Vaginal childbirth, also known as delivery or labor, is the ending phase of pregnancy where one or more fetuses pass through the birth canal from the uterus, which is a biomechanical process. However, the risky process can cause significant injuries to both the fetus and the mother, such as brachial plexus injury, pelvic floor disorders, or even death. Due to technical and ethical reasons, experiments are difficult to conduct on laboring women and their fetuses. The use of computer modeling has become a very promising and rapidly growing way to perform research to improve our knowledge of the biomechanical processes of labor and delivery. The developed simulation models in this field have either focused on the uterine active contraction or the pelvic floor muscles, individually. In addition, there are many limitations existing in the current uterus models.The goal of the project is to develop an integrated model system including the uterus, the fetus, the pelvic bones, and the pelvic muscle floor, which will allow advanced simulation and investigation within the field of biomechanics of fetal delivery. For the first step, a computational model in LS-DYNA simulating the active contraction behaviors of muscle tissue was developed, where the muscle tissue was composed of active contractile fibers using the Hill material model and the passive portion using elastic and hyperelastic material models. The model was further validated with experimental results, which demonstrated the accuracy and reliability of the modeling methodology to describe a muscle’s active contraction and relaxation behaviors. Second, a simulation model of a whole uterus during the second stage of labor was developed, which included active contractile fibers and a passive muscle tissue wall. The effects of the fiber distribution on uterine contraction behaviors were investigated and the delivery of a fetus moving through the uterus due to the contraction was simulated. The developed uterus model included several important uterine mechanical properties, such as the propagation of the contraction wave, the anisotropy of the fiber distribution, contraction intensity variation within the uterus, and the pushing effect on the fetus. Finally, an integrated model system of labor was established by incorporating the pelvic structures with the uterus and fetus models. The model system successfully delivered the fetus from the uterus and through the birth canal. The simulation results were validated based on available data and clinically observed phenomena, such as stress distribution within the uterus, values of Von Mises stress and principal stress of the pelvic floor muscles, rotation and movement of the fetus. Overall, a Finite Element Method model system simulating the labor process was developed in LS-DYNA, which will be used to investigate disorders related to labor, such as neonatal brachial plexus injury and maternal pelvic floor muscle injuries.
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