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Liquid crystal elastomers (LCEs) are stimuli-responsive materials that undergo large shape transformations after undergoing an order-disorder transition. While shape reconfigurations in LCEs are predominantly triggered by heat, there is a considerable interest in developing highly specific triggers that work at room temperature. Herein, we report the fabrication of biocatalytic LCEs that respond to the presence of urea by covalently immobilizing urease within chemically responsive LCE networks. The hydrogen-bonded LCEs developed in this work exhibited contractile strains of up to 36% upon exposure to a base. Notably, the generation of ammonia by immobilized urease triggered a disruption in the supramolecular network and a large reduction of liquid crystalline order in the films when the LCEs were exposed to urea. This reduction in order was macroscopically translated into a strain response that could be modulated by changing the concentration of urea or exposure time to the substrate. Local control of the mechanical response of the LCE was realized by spatially patterning the enzyme on the surface of the films. Subsequent exposure of enzymatically patterned LCE to urea-triggered 3D shape transformations into a curl, arch, or accordion-like structure, depending on the motif patterned on the film surface. Furthermore, we showed that the presence of salt was critical to prevent bridging of the network by the presence of ammonium ions, thereby enabling such macroscopic 3D shape changes. The large actuation potential of LCEs and the ability to translate the biocatalytic activity of enzymes to macroscopic 3D shape transformations could enable use in applications ranging from cell culture, medicine, or antifouling.

Liquid crystal polymer networks (LCNs) are stimuli-responsive materials that can be programmed to realize spatial variation in mechanical response and undergo shape transformation. Herein, we report a process to introduce chemical specificity to the stimuli response of LCNs by integrating enzymes as molecular triggers. Specifically, the enzyme urease was immobilized in LCN films via acyl fluoride conjugation chemistry. Activity assays and confocal fluorescence imaging confirmed retention of urease activity after immobilization as well as widespread distribution of enzyme on the film. The addition of urea triggered a response in the LCN whereby newly generated ammonia reacted with free acyl fluorides to form benzamide moieties. These moieties were capable of dimerizing through the formation of supramolecular hydrogen bonds, which was reflected in a 4-fold increase in Young's modulus. Through dynamic mechanical analysis and calorimetry, we further confirmed that the degree of hydrogen bonding in the LCNs could be judiciously designed to fine-tune the mechanical properties and glass transition temperature. These findings demonstrate the untapped potential of biochemical mechanisms as molecular triggers in LCNs and open the door to the use of nucleophilic chemistries in modulating the mechanical properties of LCNs.