NUMERICAL SIMULATION OF A SPERM CELL IN SHEAR FLOW NEAR AN INFINITE BOUNDARY WALL
Toshihiro Omori, Takuji Ishikawa
Tohoku University, Japan
Mammalian sperm cells must find and keep right swimming directions during their journey from ejaculation to fertilization to fin the egg cell. Though many researchers have investigated sperm motility and various long-distance navigation mechanism were proposed (eg. chemotaxis, thermotaxis), it is still not clear how sperm cells find the correct swimming direction. Recently, one possible mechanism, rheotaxis was observed experimentally, and fluid mechanics has become a subject of growing importance in sperm motility. In this study, we numerically investigated sperm cell locomotion in shear flow near a boundary wall, and clarified how fluid flows affect on the sperm motility.
Due to small size of sperm cells, fluid motion around the cell can be assumed as Stokes flow and flow field is described by a boundary integral equation, which was solved by a boundary element method. We also assumed force-free and torque-free conditions of sperm cell swimming. To mimic former experimental studies, the sperm cell near plane wall was simulated. The results showed that, under shear flow, the sperm is able to hydrodynamically change its swimming direction, allowing it to swim upwards against the flow. Which suggests that the upward swimming of sperm cells can be explained using fluid mechanics, and this can then be used to further understand physiology of sperm cell navigation.