Swine Vagina Under Planar Biaxial Loads: An Investigation of Large Deformations and Tears

Abstract

Vaginal tears are very common and can lead to severe complications such as hemorrhaging, fecal incontinence, urinary incontinence, and dyspareunia. Despite the implications of vaginal tears on women's health, there are currently no experimental studies on the tear behavior of vaginal tissue. In this study, planar equi-biaxial tests on square specimens of vaginal tissue, with sides oriented along the longitudinal direction (LD) and circumferential direction (CD), were conducted using swine as animal model. Three groups of specimens were mechanically tested: the NT group (n = 9), which had no pre-imposed tear, the longitudinal tear (LT) group (n = 9), and the circumferential tear (CT) group (n = 9), which had central pre-imposed elliptically shaped tears with major axes oriented in the LD and the CD, respectively. Through video recording during testing, axial strains were measured for the NT group using the digital image correlation (DIC) technique and axial displacements of hook clamps were measured for the NT, LT, and CT groups in the LD and CD. The swine vaginal tissue was found to be highly nonlinear and somewhat anisotropic. Up to normalized axial hook displacements of 1.15, no tears were observed to propagate, suggesting that the vagina has a high resistance to further tearing once a tear has occurred. However, in response to biaxial loading, the size of the tears for the CT group increased significantly more than the size of the tears for the LT group (p = 0.003). The microstructural organization of the vagina is likely the culprit for its tear resistance and orientation-dependent tear behavior. Further knowledge on the structure–function relationship of the vagina is needed to guide the development of new methods for preventing the severe complications of tearing.

Inflation and rupture of vaginal tissue

“…Although the composition of vaginal tissue has been established, very few studies have investigated the organization of the collagen fibres [22]. In combination with our previous study [12], the mechanical behaviour of the vaginal tissue in this study suggests a preferential orientation of collagen fibres in the axial direction.…”

“…In both Miller's study [10] and our study [11], the vagina was stretched up to sub-failure loads and, for this reason, the loading conditions that lead to tearing were not investigated. Recently, we provided the first characterization of the tear behaviour of the vagina under planar biaxial loading [12]. However, in this study, the tears were pre-imposed and the formation of a tear was not studied.…”

Material properties of skin in the flying snakeChrysopelea ornata

“…Although not statistically significant, it appeared that extensibility is higher in circumferential samples compared to longitudinal or ventral ones, across species. This result is consistent with other studies conducted on tissues having an in vivo tubular structure (McGuire, Abramowitch, et al, 2019; McGuire, Crandall, et al, 2019), where the circumferential stresses are generally higher than the axial stresses. Additionally, the ventral samples appeared to exhibit lower and less variable strain energy and strength than longitudinal or circumferential samples.…”

Engineering and women's health: a slow start, but gaining momentum

“…In the late 2000s and throughout the 2010s, a number of different research groups started to investigate the mechanical properties of the vagina-in particular as it pertains to pelvic organ prolapse. Using excised human tissue taken at the time of proplapse repair surgery [15,16], mouse models [17,18] and swine models for larger tissue sample analysis [19], researchers have been working to more completely characterize the tissue mechanics. Due to the interest in making non-destructive and minimally destructive tests on human tissue samples, procedures have also been developed based on rheological assessment of biopsy samples [20] and in vivo aspiration/suction tests that can be made in volunteers not undergoing surgery [21].…”