Abstract

Sperm-driven micromotors, consisting of a single sperm cell captured in a microcap, utilize the strong propulsion generated by the flagellar beat of motile spermatozoa for locomotion. It enables the movement of such micromotors in biological media, while being steered remotely by means of an external magnetic field. The substantial decrease in swimming speed, caused by the additional hydrodynamic load of the microcap, limits the applicability of sperm-based micromotors. Therefore, to improve the performance of such micromotors, we first investigate the effects of additional cargo on the flagellar beat of spermatozoa. We designed two different kinds of microcaps, which each result in different load responses of the flagellar beat. As an additional design feature, we constrain rotational degrees of freedom of the cell’s motion by modifying the inner cavity of the cap. Particularly, cell rolling is substantially reduced by tightly locking the sperm head inside the microcap. Likewise, cell yawing is decreased by aligning the micromotors under an external static magnetic field. The observed differences in swimming speed of different micromotors are not so much a direct consequence of hydrodynamic effects, but rather stem from changes in flagellar bending waves, hence are an indirect effect. Our work serves as proof-of-principle that the optimal design of microcaps is key for the development of efficient sperm-driven micromotors.

Graphic Abstract

中文翻译：

---

微电机介导的精子收缩可改善游泳表现

摘要

精子驱动的微电机由捕获在微帽中的单个精子细胞组成，利用活动精子鞭毛节拍产生的强大推进力进行运动。它使得此类微电机能够在生物介质中移动，同时通过外部磁场进行远程控制。由于微帽的额外流体动力负载导致游泳速度大幅下降，限制了基于精子的微电机的适用性。因此，为了提高这种微电机的性能，我们首先研究额外的货物对精子鞭毛跳动的影响。我们设计了两种不同类型的微电容器，每种微电容器都会导致鞭毛节拍的不同负载响应。作为附加的设计特征，我们通过修改盖子的内腔来限制细胞运动的旋转自由度。特别是，通过将精子头紧紧锁定在微帽内，可以大大减少细胞滚动。同样，通过在外部静磁场下对齐微电机，可以减少细胞偏航。观察到的不同微电机游泳速度的差异与其说是水动力效应的直接结果，不如说是源于鞭毛弯曲波的变化，因此是一种间接效应。我们的工作证明了微电容器的优化设计是开发高效精子驱动微电机的关键。

图文摘要