For microscale 4D photoresponsive actuators, light is crucial in two ways. First, the underlying additive manufacturing techniques rely on photopolymerization processes triggered by the absorption of light. Second, the absorption of light serves as the actuation stimulus. The two absorptions can be conflicting. While the microstructure requires strong absorption at the actuation wavelength(s), this absorption should not interfere with that of the manufacturing process. Herein, a simple strategy is proposed to overcome these limitations and allow for the fabrication of multi‐photoresponsive 3D microstructures that can be actuated at different wavelengths of light. Two‐photon 3D laser printing is selected as the fabrication technique and liquid crystalline (LC) elastomers as the functional materials. In a first step, 3D microstructures are fabricated using an aligned LC ink formulation. Thereafter, up to five different dyes exhibiting absorptions that extend over the entire visible regime (400–700 nm) are successfully incorporated into the LC microstructures by an exchange process enabling a programmable actuation by irradiating with the suitable wavelength. Furthermore, by combining dyes exhibiting orthogonal absorptions, wavelength‐selective actuations are demonstrated.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aisy.202100081.

Although recent studies indicate the impact of microbes on the central nervous systems and behavior, it remains unclear how the relationship between the functionality of the nervous system, behavior and the microbiota arise. We studied the eating behavior of Hydra, a host that has a simple nervous system and a low-complexity microbiota. To identify the neuronal subpopulations involved, we used a subpopulation specific cell ablation system and calcium imaging. The role of the microbiota was uncovered by reducing the diversity of the natural microbiota. Here, we demonstrate that different neuronal subpopulations are functioning together to control the eating behavior. The microbiota participates in control of the eating behavior since germ-free or mono-colonized animals have drastic difficulties in mouth opening. This was restored by adding a full complement of the microbiota. In summary, we provide a mechanistic explanation of how the eating behavior is controlled in Hydra and how microbes can affect the neuronal circuit.

based on a reversible phase transition at the lower critical solution temperature (LCST) due to a globule-to-coil transition. [8] Below the LCST the polymer is in a hydrophilic, hydrated state, while above the LCST it is in a hydrophobic state. In this state, the interactions of the polymer with itself lead to a higher gain in free energy than would be achieved by solvation energy. The volume of pNIPAM materials in the hydrated, swollen state is much higher than in the hydrophobic state, because water is integrated into the material in the hydrated state. [9] As the actuation of pNIPAM hydrogel is based on its water-dependent shrinkage and swelling, the actuation efficiency and the forces generated by pNIPAM-based actuators critically depend on the in-and outflow of water through the pores of the material. Therefore, the actuation effect, including actuation dynamics as well as stroke forces, can be improved by introducing pores into the material. [10,11] Whereas in previous studies template-assisted methods have proven highly suitable for introducing pores into hydrogels, they lack local microstructural control, while being excellent for structuring macroscopic samples with an interconnected structure. [10] For generating highly efficient pNIPAM-based microactuators, a precisely defined design is required and thus methods are needed that allow for their highly precise 3D structuring at the micrometer scale.The technology of additive nano-and micromanufacturing opens doors to novel and remarkable microengineering possibilities and even enables printing of simple 3D volumetric structures at small scales. [12] Direct laser writing (DLW) involving two-photon polymerization of photoresists is one of the additive manufacturing techniques that can be used to fabricate intricate and miniaturized 3D structures, as they are required for the fabrication of microactuators. By utilizing twophoton absorption and a femtosecond pulsed laser, this fabrication method allows to print in sub-micrometer resolution, even with several materials and on different types of substrates. [13,14] Direct laser writing has also proven highly suitable for fabricating 4D materials, i.e., responsive materials that change their properties due to an external stimulus. [15] For example, the shape of such materials could be controlled at the micrometer scale by temperature and light. [16] Thermoresponsive hydrogels such as poly(N-isopropylacrylamide) (pNIPAM) are highly interesting materials for generating soft actuator systems. Whereas the material has so far mostly been used in macroscopic systems, here it is demonstrated that pNIPAM is an excellent material for generating actuator systems at the micrometer scale. Two-photon direct laser writing is used to precisely structure thermoresponsive pNIPAM hydrogels at the micrometer scale based on a photosensitive resist. This study systematically shows that the surface-to-volume ratio of the microactuators is decisive to their actuation efficiency. The phase transition of the pNIPAM is also demonstrated...

The pressure on the energy sector to reduce greenhouse gas emissions is increasing. In the light of current greenhouse gas emissions in the energy sector, further expansion of renewable energy sources (RES) is inevitable to reduce emissions and reach the climate goals. This study aims at investigating structural characteristics of German counties regarding advantages for self-sufficient power systems based on RES. The modelling of the power sector based on RES is coupled with a cluster analysis in order to draw a large-scale conclusion on structural characteristics beneficial or obstructive for municipal energy systems. Ten clusters are identified with the Ward algorithm in a hierarchical-agglomerative method. The results underline a further need for RES expansion projects in order to close the gap between supply and demand. Only then, bioenergy can effectively balance the offset and support a truly self-sufficient local energy system. While the model results indicate that the majority of the counties are suitable for further expansion, this suitability is to be questioned in cluster 10. High population density is a critical characteristic, because with it come both a high demand and limited sites for further RES expansion projects.