Anisotropic permeability in deterministic lateral displacement arrays

TL;DR

This paper reveals that anisotropic permeability in DLD microfluidic arrays affects flow stability and separation accuracy, with design features influencing anisotropy, and recommends layout choices to mitigate these effects.

Contribution

It identifies the causes of anisotropic permeability in DLD arrays and provides design guidelines to prevent flow deviations affecting particle separation.

Findings

Anisotropic permeability causes lateral pressure gradients in DLD arrays.

Rotated-square layouts do not exhibit intrinsic anisotropy.

Design features like unequal gaps and asymmetric posts increase anisotropy.

Abstract

We uncover anisotropic permeability in microfluidic deterministic lateral displacement (DLD) arrays. A DLD array can achieve high-resolution bimodal size-based separation of microparticles, including bioparticles, such as cells. For an application with a given separation size, correct device operation requires that the flow remains at a fixed angle to the obstacle array. We demonstrate via experiments and lattice-Boltzmann simulations that subtle array design features cause anisotropic permeability. Anisotropic permeability indicates the microfluidic array's intrinsic tendency to induce an undesired lateral pressure gradient. This can cause an inclined flow and therefore local changes in the critical separation size. Thus, particle trajectories can become unpredictable and the device useless for the desired separation task. Anisotropy becomes severe for arrays with unequal axial and lateral gaps between obstacle posts and highly asymmetric post shapes. Furthermore, of the two equivalent array layouts employed with the DLD, the rotated-square layout does not display intrinsic anisotropy. We therefore recommend this layout over the easier-to-implement parallelogram layout. We provide additional guidelines for avoiding adverse effects of anisotropy on the DLD.