Experimental characterization of the non-linear viscoelastic properties of human female perineal tissue

The female perineum plays a critical role in several physiological processes. During childbirth, this region undergoes significant stretching, resulting in perineal trauma in over 90% of vaginal deliveries. Despite advances in obstetric care, predicting and preventing such injuries remains challenging. Computational models offer a non-invasive approach to investigate female pelvic biomechanics. However, their reliability depends on a deeper understanding of perineal mechanics, an area that remains understudied. This study addresses this gap by characterizing the mechanical behavior of the human female perineal body. Perineal samples were obtained post-mortem from six women and subjected to stress-relaxation tests and ultimate tensile tests up to failure. A genetic algorithm and finite element simulations calibrated the material parameters of a visco-hyperelastic model to fit the experimental data. Stress-relaxation tests demonstrated a 40% stress reduction after 900 seconds, highlighting the tissue's time-dependent behavior. The ultimate Cauchy stress was 224.70 ± 131.69 kPa at a stretch of 1.97. Histology revealed preferential fiber alignment with the direction of physiological stretching. Three ranges of material parameters were calibrated, enabling the data to be used in future computational simulations. The findings provide valuable insights into the mechanics of the female perineum, facilitating more accurate simulations. This study contributes to ongoing efforts to enhance the understanding, prevention, and management of pelvic floor dysfunctions. Graphic Abstract.