牛精子细胞中的自组织涡旋相与流体动力学相互作用
Self-organized vortex phases and hydrodynamic interactions in Bos taurus sperm cells
AI总结：
本研究揭示牛精子在粘弹性流体中经流动脉冲诱导形成长寿命群集相，并发现自组织涡旋态，通过实验相图与计算模型对比，预测了有序-无序相边界，为评估精子样本生育能力提供新视角。
摘要：
群集行为在从细胞到超有机体长度尺度的生物系统中均有观察，其机制和目的备受关注。本文研究了牛精子细胞在粘弹性流体中的集体动力学。这些细胞似乎不会自发地形成群集，但在经历瞬态有序流体流动脉冲后，会转变为长寿命的群集相。令人惊讶的是，这种诱导的群集相与Toner-Tu理论预测的自发极性群集相具有许多定性相似之处，如各向异性的巨大数涨落和非平凡的横向密度关联，尽管该相是诱导产生的，且在这些实验中游泳者与周围流体之间的动量守恒显然起着重要作用。我们还发现了精子细胞的自组织全局涡旋态，并绘制了以细胞密度和运动统计为函数的集体运动状态的实验相图。我们将实验与参数匹配的持续转向活性粒子计算模型进行比较，发现作为细胞密度和持久时间函数的实验有序-无序相边界可以近似地从单细胞性质的测量中预测。我们的结果可能对通过研究密集游泳精子群体的集体相行为来评估样本生育能力具有启示意义。
英文摘要：
Flocking behavior is observed in biological systems from the cellular to super-organismal length scales, and the mechanisms and purposes of this behavior are objects of intense interest. In this paper, we study the collective dynamics of bovine sperm cells in a viscoelastic fluid. These cells appear not to spontaneously flock, but transition into a long-lived flocking phase after being exposed to a transient ordering pulse of fluid flow. Surprisingly, this induced flocking phase has many qualitative similarities with the spontaneous polar flocking phases predicted by Toner-Tu theory, such as anisotropic giant number fluctuations and non-trivial transverse density correlations, despite the induced nature of the phase and the clearly important role of momentum conservation between the swimmers and the surrounding fluid in these experiments. We also find self-organized global vortex state of the sperm cells, and map out an experimental phase diagram of states of collective motion as a function of cell density and motility statistics. We compare our experiments with a parameter-matched computational model of persistently turning active particles, and find that the experimental order-disorder phase boundary as a function of cell density and persistence time can be approximately predicted from measures of single-cell properties. Our results may have implications for the evaluation of sample fertility by studying the collective phase behavior of dense groups of swimming sperm.
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