Mixed motion in deterministic ratchets due to anisotropic permeability

Nowadays microfluidic devices are becoming popular for cell/DNA sorting and fractionation. One class of these devices, namely deterministic ratchets, seems most promising for continuous fractionation applications of suspensions (Kulrattanarak et al., 2008 [1]). Next to the two main types of particle behavior, zigzag and displacement motion as noted by the inventors (Huang et al., 2004 [2]) and (Inglis et al., 2006 [3]), we have shown recently the existence of a intermediate particle behavior, which we named ‘mixed motion’. In this paper we formulate the hypothesis that the occurrence of mixed motion is correlated with anisotropy in the permeability of the obstacle array. This hypothesis we base on the comparison of experimental observations of mixed motion and the flow lane distribution as obtained from 2-D flow simulations.

Graphical abstract2D flow simulation in compact deterministic ratchets show asymmetric flow lane distribution, which implies a new type of particle motion.Figure optionsDownload full-size imageDownload high-quality image (65 K)Download as PowerPoint slideResearch highlights► Mixed motion observed in deterministic ratchets. ► Asymmetric flow lane distributions found with simulations. ► Anisotropy of permeability to is the cause of mixed motion.