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Bacteria driving droplets.
Soft Matter ( IF 2.9 ) Pub Date : 2020-01-14 , DOI: 10.1039/c9sm01839e Gabriel Ramos 1 , María Luisa Cordero , Rodrigo Soto
Soft Matter ( IF 2.9 ) Pub Date : 2020-01-14 , DOI: 10.1039/c9sm01839e Gabriel Ramos 1 , María Luisa Cordero , Rodrigo Soto
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We confine a dense suspension of motile Escherichia coli inside a spherical droplet in a water-in-oil emulsion, creating a "bacterially" propelled droplet. We show that droplets move in a persistent random walk, with a persistence time τ∼ 0.3 s, a long-time diffusion coefficient D∼ 0.5 μm2 s-1, and an average instantaneous speed V∼ 1.5 μm s-1 when the bacterial suspension is at the maximum studied concentration. Several droplets are analyzed, varying the drop radius and bacterial concentration. We show that the persistence time, diffusion coefficient and average speed increase with the bacterial concentration inside the drop, but are largely independent of the droplet size. By measuring the turbulent-like motion of the bacteria inside the drop, we demonstrate that the mean velocity of the bacteria near the bottom of the drop, which is separated from a glass substrate by a thin lubrication oil film, is antiparallel to the instantaneous velocity of the drop. This suggests that the driving mechanism is a slippery rolling of the drop over the substrate, caused by the collective motion of the bacteria. Our results show that microscopic organisms can transfer useful mechanical energy to their confining environment, opening the way to the assembly of mesoscopic motors composed of microswimmers.
中文翻译：
细菌驱动液滴。
我们将运动型大肠杆菌的稠密悬浮液限制在油包水乳液中的球形小滴内，从而形成“具有细菌作用”的小滴。我们表明，当细菌悬浮时，液滴以持续的随机游动运动，持续时间τ〜0.3 s，长时间扩散系数D〜0.5μm2s-1，平均瞬时速度V〜1.5μms-1处于最大研究浓度。分析了几个液滴，改变了液滴半径和细菌浓度。我们表明，持续时间，扩散系数和平均速度随着液滴内部细菌浓度的增加而增加，但在很大程度上与液滴大小无关。通过测量液滴内部细菌的湍流状运动，我们证明了液滴底部附近细菌的平均速度，通过薄的润滑油膜将其与玻璃基板隔开，它与液滴的瞬时速度反平行。这表明驱动机制是由细菌的集体运动引起的液滴在基底上的打滑。我们的结果表明，微观有机体可以将有用的机械能传递到其封闭环境中，从而为组装由微游泳器组成的介观电机开辟了道路。
更新日期：2020-02-13
中文翻译：
细菌驱动液滴。
我们将运动型大肠杆菌的稠密悬浮液限制在油包水乳液中的球形小滴内，从而形成“具有细菌作用”的小滴。我们表明，当细菌悬浮时，液滴以持续的随机游动运动，持续时间τ〜0.3 s，长时间扩散系数D〜0.5μm2s-1，平均瞬时速度V〜1.5μms-1处于最大研究浓度。分析了几个液滴，改变了液滴半径和细菌浓度。我们表明，持续时间，扩散系数和平均速度随着液滴内部细菌浓度的增加而增加，但在很大程度上与液滴大小无关。通过测量液滴内部细菌的湍流状运动，我们证明了液滴底部附近细菌的平均速度，通过薄的润滑油膜将其与玻璃基板隔开，它与液滴的瞬时速度反平行。这表明驱动机制是由细菌的集体运动引起的液滴在基底上的打滑。我们的结果表明，微观有机体可以将有用的机械能传递到其封闭环境中，从而为组装由微游泳器组成的介观电机开辟了道路。
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