respectively, to produce HA/SF-IPN (interpenetration network) (HS-IPN) hydrogels. HS-IPN hydrogels consisted of a SF strain with a high content of tyrosine (e.g., strain A) increased viscoelastic modules compared with those with low contents (e.g., strain B and C). Increasing the quantities of SF in HS-IPN hydrogels (e.g., HS7-IPN hydrogels with weight ratio of HA/SF, 5:7) increased viscoelastic modules of the hydrogels. In addition, the mean pores size of scaffolds of the model hydrogels were around 38.96 ± 5.05 μm which was between those of scaffolds H and S hydrogels. Since the viscoelastic modulus of the HS7-IPN hydrogel were similar to those of human nucleus pulposus (NP), it was chosen as the model hydrogel for examining the differentiation of human bone marrow-derived mesenchymal stem cell (hBMSC) to NP. The differentiation of hBMSC induced by transforming growth factor β3 (TGF-β3) in the model hydrogels to NP cells for 7 d significantly enhanced the expressions of glycosaminoglycan (GAG) and collagen type II, and gene expressions of aggrecan and collagen type II while decreased collagen type I compared with those in cultural wells. In summary, the model hydrogels consisted of SF of strain A, and high concentrations of SF showed the highest viscoelastic modulus than those of others produced in this study, and the model hydrogels promoted the differentiation of hBMSC to NP cells.

Augmentation cystoplasty in the patient with neurogenic bladder

PURPOSE

To review the indications and techniques of augmentation cystoplasty (AC) in patients with neurogenic bladder (NGB) while also examining the long-term outcomes, complications, and follow-up surgeries.

METHODS

PubMed/MEDLINE, Cochrane Library, and Embase databases were searched for articles related to AC and NGB.

RESULTS

AC is indicated for an overactive or poorly compliant bladder refractory to conservative therapies, such as anticholinergic medications and bladder botulinum toxin injections. A variety of surgical techniques using gastrointestinal segments, alternative tissues, and synthetic materials have been described, though bowel remains the most durable. Ileocystoplasty is the most common type of AC, which uses a detubularized patch of ileum that is anastomosed to a bivalved bladder. Some patients undergo concomitant surgeries at the time of AC, such as catheterizable channel creation to aid with clean intermittent catheterization, ureteral reimplantation to treat vesicoureteral reflux, and bladder outlet procedure to treat incontinence. Following AC, the majority of patients experience an improvement in bladder capacity, compliance, and continence. Most patients also experience an improvement in quality of life. AC has significant complications, such as chronic UTIs, bladder and renal calculi, metabolic disturbances, bowel problems, perforation, and malignancy. AC also has a high rate of follow-up surgeries, especially if the patient undergoes concomitant creation of a catheterizable channel.

CONCLUSIONS

Enterocystoplasty remains the gold standard for AC, though more research is needed to better evaluate the morbidity of different surgical techniques and the indications for concomitant surgeries. Experimental methods of AC with tissue engineering are a promising area for further investigation.