发表机构
University of Minnesota; University of California, Riverside; Cleveland State University（明尼苏达大学; 加州大学河滨分校; 克利夫兰州立大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过多尺度模型和模拟，揭示活性杆在微通道中逆流扩散的机制，提出一维两状态模型预测污染分布，为微流控防污设计提供理论依据。
AI 中文摘要
活性杆是细长的自驱动颗粒，可作为运动微生物（如细菌和精子细胞）的有效模型。当被限制在微流控通道中时，活性杆表现出独特的运动模式：它们倾向于沿通道壁逆流体流动方向游动。在压力驱动的通道流中，它们交替进行沿壁的长距离上游行进和主体中的短距离下游突进。这种行为对导管和微流控装置中细菌逆流污染具有实际意义。我们使用一系列模型研究了活性杆群体沿长微通道的扩散。三维模型的蒙特卡洛模拟表明，净上游输运对流速呈非单调依赖，随旋转扩散的增大而减小，并取决于通道横截面的形状。模拟还表明，上游和下游的持续停留时间遵循指数衰减分布。这促使我们推导出一个一维、两状态的速率跳跃模型。对于指数分布的持续停留时间，我们推导了连续注入杆的浓度演化方程，并确定了其长时间极限的闭式解。该分析揭示了当平均上游速度为正时，源上游存在浓度平台，否则呈指数衰减。利用从三维模拟中测得的参数，一维模型重现了蒙特卡洛模拟的浓度分布，这些结果与近期微流控装置中细菌污染的实验观察一致。
英文摘要
Active rods are elongated, self-propelled particles that serve as effective models for motile microorganisms, such as bacteria and sperm cells. When confined to a microfluidic channel, active rods exhibit a distinctive motility pattern: they tend to swim against the fluid flow along channel walls. In pressure-driven channel flow, they alternate between long upstream runs along the walls and short downstream spurts in the bulk. This behavior has practical implications for bacterial contamination of catheters and microfluidic devices against the flow. We study the spreading of a population of active rods along long microchannels using a hierarchy of models. Monte Carlo simulations of a three-dimensional model show that net upstream transport depends non-monotonically on the flow rate, decreases with rotational diffusion, and depends on the shape of the channel cross-section. The simulations also show that upstream and downstream persistence times follow exponentially decaying distributions. This motivates the derivation of a one-dimensional, two-state velocity-jump model. For exponentially distributed persistence times, we derive the evolution equation for the concentration of continuously injected rods and determine its long-time limit in closed form. This analysis reveals a concentration plateau upstream of the source when the mean upstream velocity is positive and exponential decay otherwise. Using parameters measured from the three-dimensional simulations, the one-dimensional model reproduces the concentration profiles from the Monte Carlo simulations, and these results are consistent with recent experimental observations of bacterial contamination in microfluidic devices.
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