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Cells have evolved multiple mechanisms to apprehend and adapt finely to their environment. Here we report a new cellular ability, which we term “curvotaxis” that enables the cells to respond to cell-scale curvature variations, a ubiquitous trait of cellular biotopes. We develop ultra-smooth sinusoidal surfaces presenting modulations of curvature in all directions, and monitor cell behavior on these topographic landscapes. We show that adherent cells avoid convex regions during their migration and position themselves in concave valleys. Live imaging combined with functional analysis shows that curvotaxis relies on a dynamic interplay between the nucleus and the cytoskeleton—the nucleus acting as a mechanical sensor that leads the migrating cell toward concave curvatures. Further analyses show that substratum curvature affects focal adhesions organization and dynamics, nuclear shape, and gene expression. Altogether, this work identifies curvotaxis as a new cellular guiding mechanism and promotes cell-scale curvature as an essential physical cue. The effect that microscale surface curvature has on cell migration has not been evaluated. Here the authors fabricate sinusoidal 3D surfaces and show that the cell nucleus and cytoskeleton cooperate to guide cells to concave valleys in a process they coin curvotaxis.

Metamaterials have attracted wide scientific interest to break fundamental bounds on materials properties. Recently, the field has been extending to coupled physical phenomena where one physics acts as the driving force for another. Stimuli-responsive or 4D metamaterials have been demonstrated for thermo-elasticity, magneto-optics or piezo-electricity. Herein, a soft, ultra-compact and accurate microrobot is described which can achieve controlled motion under thermal stimuli. The system consists of an organized assembly of two functional structures: a rotational and a translational element. Both elements are designed basing upon the principle of the thermoelastic bilayer plate that bends as temperature changes. Samples are fabricated using gray-tone lithography from a single polymer but with two different laser writing powers, making each part different in its thermal and mechanical behaviors. Excellent motion-controllable, reversible and stable features in a dry environment are verified by simulations and experiments, revealing broad application prospects for the designed soft micro actuators. 4D metamaterials offer the additional functionality of being responsive to external stimuli. Here, a metamaterial-based soft robot is composed of bilayer plates that can rotate and translate in response to thermal stimuli, allowing controlled motion.

This study developed a natural rubber (NR) composite reinforced with surface-modified pineapple leaf fibres (PALFs) and hemp fibres (HFs) using a layer-by-layer (sandwich-like) fabrication method. The objectives were to increase the utilisation of the natural fibres as reinforcing agents and to investigate the impact of silane fibre surface modification on the properties of the sandwich composites. Fibre surface characterisation was performed using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) to confirm the presence of functional groups from silane and cellulose. The wettability and adhesion properties of the modified fibres were also evaluated. The mechanical properties were investigated via single-fibre tensile tests. Composites with 50 phr silane-treated PALF showed the best compromise in terms of interface adhesion (48.3 mJ/m2) and tensile strength (6 MPa). This result was also supported by scanning electron microscopy (SEM), which revealed the absence of voids between the fibres and the NR matrix. Furthermore, dynamic mechanical analysis showed that the PALF composite treated with silane at 50 phr exhibited the best viscoelastic behaviour. NR composites with 50 phr silane-treated PALF have mechanical properties suitable for potential applications in engineering products.

Polymeric micropillars with a high-aspect-ratio (HAR) are of interest for a wide range of applications, including drug delivery and the micro-electro-mechanical field. While molding is the most common method for fabricating HAR microstructures, it is affected by challenges related to demolding the final structure. In this study, we present very HAR micropillars using two-photon polymerization (TPP), an established technique for creating complex 3D microstructures. Polymeric micropillars with HARs fabricated by TPP often shrink and collapse during the development process. This is due to the lack of mechanical stability of micropillars against capillary forces primarily acting during the fabrication process when the solvent evaporates. Here, we report different parameters that have been optimized to overcome the capillary force. These include surface modification of the substrate, fabrication parameters such as laser power, exposure time, the pitch distance between the pillars, and the length of the pillars. On account of adopting these techniques, we were able to fabricate micropillars with a very HAR up to 80.

The miniaturization of tools is an important step in human evolution to create faster devices as well as precise micromachines. Studies around this topic have allowed the creation of small-scale objects capable of a wide range of deformation to achieve complex tasks. Molecular arrangements have been investigated through liquid crystal polymer (LCP) to program such a movement. Smart polymers and hereby liquid crystal matrices are materials of interest for their easy structuration properties and their response to external stimuli. However, up until very recently, their employment at the microscale was mainly limited to 2D structuration. Among the numerous issues, one concerns the ability to 3D structure the material while controlling the molecular orientation during the polymerization process. This review aims to report recent efforts focused on the microstructuration of LCP, in particular those dealing with 3D microfabrication via two-photon polymerization (TPP). Indeed, the latter has revolutionized the production of 3D complex micro-objects and is nowadays recognized as the gold standard for 3D micro-printing. After a short introduction highlighting the interest in micromachines, some basic principles of liquid crystals are recalled from the molecular aspect to their implementation. Finally, the possibilities offered by TPP as well as the way to monitor the motion into the fabricated microrobots are highlighted.

