Abstract The vagina is a viscoelastic fibromuscular organ that provides support to the pelvic organs. The viscoelastic properties of the vagina are understudied but may be critical for pelvic stability. Most studies evaluate vaginal viscoelasticity under a single uniaxial load; however, the vagina is subjected to dynamic multiaxial loading in the body. It is unknown how varied multiaxial loading conditions affect vaginal viscoelastic behavior and which microstructural processes dictate the viscoelastic response. Therefore, the objective was to develop methods using extension-inflation protocols to quantify vaginal viscoelastic creep under various circumferential and axial loads. Then, the protocol was applied to quantify vaginal creep and collagen microstructure in the fibulin-5 wildtype and haploinsufficient vaginas. To evaluate pressure-dependent creep, the fibulin-5 wildtype and haploinsufficient vaginas (n = 7/genotype) were subjected to various constant pressures at the physiologic length for 100 s. For axial length-dependent creep, the vaginas (n = 7/genotype) were extended to various fixed axial lengths then subjected to the mean in vivo pressure for 100 s. Second-harmonic generation imaging was performed to quantify collagen fiber organization and undulation (n = 3/genotype). Increased pressure significantly increased creep strain in the wildtype, but not the haploinsufficient vagina. The axial length did not significantly affect the creep rate or strain in both genotypes. Collagen undulation varied through the depth of the subepithelium but not between genotypes. These findings suggest that the creep response to loading may vary with biological processes and pathologies, therefore, evaluating vaginal creep under various circumferential loads may be important to understand vaginal function.
more »
« less
History-Dependent Deformations of Rat Vaginas under Inflation
The vagina is a highly inhomogeneous, anisotropic, and viscoelastic organ that undergoes significant deformations in vivo. The mechanical attributes of this organ facilitate important physiological functions during menstruation, intercourse, and birthing. Despite the crucial mechanical role that the vagina plays within the female reproductive system, the deformations that the organ can sustain over time under constant pressure, in both the longitudinal direction (LD) and circumferential direction (CD), have not been fully characterized. This experimental study focuses on quantifying the creep properties of the vagina via ex vivo inflation testing using the rat as an animal model. Toward this end, rat vaginas were subjected to three consecutively increasing constant luminal pressures (28, 55, and 83 kPa) using a custom-built experimental setup and the resulting inhomogeneous deformations were measured using the digital image correlation (DIC) method. The vagina was found to deform significantly more in the CD than the LD at any constant pressure, suggesting that the organ primarily adapts to constant pressures by significantly changing the diameter rather that the length. The change in deformation over time was significantly higher during the first inflation test at a constant pressure of 28 kPa than during the second and third inflation tests at constant pressures of 55 and 83 kPa, respectively. The findings of this study on the mechanical behavior of the vagina could serve to advance our limited knowledge about the physiology and pathophysiology of this important reproductive organ.
more » « less- NSF-PAR ID:
- 10469025
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Integrative And Comparative Biology
- Volume:
- 62
- Issue:
- 3
- ISSN:
- 1540-7063
- Format(s):
- Medium: X Size: p. 625-640
- Size(s):
- ["p. 625-640"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Abstract Pelvic organ prolapse (POP) is a condition characterized by displacement of the vagina from its normal anatomical position leading to symptoms such as incontinence, physical discomfort, and poor self-image. Conservative treatment has shown limited success and surgical procedures, including the use of mesh, often lead to severe complications. To improve the current treatment methods for prolapse, the viscoelastic properties of vaginal tissue need to be characterized. We determined the biaxial stress relaxation response of vaginal tissue isolated from healthy pubertal gilts. Square specimens (n = 20) with sides aligned along the longitudinal directions (LD) and circumferential direction (CD) of the vagina were biaxially displaced up to 5 N. The specimens were then kept at the displacements corresponding to 5 N for 20 min in both the LD and CD, and the corresponding strains were measured using digital image correlation (DIC). The stresses in the LD and CD were found to decrease by 49.91 ± 5.81% and 46.22 ± 5.54% after 20 min, respectively. The strain in the LD and CD increased slightly from 0.080 ± 0.054 to 0.091 ± 0.064 and 0.050 ± 0.039 to 0.058 ± 0.047, respectively, but these changes were not significant (p > 0.01). By using the Peleg model, the initial decay rate and the asymptotic stress during stress relaxation were found to be significantly higher in the LD than in the CD (p≪0.001), suggesting higher stress relaxation in the LD. These findings may have implications for improving current surgical mesh, mechanical devices, and physical therapy used for prolapse treatment.more » « less
