Numerical investigation of microroller separation in structured pillar arrays

In this study, we investigate the migration of torque-driven microrollers within a structured deterministic lateral-displacement array using fully resolved simulations. We demonstrate that the external torque introduces both positive and negative zigzag modes in addition to the conventional zigzag and lateral-displacement modes. In particular, a counterclockwise torque biases the microroller toward negative zigzag migration, whereas a clockwise torque promotes positive zigzag migration and, for sufficiently large torque, can even trigger the lateral-displacement mode. Through rotation-induced near-wall translation, the applied torque continuously tunes the displacement angle and shifts the critical separation diameter, thereby enabling active regulation of microroller transport. These findings provide new insights into the transport and manipulation of active particles in structured microfluidic environments.