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International audience; Crystallization from solution is commonly described by classical nucleation theory [1], although thisignores that crystals often form via disordered nanostructures [2]. As an alternative, the classical theoryremains widely used in a “multi-step” variant, where the intermediate nanostructures merely introduceadditional thermodynamic parameters [3]. But this variant still requires validation by experimentsaddressing indeed proper time and spatial scales (ms, nm). We used in situ X-ray scattering to determinethe mechanism of magnetite crystallization and in particular how nucleation propagates at the nanometerscale within amorphous precursors [4]. We find that the self-confinement by an amorphous precursorslows down crystal growth by two orders of magnitude once the crystal size reaches the amorphousparticle size (c.a. 3 nm). Thus, not only the thermodynamic properties of transient amorphousnanostructures, but also their spatial distribution determine crystal nucleation

International audience; Cultivated pearls frequently exhibit morphological irregularities making obvious that mineral deposition was irregularly distributed onto nucleus surface. Taking advantage of experimental cultivations with short durations (from 10 days to few months), these irregular deposits predating occurrence of the nacre were investigated in Polynesian pearls by biochemical characterizations and a series of physical methods. Diversity in the resulting data suggests that various in‐depth alterations of the biomineralization mechanism may have occurred during the grafting process, leading to diversity in the biochemical pathways to nacreous deposition. This allows a precise discussion of current views about pearl formation. The “reversed shell theory” is formally disproved through point to point comparison with development of the shell growing edge. Similarity of pearl formation with “regeneration” or “shell repair” is also discussed, emphasizing the differences between these concepts.

Control over particle size, size distribution, and colloidal stability are central aims in producing functional nanomaterials. Recently, biomimetic approaches have been successfully used to enhance control over properties in the synthesis of those materials. Magnetotactic bacteria produce protein-stabilized magnetite away from its thermodynamic equilibrium structure. Mimicking the bacteria’s proteins using poly-l-arginine we show that by simply increasing the pH, the dimensions of magnetite increase and a single- to mesocrystal transformation is induced. Using synchrotron X-ray diffraction and transmission electron microscopy, we show that magnetite nanoparticles with narrow size distributions and average diameters of 10 ± 2 nm for pH 9, 20 ± 2 nm for pH 10, and up to 40 ± 4 nm for pH 11 can be synthesized. We thus selectively produce superparamagnetic and stable single-domain particles merely by controlling the pH. Remarkably, while an increase in pH brings about a thermodynamically driven decrease in size for magnetite without additives, this dependency on pH is inverted when poly-l-arginine is present., The Journal of Physical Chemistry Letters, 10 (18), ISSN:1948-7185

International audience; Magnetic chains are of fundamental and technological interest. However, 1D assemblies of magnetic nanoparticles are only metastable such that their controlled organization requires the use of templates. Bacteriophages are human-inoffensive viruses with a filamentous morphology that have been shown to exhibit great potential in materials research. Here, we thus utilized the M13 phage as a model for the formation of actuated magnetite nanoparticle superstructures. First, we built a sperm-like ensemble by covalently attaching magnetic nanoparticles to the head of the phage. Second, chain-like assemblies are obtained based on the electrostatic interactions between positively-charged magnetite nanoparticles attached to the negatively-charged phage surface. The nanoparticles-phages assembly is steered by external magnetic fields. We anticipate such materials can find applications in nanotechnology or nanomedicine.

11 pages; International audience; The byssus fibers of Mytilus mussel species have become an important role model in bioinspired materials research due to their impressive properties (e.g. high toughness, self-healing); however, Mytilids represent only a small subset of all byssus-producing bivalves. Recent studies have revealed that byssus from other species possess completely different protein composition and hierarchical structure. In this regard, Pinna nobilis byssus is especially interesting due to its very different morphology, function and its historical use for weaving lightweight golden fabrics, known as sea silk. P. nobilis byssus was recently discovered to be comprised of globular proteins organized into a helical protein superstructure. In this work, we investigate the relationships between this hierarchical structure and the mechanical properties of P. nobilis byssus threads, including energy dissipation and self-healing capacity. To achieve this, we performed in-depth mechanical characterization, as well as tensile testing coupled with in situ X-ray scattering. Our findings reveal that P. nobilis byssus, like Mytilus, possesses self-healing and energy damping behavior and that the initial elastic behavior of P. nobilis byssus is due to stretching and unraveling of the previously observed helical building blocks comprising the byssus. These findings have biological relevance for understanding the convergent evolution of mussel byssus for different species, and also for the field of bio-inspired materials.

International audience; The movement of microorganisms is not only an essential aspect of life, it also serves as a fruitful model for the development of synthetic microswimmers or microrobots with potential applications in environmental and medical fields. Here, we review the field of the magnetic microswimmers, which as indicated by the adjective, represents a dedicated branch of the general microswimmers where magnetism plays a role either for the orientation or for the locomotion of the swimmers. These swimmers, on the one hand, provide model system for studying the interplay of external physical forces with biological processes and are, on the other hand, attractive for various applications due to the possibility of remote steering by magnetic fields.The review is structured in such a way that we first present the physical background associated with the microswimmers in general, with their locomotion at low Reynolds numbers and their orientation by magnetic fields and by other mechanisms. We then review illustrative examples of magnetic swimmers, starting with the biological ones, the magnetotactic bacteria, which are bacteria forming intracellular magnetic nanoparticles to orient in magnetic field. We continue with the hybrid and synthetic microswimmers, where magnetism again plays a role for the orientation / directionality, but can also provide propulsion mechanisms. We finally emphasize the control of multiple swimmers/devices along independent trajectories as well as their interactions and collective behavior. We will look forward to the continuous development of the field and hope that this review will stimulate further research in this vibrant research area.

Cell walls of so-called “wood-materials” are constituted by a complex, highly anisotropic and hierarchically organized nanocomposite, characterized by stiff crystalline cellulose nano-fibers, parallel to each other, and embedded in a softer and less anisotropic matrix of hemicelluloses, lignin and water. This matrix is hygroscopic, and therefore swells with increasing humidity. Consequently, wood cells undergo large dimensional changes. A minimal model of wood secondary cell walls to predict water absorption has recently been developed by Bertinetti and co-workers [1] in the form of an Equation of State (EOS) that represents equivalently the water sorption versus relative humidity, as considered in chemical engineering, or the relation between osmotic pressure and volume of solutes, in the physical chemistry equation of state approach initiated by Jean Perrin. We extend hereby this model to the presence of electrolytes adsorbed in the gel part wood cell wall and compare compression wood cell walls to the extreme case of coir.

