Institut für Festkörperforschung, Forschungszentrum Jülich, Jülich, Germany.
Biophys J. 2010 Aug 9;99(4):1018-26. doi: 10.1016/j.bpj.2010.05.015.
Sperm are propelled by an actively beating tail, and display a wide variety of swimming patterns. When confined between two parallel walls, sperm swim either in circles or on curvilinear trajectories close to the walls. We employ mesoscale hydrodynamics simulations in combination with a mechanical sperm model to study the swimming behavior near walls. The simulations show that sperm become captured at the wall due to the hydrodynamic flow fields which are generated by the flagellar beat. The circular trajectories are determined by the chiral asymmetry of the sperm shape. For strong (weak) chirality, sperm swim in tight (wide) circles, with the beating plane of the flagellum oriented perpendicular (parallel) to the wall. For comparison, we also perform simulations based on a local anisotropic friction of the flagellum. In this resistive force approximation, surface adhesion and circular swimming patterns are obtained as well. However, the adhesion mechanism is now due to steric repulsion, and the orientation of the beating plane is different. Our model provides a theoretical framework that explains several distinct swimming behaviors of sperm near and far from a wall. Moreover, the model suggests a mechanism by which sperm navigate in a chemical gradient via a change of their shape.
精子通过不断摆动的尾巴进行推进，并表现出多种多样的游动模式。当被限制在两个平行壁之间时，精子要么沿圆周游动，要么沿靠近壁面的曲线轨迹游动。我们采用介观流体动力学模拟结合精子力学模型来研究壁面附近的游动行为。模拟结果表明，由于鞭毛拍打产生的流动场，精子会被壁面捕获。圆形轨迹是由精子形状的手性不对称性决定的。对于强（弱）手性，精子以紧密（宽松）的圆形游动，鞭毛的拍打平面垂直（平行）于壁面。为了进行比较，我们还基于鞭毛的局部各向异性摩擦力进行了模拟。在这种阻力近似下，同样可以得到表面附着和圆形游动模式。然而，附着机制现在是由于空间排斥，并且拍打平面的取向是不同的。我们的模型提供了一个理论框架，可以解释精子在靠近和远离壁面时的几种不同游动行为。此外，该模型还提出了一种通过改变形状来引导精子在化学梯度中导航的机制。
