Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO 80309.
Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO 80309
Proc Natl Acad Sci U S A. 2021 Jul 6;118(27). doi: 10.1073/pnas.2101807118.
Micro/nanoswimmers convert diverse energy sources into directional movement, demonstrating significant promise for biomedical and environmental applications, many of which involve complex, tortuous, or crowded environments. Here, we investigated the transport behavior of self-propelled catalytic Janus particles in a complex interconnected porous void space, where the rate-determining step involves the escape from a cavity and translocation through holes to adjacent cavities. Surprisingly, self-propelled nanoswimmers escaped from cavities more than 20× faster than passive (Brownian) particles, despite the fact that the mobility of nanoswimmers was less than 2× greater than that of passive particles in unconfined bulk liquid. Combining experimental measurements, Monte Carlo simulations, and theoretical calculations, we found that the escape of nanoswimmers was enhanced by nuanced secondary effects of self-propulsion which were amplified in confined environments. In particular, active escape was facilitated by anomalously rapid confined short-time mobility, highly efficient surface-mediated searching for holes, and the effective abolition of entropic and/or electrostatic barriers at the exit hole regions by propulsion forces. The latter mechanism converted the escape process from barrier-limited to search-limited. These findings provide general and important insights into micro/nanoswimmer mobility in complex environments.
微/纳米游泳者将各种能源转化为定向运动，在生物医学和环境应用方面具有很大的应用前景，其中许多应用涉及复杂、曲折或拥挤的环境。在这里，我们研究了自推进的催化詹纳斯粒子在复杂的相互连接的多孔空隙中的输运行为，其中决定速率的步骤涉及从腔室中逸出并通过孔迁移到相邻的腔室。令人惊讶的是，尽管纳米游泳者的迁移率小于无约束体相液体中被动（布朗）粒子的迁移率的 2 倍，但自推进纳米游泳者从腔室中逸出的速度比被动粒子快 20 倍以上。通过实验测量、蒙特卡罗模拟和理论计算相结合，我们发现自推进的细微二次效应增强了纳米游泳者的逃逸，这种效应在受限环境中得到了放大。特别是，主动逃逸受到受限短时间内异常快速的迁移率、高效的表面介导的孔搜索以及由推进力有效消除出口孔区域的熵和/或静电障碍的促进。后一种机制将逃逸过程从障碍限制转变为搜索限制。这些发现为微/纳米游泳者在复杂环境中的迁移提供了普遍而重要的见解。