SummaryThe geometrical similarity of helicoidal fiber arrangement in many biological fibrous extracellular matrices, such as bone, plant cell wall or arthropod cuticle, to that of cholesteric liquid mesophases has led to the hypothesis that they may form passively through a mesophase precursor rather than by direct cellular control. In search of direct evidence to support or refute this hypothesis, here, we studied the process of cuticle formation in the tibia of the migratory locust, Locusta migratoria, where daily growth layers arise by the deposition of fiber arrangements alternating between unidirectional and helicoidal structures. Using FIB/SEM volume imaging and scanning X-ray scattering, we show that the epidermal cells determine an initial fiber orientation from which the final architecture emerges by the self-organized co-assembly of chitin and proteins. Fiber orientation in the locust cuticle is therefore determined by both active and passive processes.

International audience; Crystallization from solution is commonly described by classical nucleation theory, although this ignores that crystals often form via disordered nanostructures. As an alternative, the classical theory remains widely used in a “multi-step” variant, where the intermediate nanostructures merely introduce additional thermodynamic parameters. But this variant still requires validation by experiments addressing indeed proper time and spatial scales (ms, nm). Here, we used in situ X-ray scattering to determine the mechanism of magnetite crystallization and in particular how nucleation propagates at the nanometer scale within amorphous precursors. We find that the self-confinement by an amorphous precursor slows down crystal growth by two orders of magnitude once the crystal size reaches the amorphous particle size (c.a. 3 nm). Thus, not only the thermodynamic properties of transient amorphous nanostructures, but also their spatial distribution determine crystal nucleation.

The movement of microswimmers is often described by active Brownian particle models. Here we introduce a variant of these models with several internal states of the swimmer to describe stochastic strategies for directional swimming such as run and tumble or run and reverse that are used by microorganisms for chemotaxis. The model includes a mechanism to generate a directional bias for chemotaxis and interactions with external fields (e.g., gravity, magnetic field, fluid flow) that impose forces or torques on the swimmer. We show how this modified model can be applied to various scenarios: First, the run and tumble motion of E. coli is used to establish a paradigm for chemotaxis and investigate how it is affected by external forces. Then, we study magneto-aerotaxis in magnetotactic bacteria, which is biased not only by an oxygen gradient towards a preferred concentration, but also by magnetic fields, which exert a torque on an intracellular chain of magnets. We study the competition of magnetic alignment with active reorientation and show that the magnetic orientation can improve chemotaxis and thereby provide an advantage to the bacteria, even at rather large inclination angles of the magnetic field relative to the oxygen gradient, a case reminiscent of what is expected for the bacteria at or close to the equator. The highest gain in chemotactic velocity is obtained for run and tumble with a magnetic field parallel to the gradient, but in general a mechanism for reverse motion is necessary to swim against the magnetic field and a run and reverse strategy is more advantageous in the presence of a magnetic torque. This finding is consistent with observations that the dominant mode of directional changes in magnetotactic bacteria is reversal rather than tumbles. Moreover, it provides guidance for the design of future magnetic biohybrid swimmers., Author summary In this paper, we propose a modified Active Brownian particle model to describe bacterial swimming behavior under the influence of external forces and torques, in particular of a magnetic torque. This type of interaction is particularly important for magnetic biohybrids (i.e. motile bacteria coupled to a synthetic magnetic component) and for magnetotactic bacteria (i.e. bacteria with a natural intracellular magnetic chain), which perform chemotaxis to swim along chemical gradients, but are also directed by an external magnetic field. The model allows us to investigate the benefits and disadvantages of such coupling between two different directionality mechanisms. In particular we show that the magnetic torque can speed chemotaxis up in some conditions, while it can hinder it in other cases. In addition to an understanding of the swimming strategies of naturally magnetotactic organisms, the results may guide the design of future biomedical devices.

10 pages; National audience; Pinna nobilis is the largest bivalve in the Mediterranean Sea. This endemic species lives in the Posidonia meadows,in the form of small sparse populations. It is a heritage species: its byssus has long been collected to be wovenand used to make gloves, hats or stoles. Protected by a European Directive (1992), P. nobilis is closely monitored,nationally and internationally. But since the end of 2016, an epidemic, which origin seems to be a protozoan parasite,decimates populations (up to 100% mortality). This event began on the Spanish coast and spreads now all around theMediterranean. Although conservation measures have been taken, the next few years could see the extinction of thisemblematic bivalve. Apart from its symbolic value, P. nobilis is a species worthy of biotechnological interest. Its shellcomprises two mineralized layers, one of which, external, calcitic, consists of large monocrystalline prisms, consideredas a model in biomineralization. Understanding their formation and growth is a challenge in biomimetics. Its byssusforms very fi ne remarkably solid fi laments, with ultrastructural properties different from those of the mussel byssus.Until now, the chemistry of this byssus remains mysterious. Understanding it is also a challenge in material physics.These different points are discussed in this article.; La Grande nacre Pinna nobilis est le plus grand bivalve de Méditerranée. Espèce endémique, elle est inféodée auxherbiers de posidonies, vivant sous forme de petites populations clairsemées. C’est une espèce patrimoniale : sonbyssus a longtemps été collecté pour être utilisé à la confection de gants, bonnets ou étoles. Protégée par uneDirective Européenne (1992), P. nobilis fait l’objet d’une surveillance étroite au plan national et international. Or depuisfi n 2016, une épidémie, dont l’origine semble être un parasite protozoaire, décime les populations (jusqu’à 100 %de mortalité). Détectée au départ sur les côtes espagnoles, elle s’étend sur tout le pourtour méditerranéen.Bien que des mesures aient été prises, les prochaines années pourraient voir l’extinction de ce bivalve emblématique.Hormis sa valeur symbolique, P. nobilis est une espèce digne d’intérêt en science des matériaux et composites bioinspirés.En effet, sa coquille comprend deux couches minéralisées, dont l’une, externe, est constituée de grandsprismes calcitiques d’aspect monocristallin, simples en apparence, mais présentant une structuration multi-échelletrès complexe. Comprendre leur formation et leur croissance est un challenge en biomimétique. Son byssus formedes fi laments très fi ns remarquablement solides, aux propriétés ultrastructurales différentes de celles du byssus demoule. Jusqu’à présent, la chimie de ce byssus reste mystérieuse. L’appréhender est aussi une gageure en physiquedes matériaux. Ces différents points sont abordés dans cet article.

