Interactions of fibers with pillars: toward a sorting device

Flowing suspensions of elongated particles are encountered in many biological and industrial systems. The motion of the particles results from the complex interplay between the surrounding flow, internal elastic forces, as well as potential interactions with obstacles and walls. In this work, we conduct experiments and simulations to study the transport of fibers interacting with pillars in a microfluidic channel. In the case of rigid fibers, we identify four dominant behaviors depending on their position and orientation as they enter the channel. The geometrical and mechanical properties of the fibers also affect their trajectory, especially if they hit the pillars. Long and stiff fibers are indeed found to be much more laterally displaced by the pillars than short and flexible ones which rather tend to flow back along their initial streamline with no significant deviation. Based on these findings, we make suggestions on how to optimize a microfluidic device to sort fibers by length and/or flexibility.