Cells and bacteria use mechanotransduction processes to transform a mechanical force into a chemical/biochemical response. The area of chemistry where chemical reactions are induced by mechanical ...forces is called mechanochemistry. Over the last few years, chemists developed force-induced reactions affecting covalent bonds in molecules under tension which requires high energy input and/or high intensity forces. In contrast, in nature, mechanotransduction processes take place with forces of much weaker intensity and much less demanding energy. They are mainly based on protein conformational changes or changes in supramacromolecular architectures. Mechanochemistry based on such low-energy-demanding processes and which does not affect chemical bonds can be called soft-mechanochemistry. In this feature article, we first discuss some examples of soft-mechanochemistry processes encountered in nature, in particular, cryptic sites, allowing us to define more precisely the concepts underlying soft-mechanochemistry. A series of examples, developed over the past few years, of chemomechanoresponsive systems based on soft-mechanochemistry principles are given. We describe, in particular, cryptic site surfaces, enzymatically active films whose activity can be modulated by stretching and films where stretching induces changes in their fluorescence properties. Finally, we give our view of the future of soft-mechanochemistry.
Macromolecular coatings play an important role in many technological areas, ranging from the car industry to biosensors. Among the different coating technologies, electrochemically triggered ...processes are extremely powerful because they allow in particular spatial confinement of the film buildup up to the micrometer scale on microelectrodes. Here, we review the latest advances in the field of electrochemically triggered macromolecular film buildup processes performed in aqueous solutions. All these processes will be discussed and related to their several applications such as corrosion prevention, biosensors, antimicrobial coatings, drug-release, barrier properties and cell encapsulation. Special emphasis will be put on applications in the rapidly growing field of biosensors. Using polymers or proteins, the electrochemical buildup of the films can result from a local change of macromolecules solubility, self-assembly of polyelectrolytes through electrostatic/ionic interactions or covalent cross-linking between different macromolecules. The assembly process can be in one step or performed step-by-step based on an electrical trigger affecting directly the interacting macromolecules or generating ionic species.
Supramolecular metal-phenolic thin films attract an increasing interest since they allow the design of new types of self-assembling materials, such as tunable electronics or biomaterials. In this ...study, a new electrotriggered self-assembly of tannic acid-Fe(III) (TA-Fe(III)) nanocoatings was developed using the morphogenic approach with Fe(III) ions as a morphogen. Morphogens are molecules or ions produced locally that diffuse into the solution and induce a chemical reaction or interaction in a confined space near a surface. Using a mixture of TA and Fe(II) ions in contact with an electrode, a confined electrogenerated gradient of Fe(III) was obtained by application of an anodic current to locally form TA-Fe(III) coordination complexes. TA-Fe(III) nanocoatings, based on di- and tri-coordinated complexes, were thus obtained. Both the film thickness and its self-assembly kinetics were tuned by controlling the Fe(II)/TA molar ratio of the building solution, the intensity, and the duration of the applied current. We showed that this strategy can be applied to two other polyphenols (gallic acid and rosmarinic acid). This new electrotriggered confined self-assembly of metal–polyphenol gives new perspectives in applications such as antioxidant coating.
Poly(lactic acid) (PLA) represents one of the most promising and attractive biobased polymer for the industrial development of environmentally sustainable packaging. However, oxygen and water ...barrier properties of PLA based films cannot compete with those of commercially available composite multilayers. To fill this gap, we used the layer-by-layer deposition technique on commercially used PLA thin films (30 μm thick) in order to increase their barrier properties to oxygen and water vapor. Nanometric films were grown by alternating branched poly(ethylene imine) (BPEI), hydrophobic fluorinated polymer (Nafion), and montmorillonite clay (MMT) layers with the aim of obtaining low gas permeability in both dry and moist conditions as well as low water vapor permeability. Two different kinds of architectures were designed and successfully prepared, based on a 4 layer repeating unit (BPEI/MMT/BPEI/Nafion), represented here as quadlayer (QL), and on a 6 layer repeating-unit ((BPEI/Nafion)2/BPEI/MMT), hexalayer (HL). Reduction in oxygen and water permeabilities is observed for films based on both types of repeat units. The reduction of the permeabilities increases with the number of quad and hexalayers achieving reductions in terms of oxygen permeability in both dry and humid conditions up to 98% and 97% respectively for 10 HL and QL. Furthermore, a reduction of 78% of water vapor transmission rate through the functionalized film was obtained for these films. As far as oxygen permeability is concerned, HL films are more efficient than QL films for smaller numbers of deposition units. These properties are shown to result from the complementarity between the presence of BPEI/Nafion and MMT layers.