Mutualistic symbioses are often a source of evolutionary innovation and drivers of biological diversification1. Widely distributed in the microbial world, particularly in anoxic settings2,3, they often rely on metabolic exchanges and syntrophy2,4. Here, we report a mutualistic symbiosis observed in marine anoxic sediments between excavate protists (Symbiontida, Euglenozoa)5 and ectosymbiotic Deltaproteobacteria biomineralizing ferrimagnetic nanoparticles. Light and electron microscopy observations as well as genomic data support a multi-layered mutualism based on collective magnetotactic motility with division of labour and interspecies hydrogen-transfer-based syntrophy6. The guided motility of the consortia along the geomagnetic field is allowed by the magnetic moment of the non-motile ectosymbiotic bacteria combined with the protist motor activity, which is a unique example of eukaryotic magnetoreception7 acquired by symbiosis. The nearly complete deltaproteobacterial genome assembled from a single consortium contains a full magnetosome gene set8, but shows signs of reduction, with the probable loss of flagellar genes. Based on the metabolic gene content, the ectosymbiotic bacteria are anaerobic sulfate-reducing chemolithoautotrophs that likely reduce sulfate with hydrogen produced by hydrogenosome-like organelles6 underlying the plasma membrane of the protist. In addition to being necessary hydrogen sinks, ectosymbionts may provide organics to the protist by diffusion and predation, as shown by magnetosome-containing digestive vacuoles. Phylogenetic analyses of 16S and 18S ribosomal RNA genes from magnetotactic consortia in marine sediments across the Northern and Southern hemispheres indicate a host–ectosymbiont specificity and co-evolution. This suggests a historical acquisition of magnetoreception by a euglenozoan ancestor from Deltaproteobacteria followed by subsequent diversification. It also supports the cosmopolitan nature of this type of symbiosis in marine anoxic sediments. Here, the authors identify a mutualistic symbiosis between a non-motile, magnetic deltaproteobacterium and a protist, resulting in eukaryotic magnetoreception in marine anoxic sediments.

Benders, such as bilayers, are well-known shape-changing structures which bend upon activation by a stimulus, such as temperature. The objective of this contribution is to propose new shape-changing rod-like structures, referred to as twisters, which twist upon activation. A simple biomimetic design principle based on symmetry considerations is proposed. FEM simulations show that the proposed design does feature a twisting instability in reaction to an increasing stimulus. A simpler generic mechanical model with two state variables, whose kinematics is inspired from the FEM simulations, is then proposed and its governing equations are derived analytically. As in the FEM simulations, such twisters are shown to first stretch as the stimulus increases until a bifurcation is reached, then, they undergo a mixed stretching–twisting regime. An accurate approximation of the bifurcation point is derived and serves as a guideline for the design of twisters in accordance with chosen specifications. Results are illustrated using twisters with three different behaviours.

Magnetotactic bacteria (MTB) are a heterogeneous group of Gram-negative prokaryotes, which all produce special magnetic organelles called magnetosomes. The magnetosome consists of a magnetic nanoparticle, either magnetite (Fe3O4) or greigite (Fe3S4), embedded in a membrane, which renders the systems colloidaly stable, a desirable property for biotechnological applications. Although these bacteria are able to regulate the formation of magnetosomes through a biologically-controlled mechanism, the environment in general and the physico-chemical conditions surrounding the cells in particular also influence biomineralization. This work thus aims at understanding how such external conditions, in particular the extracellular oxidation reduction potential, influence magnetite formation in the strain Magnetospirillum magneticum AMB-1. Controlled cultivation of the microorganisms was performed at different redox potential in a bioreactor and the formation of magnetosomes was assessed by microscopic and spectroscopic techniques. Our results show that the formation of magnetosomes is inhibited at the highest potential tested (0 mV), whereas biomineralization is facilitated under reduced conditions (-500 mV). This result improves the understanding of the biomineralization process in MTB and provides useful information in sight of a large scale production of magnetosomes for different applications. © 2019 Olszewska-Widdrat, Schiro, Reichel and Faivre.

The field of synthetic microswimmers, micro-robots moving in aqueous environments, has evolved significantly in the last years. Micro-robots actuated and steered by external magnetic fields are of particular interest because of the biocompatibility of this energy source and the possibility of remote control, features suited for biomedical applications. While initial work has mostly focused on helical shapes, the design space under consideration has widened considerably with recent works, opening up new possibilities for optimization of propellers to meet specific requirements. Understanding the relation between shape on the one hand and targeted actuation and steerability on the other hand requires an understanding of their propulsion behavior. Here we propose hydrodynamic simulations for the characterization of rigid micropropellers of any shape, actuated by rotating external magnetic fields. We approximate the shape of micropropellers by an ensemble of rigidly connected spheres, for which the mobility matrices can be calculated via the method of reflections. We characterize the influence of model parameters such as bead size, distance between beads and magnetic properties on the swimming behavior of helical propellers to identify optimal simulation parameters. We then apply the simulation to randomly shaped propeller, specifically to a recently characterized propeller shape and study their frequency- dependent swimming behaviors. The simulations show that the orientation of the magnetic moment with respect to the propeller’s internal coordinate system has a strong impact on the propulsion behavior and has to be known with a precision of ≤ 5 ◦ to predict the propeller’s velocity-frequency curve. This result emphasizes the importance of the magnetic properties of the micropropellers for the design of desired functionalities for potential biomedical applications, and in particular the importance of their orientation within the propeller’s structure.

International audience; Many motile microorganisms swim and navigate in chemically and mechanically complex environments. These organisms can be functionalized and directly used for applications (biohybrid approach), but also inspire designs for fully synthetic microbots. The most promising designs of biohybrids and bioinspired microswimmers include one or several magnetic components, which lead to sustainable propulsion mechanisms and external controllability. This Review addresses such magnetic microswimmers, which are often studied in view of certain applications, mostly in the biomedical area, but also in the environmental field. First, propulsion systems at the microscale are reviewed and the magnetism of microswimmers is introduced. The review of the magnetic biohybrids and bioinspired microswimmers is structured gradually from mostly biological systems toward purely synthetic approaches. Finally, currently less explored parts of this field ranging from in situ imaging to swarm control are discussed.

