Designing constricted microchannels to selectively entrap soft particles

The entrapment of micron-sized particles in microscopic pores is beneficial for the efficient functioning of filtration systems and microfluidic devices for analyzing individual biological cells. To optimize the performance of these systems, it is important to isolate factors that regulate the passage of particles through micron-sized constrictions. Using computational modeling, we investigate the fluid-driven motion of compliant particles through constrictions, which are formed by pillars that extend from the top and bottom walls of a microchannel. The particles are modeled as fluid-filled capsules that have elastic shells and simulate biological cells or polymeric microcapsules. The separation between the pillars is similar to 10% larger than the diameter of the undeformed capsules. We introduce an attractive interaction between the capsules and the tops of the pillars and vary the elasticity of both the capsules and pillars. Surprisingly, we find that this simple system shows a selectivity toward capsules of intermediate stiffness. Softer capsules are readily deformed by the viscous forces and do not experience the attractive interaction with the pillars, while stiffer capsules cannot deform to maximize the favorable contact with the sticky tops. By varying the elasticity of the pillars, we can tailor the range of capsules that become stuck between the pillars. The findings provide guidelines for designing filtration systems and yield insight into the factors that drive particles to block microscopic channels.