-
Abstract Higher reproductive age is associated with an increased risk of gestational diabetes, pre-eclampsia, and severe vaginal tearing during delivery. Further, menopause is associated with vaginal stiffening. However, the mechanical properties of the vagina during reproductive aging before the onset of menopause are unknown. Therefore, the first objective of this study was to quantify the biaxial mechanical properties of the nulliparous murine vagina with reproductive aging. Menopause is further associated with a decrease in elastic fiber content, which may contribute to vaginal stiffening. Hence, our second objective was to determine the effect of elastic fiber disruption on the biaxial vaginal mechanical properties. To accomplish this, vaginal samples from CD-1 mice aged 2–14 months underwent extension-inflation testing protocols (n = 64 total; n = 16/age group). Then, half of the samples were randomly allocated to undergo elastic fiber fragmentation via elastase digestion (n = 32 total; 8/age group) to evaluate the role of elastic fibers. The material stiffness increased with reproductive age in both the circumferential and axial directions within the control and elastase-treated vaginas. The vagina demonstrated anisotropic mechanical behavior, and anisotropy increased with age. In summary, vaginal remodeling with reproductive age included increased direction-dependent material stiffness, which further increased following elastic fiber disruption. Further work is needed to quantify vaginal remodeling during pregnancy and postpartum with reproductive aging to better understand how age-related vaginal remodeling may contribute to an increased risk of vaginal tearing.more » « less
-
more » « less
Abstract The vagina undergoes large finite deformations and has complex geometry and microstructure, resulting in material and geometric nonlinearities, complicated boundary conditions, and nonhomogeneities within finite element (FE) simulations. These nonlinearities pose a significant challenge for numerical solvers, increasing the computational time by several orders of magnitude. Simplifying assumptions can reduce the computational time significantly, but this usually comes at the expense of simulation accuracy. This study proposed the use of reduced order modeling (ROM) techniques to capture experimentally measured displacement fields of rat vaginal tissue during inflation testing in order to attain both the accuracy of higher‐fidelity models and the speed of simpler simulations. The proper orthogonal decomposition (POD) method was used to extract the significant information from FE simulations generated by varying the luminal pressure and the parameters that introduce the anisotropy in the selected constitutive model. A new data‐driven (DD) variational multiscale (VMS) ROM framework was extended to obtain the displacement fields of rat vaginal tissue under pressure. For comparison purposes, we also investigated the classical Galerkin ROM (G‐ROM). In our numerical study, both the G‐ROM and the DD‐VMS‐ROM decreased the FE computational cost by orders of magnitude without a significant decrease in numerical accuracy. Furthermore, the DD‐VMS‐ROM improved the G‐ROM accuracy at a modest computational overhead. Our numerical investigation showed that ROM has the potential to provide efficient and accurate computational tools to describe vaginal deformations, with the ultimate goal of improving maternal health.
-
null (Ed.)Abstract The vagina is an important organ of the female reproductive system that has been largely understudied in the field of biomechanics. In recent years, some research has been conducted to evaluate the mechanical properties of the vagina, but much has focused on characterizing the passive mechanical properties. Because vaginal contractions play a central role in sexual function, childbirth, and development and treatment of pelvic floor disorders, the active mechanical properties of the vagina must be also quantified. This review surveys and summarizes published experimental studies on the active properties of the vagina including the differences in such properties determined by anatomic regions and orientations, neural pathways, life events such as pregnancy and menopause, pelvic floor disorders such as prolapse, and surgical mesh treatment. Conflicting experimental findings are presented, illustrating the need for further research on the active properties of the vagina. However, consensus currently exists regarding the negative impact of surgical mesh on vaginal contractility. This review also identifies knowledge gaps and future research opportunities, thus proving a firm foundation for novice and experienced researchers in this emerging area of biomechanics and encouraging more activity on women's sexual and reproductive health research.more » « less
