Lin Szu-Ning, Lo Wei-Chang, Lo Chien-Jung
Department of Physics and Graduate Institute of Biophysics, National Central University, Jhongli, Taiwan 32001, Republic of China.
Soft Matter. 2014 Feb 7;10(5):760-6. doi: 10.1039/c3sm52120f.
Self-propelled particles (SPP) exhibit complex collective motions, mimicking autonomous behaviors that are often seen in the natural world, but essentially are generated by simple mutual interactions. Previous research on SPP systems focuses on collective behaviors of a uniform population. However, very little is known about the evolution of individual particles under the same global influence. Here we show self-organized rotating spiral coils in a two-dimensional (2D) active system. By using swarming bacteria Vibrio alginolyticus as an ideal experimental realization of a well-controlled 2D self-propelled system, we study the interaction between ultra-long cells and short background active cells. The self-propulsion of long cells and their interactions with neighboring short cells leads to a self-organized, stable spiral rotational state in 2D. We find four types of spiral coils with two main features: the rotating direction (clockwise or counter-clockwise) and the central structure (single or double spiral). The body length of the spiral coils falls between 32 and 296 μm and their rotational speed is within a range from 2.22 to 22.96 rad s(-1). The dynamics of these spiral coils involves folding and unfolding processes, which require local velocity changes of the long bacterium. This phenomenon can be qualitatively replicated by a Brownian dynamics simulation using a simple rule of the propulsion thrust, imitating the reorientation of bacterial flagella. Apart from the physical and biological interests in swarming cells, the formation of self-organized spiral coils could be useful for the next generation of microfabrication.
自驱动粒子（SPP）展现出复杂的集体运动，模拟了自然界中常见的自主行为，但本质上是由简单的相互作用产生的。先前对SPP系统的研究集中在均匀群体的集体行为上。然而，对于在相同全局影响下单个粒子的演化却知之甚少。在此，我们展示了二维（2D）活性系统中的自组织旋转螺旋线圈。通过使用溶藻弧菌作为一个可控的二维自驱动系统的理想实验实例，我们研究了超长细胞与短背景活性细胞之间的相互作用。长细胞的自推进及其与相邻短细胞的相互作用导致了二维空间中自组织的、稳定的螺旋旋转状态。我们发现了四种类型的螺旋线圈，具有两个主要特征：旋转方向（顺时针或逆时针）和中心结构（单螺旋或双螺旋）。螺旋线圈的体长在32至296μm之间，其旋转速度在2.22至22.96弧度每秒（-1）的范围内。这些螺旋线圈的动力学涉及折叠和展开过程，这需要长细菌的局部速度变化。这种现象可以通过使用推进推力的简单规则进行布朗动力学模拟定性地复制，模仿细菌鞭毛的重新定向。除了对群体细胞的物理和生物学兴趣之外，自组织螺旋线圈的形成可能对下一代微制造有用。
