Bull sperm rheotaxis and kinematics in microfluidic channels with different heights

Abstract

Recently, microfluidics has attracted a lot of attention in reproduction due to its ability to simulate the natural environment inside the female reproductive tract and its ability to separate high-quality sperm cells using rheotaxis as a selection mechanism. Positive rheotaxis refers to the ability of the sperm to direct itself and swim against liquid current during the fertilization journey. In this study, we investigated the effects of various microchannel heights on sperm positive rheotaxis (PR) and sperm kinematics. We used two microchannels with the same width (200µm) and different heights (channel 1= 20 µm height and channel 2= 100 µm height). Sperm samples were obtained from two bulls with known fertility and analyzed using CASA. The results showed that PR and all sperm kinematics (VCL, VSL, VAP, and BCF), except linearity, were significantly higher in microchannel 2 with a greater height (100 µm) than in microchannel 1 with a lower height (20 µm). Our findings indicate that PR percentage and sperm kinematic values in microfluidic platforms depend mainly on microchannel dimensions, which have a direct influence on the velocity profile inside the channel. These results could be useful for the development of microfluidic devices used for sperm separation and selection in the future.