Mechanical Characterization of Ring Pessary Folding

Understanding the mechanical properties of current pessaries is important to improve on existing designs and innovate on novel solutions. Our objective was to mechanically characterize the force required to compress ring pessaries into a folded shape. We hypothesized that the force required to fold ring pessaries would scale inversely with the diameter squared. We conducted a compression test on ring pessaries to analyze their folding behavior using a mechanical universal testing system. Ring pessaries size #1 through #7 (diameters 50.1–86.7 mm) were placed in the testing platform in a vertical orientation with the bending axis in the horizontal plane. An axial load was applied to induce deformation. With application of an axial force, all pessaries first showed in-plane deformation followed by out-of-plane buckling. Increasing force resulted in a transition between in-plane deformation and out-of-plane buckling, during which the pessary began to fold, analogous to classic Euler buckling of columns. This transition was reflected in the loading curve as a sharp change in slope between the initial strain-softening region and a subsequent nearly horizontal plateau region. The force at the transition point ranged from 4.4 N for a size #7 pessary to 23.5 N for a size #1 pessary. The relationship between force and diameter at the transition point appeared to approximate a 1/L2 dependence, where L is the pessary diameter. Pessary mechanics show buckling and folding behavior with a dependence on pessary architecture. The force required to fold ring pessaries scales inversely with the pessary diameter squared.