Magnetic Cilia with Programmable Beating Patterns for Vortex-Driven Mixing in Microfluidics.

Artificial cilia are widely employed in microfluidic platforms, where their beating motion is harnessed to emulate the fluid transport capabilities of natural motile cilia. In particular, metachronal beating, characterized by phase-shifted motion among adjacent cilia, has proven to be effective for directional fluid transport. However, its potential for micromixing remains limited due to its inherently planar wave propagation, which offers room for improvement in generating strong vortices. To address this, three magnetically actuated artificial cilia carpets are fabricated with identical structural designs featuring spatially varied cilia orientations to embed controlled orientational asymmetry. To realize distinct motion patterns, each carpet is magnetized with a single, unique magnetization profile such that one carpet corresponds to one beating mode, including synchronous, symplectic metachronal, or antiplectic metachronal, and is actuated externally to generate its respective motion. For demonstration purposes, two different experiments are conducted, including micromixing and photocatalytic dye degradation. The results reveal that metachronal motion alone is insufficient to enhance micromixing, thereby highlighting the need for integration with orientational asymmetry. Compared to the aligned cilia carpet (control), superior mixing efficiency of 87% and a 3-fold enhancement in dye degradation are observed in the inclined cilia carpet actuated with antiplectic metachronal motion. This enhanced hydrodynamic activity is further substantiated through μPIV experiments. These findings define metachrony as a dual-function paradigm for both fluid propulsion and vortex-enabled microfluidic mixing.