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Stimuli-responsive liquid crystal elastomers with molecular orientation coupled to rubber-like elasticity show a great potential as elements in soft robotics, sensing, and transport systems. The orientational order defines their mechanical response to external stimuli, such as thermally activated muscle-like contraction. Here we demonstrate a dynamic thermal control of the surface topography of an elastomer prepared as a coating with a pattern of in-plane molecular orientation. The inscribed pattern determines whether the coating develops elevations, depressions, or in-plane deformations when the temperature changes. The deterministic dependence of the out-of-plane dynamic profile on the in-plane orientation is explained by activation forces. These forces are caused by stretching-contraction of the polymer networks and by spatially varying molecular orientation. The activation force concept brings the responsive liquid crystal elastomers into the domain of active matter. The demonstrated relationship can be used to design coatings with functionalities that mimic biological tissues such as skin.

Extracellular microenvironment is highly dynamic where spatiotemporal regulation of cell-instructive cues such as matrix topography tightly regulates cellular behavior. Recapitulating dynamic changes in stimuli-responsive materials has become an important strategy in regenerative medicine to generate biomaterials which closely mimic the natural microenvironment. Here, light responsive liquid crystal polymer networks are used for their adaptive and programmable nature to form hybrid surfaces presenting micrometer scale topographical cues and changes in nanoscale roughness at the same time to direct cell migration. This study shows that the cell speed and migration patterns are strongly dependent on the height of the (light-responsive) micrometer scale topographies and differences in surface nanoroughness. Furthermore, switching cell migration patterns upon in situ temporal changes in surface nanoroughness, points out the ability to dynamically control cell behavior on these surfaces. Finally, the possibility is shown to form photoswitchable topographies, appealing for future studies where topographies can be rendered reversible on demand.

Photoactivated reversible addition fragmentation chain transfer (RAFT)-based dynamic covalent chemistry is incorporated into liquid crystalline networks (LCNs) to facilitate spatiotemporal control of alignment, domain structure, and birefringence. The RAFT-based bond exchange process, which leads to stress relaxation, is used in a variety of conditions, to enable the LCN to achieve a near-equilibrium structure and orientation upon irradiation. Once formed, and in the absence of subsequent triggering of the RAFT process, the (dis)order in the LCN and its associated birefringence are evidenced at all temperatures. Using this approach, the birefringence, including the formation of spatially patterned birefringent elements and surface-active topographical features, is selectively tuned by adjusting the light dose, temperature, and cross-linking density.

The light-induced surface topography of a liquid crystal polymer coating is brought into a patterned oscillatory deformation. A dichroic photo-responsive azobenzene is co-aligned with the planar oriented nematic liquid crystal network molecules which makes the surface deformation sensitive to polarized UV light. Locally selective actuation is achieved in coatings with a complex alignment pattern. Dynamic oscillation, as controlled by the actuation and relaxation kinetics of the polymer, is obtained by a continuous change in the polarization of the UV source. The atypical deformation at the defect lines between the domains is of special interest. The amplitude and presence of the oscillation can be manipulated by changing the ratio between blue and UV light and by varying the ambient temperature of the coating.

Properties such as friction, wettability and visual impact of polymer coatings are influenced by the surface topography. Therefore, control of the surface structure is of eminent importance to tuning its function. Photochromic azobenzene-containing polymers are an appealing class of coatings of which the surface topography is controllable by light. The topographies form without the use of a solvent, and can be designed to remain static or have dynamic properties, that is, be capable of reversibly switching between different states. The topographical changes can be induced by using linear azo polymers to produce surface-relief gratings. With the ability to address specific regions, interference patterns can imprint a variety of structures. These topographies can be used for nanopatterning, lithography or diffractive optics. For cross-linked polymer networks containing azobenzene moieties, the coatings can form topographies that disappear as soon as the light trigger is switched off. This allows the use of topography-forming coatings in a wide range of applications, ranging from optics to self-cleaning, robotics or haptics.

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