Unveiling the Rolling to Kayak Transition in Propelling Nanorods with Cargo Trapping and Pumping

Abstract

Magnetic nanorods driven by rotating fields in water can be rapidly steered along any direction while generating strong and localized hydrodynamic flow fields. Here we show that, when raising the frequency of the rotating field, these nanopropellers undergo a dynamic transition from a rolling to a kayak-like motion due to the increase in viscous drag and acquire a finite inclination angle with respect to the plane perpendicular to the bottom surface. We explain these experimental observations with a theoretical model which considers the nanorod as a pair of ferromagnetic particles hydrodynamically interacting with a close stationary surface. Further, we quantify how efficiently microscopic cargoes can be trapped or expelled from the moving nanorod and use numerical simulations to unveil the generated hydrodynamic flow field. These propulsion regimes can be implemented in microfluidic devices to perform precise operations based on the selective sorting of microscopic cargoes.

Magnetic Lateral Ladder for Unidirectional Transport of Microrobots: Design Principles and Potential Applications of Cells‐on‐Chip

“…Figure 1b demonstrates that each driving magnetic field can induce multifarious microrobot movements, where driving methods are optimized for each type. [12,[45][46][47][48]52,[65][66][67][68] In most cases, microrobots exhibit established directionality in their movements. However, the field-dependent approach cannot selectively control individual microrobots, causing all microrobots in the field-affected space to exhibit the same directionality without considering their interaction with the surrounding environment.…”

“…Figure 1b demonstrates that each driving magnetic field can induce multifarious microrobot movements, where driving methods are optimized for each type. [ 12,45–48,52,65–68 ]…”

Magnetically Manipulated Optoelectronic Hybrid Microrobots for Optically Targeted Non‐Genetic Neuromodulation

“…This position reduced the area of the circular trajectory described by the tip of the MOHR and subsequently diminished the rectification in translational motion, which caused the quick switch. [42,43] Meanwhile, the actuation mode change showed a sharp speed decrease along with the wobbling mode (Movie S5, Supporting Information).…”