Chiral cilia carpets on curved surfaces

在低雷诺数流体环境中，纤毛对生物游动行为的促进作用在生物物理学中得到了广泛研究。运动纤毛是结构上手性细长的蛋白质附属物，其几何和动力学特性使它们能够促进细胞运动和液体运输。许多纤毛系统可以组织和响应外部刺激，为微生物提供重要功能，包括定向运动和滑行。有趣的是，这种纤毛协调并不一定是生物体在单个纤毛水平上主动调节的，而是可以被描述为纤毛之间流体动力相互作用产生的一种新兴现象。最近，F.孟、R. Bennett、N. Uchida和R. Golestanian研究了纤毛地毯中这种紧急协调的一个例子（“模型纤毛阵列中的超越性协调条件”，PNAS, 2021）。研究表明，排列在平面上的纤毛的自组织跳动可以从它们之间的水动力相互作用中理解。我的研究旨在研究纤毛地毯在微游泳者运动中的作用，通过考虑纤毛地毯在浸入并穿过周围流体的曲面上的自组织。具体来说，在这种配置中，我想确定纤毛跳动的自组织和同步机制，以及由此产生的协调如何促进受控游泳。这项研究与纤毛虫的运动性研究有关，纤毛虫是一大类海洋微生物，其特征是在其体表上存在许多纤毛虫。其中包括海星（Patiria miniata），其手性游泳动力学促进了水动力学稳定活性晶体的形成，最近由t.h, Tan， A. Mietke等人研究（“活手性晶体的奇异动力学”，Nature, 2022）。这项工作将为研究这些胚胎的动力学特性提供理论框架，这些特性是手性游泳和主动晶体形成的基础。与生物物理学实验家的合作和纤毛细胞运动的测量将使理论的预测得到验证。该项目属于EPSRC生物物理和软物质物理研究领域，将在Alexander Mietke博士的指导下进行。

Swimming behaviour of organisms in low Reynold's number fluid environments facilitated by cilia has been widely studied in biological physics. Motile cilia are structurally chiral slender protein appendages whose geometric and dynamical characteristics allow them to facilitate cell motility and fluid transport. Systems of many cilia can organise and respond to external stimuli to provide important functions for microorganisms, including directed motion and taxis. Interestingly, this ciliar coordination is not necessarily actively regulated by the organism at the level of the individual cilia, but can instead be described as an emergent phenomenon arising from the hydrodynamic interactions between the cilia. An example of such emergent coordination in cilia carpets was recently studied by F. Meng, R. Bennett, N. Uchida, and R. Golestanian ("Conditions for metachronal coordination in arrays of model cilia", PNAS, 2021). There, it was shown that self-organised beating of cilia arrayed on a flat surface can be understood from the hydrodynamic interactions between them. My research aims to investigate the role of cilia carpets for microswimmer motility by considering their self-organisation on a curved surface that is immersed and moving through the surrounding fluid. Specifically, in this configuration, I want to identify self-organisation and synchronisation mechanisms of ciliary beating, and how the resulting coordination can facilitate controlled swimming. This research is relevant to the study of the motility of ciliates - a large class of marine microorganisms that are characterised by the presence of many cilia on their body surface. These include starfish (Patiria miniata), whose chiral swimming dynamics facilitate the formation of hydrodynamically stablised active crystals recently studied by T. H, Tan, A. Mietke, et al. ("Odd dynamics of living chiral crystals", Nature, 2022). This work will provide a theoretical framework to investigate the dynamical properties of these embryos that underpin chiral swimming and active crystal formation. Collaboration with biophysics experimentalists and measurement of the motion of ciliate cells would allow predictions of the theory to be tested. This project falls within the EPSRC Biophysics and Soft Matter Physics research area and will be conducted under the supervision of Dr Alexander Mietke.