Wood cell walls when contacted with humid atmosphere or an aqueous solution containing electrolytes or polymers undergo the phenomenon of swelling. In this work, experimental data were produced to quantify the effects of the adsorption water and solutes, which were introduced in the material by equilibration with a solution used as osmotic reservoir. For this reason, different environmental setups have been developed, allowing the control of temperature, water chemical potential, and ionic strength during the sorption process. The aim of this paper is to describe three experimental setups, focused on different levels: at the nanometric scale, small-angle scattering at controlled humidity; at the mesoscopic scale, environmental scanning electron microscopy; and at the macroscopic scale, tensile stage involving immersion of samples in solutions. Applicability and efficiency of the three setups are described. Moreover, it was shown how the combination of the results obtained via the three methodologies can be compared to expectations from a general Equation of State (EOS approach), where wood swelling with water and salt solutions is presented as the dependence of the distance between adjacent cellulose fibrils on the osmotic pressure. The total pressure calculated takes into account chemical, colloidal and mechanical terms in the force balance of the wood cell wall.

11 pages; International audience; Numerous mussel species produce byssal threads - tough proteinaceous fibers, which anchor mussels in aquatic habitats. Byssal threads from Mytilus species, which are comprised of modified collagen proteins - have become a veritable archetype for bio-inspired polymers due to their self-healing properties. However, threads from different species are comparatively much less understood. In particular, the byssus of Pinna nobilis comprises thousands of fine fibers utilized by humans for millennia to fashion lightweight golden fabrics known as sea silk. P. nobilis is very different from Mytilus from an ecological, morphological and evolutionary point of view and it stands to reason that the structure-function relationships of its byssus are distinct. Here, we performed compositional analysis, X-ray diffraction (XRD) and transmission electron microscopy (TEM) to investigate byssal threads of P. nobilis, as well as a closely related bivalve species (Atrina pectinata) and a distantly related one (Pinctada fucata). This comparative investigation revealed that all three threads share a similar molecular superstructure comprised of globular proteins organized helically into nanofibrils, which is completely distinct from the Mytilus thread ultrastructure, and more akin to the supramolecular organization of bacterial pili and F-actin. This unexpected discovery hints at a possible divergence in byssus evolution in Pinnidae mussels, perhaps related to selective pressures in their respective ecological niches.

Holotomography, a phase-sensitive synchrotron-based (µCT) modality, is a quantitative 3D imaging method. By exploiting partial spatial X-ray coherence, bones can be imaged volumetrically with high resolution coupled with impressive density sensitivity. This tomographic method reveals the main characteristics of the important tissue compartments in forming bones, including the rapidly changing soft tissue and the partially or fully mineralized bone regions, while revealing subtle density differences in 3D. Here, we show typical results observed within the growing femur bone midshafts of healthy mice that are 1, 3, 7, 10, and 14 days old (postpartum). Our results make use of partially coherent synchrotron radiation employing inline Fresnel propagation in multiple tomographic datasets obtained in the imaging beamline ID19 of the European Synchrotron Radiation Facility. The exquisite detail creates maps of the juxtaposed soft, partially mineralized and highly mineralized bone revealing the environment in which bone cells create and shape the matrix. This high-resolution 3D data can be used to create detailed computational models to study the dynamic processes involved in bone tissue formation and adaptation. Such data can enhance our understanding of the important biomechanical interactions directing maturation and shaping of the bone micro- and macro-geometries.

DPDAK is a software for simple and fast on- and offline reduction and analysis of X-ray scattering data. It is an open-source software with a plug-in structure allowing tailored extensions., X-ray scattering experiments at synchrotron sources are characterized by large and constantly increasing amounts of data. The great number of files generated during a synchrotron experiment is often a limiting factor in the analysis of the data, since appropriate software is rarely available to perform fast and tailored data processing. Furthermore, it is often necessary to perform online data reduction and analysis during the experiment in order to interactively optimize experimental design. This article presents an open-source software package developed to process large amounts of data from synchrotron scattering experiments. These data reduction processes involve calibration and correction of raw data, one- or two-dimensional integration, as well as fitting and further analysis of the data, including the extraction of certain parameters. The software, DPDAK (directly programmable data analysis kit), is based on a plug-in structure and allows individual extension in accordance with the requirements of the user. The article demonstrates the use of DPDAK for on- and offline analysis of scanning small-angle X-ray scattering (SAXS) data on biological samples and microfluidic systems, as well as for a comprehensive analysis of grazing-incidence SAXS data. In addition to a comparison with existing software packages, the structure of DPDAK and the possibilities and limitations are discussed.

The iron oxide mineral magnetite (Fe 3 O 4 ) is produced by various organisms to exploit magnetic and mechanical properties. Magnetotactic bacteria have become one of the best model organisms for studying magnetite biomineralization, as their genomes are sequenced and tools are available for their genetic manipulation. However, the chemical route by which magnetite is formed intracellularly within the so-called magnetosomes has remained a matter of debate. Here we used X-ray absorption spectroscopy at cryogenic temperatures and transmission electron microscopic imaging techniques to chemically characterize and spatially resolve the mechanism of biomineralization in those microorganisms. We show that magnetite forms through phase transformation from a highly disordered phosphate-rich ferric hydroxide phase, consistent with prokaryotic ferritins, via transient nanometric ferric (oxyhydr)oxide intermediates within the magnetosome organelle. This pathway remarkably resembles recent results on synthetic magnetite formation and bears a high similarity to suggested mineralization mechanisms in higher organisms.

