Student Yokohama National University, United States
Introduction:: I Infertility is a contributing factor to the declining birth rates and is a growing social concern. Approximately 10-20% of couples have fertility problems, with nearly half of these cases attributed to insufficient or abnormal sperm. The efficient sorting of motile sperm is important for successful infertility treatments. Recent investigations have focused on sorting highly motile sperm in microfluidic channels. This study proposes a novel model that takes into account the swimming characteristics of sperm and numerically investigates their motion in microfluidic channels to develop a more efficient sperm sorter. Most numerical simulations of swimming sperm have been limited due to computational costs and difficulties in application to actual microfluidic channels. This study presents a simplified sperm swimming model that can be analyzed on the same spatio-temporal scale as the environment in the microfluidic channel.
Materials and Methods:: Sperm motility was assumed to be a random walk, with the sperm velocity and straightness obtained from the experiment input as the initial values. We constructed a rheotaxis model in which, a sperm rotated depending to a given velocity gradient. A thigmotaxis model was also developed, in which the velocity component perpendicular to the wall reduced near the wall.
Results, Conclusions, and Discussions:: Using these models, sperm motion in a microfluidic channel with a tapered area was investigated. The simulation results showed that sperm does not accumulate at all when there is no flow in the channel. However, as the flow velocity was increased, the number of sperm accumulating in the taper portion increased, but as the flow velocity was further increased, the sperm accumulation in the taper portion decreased. This was in good agreement with the results obtained from in vitro experiments.
In this study, we constructed a simplified sperm swimming model to predict the performance of the microfluidic channels. The model successfully reproduced the characteristic properties of sperm, that is thigmotaxis and rheotaxis. The model was applied to a microfluidic channel with a taper, and the results successfully predicted sperm accumulation within the taper. Results provide valuable information to enhance sperm sorter geometry for greater efficiency. Furthermore, it is also expected to aid in the fields of assisted reproductive technology and animal husbandry.
