Bio-Inspired 3D Responsive Polymeric Microstructures Based on Liquid Crystalline Elastomers

Abstract

Dynamic functions of biological organisms often rely on arrays of active microstructures undergoing nearly unlimited repertoire of pre-determined and self-regulated reconfigurations and motions, most of which are difficult or not yet possible to achieve in synthetic systems. In the first part, I will introduce stimuli-responsive microstructures based on liquid crystalline elastomers (LCEs) that display a broad range of hierarchical, even mechanically-unfavored deformation behaviors. By polymerizing molded prepolymer in patterned magnetic fields, we encode any desired mesogen alignment into the resulting LCE microstructures which is then read-out upon heating above the nematic-isotropic transition (TN-I) as a specific prescribed deformation, such as twisting, in- and out-of-plane tilting, stretching or contraction. By further introducing light-responsive moieties, we demonstrate unique multi-functionality of the LCEs capable of three actuation modes: self-regulated bending towards the light source at T<TN-I, magnetic field-encoded pre-determined deformation at T>TN-I, and direction-dependent self-regulated motion towards light at T>TN-I. We further develop this platform for the creation of patterned arrays of microstructures or even cellular structures with encoded multiple area-specific deformation modes and demonstrate their function in responsive release of cargo, image concealment, and light-controlled reflectivity. In the second part, we have developed a polymeric material platform exhibiting mechanical responses with tunable monotonicity based on LCE by manipulating the coupling between mesogenic groups and polymer backbones through well designed phase transitions. The key to realize such adaptable monotonicity of responses is to build up a material platform with non-monotonic responses. The phase behavior of our LCE was studied in detail with x-ray scattering experiments and the mechanism for the uncommon non-monotonic mechanical behavior was proposed. More importantly, like living systems, the monotonicity of the mechanical responses in a single LCE microstructure (i.e., monotonically increasing, monotonically decreasing and non-monotonic change) can be switched by simply changing the range of the external stimulus (i.e., environmental temperature). Overall, these results provide the basis of a versatile class of active microstructures that enable a palette of deformation behaviors with the change of external stimuli. We foresee this platform can be widely applied in switchable adhesion, information encryption, autonomous antennae, energy harvesting, soft robotics, and smart buildings.