By Lina Sorg
Fertilization in mammals involves coordination among movement of spermatozoa, uterus and oviduct contraction, and the beating of cilia. “There is no better illustration of complex fluid-structure interactions than mammalian reproduction,” Fauci said. Elastic structures generate forces that drive fluid motion, and fluid dynamics in the environment determine the structures’ configuration and arrangement. For example, for sperm flagella to successfully move into the oviduct, uterine peristalsis and flagellar and ciliary beating must occur. Sperm may also need to change their oscillation patterns to escape potential adherence to oviduct epithilia; otherwise they risk getting caught in the mucosal folds.
She then posed a series of questions to the full lecture hall that included the following: (1) what are the biochemical pathways that initiate hyperactivation? (2) How do these biochemical signals change the internal force-generating mechanisms? (3) What are the complications? Fauci also addressed the many choices accompanying development of a mathematical model, including the decision to model in two or three dimensions. “Life is 3D, but perhaps we could learn something from 2D models” Fauci said. Thus, even though the waveform is planar, the fluid mechanics are three-dimensional and hence can be studied in two dimensions.
Lastly, Fauci described a model simulating the process of human reproduction, where the fetus is manifested as a rigid cylinder and the uterus as a flexible tube. This is then used to measure the fluid dynamics forces, as very little information is known about the forces a fetus experiences during birth. She concluded with a humorous motivation for those in the field. "For the fluid mechanists in the audience, forget the baby,” she said, “this is an interesting fluid mechanics problem!” Pausing, she added cheekily,” I didn't really mean forget the baby.”