Tearing of Vaginal Tissue under Biaxial Loading: Implications for Women's Health

Around 80% of women experience vaginal tears during labor when the diameter of the vagina must increase from ~2.5 cm to ~9.5 cm to allow the passage of a full-term baby. Vaginal tears vary from superficial cuts of the mucosal lining to tears propagating through the entire vaginal wall and into the surrounding tissues and organs. Complications associated with vaginal tears include postpartum hemorrhaging, fecal incontinence, urinary incontinence, and dyspareunia. Beyond the agonizing pain, these complications are emotionally and psychologically traumatic for women. Prevention, evaluation, and treatment of vaginal tears and subsequent conditions are limited due to the lack of studies examining the mechanical behavior of the pelvic floor tissues. Therefore, the mechanical response of healthy and torn vaginal tissue is investigated here to establish quantitative metrics for maternal healthcare.

Toward this end, swine and rat vaginal tissue is subjected to biaxial loads until tearing to reveal its mechanical properties. The resulting large inhomogeneous deformations are measured by the digital image correlation optical method to calculate material strain. The influence of these strains near to and far from the immediate vicinity of the tears on the tearing behavior is studied. Coupling mechanisms of the mechanical properties in the circumferential and axial directions as well as their effect on the nature of tear resistance is studied. Collagen fibers, the component within tissue responsible for its strength under tension, are imaged using a multiphoton microscopy technique known as second-harmonic generation imaging to investigate the change in organization with mechanical loading. Furthermore, imaging is performed in the near-regions of tears to reveal the relationship between collagen fibers and tearing resistance. The data collected through these studies provide new knowledge on the nonlinear elastic behavior of vaginal tissue, the geometrical and micro-structural characteristics of tears, and the mechanisms that contribute to the formation and propagation of tears.

The mechanical properties and tearing mechanisms of vaginal tissue will be crucial in developing new prevention and treatment methods for maternal trauma following childbirth. Episiotomy, late-term stretching, surgical treatment with graft materials and other protocols will all benefit from a mechanically-informed perspective. It is our hope that this work will raise awareness to the serious complexities of pelvic floor trauma and encourage a more refined and systematic approach to the inspection, imaging, and treatment of all vaginal tears following delivery.

This work was supported in part by the National Science Foundation fund #1511603 and the Institute for Critical Technology and Sciences at Virginia Tech.