Selective particle capture by asynchronously beating cilia
Update: 2016-02-02 13:35:53      Author: yangjuan@csrc.ac.cn

The separation and filtration of particles in a fluid medium are essential to many technological and biological processes. Technological applications include controlling indoor and outdoor air quality, manufacturing pharmaceuticals and powders, and sorting cells in microfluidic “lab-on-chip” devices [1]. The health of aquatic ecosystems is largely impacted by filter feeding animals, which provide attractive biological paradigms for particle filtration. Filter feeders remove particulate food from the surrounding water by passing the water over specialized filtering structures. One of the capture strategies is to use the same cilia to generate feeding currents and to intercept particles when the particles are on the downstream side of the cilia [2]. Previous analysis provides valuable insights into the geometric effect but does not elucidate the hydrodynamic mechanisms underlying cilia-particle interactions. 

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Fig. 1. Particle motion in cilia-generated flows. Particle color represents the initial particle position in the x direction.

Recently, a research team from CSRC and University of Southern California shed some light on the capture process. In their study, a 3D computational model of ciliary bands interacting with flow suspended particles was developed and particle trajectories for a range of particle sizes were calculated. Consistent with experimental observations, they found optimal particle sizes that maximize capture rate. The optimal size depends nonlinearly on cilia spacing and cilia coordination, synchronous vs. asynchronous. These parameters affect the cilia-generated flow field, which in turn affects particle trajectories. The low capture rate of smaller particles is due to the particles' inability to cross the flow streamlines of neighboring cilia. Meanwhile, large particles have difficulty entering the sub-ciliary region once advected downstream, also resulting in low capture rates. The optimal range of particle sizes is enhanced when cilia beat asynchronously. These findings have potentially important implications on the design and use of biomimetic cilia in processes such as particle sorting in microfluidic devices.

For more information, please see the paper: “Selective particle capture by asynchronously beating cilia”, Y. Ding and E. Kanso, Physics of Fluids 27, 121902 (2015).

[1] E. L. Jackson and H. Lu, Current Opinion in Chemical Engineering 2, 398-404 (2013).

[2] H. U. Riisgard, C. Nielsen, and P. S. Larsen, Marine Ecology-Progress Series 207, 33-51 (2000).

 


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