Augmentation Cystoplasty of Diseased Porcine Bladders with Bi-Layer Silk Fibroin Grafts
Saif Affas, MD1, Frank-Mattias Schafer, MD1, Khalid Algarrahi, MD1, Vivian Cristofaro, PhD2, Maryrose Sullivan, PhD2, Xuehui Yang, MSc1, Kyle Costa, BSc1, Bryan Sack, MD1, Jill Macoska, PhD3, Gokhan Gundogdu, MD1, Catherine Seager, MD1, Carlos R. Estrada, MD, MBA1, Joshua R. Mauney, PhD1.
1Boston Children's Hospital, Boston, MA, USA, 2Boston VA Medical Center, Boston, MA, USA, 3The University of Massachusetts, Boston, MA, USA.
Background: Partial bladder outlet obstruction (pBOO) from congenital disorders such as posterior urethral valves and neurogenic bladder results in reduced bladder capacity, impaired compliance, incontinence, and possibly renal damage. Enterocystoplasty is utilized in patients that fail medical management. However, this procedure is associated with significant complications including chronic urinary tract infection and metabolic abnormalities. Bi-layer, silk fibroin (BLSF) matrices derived from Bombyx mori silkworm cocoons represent promising acellular grafts for bladder tissue engineering due to their low immunogenicity, robust mechanical properties, and tunable biodegradability. Preclinical validation of this scaffold technology for augmentation cystoplasty in a large animal model of pBOO is a crucial step toward clinical translation. The objective of this study is to develop a minimally invasive, porcine model of pBOO and determine the ability of BLSF matrices to mediate functional tissue formation in diseased bladders subjected to obstruction. Methods: Sixteen adult female, mini-swine were fitted with a transient urinary catheter containing controlled release valves capable of producing either mild (m-pBOO, 35±10 cmH2O, N=5) or severe (s-pBOO, 70±15 cmH2O, N=11) urinary outlet resistance for a period of 2 or 4 weeks, respectively. Following obstructive insults, augmentation cystoplasty was performed with BLSF grafts (6 cm diameter) and animals were harvested at 1 or 3 months post-repair. Outcome evaluations were performed at baseline prior to pBOO, 4 weeks following initiation of pBOO, and at 1 or 3 months after bladder reconstruction and included urodynamics, cystography, histological and immunohistochemical analyses, and ex vivo contractility assessments. Nonsurgical control (NSC, N=3) swine were tested in parallel. Results: Urodynamic evaluations of swine following m-pBOO and s-pBOO displayed significant reductions in bladder capacity reflecting 63±19% and 39±13% of noninjured levels, while the s-pBOO cohort demonstrated a 61% decline in bladder compliance from baseline. Histological assessments revealed that both injured groups displayed significant 4-5-fold increases in collagen content over controls. In contrast to m-pBOO, s-pBOO caused a significant reduction in smooth muscle content, urothelial dysplasia, increased vascularity, and diminished agonist-induced contractility relative to NSC. By 3 months post-reconstruction, bladder capacity and compliance in the augmented s-pBOO group were significantly increased over post-pBOO values reflecting 79±19% and 171±75% of baseline quantities, respectively. In addition, bladder capacity in the m-pBOO cohort was similar to pre-injury measurements. Neotissues were present at graft sites 3 months post-op in both injury groups and displayed SM22α+ smooth muscle, pan-cytokeratin+ epithelia, vessels lined with CD31+ endothelial cells, and neurofilament 200+ nerve trunks. All de novo tissues demonstrated contractile responses to KCl, electrical field stimulation, α,β-methyleneATP, and carbachol. Conclusion: We show that a novel large animal model of pBOO allows for specific modulation of bladder injury responses which are consistent with clinically-relevant, disease phenotypes. Utilizing this model, we demonstrate that BLSF scaffolds can promote improvements in bladder capacity and compliance as well as support the formation of neotissues with functional properties in diseased bladders.
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