Patterned and Collective Motion of Densely Packed Tapered Multiresponsive Liquid Crystal Cilia

Abstract

Cilia are of vital importance for myriad of natural functions such as the propulsion of microorganisms or the cleaning of the mammalian respiratory system. These cilia often show coupled 3D shape changes, such as waves, to perform their function. Here, we present a versatile platform to fabricate artificial micrometer-sized azobenzene-doped liquid crystal polymer cilia by replica molding from a track-etched polyimide membrane. The cilia are tuneable in their size and show excellent homogeneity and high number densities over large areas. By electrically aligning the liquid crystal monomers in a splay alignment during photopolymerization, the symmetry in most cilia is broken, which allows them to reversibly bend toward a predetermined side when exposed to heat or UV light. When the applied stimulus is carefully controlled, the response can be tuned in speed and magnitude. Addressing both the trans- and cis-isomers of the azobenzene derivative simultaneously makes the cilia oscillate out of plane continuously in a preprogrammed pattern with a frequency and amplitude of choice, without any obvious signs of fatigue. Thanks to the versatility of this cilia platform, a wide range of applications such as transporting loads in confined spaces, self-cleaning surfaces, haptics, or energy generation is foreseen.