PLoS one 12(9), e0184881 - (2017). doi:10.1371/journal.pone.0184881, Purified myelin membranes (PMMs) are the starting material for biochemical analyses such as the isolation of detergent-insoluble glycosphingolipid-rich domains (DIGs), which arebelieved to be representatives of functional lipid rafts. The normal DIGs isolation protocol involves the extraction of lipids under moderate cooling. Here, we thus address the influence of cooling on the structure of PMMs and its sub-fractions. Thermodynamic and structural aspects of periodic, multilamellar PMMs are examined between 4 ̊C and 45 ̊C andin various biologically relevant aqueous solutions. The phase behavior is investigated by small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). Complementar y neutron diffraction (ND) experiments with solid-supported myelin multilayers confirm that the phase behavior is unaffected by planar confinement. SAXS and NDconsistently show that multilamellar PMMs in pure water become heterogeneous when cooled by more than 10– 15 ̊C below physiologica l temperature, as during the DIGs isolationprocedure. The heterogeneous state of PMMs is stabilized in physiological solution, where phase coexistence persists up to near the physiological temperature . This result supports the general view that membranes under physiological conditions are close to critical points for phase separation. In presence of elevated Ca 2+ concentrations ( > 10 mM),phase coexistence is found even far above physiologica l temperatures. The relative fractions of the two phases, and thus presumably also their compositions, are found to varywith temperature. Depending on the con- ditions, an “expanded ” phase with larger lamellar period or a “compacted” phase with smaller lamellar period coexists with the nativephase. Both expanded and compacted periods are also observed in DIGs under the respective conditions. The observed subtle tem- perature-dependenc e of the phase behaviorof PMMs suggests that the composition of DIGs is sensitive to the details of the isolation protocol., Published by PLoS, Lawrence, Kan.

The complex arrangement of the extracellular matrix (ECM) produced by cells during tissue growth, healing and remodelling is fundamental to tissue function. In connective tissues, it is still unclear how both cells and the ECM become and remain organized over length scales much larger than the distance between neighbouring cells. While cytoskeletal forces are essential for assembly and organization of the early ECM, how these processes lead to a highly organized ECM in tissues such as osteoid is not clear. To clarify the role of cellular tension for the development of these ordered fibril architectures, we used an in vitro model system, where pre-osteoblastic cells produced ECM-rich tissue inside channels with millimetre-sized triangular cross sections in ceramic scaffolds. Our results suggest a mechanical handshake between actively contracting cells and ECM fibrils: the build-up of a long-range organization of cells and the ECM enables a gradual conversion of cell-generated tension to pre-straining the ECM fibrils, which reduces the work cells have to generate to keep mature tissue under tension.

International audience; The complex structure of bone requires a structural description of the material at different hierarchical levels. At the micrometer level, collagen fi bril orientation and osteocyte network architecture can be described by different light microscopy methods. However, further investigation of the nanostructure of bone requires high-resolution techniques such as electron microscopy as well as x-ray scattering methods. The basic building blocks at the nanometer level are organic type I collagen fi brils reinforced by nanoparticles of carbonated apatite mineral. Most commonly, these fi brils aggregate into lamellae of about 5 μm width, in both compact and spongy bone. The architecture of the mineral platelets and the collagen fi brils infl uences the mechanical properties. Models of twisted and rotated plywood motifs have been proposed, although detailed quantitative characterization at length scales comparable to typical tissue unit sizes are still lacking. Here, we describe a scanning small-angle x-ray scattering (SAXS) method to reconstruct the variation of the three-dimensional habit of mineral platelets within osteonal bone. We fi nd that the platelets change their orientation at micrometer resolution and are organized structurally by a repeating unit of about 5 μm, which is in agreement with previous wide-angle x-ray diffraction microtexture measurements. At the spatial resolution of the microbeam used (1 μm), we observe fi ber geometry. The presented SAXS reconstruction technique could also be applied to the analysis of nanoparticle orientation in highly textured biomaterials.

Aim: We report the physicochemical analysis of nanosystems intended for cardiovascular applications and their toxicological characterization in static and dynamic cell culture conditions. Methods: Size, polydispersity and ζ-potential were determined in 10 nanoparticle systems including liposomes, lipid nanoparticles, polymeric and iron oxide nanoparticles. Nanoparticle effects on primary human endothelial cell viability were monitored using real-time cell analysis and live-cell microscopy in static conditions, and in a flow model of arterial bifurcations. Results & conclusions: The majority of tested nanosystems were well tolerated by endothelial cells up to the concentration of 100 μg/ml in static, and up to 400 μg/ml in dynamic conditions. Pilot experiments in a pig model showed that intravenous administration of liposomal nanoparticles did not evoke the hypersensitivity reaction. These findings are of importance for future clinical use of nanosystems intended for intravascular applications.

Proceedings of the National Academy of Sciences of the United States of America 113(34), 9521 - 9526(2016). doi:10.1073/pnas.1603898113, In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers’ global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces., Published by National Acad. of Sciences, Washington, DC

An X-ray scanning imaging technique using the integrated intensity of the small-angle X-ray scattering (SAXS) signal is presented. The technique is based on two-dimensional scanning of a thin sample section with an X-ray microbeam, collecting SAXS patterns at every scanning step using a two-dimensional detector. The integrated intensity within pre-defined regions of interest of the SAXS patterns is used to image bulk nanostructural features in the specimen with micrometre resolution which are usually not accessible by other methods such as light microscopy or scanning electron microscopy. The possibilities and limitations of the method are discussed with particular emphasis on the sources of contrast in the SAXS region for three biological specimens: cortical bone, eggshell and hair. Two main sources of image contrast are identified in the form of orientation effects for strongly anisotropic systems like cortical bone and differences in the local volume fraction of the scattering entities in eggshell. Moreover, other parameters than the integrated intensity can be quantitatively deduced from the SAXS patterns, for instance, the mean thickness of mineral platelets in bone or the strain distributions in a hair deformed plastically by microindentation.

International audience; Organic additives are known to help minerals grow into complex shapes, which are beneficial for achieving various functional (e.g. optical) properties. Calcite-based microlens arrays (MLAs) are good examples of functional materials produced via the self-assembly of amorphous calcium carbonate (ACC) nanoparticles followed by a heat-mediated phase transformation into calcite. The optical transparency of the MLAs is preserved due to the nanocrystalline nature of the calcite formed. In this paper, we investigate the corresponding structural changes by mapping the local lattice parameters and size of calcite crystallites within individual microlenses. We find that the driving force for producing calcite with a crystallite size of 10 nm is the minimization of residual strains and related elastic energy by plastic deformation, which includes grain boundary formation and twinning. Local strains/stresses originate from transformation-associated macroscopic volume changes, which arise because of the differences in specific volume (per CaCO3 molecule) of ACC and calcite, firstly due to water loss and then to short-order atomic rearrangements. MLAs fabricated in this way represent a striking example for a stress-engineered nanocrystalline material produced with almost no energy cost through phase transformation, as compared to grain refinement by mechanical processing

International audience; Nearly equal volume fractions of biosilica and proteins are found in the micron-thick axial filament of the anchor spicule of the marine sponge Monorhaphis chuni. Chemical composition and mechanical properties of this unique composite material are characterized by confocal Raman spectroscopy and by nanoindentation and nanoscale elastic modulus mapping, respectively.

