Flow Tweezing of Anisotropic Magnetic Particles in a Dynamic Magnetic Trap

Unravelling the dynamics of anisotropic particles in fluids is critical for a range of applications in micro-robotics, lab-on-chip biochemical assays, environmental remediation, and purification. However, controlled transport of an anisotropic particle in a fluidic flow has proven nontrivial owing to the coupling of the particle’s rotation movement with the hydrodynamic flow, leading to complex flow trajectories and motion dynamics. Here, we report the dynamic tweezing of an anisotropic magnetic particle structure in a rotating magnetic trap. We reveal a series of unconventional motion modes and dynamics of the particle transporting in a confined fluidic flow, which manifest themselves as transitions from on-trap centre rolling to large-area revolution and off-trap centre rolling with varying rotating frequencies. The revolution of a particle is observed to shift to off-centre rolling at varied flow velocities, which is absent for the common scenario when the particle is purely trapped in a medium flow. Our findings unlock a new strategy to determine local magnetic tweezing force profile and flow conditions in arbitrary flow channels, revealing strong potential for microfluidics, chemical reactors and in-vivo endovascular flow measurement.