抄録
The swimming process by which mammal spermatozoa progress towards an egg within the reproductive organs is important in achieving successful internal fertilization. The viscosity of oviductal mucus is more than two orders of magnitude greater than that of water, and oviductal mucus also has viscoelasticity. In this study, we experimentally observed sperm motion in Newtonian and non-Newtonian fluids using the semen of Japanese cattle in order to investigate the effect of viscoelasticity on bovine sperm motility. Furthermore, we visualized flow around sperm by conducting PIV analysis, and investigated shear rate surrounding sperm. We obtained the following results from the experiments. Bovine sperm swim more linearly in high viscous non-Newtonian fluid than in low viscous Newtonian fluid. Bovine sperm swim generating some vortices surrounding flagellum. Especially, the vortices in low viscosity fluid were formed more largely and strongly than one of in non-Newtonian fluid. In low viscosity fluid, high shear rate area distributed wholly around sperm head, whereas in non-Newtonian fluid, high shear rate area distributed only partly around sperm head. This deference in shear rate area imply that sperm changes the way of swinging according to the surrounding fluid. The difference in the way of swimming may lead to the change in linearity of sperm motion.