Localized molecular self‐assembly processes leading to the growth of nanostructures exclusively from the surface of a material is one of the great challenges in surface chemistry. In the last decade, ...several works have been reported on the ability of modified or unmodified surfaces to manage the self‐assembly of low‐molecular‐weight hydrogelators (LMWH) resulting in localized supramolecular hydrogel coatings mainly based on nanofiber architectures. This Minireview highlights all strategies that have emerged recently to initiate and localize LMWH supramolecular hydrogel formation, their related fundamental issues and applications.
From the bottom to the top: Spatial control of the self‐assembly can be triggered by the surface itself. Different strategies have been developed to grow supramolecular hydrogels at the solid–liquid interface.
The alternate deposition of polyanions and polycations on a solid substrate leads to the formation of nanometer to micrometer films called Polyelectrolyte Multilayers. This step‐by‐step construction ...of organic films constitutes a method of choice to functionalize surfaces with applications ranging from optical to bioactive coatings. The method was originally developed by dipping the substrate in the different polyelectrolyte solutions. Recent advances show that spraying the polyelectrolyte solutions onto the substrate represents an appealing alternative to dipping because it is much faster and easier to adapt at an industrial level. Multilayer deposition by spraying is thus greatly gaining in interest. Here we review the current literature on this deposition method. After a brief history of polyelectrolyte multilayers to place the spraying method in its context, we review the fundamental issues that have been addresses so far. We then give an overview the different fields where the method has been applied.
Design of nanometer to micrometer thin films by spraying solutions of polyelectrolyte is a recent emerging concept in the field of surface coating. Herein the origin of this new process, the fundamental issues, and the resulting potential applications relative to spray assisted deposition from the current literature are reviewed.
Nature uses systems of high complexity coordinated by the precise spatial and temporal control of associated processes, working from the molecular to the macroscopic scale. This living organization ...is mainly ensured by enzymatic actions. Herein, we review the concept of Localized Enzyme-Assisted Self-Assembly (LEASA). It is defined and presented as a straightforward and insightful strategy to achieve high levels of control in artificial systems. Indeed, the use of immobilized enzymes to drive self-assembly events leads not only to the local formation of supramolecular structures but also to tune their kinetics and their morphologies. The possibility to design tailored complex systems taking advantage of self-assembled networks through their inherent and emergent properties offers new perspectives for the design of novel, more adaptable materials. As a result, some applications have already been developed and are gathered in this review. Finally, challenges and perspectives of LEASA are introduced and discussed.
LEASA, a powerful tool to spatiotemporally control supramolecular hydrogels. Display omitted
•LEASA is a universal approach to direct supramolecular hydrogel on all materials of any kind, any size and any shape.•The growth kinetic of the hydrogel, its thickness, its morphological and mechanical features can be tuned through the enzyme surface density, the introduction of a seeding layer, the use of a multi-enzymatic system and the concentration of precursors.•LEASA is highly suitable to support catalytic hydrogel, design smart materials and for biomedical developements.
Inspired by biology, one current goal in supramolecular chemistry is to control the emergence of new functionalities arising from the self‐assembly of molecules. In particular, some peptides can ...self‐assemble and generate exceptionally catalytically active fibrous networks able to underpin hydrogels. Unfortunately, the mechanical fragility of these materials is incompatible with process developments, relaying this exciting field to academic curiosity. Here, we show that this drawback can be circumvented by enzyme‐assisted self‐assembly of peptides initiated at the walls of a supporting porous material. We applied this strategy to grow an esterase‐like catalytically active supramolecular hydrogel (CASH) in an open‐cell polymer foam, filling the whole interior space. Our supported CASH material is highly efficient towards inactivated esters and enables the kinetic resolution of racemates. This hybrid material is robust enough to be used in continuous flow reactors, and is reusable and stable over months.
CASH flow: Catalytically active supramolecular hydrogels (CASHs) generated from a porous polymer foam by an enzyme‐assisted self‐assembly strategy are ideal catalytic phases for continuous flow. A hydrogel prepared from an original bis‐phosphorylated heptapeptide enables highly efficient ester hydrolysis and kinetic resolution.
Display omitted
Enzyme-assisted self-assembly confined within host materials leads to Liesegang-like spatial structuration when precursor peptides are diffusing through an enzyme-functionalized ...hydrogel. It is shown here that playing on peptide and enzyme concentrations results in a transition from continuous self-assembled peptide areas to individual microglobules. Their morphology, location, size and buildup mechanism are described. Additionally, it is also found that the enzymes adsorb onto the peptide self-assemblies leading to co-localization of peptide self-assembled microglobules and enzymes. Finally, we find that large microglobules grow at the expense of smaller ones present in their vicinity in a kind of Ostwald ripening process, illustrating the dynamic nature of the peptide self-assembly process within host hydrogels.
The diffusion of adequate peptide through an enzyme-embedded host hydrogel leads to the in situ start-up and growth of an interpenetrated fibrous network. Based on the enzyme-assisted self-assembly ...concept, both chemistry and mechanical features of the hybrid hydrogel can be tuned.
PDF
