Temperature‐Responsive 4D Liquid Crystal Microactuators Fabricated by Direct Laser Writing by Two‐Photon Polymerization

Abstract

Over the past decade, progress in direct laser writing by two‐photon polymerization (DLW‐TPP) of stimuli‐responsive materials has made considerable inroads into the realization of microactuators. With the focus on performing complex tasks such as walking, grasping, or delivering drugs, these actuators require a controlled preprogrammed actuation. Liquid crystalline microactuators enable such programmed movement when the mesogenic alignment can be successfully controlled. To date, this has necessitated low crosslink density networks, which are not readily conducive to the fabrication of 3D geometries. Herein, a liquid crystalline photoresist is reported, which results in a highly crosslinked network, that permits fabrication of 4D microactuators having a highly crosslinked network in which the molecular alignment is determined by the alignment layers in the cell construct. In addition to controllable deformation of the microactuators, they also display a characteristic and unique polarization color that can be used for both identification and reporting in real time, enabling their integration into sensing and anti‐anticounterfeiting microdevices.

Liquid crystal-based structural color actuators

“…Production of structural color actuators has been generated primarily from making cells or deposition by bar or spin coating on surfaces. Some new options are becoming available, including direct ink writing for macroscopic actuating objects (called “4D printing”, with the fourth dimension being time) 97 , and two-photon processes for microscopic objects 73 , 98 . One advantageous feature from all these production techniques is that the liquid crystalline mixtures are not all that different, and so adapting mixtures for different deposition techniques is much simplified.…”

Printing on Particles: Combining Two‐Photon Nanolithography and Capillary Assembly to Fabricate Multimaterial Microstructures

“…If these microactuators have sequential and/or orthogonal triggers, such as light, temperature, or chemicals, one could control each link individually and create devices with programmable responses. [1,8,13,29,37,43,44] The wide variety of available colloidal particles will in the future enable us to encapsulate drugs, catalyze specific reactions, or selectively bind bio-molecules, micro-organisms, or pollutants for a broad range of applications, where the integration of the materials used for the links and the particles can complement each other in both form and function.…”

Smart Nematic Liquid Crystal Polymers for Micromachining Advances

“…Several movement patterns have been studied, from rotating to walking in a straight direction with an average speed of 37 μm s −1 . The third example ( Figure 6 C) shows structures also aligned with an LC cell where the LC photoresist is infiltrated [ 56 ]. TPP is used to make two structures for optical and polarized characterization, the first one is a woodpile, and the second is a spiral disk.…”

“…Copyright 2015, Wiley-VCH. ( C ) Micro-structuration of a woodpile and a spiral disc with observed expansion under thermal actuation [ 56 ]. Reproduced under the terms of the Creative Commons CC BY 4.0 license.…”