Supported Supramolecular Hydrogel Nanoarchitectonics for Tunable Biocatalytic Flow Activity.

Enzymatically-active polyelectrolyte multilayers containing n layers of phosphatase (APn-PEM) induce the formation of supported biocatalytic supramolecular hydrogels when brought in contact with the precursor tripeptide Fmoc-FFpY (Fmoc = N-fluorenylmethyloxycarbonyl; F = Phenylalanine; Y = Tyrosine; p = phosphate group). APn-PEM triggers the spatially-localized hydrogelation reaching 2, 17 and 350 µm of thickness for n = 1, 2 and 3, respectively. As observed by cryo scanning electron microscopy, a dense nanofibrous network underpinning the hydrogel shows parallelly orientated Fmoc-FFY peptide-based fibrils, perpendicular to the substrate. For the gel generated by the AP3-PEM, fluorescence confocal microscopy images show that during the peptide self-assembly, some enzymes are distributed in the hydrogel, preferentially located in few dozens of micrometers above the substrate. In addition, a self-assembly growth rate of 5 µm min-1 is determined when the hydrogelation starts. Through transmission electron microscopy immuno-labelling experiments on self-assemblies generated in solution, we observe that AP are decorating the Fmoc-FFY nanofibers. It is observed both a long-term stability and a higher biocatalytic activity of the so AP-encapsulated hydrogel compared to the bare APn-PEM. This bioactivity can be tuned by the number n in batch and under continuous flow conditions. To illustrate the versatility of this enzyme-supported strategy, multi-catalytic transformations in continuous flow conditions have been successfully carried out using supported supramolecular hydrogel.

Tuning the water intrinsic permeability of PEGDA hydrogel membranes by adding free PEG chains of varying molar masses.

We explore the effect of poly(ethylene glycol) (PEG) molar mass on the intrinsic permeability and structural characteristics of poly(ethylene glycol) diacrylate PEGDA/PEG composite hydrogel membranes. We observe that by varying the PEG content and molar mass, we can finely adjust the water intrinsic permeability by several orders of magnitude. Notably, we show the existence of maximum water intrinsic permeability, already identified in a previous study to be located at the critical overlap concentration C* of PEG chains, for the highest PEG molar mass studied. Furthermore, we note that the maximum intrinsic permeability follows a non-monotonic evolution with respect to the PEG molar mass and reaches its peak at 35 000 g mol-1. Besides, our results show that a significant fraction of PEG chains is irreversibly trapped within the PEGDA matrix even for the lowest molar masses down to 600 g mol-1. This observation suggests the possibility of covalent grafting of the PEG chains onto the PEGDA matrix. CryoSEM and AFM measurements demonstrate the presence of large micron-sized cavities separated by PEGDA-rich walls whose nanometric structures strongly depend on the PEG content. By combining our permeability and structural measurements, we suggest that the PEG chains trapped inside the PEGDA-rich walls induce nanoscale defects in the crosslinking density, resulting in increased permeability below C*. Conversely, above C*, we speculate that partially trapped PEG chains may form a brush-like arrangement on the surface of the PEGDA-rich walls, leading to a reduction in permeability. These two opposing effects are anticipated to exhibit molar-mass-dependent trends, contributing to the non-monotonic variation of the maximum intrinsic permeability at C*. Overall, our results demonstrate the potential to fine-tune the properties of hydrogel membranes, offering new opportunities for separation applications.

Sieving and Clogging in PEG-PEGDA Hydrogel Membranes.

