Light-​actuated artificial cilia based on liquid crystal networks

The use of liquid crystal networks (LCNs) for trigger-driven cilia combines control over the deformation direction with a large work potential. Photopolymerization of mesogenic monomers in their nematic phase leads to well-ordered densely cross-linked, glassy polymers which can be structured into small cilia attached to a substrate. The fabrication of the cilia is compatible with standard micro-fabrication techniques such as lithography and printing. These techniques allow control of the molecular orientation both in the plane and into the third dimension through the thickness of the film. Patterned films can be created with various orientation patterns of the network molecules. The geometry change of the cilia is driven by small decreases in molecular order. Besides their response to heat and chemical agents the LCN cilia can be engineered to respond to light. Cilia with a splayed or twisted nematic director profile show large out-of-plane bending, amplifying the small in-plane deformations. Photo-responsive responsive cilia with these alignments show fast deformation kinetics and large, reversible responses. With a micro-fluidic application in mind, an example of inkjet-printed cilia is given here. The cilia have subunits that can be selectively driven by changing the wavelength of the light trigger. The example shows the ability to miniaturize these systems and the versatility of the LCNs.