Department of Physics and Astronomy, University of North Carolina, Chapel Hill, 27599, USA.
Proc Natl Acad Sci U S A. 2010 Sep 7;107(36):15670-5. doi: 10.1073/pnas.1005127107. Epub 2010 Aug 26.
Living systems employ cilia to control and to sense the flow of fluids for many purposes, such as pumping, locomotion, feeding, and tissue morphogenesis. Beyond their use in biology, functional arrays of artificial cilia have been envisaged as a potential biomimetic strategy for inducing fluid flow and mixing in lab-on-a-chip devices. Here we report on fluid transport produced by magnetically actuated arrays of biomimetic cilia whose size approaches that of their biological counterparts, a scale at which advection and diffusion compete to determine mass transport. Our biomimetic cilia recreate the beat shape of embryonic nodal cilia, simultaneously generating two sharply segregated regimes of fluid flow: Above the cilia tips their motion causes directed, long-range fluid transport, whereas below the tips we show that the cilia beat generates an enhanced diffusivity capable of producing increased mixing rates. These two distinct types of flow occur simultaneously and are separated in space by less than 5 microm, approximately 20% of the biomimetic cilium length. While this suggests that our system may have applications as a versatile microfluidics device, we also focus on the biological implications of our findings. Our statistical analysis of particle transport identifying an enhanced diffusion regime provides novel evidence for the existence of mixing in ciliated systems, and we demonstrate that the directed transport regime is Poiseuille-Couette flow, the first analytical model consistent with biological measurements of fluid flow in the embryonic node.
生命系统利用纤毛来控制和感知流体的流动，以实现多种目的，如泵送、运动、进食和组织形态发生。除了在生物学中的应用，人工纤毛的功能阵列还被设想为一种潜在的仿生策略，用于在微流控芯片设备中诱导流体流动和混合。在这里，我们报告了由磁驱动的仿生纤毛阵列产生的流体输运，其大小接近其生物对应物的大小，在这个尺度上，平流和扩散竞争决定了质量输运。我们的仿生纤毛再现了胚胎节点纤毛的拍打形状，同时产生了两种明显分离的流体流动区域：在纤毛尖端上方，其运动导致定向、长程的流体输运，而在尖端下方，我们表明纤毛的拍打产生了增强的扩散率，能够提高混合速率。这两种不同类型的流动同时发生，并且在空间上的分离小于 5 微米，约为仿生纤毛长度的 20%。虽然这表明我们的系统可以作为一种通用的微流控设备应用，但我们也关注我们发现的生物学意义。我们对粒子输运的统计分析确定了增强的扩散区域，为纤毛系统中存在混合提供了新的证据，并且我们证明了定向输运区域是泊肃叶-库埃特流，这是与胚胎节点中流体流动的生物学测量结果一致的第一个分析模型。