Mammalian cells have been widely shown to respond to nano- and microtopography that mimics the extracellular matrix. Synthetic nano- and micron-sized structures are therefore of great interest in the field of tissue engineering, where polymers are particularly attractive due to excellent biocompatibility and versatile fabrication methods. Ordered arrays of polymeric pillars provide a controlled topographical environment to study and manipulate cells, but processing methods are typically either optimized for the nano- or microscale. Here, we demonstrate polymeric nanopillar (NP) fabrication using 3D direct laser writing (3D DLW), which offers a rapid prototyping across both size regimes. The NPs are interfaced with NIH3T3 cells and the effect of tuning geometrical parameters of the NP array is investigated. Cells are found to adhere on a wide range of geometries, but the interface depends on NP density and length. The Cell Interface with Nanostructure Arrays (CINA) model is successfully extended to predict the type of interface formed on different NP geometries, which is found to correlate with the efficiency of cell alignment along the NPs. The combination of the CINA model with the highly versatile 3D DLW fabrication thus holds the promise of improved design of polymeric NP arrays for controlling cell growth.

The need for functional materials has triggered significant endeavors in the design and assembly of functionalized interfaces with specific optical characteristics. In the world of color, structural and plasmonic colors represent a smart alternative to materials colored by pigments or dyes. In particular, plasmonic color in polymer materials allows the mechanochromism phenomenon. Hence, this work has focused on the development of a hybrid material able to change its color at will. To achieve this, nature has been the source of inspiration, especially the “chameleon effect”. Like the chameleon, the hybrid polymer material filled with metallic nanoparticles was able to change color by varying the distance between nanoparticles under constraint. This effect could be permanent and reversible by varying the matrix. As the colors of metallic nanoparticles do not bleach, this concept also avoids any fading or vanishing color effects. This technology opens new routes in colored materials and the mechanochromism phenomenon.

Wet-chemistry synthesized Gold nanourchins (Au NUs), characterized by spiky morphologies with spherical cores, exhibit complex and geometry-dependent plasmonic properties distinct from those of symmetrical nanostructures. While plasmon hybridization and mode coupling in branched nanostructures have been broadly studied, the specific optical behavior of Au NUs-particularly regarding spike length distribution and ultrafast dynamics-remains underexplored. This study investigates the steady-state and transient absorption spectra of Au NUs with 50-80 nm cores and 5-20 nm spikes, revealing multiple resonance bands. Transient absorption spectroscopy at various excitation wavelengths confirmed the presence of distinct resonances. Electromagnetic simulations based on TEM tomography-inspired models identified two key extinction bands: a green-wavelength dark mode resonance and a red-nIR spike-induced resonance attributed to the lightning rod effect. Simulations further showed that short, uniformly distributed spikes (aspect ratio <= 1) weakly excite dark resonances, while longer spikes (aspect ratio > 1) induce hybridized longitudinal resonances and significant redshifts. Broad spike length distributions result in multiple coexisting resonances, aligning with experimental extinction spectra. A preliminary surface-enhanced Raman scattering study using 2-naphthalene thiol confirmed stronger enhancement for long-spiked Au NUs under 785 nm excitation, validating the field enhancement potential of the identified resonances.

The Early Cretaceous period is characterized by widespread carbonate production in tropical and subtropical epicontinental seas, which was modulated by changes in sea‐level, detrital and nutrient fluxes, and the global carbon cycle. As a result, carbonate platforms were sensitive recorders of environmental change, which often anticipated global environmental perturbations. A good example is provided by the northern Tethyan carbonate platform, which is presently preserved in the central European Helvetic Alps. There, the latest early to late Valanginian Weissert episode of global change, which is defined by the first important positive shift in δ13C records of the Cretaceous, is expressed by a prolonged, stepwise drowning phase. In this contribution, a detailed reconstruction of palaeoenvironmental change before and during the Weissert episode is provided based on three representative sections of the Helvetic platform. The sections are placed along a deepening transect and correlated by means of ammonite and microfossil biostratigraphy, sequence stratigraphy and δ13C chemostratigraphy. In a first phase of palaeoenvironmental change during the latest Berriasian, photozoan carbonate production was stopped by a major and hitherto undetected drowning episode, which was followed by a phase of renewed carbonate production by heterozoan biota. This phase was linked to major sea‐level rise, a change to a more humid climate and strong regional subsidence associated with tectonic block tilting. During the Valanginian, the circulation of nutrient‐enriched sea waters prevented a return to oligotrophic conditions and two further drowning episodes occurred, which are both documented by condensed phosphate‐rich beds and dated as middle early Valanginian and late Valanginian to early Hauterivian. The exact causes of the three‐step deterioration in carbonate production are not established but a link to episodic volcanic activity is likely, eventually related to the formation of the Paranà‐Etendeka large igneous province. The Helvetic platform underwent a major transgression and tectonic block tilting during the latest Berriasian, which led to the disappearance of photozoan carbonates. After this first drowning episode, the platform recovered with a heterozoan carbonate production, typifying higher nutrient levels in the early Valanginian and the weakening of carbonate systems before the major drowning of the Valanginian. The settlement of heterozoan faunas is thereafter observed in other west Tethyan platforms. It coincides with a negative shift in d13C values and might correspond to the onset of the Paranà Etendekà LIP.