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

Abstract

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.

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

“…Prior to surgery, animals were fasted overnight with unabated access to water. General anesthesia was induced and maintained in swine as previously described ( Gundogdu et al, 2021a ). Animals were then fixed in the supine position and renal sonography was performed as described below.…”

“…This stent was fixed to the stoma edges with two additional nylon sutures. Both ureteral and conduit stents were replaced in all swine at 1 and 2 months post-operatively or at intermediate timepoints if stent dislodgement occurred, using standard procedures ( Gundogdu et al, 2021a ). Briefly, an 8.5 French, 90 cm single J stent (Gyrus Medical Ltd., Wokingham, United Kingdom) was deployed into the renal pelvis using guidewire assistance and conduit stents were replaced as previously described.…”

“…Protein-based, bi-layer silk fibroin (BLSF) grafts represent an ideal platform for the construction of urinary conduits due to their high tensile strength and elasticity, low immunogenicity, and tunable biodegradability ( Sack et al, 2016 ). These matrices can be easily sutured and utilized as sheets or tubes for urinary tract reconstruction ( Affas et al, 2019 ; Gundogdu et al, 2021a ). The structural architecture of the bi-layer matrix prevents urinary extravasation at scaffold integration sites via a fluid-tight film component, while an annealed porous foam layer supports surrounding tissue ingrowth ( Seth et al, 2013 ; Tu et al, 2013 ).…”

“…The structural architecture of the bi-layer matrix prevents urinary extravasation at scaffold integration sites via a fluid-tight film component, while an annealed porous foam layer supports surrounding tissue ingrowth ( Seth et al, 2013 ; Tu et al, 2013 ). Previous studies from our laboratory have demonstrated the utility of these scaffolds for augmentation cystoplasty, urethroplasty, corporoplasty and ureteroplasty in preclinical animal models ( Algarrahi et al, 2018 ; Affas et al, 2019 ; Gundogdu et al, 2021a ; Gundogdu et al, 2021b ). BLSF grafts have also been shown to promote formation of innervated, vascularized neotissues with functional contractile/relaxation properties and less inflammatory reactions compared to traditional decellularized matrices such as SIS scaffolds ( Chung et al, 2014a ; Chung et al, 2014b ; Algarrahi et al, 2015 ).…”

Gelatin-grafted tubular asymmetric scaffolds promote ureteral regeneration via activation of the integrin/Erk signaling pathway

“…Great attention has been focused on ureteral tissue engineering as a potential alternative of autologous grafts. Many materials, like acellular matrices, natural polymers, and synthetic polymers, have been studied and developed ( Liao et al, 2013 ; Meng et al, 2015 ; de Jonge et al, 2018 ; Zhao et al, 2019 ; Gundogdu et al, 2021 ). However, ureteral repair has not been optimized because of the frequent formation of the fistula or/and stenosis caused by the insufficient bio-features of materials.…”