Chemically Powered High-Aspect-Ratio Cilia with Tunable Biomimetic Motion

Abstract Cilia are ubiquitous biological actuators that drive essential functions ranging from clearing contaminants from mammalian lungs to enabling locomotion and feeding in microorganisms. Their utility has inspired the development of artificial cilia. Yet while natural cilia operate through the conversion of chemical energy to mechanical motion, most artificial cilia made to date are externally powered using various fields. Most of these systems have also been of relatively low aspect ratios in comparison to their biological counterparts. In this work we report the synthesis and characterization of chemically powered, high-aspect-ratio artificial cilia with microscale diameters that exhibit individually autonomous, biomimetic oscillatory motion. Actuated using an oscillatory chemical reaction, the reaction catalyst is incorporated into the soft cilia hydrogel material where periodic oxidation and reduction of the catalyst induced periodic swelling and deswelling to generate motion. A customizable, 3D printed mold-based fabrication strategy is developed. The catalyst distribution, concentration, and cilium cross-sectional geometry are systematically varied across representative discrete levels to assess their influence on motion. The results show that motion is strongly governed by the interplay between catalyst loading and geometric asymmetry. Increasing the catalyst-containing stalk fraction and catalyst concentration enhances oscillation amplitude and motion regularity, whereas lower catalyst concentrations favor faster oscillatory dynamics. Geometric asymmetry enhances the speed, amplitude and periodic regularity of motion of these low Reynolds number structures. These findings demonstrate tunable motion in chemically driven artificial cilia and establish a framework for the design of biomimetic, chemically powered microscale actuators with potential applications in soft robotics.