International audience; Three elephant tusks recovered from a 18th century Dutch shipwreck in Brittany seawaters were analyzed to study early diagenetic changes of ivory in a marine environment. Micro-small angle X-ray scattering (μSAXS) analysis revealed sub-microscopic structural modifications of ivory (hydroxyapatite particle thickness, mineralized collagen fibers organization and orientation). Chemical compositional changes of the organic fraction (nitrogen and carbon loss) and of the mineral part (magnesium loss, carbonate, calcium, chlorine and strontium uptake) were investigated by non-invasive micro-Particle Induced X-ray Emission/ Gamma-ray Emission/ Rutherford and Elastic Backscattering Spectrometry analysis (μPIXE/PIGE/RBS/EBS). These chemical and structural markers can serve as proxies for the early diagenesis of elephant tusk in marine settings. The results show that the macroscopic preservation state of the tusk surface does not reflect its microscopic preservation state. A diagenetic sequence is proposed, depending on the local environment of each tusk. First, collagen hydrolysis and ion adsorptions from the marine environment are proposed to occur. Second, a tusk buried in the sand was protected from Ca enrichment of the surface and the formation of a flaky white concretion whereas tusks out of the sand were subjected to these latter phenomena as well as sea-urchin attacks. Third, ion leaching and uptake, increased crystallinity of the hydroxyapatite crystals, and the modifications of the mineralized collagen fiber network are assumed to happen for all three tusks with different level of completion.

International audience; Biological materials typically display complex morphologies and hierarchical architectures, properties that are hardly matched by synthetic materials. Understanding the biological control of mineral properties will enable the development of new synthetic approaches toward biomimetic functional materials. Here, we combine biocombinatorial approaches with a proteome homology search and in vitro mineralization assays to assess the role of biological determinants in biomimetic magnetite mineralization. Our results suggest that the identified proteins and biomimetic polypeptides influence nucleation in vitro. Even though the in vivo role cannot be directly determined from our experiments, we can rationalize the following design principles: proteins, larger complexes, or membrane components that promote nucleation in vivo are likely to expose positively charged residues to a negatively charged crystal surface. In turn, components with acidic (negatively charged) functionality are nucleation inhibitors, which stabilize an amorphous structure through the coordination of iron.

International audience; Bone's mineral properties, such as particle thickness and degree of alignment have been associated with bone quality. Bone formation, remodeling, aging of the tissue and mineral homeostasis influence mineral particle properties leading to specific patterns across bone. Scanning small angle X-ray scattering (sSAXS) with synchrotron radiation is a powerful tool, which allows us to study bone's nanoscale mineral properties in a position-resolved way. We used sSAXS, fluorescence light microscopy and backscattered electron (BSE) imaging to study bone's mineral properties at the tibial midshaft of in vivo-loaded mice. By combining these techniques, we could detect local changes in mineral properties. Regions labeled with calcein fluorochrome have lower mean mineral thickness and degree of mineral alignment. We also observed thinner and less aligned mineral particles near blood vessels. We conclude that mineral properties (i) are altered by fluorochrome labeling and (ii) depend on the proximity to blood vessels.

The magnetosome-associated protein mamP is an iron oxidase that reveals a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c-type cytochrome exclusively found in magnetotactic bacteria. Magnetotactic bacteria use a specialized organelle known as the magnetosome, a biomineralized crystal of magnetite (Fe(II)Fe(III)2O4) or greigite (Fe(II)Fe(III)2S4), to sense and align along the Earth's magnetic field. This paper presents the X-ray crystal structure of the magnetosome-associated protein MamP, revealing a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains. The authors also establish that MamP is an iron oxidase that contributes to the formation of iron(III) ferrihydrite, and is therefore important for mechanisms of iron management during magnetosome biogenesis. Magnetotactic bacteria align along the Earth’s magnetic field using an organelle called the magnetosome, a biomineralized magnetite (Fe(ii)Fe(iii)2O4) or greigite (Fe(ii)Fe(iii)2S4) crystal embedded in a lipid vesicle. Although the need for both iron(ii) and iron(iii) is clear, little is known about the biological mechanisms controlling their ratio1. Here we present the structure of the magnetosome-associated protein MamP and find that it is built on a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c-type cytochrome exclusively found in magnetotactic bacteria. Mutational analysis, enzyme kinetics, co-crystallization with iron(ii) and an in vitro MamP-assisted magnetite production assay establish MamP as an iron oxidase that contributes to the formation of iron(iii) ferrihydrite eventually required for magnetite crystal growth in vivo. These results demonstrate the molecular mechanisms of iron management taking place inside the magnetosome and highlight the role of magnetochrome in iron biomineralization.

International audience; Biological materials are often hierarchically structured from the nanometer to the macroscopic scale. Specific characterization methods are needed to characterize the structures at these different length scales. This chapter reviews -based on the example of bone- the use of X-ray scattering methods to explore representative and quantitative structure information as well as structure-function relations in hierarchically structured biological materials. X-ray scattering techniques are particularly well suited for the characterization of the form and organization of organic and inorganic components in those materials. When nanometer-sized structures are exposed to X-rays, details of the internal material structure can be revealed by the analysis of the resulting interference patterns. Fundamental aspects of wide and small angle X-ray scattering (WAXS and SAXS) are discussed with specific focus on bone studies. An important field of research using X-ray scattering techniques, is the in situ combination with mechanical testing, which allows investigating changes in structure under specific loading conditions. Another common application is the structural study of heterogeneities or local structures within a sample using a narrow focused X-ray beam. Furthermore, in scanning mode, where the specimen is displaced step by step across a microbeam while collecting a SAXS/WAXS pattern at each step, complex structural maps of the sample can be derived. A natural extension of the method toward imaging is described in the context of X-ray imaging with scattering contrast.

