Location: Warmwater Aquaculture Research UnitTitle: Stress state and strain rate dependence of the human placenta) Author
Submitted to: Annals of Biomedical Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/4/2012
Publication Date: N/A
Citation: Interpretive Summary: Pregnant women and their fetuses are particularly susceptible to injury from falls and automotive accidents. This is because the pregnancy, especially the placenta, is not well protected and supported by bones and ligament. Studying trauma is essential to engineering better safety equipment, but ethical and practical issues make pregnant trauma difficult to study. Fortunately, computer simulations of car crashes are a promising way of studying pregnant trauma without the need for expensive and difficult physical experiments. These simulations require mathematical equations about how the materials respond to forces, and more detailed information can make the simulations more accurate. Previous studies have only looked at how placenta responds to a pulling force, but car crashes cause a combination of pulling, squeezing, and twisting forces. Moreover, many materials have been shown to respond differently to the different types of forces. In this study we tested human placenta under each separate type of force. Our results showed that the way placenta responds to the separate types of force is very different. Briefly, placenta resists twisting less than squeezing, and resists squeezing less than pulling. The data sets we obtained show that all 3 types of load are important to include in computer simulations. Future research will incorporate our data into computer simulations of pregnant trauma. These simulations will then be used to study pregnant trauma and improve safety equipment for pregnant women.
Technical Abstract: 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.