Hydrogels are promising systems for separation applications due to their structural characteristics (i.e., hydrophilicity and porosity). In our study, we investigate the permeation of suspensions of rigid latex particles of different sizes through free-standing hydrogel membranes prepared by photopolymerization of a mixture of poly(ethylene glycol) diacrylate (PEGDA) and large poly(ethylene glycol) (PEG) chains of 300,000 g·mol-1 in the presence of a photoinitiator. Atomic force microscopy and cryoscanning electron microscopy (cryoSEM) were employed to characterize the structures of the hydrogel membranes. We find that the 20 nm particle permeation depends on both the PEGDA/PEG composition and the pressure applied during filtration. In contrast, we do not measure a significant permeation of the 100 nm and 1 µm particles, despite the presence of large cavities of 1 µm evidenced by the cryoSEM images. We suggest that the PEG chains induce local nanoscale defects in the cross-linking of PEGDA-rich walls separating the micrometer-sized cavities, which control the permeation of particles and water. Moreover, we discuss the decline of the permeation flux observed in the presence of latex particles compared to that of pure water. We suggest that a thin layer of particles forms on the surface of the hydrogels.

Impact of polymorphism in oleogels of N-palmitoyl-L-phenylalanine.

Gels of edible oils, also called oleogels, are developed as alternative products of solid fats to limit the uptake of saturated and trans-unsaturated fats and lower the associated risk of coronary disease. The gelation of oils can be achieved with a low molecular weight organogelator (LMWO), a compound that self-assembles at low concentrations in a solid 3D network and provides the mixture its solid-like behavior. We have studied N-palmitoyl-L-phenylalanine (Palm-Phe), an endogenous compound (i.e. naturally present in the human body) as a model LMWO of rapeseed oil. Palm-Phe forms gels at a concentration of 1 wt% in rapeseed oil. We have studied the thermodynamic and mechanical behavior of the corresponding gels. As evidenced by DSC and rheology, this system exhibits two transitions upon heating, in addition to the sol-gel transition, a gel-gel transition between two polymorphic gels. The structural differences between both polymorphs were revealed using cryo-SEM, X-rays scattering, and FTIR experiments. The metastability of one of the polymorphs was proven by ageing and annealing experiments.

Thermodynamics, morphology and molecular structure of molecular compounds in trisamide triarylamine organogels and pseudo-organogels.

In this paper, potentially-gelling binary systems are investigated by DSC, X-ray and Electron microscopy in order to assess their gel status and the role of the Hansen solubility parameter. The low molecular weight organogelator is a Triarylamine Trisamide (TATA) while the solvents consist of a series of halogeno-ethanes and of toluene. Temperature-concentration phase diagrams are mapped out from DSC traces. They reveal the existence of one or more TATA/solvent molecular compounds. The X-ray data, that display different diffraction patterns depending on the solvent and the temperature, show the existence of different molecular structures, and thus confirm the outcome of the T-C phase diagram. Tentative molecular organizations are also discussed in light of previous results obtained in the solid state. The morphology by TEM on dilute systems, and TEM on more concentrated systems highlight the degree of physical cross-links, which leads one to regard some systems as pseudo-gels.

Hierarchical Self-Assembly and Multidynamic Responsiveness of Fluorescent Dynamic Covalent Networks Forming Organogels.

Smart stimuli-responsive fluorescent materials are of interest in the context of sensing and imaging applications. In this project, we elaborated multidynamic fluorescent materials made of a tetraphenylethene fluorophore displaying aggregation-induced emission and short cysteine-rich C-hydrazide peptides. Specifically, we show that a hierarchical dynamic covalent self-assembly process, combining disulfide and acyl-hydrazone bond formation operating simultaneously in a one-pot reaction, yields cage compounds at low concentration (2 mM), while soluble fluorescent dynamic covalent networks and even chemically cross-linked fluorescent organogels are formed at higher concentrations. The number of cysteine residues in the peptide sequence impacts directly the mechanical properties of the resulting organogels, Young's moduli varying 2500-fold across the series. These materials underpinned by a nanofibrillar network display multidynamic responsiveness following concentration changes, chemical triggers, as well as light irradiation, all of which enable their controlled degradation with concomitant changes in spectroscopic outputs─self-assembly enhances fluorescence emission by ca. 100-fold and disassembly quenches fluorescence emission.

Gel-to-gel non-variant transition of an organogel caused by polymorphism from nanotubes to crystallites.