The properties of wood and wood-based materials are strongly dependent on the properties of the fibres, that is, the cell wall properties. It is thus highly important to be able to mechanically characterise cell walls in order to understand structure–property relationships. This article gives a brief overview of the state of the art in experimental techniques to characterise the mechanical properties of wood at both the level of the single cell and that of the cell wall. Challenges, opportunities, drawbacks and limitations of single fibre tensile tests and nanoindentation are discussed with respect to the wood material properties.

Understanding the mechanical response of wood to external loads is essential to understand (and predict) the stability of living trees or equally important for the behaviour of wood when it is used for construction purposes. In general, wood is a hierarchically structured material: a sophisticatedarchitecture at several length scales, from the mm to the nm level, allows ingenious control of various functions. This highlights the importance of studying wood at several length scales. Here we will focus on wood micromechanical data which can serve as - besides a deeper understanding of the material properties in general - important input parameters in applications such as manufacture of fibre-based products like cardboard and paper which helps this resource to be used in targeted, efficient, economic and sustainable ways.In the presentation, a brief overview of the state of the art of two frequently used methods that allow experimental characterization of mechanical properties at the cell and cell wall level, namely single fibre microtensile tests and nanoindentation, will be given.Since 1959, the year when Jayne published his paper “Mechanical properties of wood fibres” [1], the first experimental procedure describing single wood fibre testing, many different procedures have been developed. Key developments will be summarized.Nanoindentation, in comparison with tensile tests, is a rather young experimental technique that was applied on wood in 1997 by Wimmer et al. [2] for the first time. Again, key developments since then will be summarized.For both techniques sample preparation is not straightforward. Whereas single fibre tests demand the isolation of tracheids, fibre tracheids or libriform fibres, nanoindentation requires flat surfaces and an adapted indentation size compared to the cell wall thickness (i.e., correct choice of the loadingunloading conditions and measurements correction if necessary). Challenges, limitations and drawbacks will be discussed, also with respect to controlling relative humidities.Finally, examples for micromechanical properties will be given and a summarizing collection of data from literature, both for microtensile tests and nanoindentation, will be presented.

Raman imaging of plant cell walls represents a nondestructive technique that can provide insights into chemical composition in context with structure at the micrometer level (

International audience; A model describing the size and arrangement of mineral particles in bone tissues is used to analyse the results of a scanning small-angle X-ray scattering (SAXS) experiment on a pathological bone biopsy. The overall description assumes that the nanometre-sized mineral platelets are arranged in a parallel fashion with possible fluctuations in their relative position, orientation and thickness. This method is tested on a thin sample section obtained from the biopsy of an osteoporotic patient treated with a high cumulative dose of NaF. The mineralization pattern of fluorotic bone is known to exhibit significant differences as compared to healthy bone in terms of density, particle size and organization. This is the first attempt to provide quantitative indicators of the degree of regularity in the packing of the mineral platelets in human pathological bone. Using scanning SAXS with a synchrotron microbeam of 15 mm allows discrimination between pathological and healthy bone at the tissue level. Additionally, the benefits of this method are discussed with respect to the accuracy of particle size determination using SAXS.

Self-assembled collagen−apatite matrix is prepared through a simple “one-pot” coprecipitation method. Hierarchical structures are reproduced that closely mimic the complex organization in bone tiss...

In order to study the formation of magnetite in magnetotactic bacteria, FORC diagrams were measured on a set of cultured Magnetospirillum gryphiswaldense, following an assay in which the iron uptake is used only for magnetite formation and not for cell growth. This enabled us to follow the magnetite formation independently of growth. The FORC diagrams showed a clear evolution from a size-distribution with a majority of superparamagnetic grains, to a distribution dominated by stable, single-domain grains, but still containing some superparamagnetic particles. TEM observations confirm this evolution. According to the saturation isothermal remanent magnetization cooling and warming curves, the Verwey transition can only be seen in the most mature samples, and slightly below 120 K. This suggests that the samples may have suffered from some partial oxidation.

The feasibility of Fourier transform infrared (FT-IR) microscopy to monitor in situ the enzymatic degradation of wood was investigated. Cross-sections of poplar wood were treated with cellulase Onozuka RS within a custom-built fluidic cell. Light-optical micrographs and FT-IR spectra were acquired in situ from normal and tension wood fibers. Light-optical micrographs showed almost complete removal of the gelatinous (G) layer in tension wood. No structural and spectral changes were observed in the lignified cell walls. The accessibility of cellulose within the lignified cell wall was found to be the main limiting factor, whereas the depletion of the enzyme due to lignin adsorption could be ruled out. The fast, selective hydrolysis of the crystalline cellulose in the G-layer, even at room temperature, might be explained by the gel-like structure and the highly porous surface. Young plantation grown hardwood trees with a high proportion of G-fibers thus represent an interesting resource for bioconversion to fermentable sugars in the process to bioethanol.

The mechanism of active stress generation in tension wood is still not fully understood. To characterize the functional interdependency between the G-layer and the secondary cell wall, nanostructural characterization and mechanical tests were performed on native tension wood tissues of poplar (Populus nigra x Populus deltoids) and on tissues in which the G-layer was removed by an enzymatic treatment. In addition to the well-known axial orientation of the cellulose fibrils in the G-layer, it was shown that the microfibril angle of the S2-layer was very large (about 36 degrees). The removal of the G-layer resulted in an axial extension and a tangential contraction of the tissues. The tensile stress-strain curves of native tension wood slices showed a jagged appearance after yield that could not be seen in the enzyme-treated samples. The behaviour of the native tissue was modelled by assuming that cells deform elastically up to a critical strain at which the G-layer slips, causing a drop in stress. The results suggest that tensile stresses in poplar are generated in the living plant by a lateral swelling of the G-layer which forces the surrounding secondary cell wall to contract in the axial direction.

International audience; A fully automated procedure to extract and to image local fibre orientation in biological tissues from scanning X-ray diffraction is presented. The preferred chitin fibre orientation in the flow sensing system of crickets is determined with high spatial resolution by applying synchrotron radiation based X-ray microbeam diffraction in conjunction with advanced sample sectioning using a UV micro-laser. The data analysis is based on an automated detection of azimuthal diffraction maxima after 2D convolution filtering (smoothing) of the 2D diffraction patterns. Under the assumption of crystallographic fibre symmetry around the morphological fibre axis, the evaluation method allows mapping the three-dimensional orientation of the fibre axes in space. The resulting two-dimensional maps of the local fibre orientations – together with the complex shape of the flow sensing system – may be useful for a better understanding of the mechanical optimization of such tissues.

