Evaluation of Bi-Layer Silk Fibroin Grafts for Penile Tunica Albuginea Repair in a Rabbit Corporoplasty Model
Gokhan Gundogdu, MD1, Zhamishid Okhunov, MD1, Stephanie Starek, LAT1, Faith Veneri, BS1, Sarah A. Holzman, MD2, Maryrose P. Sullivan, PhD3, Antoine E. Khoury, MD2, Joshua R. Mauney, PhD1.
1UC Irvine, Orange, CA, USA, 2CHOC Children's and UC Irvine, Orange, CA, USA, 3Harvard Medical School, Veteran's Affairs Boston Healthcare System, Brigham and Women's Hospital, Boston, MA, USA.
Background: Complete correction of penile curvature in hypospadias is critical to prevent long term complications and preserve future sexual and erectile function. Higher degrees of chordee require corporoplasty for adequate correction and preservation of penile length. While autologous grafts and flaps can be used to replace tunica albuginea in corporoplasty, the availability of autologous tissue can be limited in hypospadias patients, especially patients with concomitant cryptorchidism. Therefore, there is a need for new biomaterial options for corporoplasty. Acellular, bi-layer silk fibroin (BLSF) biomaterials represent promising platforms for corporoplasty given their low immunogenicity. Additionally, the BLSF’s bi-layer architecture has the potential to preserve hemodynamics during erection with a fluid-tight film layer preventing blood extravasation from the corpus cavernosa. Here, we investigate BLSF scaffolds to support functional tissue regeneration of tunica albuginea defects in a rabbit corporoplasty model.
Methods: Eighteen adult male, New Zealand white rabbits were randomized into 4 experimental groups and treated as 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). Three months following surgery, end-point evaluations of reconstructed penile tissues and NSC included cavernosography, cavernosometry, histological(Masson’s trichrome, Verhoeff Van Gieson stains), immunohistochemical (collagen type I), and histomorphometric assessments. Kruskal-Wallis (KW) test was used for statistical analysis of quantitative data with the post hoc Dunn's test for pairwise comparisons.
Results: All rabbits survived corporoplasty procedures and were maintained for 3 months until scheduled euthanasia. There were no significant differences (KW, p>0.05) in mean operative times between experimental cohorts (BLSF scaffolds, 67±13 minutes; SIS implants, 78±22 minutes; TV flaps, 83±13 minutes). No significant differences (KW, p>0.05) in maximum intracorporal (ICP) values were observed between NSC (296±6 cmH2O) and experimental groups (BLSF: 240±70 cmH2O; SIS: 286±21 cmH2O; TV: 269±51 cmH2O). Rabbits repaired with BLSF scaffolds or TV flaps achieved full rigid erections in 80% of their respective cohorts, in contrast to 40% of animals reconstructed with SIS grafts. Peak erections were maintained for 5 minutes in 60% of rabbits implanted with BLSF biomaterials, while only 20% of animals reconstructed with SIS or TV flaps supported maximum ICP values for the same duration. Graft perforation occurred in 60% of the TV group at maximum ICP levels in comparison to 20% of the BLSF cohort. Neotissues supported by SIS and BLSF scaffolds were composed of collagen type I and elastin fibers similar to the architecture in NSC. In contrast to the BLSF group, quantitation of total collagen content in the penile corpora of Masson’s trichrome stained specimens demonstrated a significant 15-17 fold increase in corporal fibrosis in SIS and TV cohorts compared to NSC (Figure 1).
Conclusions: BLSF biomaterials represent an emerging platform for corporoplasty and produce superior functional and histological outcomes in comparison to TV flaps and SIS grafts for tunica albuginea replacement. 
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