Stress State and Strain Rate Dependence of the Human Placenta
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Maternal trauma (MT) in automotive collisions is a source of injury, morbidity, and mortality for both mothers and fetuses. The primary associated pathology is placental abruption in which the placenta detaches from the uterus leading to hemorrhaging and termination of pregnancy. In this study, we focused on the differences in placental tissue response to different stress states (tension, compression, and shear) and different strain rates. Human placentas were obtained (n = 11) for mechanical testing and microstructure analysis. Specimens (n = 4+) were tested in compression, tension, and shear, each at three strain rates (nine testing protocols). Microstructure analysis included scanning electron microscopy, histology, and interrupted mechanical tests to observe tissue response to various loading states. Our data showed the greatest stiffness in tension, followed by compression, and then by shear. The study concludes that mechanical behavior of human placenta tissue (i) has a strong stress state dependence and (ii) behaves in a rate dependent manner in all three stress states, which had previously only been shown in tension. Interrupted mechanical tests revealed differences in the morphological microstructure evolution that was driven by the kinematic constraints from the different loading states. Furthermore, these structure–property data can be used to develop high fidelity constitutive models for MT simulations.
KeywordsHuman placenta biomechanics Stress state dependence Strain rate dependence Maternal traumatic injury Placental abruption
This study is supported by the MAFES SRI (awarded to JL) and Health Resources and Services Administration (HRSA) (DHHS R1CRH10429-01-00). We thank Karen Tiffen, RNC, Chrissy Poole, RNC, Dana Brooks, RNC, Cindy Patton, RN, Heather McMillian, ST, Bella Oswalt, ST, Sonya Anderson, RN, Rene Guines, ST, and other staff members of the Labor & Delivery Unit at OCH Regional Medical Center for their assistance with patient eligibility and tissue procurement; we also appreciate help from Amanda Lawrence (MSU EM Center) for her assistance in SEM imaging. We would also like to thank the Center for Advanced Vehicular Systems (CAVS) at the Mississippi State University for helping to support this research effort.
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