International audience; Deformation mechanisms occurring on the nanometer scale during indentation of bulk polymer fibres were investigated by means of scanning wide-angle diffraction scattering (WAXS) using beams of micrometer size at the ESRF microfocus beamline (ID13). Elastic processes could be evidenced in-situ using a dedicated microindenter device. The most important changes appear in the form of local crystalline reorientation which can be quantified by analysis of the azimuthal profiles of the WAXS reflections. The texture and phase-transitions induced by plastic deformation at higher loads was also measured and the differences between high performance fibres and a more traditional semicrystalline polymer are emphasized.

International audience; We report here for the first time on surface immobilization of hollow faceted polyhedrons formed fromcatanionic surfactant mixtures. We find that electrostatic interaction with the substrate dominates their adhesionbehavior. Using polyelectrolyte coated surfaces with tailored charge densities, polyhedrons can thus beimmobilized without complete spreading, which allows for further study of their mechanical properties usingAFM force measurements. The elastic response of individual polyhedrons can be locally resolved, showingpronounced differences in stiffness between faces and vertexes of the structure, which makes these systemsinteresting as models for structurally similar colloidal scale objects such as viruses, where such effects arepredicted but cannot be directly observed due to the smaller dimensions. Elastic constants of the wall materialare estimated using shell and plate deformation models and are found to be a factor of 5 larger than those forneutral lipidic bilayers in the gel state. We discuss the molecular origins of this high stiffness

International audience; A large variety of organisms are capable of synthesizing hard matter in a process called biomineralization [1]. The transformation of a genetic blueprint into minerals such as, for example, calcium phosphate in bones and calcium carbonate in eggs or seashells provides a mechanical support for organismic growth and protection against predators, respectively. Iron oxides formed by fishes and birds provide them with magnetic properties used for magnetoreception and orientation [2], [3]. The biomineralization processes are remarkable for numerous reasons: organisms, contrary to engineers, have to form these biological materials with a limited subset of biologically available chemical elements and at physiological conditions. Still, these reduced means are not at the detriment of their function, which often surpasses man-made materials based on equivalent elements [4]. Therefore, understanding how biomineralizing organisms process chemical elements based on their genetic program is of primary interest. However, the biological mechanisms behind biomineralization have remained unclear, partly because of limited genetic knowledge: model organisms are limited to a few unicellular organisms [5], [6]. Therefore, the question has arisen of what genetic approach to use to get genetic information about the large majority of organisms that have remained intractable.

Pinna nobilis is the largest bivalve in the Mediterranean Sea. This endemic species lives in the Posidonia meadows,in the form of small sparse populations. It is a heritage species: its byssus has long been collected to be wovenand used to make gloves, hats or stoles. Protected by a European Directive (1992), P. nobilis is closely monitored,nationally and internationally. But since the end of 2016, an epidemic, which origin seems to be a protozoan parasite,decimates populations (up to 100% mortality). This event began on the Spanish coast and spreads now all around theMediterranean. Although conservation measures have been taken, the next few years could see the extinction of thisemblematic bivalve. Apart from its symbolic value, P. nobilis is a species worthy of biotechnological interest. Its shellcomprises two mineralized layers, one of which, external, calcitic, consists of large monocrystalline prisms, consideredas a model in biomineralization. Understanding their formation and growth is a challenge in biomimetics. Its byssusforms very fi ne remarkably solid fi laments, with ultrastructural properties different from those of the mussel byssus.Until now, the chemistry of this byssus remains mysterious. Understanding it is also a challenge in material physics.These different points are discussed in this article., La Grande nacre Pinna nobilis est le plus grand bivalve de Méditerranée. Espèce endémique, elle est inféodée auxherbiers de posidonies, vivant sous forme de petites populations clairsemées. C’est une espèce patrimoniale : sonbyssus a longtemps été collecté pour être utilisé à la confection de gants, bonnets ou étoles. Protégée par uneDirective Européenne (1992), P. nobilis fait l’objet d’une surveillance étroite au plan national et international. Or depuisfi n 2016, une épidémie, dont l’origine semble être un parasite protozoaire, décime les populations (jusqu’à 100 %de mortalité). Détectée au départ sur les côtes espagnoles, elle s’étend sur tout le pourtour méditerranéen.Bien que des mesures aient été prises, les prochaines années pourraient voir l’extinction de ce bivalve emblématique.Hormis sa valeur symbolique, P. nobilis est une espèce digne d’intérêt en science des matériaux et composites bioinspirés.En effet, sa coquille comprend deux couches minéralisées, dont l’une, externe, est constituée de grandsprismes calcitiques d’aspect monocristallin, simples en apparence, mais présentant une structuration multi-échelletrès complexe. Comprendre leur formation et leur croissance est un challenge en biomimétique. Son byssus formedes fi laments très fi ns remarquablement solides, aux propriétés ultrastructurales différentes de celles du byssus demoule. Jusqu’à présent, la chimie de ce byssus reste mystérieuse. L’appréhender est aussi une gageure en physiquedes matériaux. Ces différents points sont abordés dans cet article.

International audience; Heat-triggered fruit opening and delayed release of mature seeds are widespread among plants in fire-prone ecosystems. Here, the material characteristics of the seed-containing follicles of Banksia attenuata (Proteaceae), which open in response to heat frequently caused by fire, are investigated. Material analysis reveals that long-term dimensional stability and opening temperatures of follicles collected across an environmental gradient increase as habitats become drier, hotter, and more fire prone. A gradual increase in the biaxial curvature of the hygroscopic valves provides the follicles in the driest region with the highest flexural rigidity. The irreversible deformation of the valves for opening is enabled via a temperature-dependent reduction of the elastic modulus of the innermost tissue layer, which then allows releasing the stresses previously generated by shrinkage of the fiber bundles in the adjacent layer during follicle drying. These findings illustrate the level of sophistication by which this species optimizes its fruit opening mechanism over a large distribution range with varying environmental conditions, and may not only have great relevance for developing biomimetic actuators, but also for elucidating the species' capacity to cope with climatic changes.