Microfluidic Mixing with the Dynamic Control of Magnetic Actuation

Abstract

Mixing under laminar flow conditions remains a key challenge in microfluidic systems due to limited convective transport. Overcoming this limitation is essential for the advancement of real-time biochemical analyses, point-of-care diagnostics, and autonomous lab-on-chip operations. This study investigates magnetically actuated microrobots that utilizes moment of inertia as mobile mixers to enhance fluid interface elongation and promote effective mixing. A modular design approach is used to fabricate microrobots with asymmetric mass distributions optimized for rotational dynamics. The experimental results show that increasing the moment of inertia and promoting sustained angular momentum improve the mixing performance. The longer arm length of the high-inertia design also increases the geometric swept area, extending the hydrodynamic reach and supporting enhanced mixing. A high-inertia three-robot configuration achieves up to 80% mixing efficiency, surpassing the lower-inertia setup by 10% due to enhanced interface stretching and vorticity generation. Circulation and vorticity analyses reveal that counter-rotational motion and spatial placement amplify local shear rates, accelerating dye dispersion through continuous interface elongation. Furthermore, dynamic actuation patterns enable real-time control of the mixing state by modulating flow-induced interface evolution. Herein, new insights are offered into designing and controlling microrobotic actuators for adaptive microscale mixing with applications in lab-on-chip and diagnostic systems.