An amide based gelator forms gels in trans-decalin. Below concentrations of 1 wt% the gels melt at temperatures varying with concentration. Above a concentration of 1 wt%, upon heating, the gel transforms into an opaque gel at an invariant temperature, and melts at higher temperature. The gel-to-gel transition is evidenced by several techniques: DSC, rheology, NMR, OM and turbidimetry. The phase diagram with the domain of the existence of both morphs was mapped by these techniques. Optical and electronic microscopy studies show that the first gel corresponds to the self-assembled nanotubes while the second gel is formed by crystalline fibers. The fibers are crystalline, as shown by the presence of Bragg peaks in the scattering curves. Both morphs correspond to a different H-bonding pattern as shown by FTIR. The first gel forms at a higher cooling rate, is metastable and transforms slowly into the second one. The second gel is stable. It forms at a low cooling rate, or by thermal annealing or aging of the first gel.

Autonomous Growth of a Spatially Localized Supramolecular Hydrogel with Autocatalytic Ability.

Autocatalysis and self-assembly are key processes in developmental biology and are involved in the emergence of life. In the last decade both of these features were extensively investigated by chemists with the final goal to design synthetic living systems. Herein, we describe the autonomous growth of a self-assembled soft material, that is, a supramolecular hydrogel, able to sustain its own formation through an autocatalytic mechanism that is not based on any template effect and emerges from a peptide (hydrogelator) self-assembly. A domino sequence of events starts from an enzymatically triggered peptide generation followed by self-assembly into catalytic nanofibers that induce and amplify their production over time, resulting in a 3D hydrogel network. A cascade is initiated by traces (10-18 m) of a trigger enzyme, which can be localized allowing for a spatial resolution of this autocatalytic buildup of hydrogel growth, an essential condition on the route towards further cell-mimic designs.

Covalently Trapped Triarylamine-Based Supramolecular Polymers.

C3 -Symmetric triarylamine trisamides (TATAs), decorated with three norbornene end groups, undergo supramolecular polymerization and further gelation by π-π stacking and hydrogen bonding of their TATA cores. By using subsequent ring-opening metathesis polymerization, these physical gels are permanently crosslinked into chemical gels. Detailed comparisons of the supramolecular stacks in solution, in the physical gel, and in the chemical gel states, are performed by optical spectroscopies, electronic spectroscopies, atomic force microscopy, electronic paramagnetic resonance spectroscopy, X-ray scattering, electronic transport measurements, and rheology. The results presented here clearly evidence that the core structure of the functional supramolecular polymers can be precisely retained during the covalent capture whereas the mechanical properties of the gels are concomitantly improved, with an increase of their storage modulus by two orders of magnitude.

Phase Separation in Supramolecular Hydrogels Based on Peptide Self-Assembly from Enzyme-Coated Nanoparticles.

Spatial localization of biocatalysts, such as enzymes, has recently proven to be an effective process to direct supramolecular self-assemblies in a spatiotemporal way. In this work, silica nanoparticles (NPs) functionalized covalently by alkaline phosphatase (NPs@AP) induce the localized growth of self-assembled peptide nanofibers from NPs by dephosphorylation of Fmoc-FFpY peptides (Fmoc: fluorenylmethyloxycarbonyl; F: phenylalanine; Y: tyrosine; p: phosphate group). The fibrillary nanoarchitecture around NPs@AP underpins a homogeneous hydrogel, which unexpectedly undergoes a macroscopic shape change over time. This macroscopic change is due to a phase separation leading to a dense phase (in NPs and nanofibers) in the center of the vial and surrounded by a dilute one, which still contains NPs and peptide self-assemblies. We thus hypothesize that the phase separation is not a syneresis process. Such a change is only observed when the enzymes are localized on the NPs. The dense phase contracts with time until reaching a constant volume after several days. For a given phosphorylated peptide concentration, the dense phase contracts faster when the NPs@AP concentration is increased. For a given NPs@AP concentration, it condenses faster when the peptide concentration increases. We hypothesize that the appearance of a dense phase is not only due to attractive interactions between NPs@AP but also to the strong interactions of self-assembled peptide nanofibers with the enzymes, covalently fixed on the NPs.

