Zhang Shuaizhong, Cui Zhiwei, Wang Ye, den Toonder Jaap M J
Microsystems, Department of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
Lab Chip. 2020 Oct 7;20(19):3569-3581. doi: 10.1039/d0lc00610f. Epub 2020 Aug 26.
Biological cilia that generate fluid flow or propulsion are often found to exhibit a collective wavelike metachronal motion, i.e. neighboring cilia beat slightly out-of-phase rather than synchronously. Inspired by this observation, this article experimentally demonstrates that microscopic magnetic artificial cilia (μMAC) performing a metachronal motion can generate strong microfluidic flows, though, interestingly, the mechanism is different from that in biological cilia, as is found through a systematic experimental study. The μMAC are actuated by a facile magnetic setup, consisting of an array of rod-shaped magnets. This arrangement imposes a time-dependent non-uniform magnetic field on the μMAC array, resulting in a phase difference between the beatings of adjacent μMAC, while each cilium exhibits a two-dimensional whip-like motion. By performing the metachronal 2D motion, the μMAC are able to generate a strong flow in a microfluidic chip, with velocities of up to 3000 μm s in water, which, different from biological cilia, is found to be a result of combined metachronal and inertial effects, in addition to the effect of asymmetric beating. The pumping performance of the metachronal μMAC outperforms all previously reported microscopic artificial cilia, and is competitive with that of most of the existing microfluidic pumping methods, while the proposed platform requires no physical connection to peripheral equipment, reduces the usage of reagents by minimizing "dead volumes", avoids undesirable electrical effects, and accommodates a wide range of different fluids. The 2D metachronal motion can also generate a flow with velocities up to 60 μm s in pure glycerol, where Reynolds number is less than 0.05 and the flow is primarily caused by the metachronal motion of the μMAC. These findings offer a novel solution to not only create on-chip integrated micropumps, but also design swimming and walking microrobots, as well as self-cleaning and antifouling surfaces.
产生流体流动或推进作用的生物纤毛通常呈现出集体波状的顺次运动，即相邻纤毛的摆动略有相位差而非同步摆动。受此观察结果启发，本文通过实验证明，进行顺次运动的微观磁性人工纤毛（μMAC）能够产生强大的微流体流动，不过有趣的是，通过系统的实验研究发现，其机制与生物纤毛不同。μMAC由一个简易的磁性装置驱动，该装置由一排棒状磁体组成。这种布局在μMAC阵列上施加了一个随时间变化的非均匀磁场，导致相邻μMAC摆动之间产生相位差，而每个纤毛呈现二维鞭状运动。通过进行顺次二维运动，μMAC能够在微流体芯片中产生强大的流动，在水中速度可达3000μm/s，与生物纤毛不同，这被发现是顺次和惯性效应以及不对称摆动效应共同作用的结果。顺次μMAC的泵送性能优于之前报道的所有微观人工纤毛，与大多数现有微流体泵送方法具有竞争力，同时该平台无需与外围设备进行物理连接，通过最小化“死体积”减少试剂用量，避免不良电效应，并能适应多种不同流体。二维顺次运动在纯甘油中也能产生速度高达60μm/s的流动，其中雷诺数小于0.05，流动主要由μMAC的顺次运动引起。这些发现不仅为制造片上集成微泵提供了一种新的解决方案，还为设计游泳和行走的微型机器人以及自清洁和防污表面提供了新方案。
