A Novel Engineered Sling Treats Stress Incontinence without Adhesion Formation in a Rat Model

Objectives: The polypropylene (PP) mesh mid-urethral sling is the current standard of care for surgical treatment of stress urinary incontinence (SUI). Postoperative complications requiring mesh excision and removal can be difficult due to substantial tissue infiltration into the large mesh pores. A new mesh implant was developed using expanded polytetrafluoroethylene (PTFE) with similar tensile strength and compliance as PP, but with a microporous structure. This study compared the novel PTFE implant to PP in (1) the treatment of SUI in an acute pre-clinical rat model and (2) the ease of implant extraction, adhesion formation, and induced histological changes 1 week after implantation.

Methods: We obtained normal baseline cystometry with leak point pressure (LPP) values on 12 female Sprague-Dawley rats via suprapubic bladder catheter. Bilateral pudendal nerve transection (PNT) was then performed to induce SUI and cystometry with LPP was repeated. Either the novel PTFE implant or the PP implant was then placed under the mid-urethra and anchored to the rectus muscle and fascia via laparotomy. Final cystometry with LPP values were measured. Separately, 14 female Sprague-Dawley rats underwent bilateral PNT followed by placement of either the novel PTFE implant, a PP implant, or sham implantation. One week after implantation, implant removal was timed and adhesions were scored on a 3-point grading scale (0=no adhesions, 1=thin adhesions, 2=focal dense adhesions, 3=dense widespread adhesions). The urethra and anterior vagina were dissected en bloc for histology. One-way ANOVA compared cytometry and LPP results; two-tail T-test compared removal times; and Chi-squared test compared adhesion scores with p< 0.05 indicating a statistically significant difference. Histology was assessed qualitatively.

Results: PNT resulted in significantly decreased LPP compared to control (p < 0.001). This decreased LPP recovered after implantation of either PTFE (p=0.03) or PP (p < 0.01) implants (see Figure). LPP was not significantly different between control, PTFE, or PP implants. There were no differences between groups in baseline pressure, residual volume, bladder capacity, bladder compliance, peak voiding pressure, or duration of voiding cycle. PTFE implants took significantly less time to remove (2.7 ± 1.3 sec) compared to PP implants (428 ± 134.6 sec; p=0.002). PTFE implants created significantly less adhesions (0 ± 0) than PP implants (2 ± 0; p=0.001). All groups had a comparable mild inflammatory response as seen with H&E. Both implant types induced a slight increase of collagen infiltration compared to sham implantation as seen on Masson’s Trichrome.

Conclusions: PNT successfully modeled SUI in this pre-clinical rat model. PTFE and PP implants comparably resolved the acute PNT-induced SUI. PTFE implants did not create adhesions 1 week after implantation, which enabled significantly faster removal. PP and PTFE induced similar histologic changes. This novel PTFE implant has the potential to improve SUI, while allowing easy extraction should removal be necessary.