Dynamic Rotating Liquid Marble for Directional and Enhanced Mass Transportation in Three-Dimensional Microliter Droplets

The ability of an artificial microdroplet to mimic the rotational behaviors of living systems is crucial for dynamic mass transportation but remains challenging to date. Herein, we report dynamic microdroplet rotation using a liquid marble (RLM) and achieve precise control over mass transportation and distribution in a three-dimensional (3D) microdroplet. RLM rotates synchronously with an external magnetic field, creating circular hydrodynamic flow and an outward centrifugal force. Such spin-induced phenomena direct a spiral movement of entrapped molecules and accelerate their diffusion and homogenization in the entire liquid. Moreover, we demonstrate the rotation rate-controlled (between 0 and 1300 rpm) modulation of shell-catalyzed reaction kinetics from 0.13 to 0.62 min^-1. The directed acceleration of reactants toward a catalytically active shell surface is 3-fold faster than conventional stir bar-based convective flow. RLM as an efficient magnetohydrodynamics transducer will be valuable for dynamical control over mass transportation in microdroplet-based chemical, biological, and biomedical studies.