Design and Material Characterization of an Inflatable Vaginal Dilator

Abstract

There are more than 13,000 new cases of cervical cancer each year in the United States and approximately 245,000 survivors. External beam radiation and brachytherapy are the front-line treatment modalities, and 60% of patients develop vaginal damage and constriction, i.e., stenosis of the vaginal vault, greatly impeding sexual function. The incidence of vaginal stenosis (VS) following radiotherapy (RT) for anorectal cancer is 80%. VS causes serious quality of life (QoL) and psychological issues, and while standard treatment using self-administered plastic dilators is effective, acceptance and compliance are often insufficient. Based on published patient preferences, we have pursued the design of a soft inflatable dilator for treating radiotherapy-induced vaginal stenosis (VS). The critical component of the novel device is the dilator balloon wall material, which must be compliant yet able to exert therapeutic lateral force levels. We selected a commercially available silicone elastomer and characterized its stress-strain characteristics and hyperelastic properties. These parameters were quantified using uniaxial tensile testing and digital image correlation (DIC). Dilator inflation versus internal pressure was modeled and experimentally validated in order to characterize design parameters, particularly the dilator wall thickness. Our data suggest that an inflatable silicone elastomer-based vaginal dilator warrants further development in the context of a commercially available, well-tolerated, and effective device for the graded, controlled clinical management of radiotherapy-induced VS.

Keywords: Mooney–Rivlin model; digital image correlation; finite element analysis; hyperelastic materials; inflatable vaginal dilator; silicone.

Figure 1

MRI image (A) before and (B) after pelvic irradiation treatment. The black arrows of (B) show the shorting and narrowing of the upper 2/3 of the vaginal anatomy [14].

Figure 2

Commercially available vaginal dilators.

Figure 3

Inflatable dilator.

Figure 4

Manufacturing steps of an inflatable vaginal dilator. (a) 3D printed inner rod and mold housing; (b) molding of silicone sleeve; (c) thin silicone sleeve after removing from the mold; (d) assembled inner rod and silicone sleeve.

Figure 5

Stress–strain curve of elastic and hyperelastic material.

Figure 6

Stress–stretch plot of two-term Mooney–Rivlin curve fit [39,40,41].

Figure 7

(a) Uniaxial tensile tester, (b) coupon specimen with random dot pattern, and (c) high-resolution digital camera.

Figure 8

Stress–stretch experimental data and Mooney–Rivlin fit for silicone.

Figure 9

Stress–stretch plot of two-term Mooney–Rivlin curve fit (from the literature and experiment) [39,40,41].

Figure 10

Boundary conditions of vaginal dilator for finite element analysis.

Figure 11

Longitudinal cross-section of dilator (2 mm wall thickness) as a function of pressure calculated using finite element analysis compared to real image of dilator.

Figure 12

Area of longitudinal cross-section dilator as a function of pressure for wall thicknesses of 2 mm, 2.5 mm, 3 mm, and 3.5 mm, respectively (numerical results).

Figure 13

Experimental setup.

Figure 14

Area of longitudinal cross-section dilator versus pressure for wall thicknesses of 2 mm, 2.5 mm, 3 mm, and 3.5 mm, respectively (experimental results).