With the advent of direct laser writing using two-photon polymerization, the generation of high-resolution three-dimensional microstructures has increased dramatically. However, the development of stimuli-responsive photoresists to create four-dimensional (4D) microstructures remains a challenge. Herein, we present a supramolecular cholesteric liquid crystalline photonic photoresist for the fabrication of 4D photonic microactuators, such as pillars, flowers, and butterflies, with submicron resolution. These micron-sized features display structural color and shape changes triggered by a variation of humidity or temperature. These findings serve as a roadmap for the design and creation of high-resolution 4D photonic microactuators.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202104390.Recent years have seen major advances in the developments of both additive manufacturing concepts and responsive materials. When combined as 4D printing, the process can lead to functional materials and devices for use in health, energy generation, sensing, and soft robots. Among responsive materials, liquid crystals, which can deliver programmed, reversible, rapid responses in both air and underwater, are a prime contender for additive manufacturing, given their ease of use and adaptability to many different applications. In this paper, selected works are compared and analyzed to come to a didactical overview of the liquid crystal-additive manufacturing junction. Reading from front to back gives the reader a comprehensive understanding of the options and challenges in the field, while researchers already experienced in either liquid crystals or additive manufacturing are encouraged to scan through the text to see how they can incorporate additive manufacturing or liquid crystals into their own work. The educational text is closed with proposals for future research in this crossover field.

The integration of light tracking and light guiding within fiber arrays is an intriguing challenge. In this study, an advanced drop casting/drawing method is applied to fabricate a fiber array capable of not only performing sunflower‐inspired light tracking, but also light guiding. The fiber arrays are constructed with various liquid crystal networks by adjusting the location of photoresponsive azobenzene moieties in the polymer network to understand the correlation between the extent of photoresponse and azobenzene location. Incorporating the azobenzene in the main chain oligomer renders these fibers with advanced photoresponse in both air and water. The fibers are able to track a light source and to guide the collected light, making these responsive actuator arrays potentially attractive for advanced photovoltaic and optical elements.

Soft actuators allowing multifunctional, multishape deformations based on single polymer films or bilayers remain challenging to produce. In this contribution, direct ink writing is used for generating patterned actuators, which are in between single- and bilayer films, with multifunctionality and a plurality of possible shape changes in a single object. The key is to use the controlled deposition of a light-responsive liquid crystal ink with direct ink writing to partially cover a foil at strategic locations. We found patterned films with 40% coverage of the passive substrate by an active material outperformed “standard” fully covered bilayers. By patterning the film as two stripes, a range of motions, including left- and right-handed twisting and bending in orthogonal directions, could be controllably induced in the same actuator. The partial coverage also left space for applying liquid crystal inks with other functionalities, exemplified by fabricating a light-responsive green reflective actuator whose reflection can be switched “on” and “off”. The results presented here serve as a toolbox for the design and fabrication of patterned actuators with dramatically expanded shape deformation and functionality capabilities.

An optical time−temperature steam sensor is presented based on the loss of structural color in a supramolecularly cross-linked cholesteric liquid crystal photonic coating. A gradual decrease in the selective reflection band is observed upon exposure to temperatures above 105°C related to the cholesteric to isotropic transition temperature. The linear polymers with carboxylic acid side chains provide physical cross-linking through hydrogen bonding that allows a time−temperature-dependent order loss through the dynamic equilibrium between supramolecular dimer and free monomer states. Steam is accelerating the color loss, and autoclave experiments show that the photonic supramolecular polymer is applicable as a steam sterilization sensor for medical applications.