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Responsive materials have been used to generate structures with built-in complex geometries, linear actuators and microswimmers. These results suggest that complex, fully functional machines composed solely from shape-changing materials might be possible . Nonetheless, to accomplish rotary motion in these materials still relies on the classical wheel and axle motifs. Here we explore geometric zero-energy modes to elicit rotary motion in elastic materials in the absence of a rigid wheel travelling around an axle. We show that prestrained polymer fibres closed into rings exhibit self-actuation and continuous motion when placed between two heat baths due to elastic deformations that arise from rotational-symmetry breaking around the rod's axis. Our findings illustrate a simple but robust model to create active motion in mechanically prestrained objects.

Si NMR spectra of the photocured films F1-F3 (Fig. S1). CP-MAS 13 C NMR spectra of the photocured films F1-F3 (Fig. S2). In situ photographs of the moving tip during a scratch experiment for F1 and F3 films when applying an increasing normal load (Fig. S3).

The surfaces of plant leaves are rarely smooth and often possess a species-specific micro- and/or nano-structuring. These structures usually influence the surface functionality of the leaves such as wettability, optical properties, friction and adhesion in insect–plant interactions. This work presents a simple, convenient, inexpensive and precise two-step micro-replication technique to transfer surface microstructures of plant leaves onto highly transparent soft polymer material. Leaves of three different plants with variable size (0.5–100 µm), shape and complexity (hierarchical levels) of their surface microstructures were selected as model bio-templates. A thermoset epoxy resin was used at ambient conditions to produce negative moulds directly from fresh plant leaves. An alkaline chemical treatment was established to remove the entirety of the leaf material from the cured negative epoxy mould when necessary, i.e. for highly complex hierarchical structures. Obtained moulds were filled up afterwards with low viscosity silicone elastomer (PDMS) to obtain positive surface replicas. Comparative scanning electron microscopy investigations (original plant leaves and replicated polymeric surfaces) reveal the high precision and versatility of this replication technique. This technique has promising future application for the development of bioinspired functional surfaces. Additionally, the fabricated polymer replicas provide a model to systematically investigate the structural key points of surface functionalities.

The formation of polydopamine composite membranes at the water/air interface using different chemical strategies is reported. The use of either small molecules (urea, pyrocatechol) or polymers paves the way to understand which kind of compounds can be used for the formation of PDA-composite free-standing membranes produced at the water/air interface. On the basis of these screening results, we have found that alginate grafted with catechol groups allows the formation of robust free-standing films with asymmetric composition, stimuli-responsiveness, and self-healing properties. The stickiness of these membranes depends on the relative humidity, and its adhesion behavior on PDMS was characterized using the JKR method. Thus, alginate-catechol polydopamine films appear as a new class of PDA composites, mechanically robust through covalent cross-linking and based on fully biocompatible constituting partners. These results open the door to potential applications in the biomedical field.

The surfaces of animals, plants and abiotic structures are not only important for organismal survival, but they have also inspired countless biomimetic and industrial applications. Additionally, the surfaces of animals and plants exhibit an unprecedented level of diversity, and animals often move on the surface of plants. Replicating these surfaces offers a number of advantages, such as preserving a surface that is likely to degrade over time, controlling for non-structural aspects of surfaces, such as compliance and chemistry, and being able to produce large areas of a small surface. In this paper, we compare three replication techniques among a number of species of plants, a technical surface and a rock. We then use two model parameters (cross-covariance function ratio and relative topography difference) to develop a unique method for quantitatively evaluating the quality of the replication. Finally, we outline future directions that can employ highly accurate surface replications, including ecological and evolutionary studies, biomechanical experiments, industrial applications and improving haptic properties of bioinspired surfaces. The recent advances associated with surface replication and imaging technology have formed a foundation on which to incorporate surface information into biological sciences and to improve industrial and biomimetic applications. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology’.

A difunctional methacrylate oligomer was mixed with a variable amount of a MAPTMS precursor in the presence of both a radical and a cationic photoinitiator. The simultaneous photolysis of both photosensitive molecules upon UV irradiation allowed the single‐step generation of a type‐II polymethacrylate/polysiloxane nanocomposite film. Methacrylate and methoxysilyl conversions during irradiation were efficiently monitored by FTIR spectroscopy. The inorganic structure of the resulting silica‐based hybrid films was characterized using 29Si solid‐state NMR. Finally, the reinforcement ability of the resulting hybrid films was also assessed by using a unique range of characterization techniques: DMA, scratch test, and nanoindentation. magnified image

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