Department of Mechanical Engineering, Birla Institute of Technology and Science-Pilani, K K Birla Goa Campus, Zuarinagar, Sancoale, Goa, 403726, India.
Department of Biological Sciences, Birla Institute of Technology and Science-Pilani, K K Birla Goa Campus, Zuarinagar, Sancoale, Goa 403726, India.
Phys Biol. 2024 Sep 24;21(6). doi: 10.1088/1478-3975/ad7b1a.
Rheotaxis is a fundamental mechanism of sperm cells that guides them in navigating towards the oocyte. The present study investigates the phenomenon of sperm rheotaxis in Newtonian and non-Newtonian fluid media, which for the first time explores a viscosity range equivalent to that of the oviductal fluid of the female reproductive tract in rectilinear microfluidic channels. Three parameters, the progressive velocity while performing rheotaxis, the radius of rotation during rheotaxis, and the percentage of rheotactic sperm cells in the bulk and near-wall regions of the microfluidic channel were measured. Numerical simulations of the flow were conducted to estimate the shear rate, flow velocity, and the drag force acting on the sperm head at specific locations where the sperms undergo rheotaxis. Increasing the flow velocity resulted in a change in the position of rheotactic sperm from the bulk center to the near wall region, an increase and subsequent decrease in the sperm's upstream progressive velocity, and a decrease in the radius of rotation. We observed that with an increase in viscosity, rheotactic sperms migrate to the near wall regions at lower flow rates, the upstream progressive velocity of the sperm decreases for Newtonian and increases for non-Newtonian media, and the radius of rotation increases for Newtonian and decreases for non-Newtonian media. These results quantify the effects of fluid properties such as viscosity and flow rate on sperm rheotaxis and navigation, thereby paving the way for manipulating sperm behavior in microfluidic devices, potentially leading to advancements in assisted reproduction techniques.
趋流性是精子的一种基本运动机制，可引导其向卵子游动。本研究调查了在牛顿流体和非牛顿流体介质中精子趋流性的现象，这首次在直线微流控通道中探索了与雌性生殖道卵卵管液相当的粘度范围。测量了在趋流性过程中精子的渐进速度、趋流过程中的旋转半径以及微流道 bulk 和近壁区域中趋流性精子的百分比等三个参数。对流动进行了数值模拟，以估计在精子经历趋流性的特定位置处的剪切率、流速和作用在精子头部的阻力。增加流速会导致趋流性精子从 bulk 中心移动到近壁区域，精子的上游渐进速度增加然后减小，旋转半径减小。我们观察到，随着粘度的增加，趋流性精子在较低流速下迁移到近壁区域，牛顿流体中精子的上游渐进速度减小，而非牛顿流体中增加，牛顿流体中旋转半径增加，而非牛顿流体中减小。这些结果量化了诸如粘度和流速等流体性质对精子趋流性和导航的影响，从而为在微流控装置中操纵精子行为铺平了道路，可能会推动辅助生殖技术的发展。
