Swimming Behaviour of a Sperm-Flagella Driven Micro-Bio-Robot: From Fundamental Studies to Biomedical Applications

混合微游泳体是一种具有生物动力源的人工合成微结构推进系统，是一种具有吸引力的小尺度控制驱动方法。特别是，生物游泳者提供了一个生物相容的解决方案的运动和货物交付在低雷诺数制度。我们的杂交微游泳器方法包括铁磁性纳米膜，它卷成微管并捕获单个牛精子。单个运动细胞能够推动卷起的微管向前移动，而外部磁场可以用来引导精子鞭毛驱动的微型机器人到达所需的位置。正如我们的项目标题所揭示的那样，这项工作的目的一方面是为了更深入地了解微管限制下精子的运动，另一方面是为了逐步实现精子驱动的微型生物机器人有望实现的生物医学应用。本项目基础研究的主要目标是了解精子驱动的微生物机器人在更现实环境中的生物物理动力学。这包括高粘度介质、非牛顿流体和其他条件，这些条件是在精子的自然环境中给定的，也通常是在体液中。此外，我们将研究刺激对精子驱动的微型生物机器人的影响，并探讨其作为控制机制的适用性。趋向性机制，如流变性（对流体流动的取向）和thigmotaxis（与表面的相互作用）将是我们研究的重点。在基于出租车的环境中，精子驱动的微生物机器人的不同控制机制的相互作用将是特别有趣和具有挑战性的。例如，需要多大的最小磁场强度才能推翻流变定向，精子驱动的微型生物机器人在磁场关闭后会在水流中重新定向吗？这些和进一步的问题将在项目的这一部分中解决。此外，我们计划研究精子驱动的微型生物机器人与积云细胞层的相互作用，积云细胞层是精子在通往卵母细胞的途中遇到的粘性细胞层。微管的表面修饰将被实施，以局部降解积云细胞，并释放通往卵母细胞的道路。将探索精子驱动的微型生物机器人作为活性药物载体的潜力。总之，这将导致对精子运动的基本理解取得重要进展，同时也有助于精子驱动的微生物机器人在辅助生殖或药物输送中的应用。

Hybrid microswimmers which contain a biological power source for the propulsion of artificially synthetized microstructures is an appealing approach for the controlled actuation on the small scale. In particular, biological swimmers offer a biocompatible solution for the motion and cargo delivery in the low Reynolds number regime. Our approach to a hybrid microswimmer consists of ferromagnetic nanomembranes which roll up into microtubes and capture single bovine spermatozoa. The single motile cell is able to propel the rolled up microtube forward while an external magnetic field can be used to guide the sperm-flagella driven micro-bio-robot to desired locations. As our project title reveals, the aim of this work is, on the one hand to gain a deeper understanding of sperm motion in the confinement of microtubes, on the other hand to go step by step towards biomedical applications which the sperm-driven micro-bio-robots are promising for. The main goal of the fundamental studies of this project is to understand the biophysical dynamics of sperm-driven micro-bio-robots in more realistic environments. This includes higher viscosity media, non-Newtonian fluids and other conditions that are given in the natural surroundings of spermatozoa and also in general in body fluids. Furthermore, we will investigate the influence of stimuli on the sperm-driven micro-bio-robots and explore their suitability as control mechanisms. Taxis mechanisms such as rheotaxis (orientation against fluid flow) and thigmotaxis (interaction with surfaces) will be in the focus of our investigations. Especially interesting and challenging in the taxis-based context will be the interplay of the different control mechanisms of the sperm-driven micro-bio-robots. For instance, what is the minimum magnetic field strength needed to overrule the rheotactic orientation, will the sperm-driven micro-bio-robot reorient in the flow after the magnetic field is turned off? These and further questions will be addressed in this part of the project. Furthermore, we plan to study the interaction of the sperm-driven micro-bio-robots with the cumulus cell layer, which is a viscous cell layer which the spermatozoa encounter on their way to the oocyte. Surface modifications of the microtubes will be implemented in order to degrade the cumulus cells locally and free the way to the oocyte. The potential of the sperm-driven micro-bio-robots to serve as active drug carriers will be explored. In summary, this will lead to important progress in the fundamental understanding of sperm motion but also be helpful towards applications of the sperm-driven micro-bio-robots in assisted reproduction or drug delivery.