Motility-dependent selective transport of active matter in trap arrays: Separation methods based on trapping-detrapping and deterministic lateral displacement

TL;DR

This paper introduces novel theoretical methods for separating active matter based on motility using trap arrays, applicable to biological cells and synthetic particles, advancing motility-based separation techniques.

Contribution

The paper proposes two new separation methods based on trapping-detrapping and deterministic lateral displacement for motile active matter, demonstrated through numerical simulations.

Findings

Effective separation of motile and immotile species demonstrated

Methods applicable to biological and synthetic active particles

Potential for improved biological sorting and nanoparticle separation

Abstract

Selecting active matter based on its motility represents a challenging task, as it requires different approaches than common separation techniques intended for separation based on, e.g., size, shape, density, and flexibility. This motility-based selection is important for, e.g., selecting biological species, such as bacteria or highly motile sperm cells for medically assisted reproduction. Common separation techniques are not applicable for separating species based on motility as such species can have indistinguishable physical properties, i.e., size, shape, density, and differ only by their ability to execute self-propelled motion as, e.g., motile, and immotile sperm cells. Therefore, selecting active species based on motility requires completely different approaches. Some of these have been developed including sperm cell selection techniques, e.g., swim-up techniques, passive selection methods based on the ability of highly motile sperm cells to swim across streamlines, as well as more sophisticated techniques. Here we theoretically demonstrate via numerical simulations various efficient methods of selection and separation based on the motility of active species using arrays of traps. Two approaches are proposed: one allowed the selective escape of motile species from traps, and the other one relying on a deterministic lateral displacement (DLD)-type method. As a model system, we consider self-propelled Janus particles whose motility can be tuned. The resulted separation methods are applicable for separation of biological motile species, such as bacteria or sperm cells, as well as for Janus micro- and nanoparticles.