Supported Catalytically Active Supramolecular Hydrogels for Continuous Flow Chemistry.

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.

Palmitoylethanolamide gels edible oils.

Palmitoylethanolamide (PEA) is an endogenous compound with no adverse effect for oral intakes of a gram per day. We show that PEA gels edible oils at concentrations as low as 0.5 wt%. The elastic moduli values of the formed gels are 1400 Pa at 1 wt% and 9000 Pa at 2 wt%. The study of the gels by cryo-SEM, optical microscopy and WAXS show that PEA forms lamellar solid aggregates with widths of several tens of micrometers. Upon heating, the sample shows two transitions. The first one is the gel-to-sol transition, observed by rheology and defined by the switch from a solid to a liquid behavior. During this transition, the solid particles remain but do no longer form a network. The second transition, observed at higher temperature by DSC corresponds to the melting of the solid particles.

PEG-in-PDMS drops stabilised by soft silicone skins as a model system for elastocapillary emulsions with explicit morphology control.

HYPOTHESIS: The morphology of ordinary macro-emulsions is controlled by their high interfacial energies, i.e., by capillarity, leading to well-known structural features which can be tuned only over a narrow range. We claim here that a more explicit control over a much wider range of morphologies can be obtained by producing "elastocapillary emulsions" in which interfacial elasticity acts simultaneously with interfacial tension. EXPERIMENTS: We develop a model-system composed of PEG-in-PDMS emulsions, in which a catalyst diffuses from the PEG drops into the silicone matrix containing two reactive silicone polymers, which are cross-linked in a non-reactive silicone matrix to form a silicone gel of controlled thickness and mechanical properties on the drop surface. We characterise the cross-linking process of the gel in bulk and at the interface, and we analyse the skin growth kinetics. We then use the obtained understanding to produce emulsions with controlled elastocapillary interfaces using in-flow-chemistry in a purpose-designed millifluidic circuit. FINDINGS: We show that this approach allows to create interfaces over the full range of elastocapillary properties, and that very different emulsion morphologies can be generated depending on whether capillarity or elasticity dominates. These findings advance our fundamental understanding of the morphology of emulsions with complex interfaces, and they are of importance for the design of polymerised High Internal Phase Emulsions (polyHIPEs) with original structure/property relations. They will also be useful for the design of silicone capsules with fine-tuned mechanical properties.

pH-switchable pickering emulsions stabilized by polyelectrolyte-biosurfactant complex coacervate colloids.

HYPOTHESIS: Polyelectrolyte-surfactant complexes (PESCs) have long been employed as oil-in-water (o/w) emulsions stabilizers, but never in the structure of colloidal complex coacervates providing a Pickering effect. The complexed state of PESCs could make them unsuitable o/w Pickering emulsifiers, which instead require a balance between colloidal structure and stability, amphiphilicity and wettability. Here we hypothesize that PESCs coacervates are efficient Pickering stabilizers. Instead of classical surfactants, we employ sophorolipid (SL) biosurfactants, atypical anionic/neutral stimuli-responsive biosurfactants. Despite their tunable charge and mild amphiphilic character, they can be used in combination with cationic/neutral polyelectrolytes (chitosan, CHL, or poly-l-lysine, PLL) to form PESC coacervates for the development of biobased, but also pH-switchable, Pickering emulsions. EXPERIMENTS: Aqueous solutions of SL-CHL (or SL-PLL) complex coacervates are emulsified with dodecane. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy under cryogenic conditions (cryo-SEM) demonstrate the Pickering effect, while optical microscopy and oscillatory rheology respectively assess the emulsion formation and relative viscoelastic properties. FINDINGS: Both SL-CHL and SL-PLL PESCs stabilize o/w emulsions up to Φoil of 0.7 only in the pH region of complex coacervation (6 < pH < 9): outside this range, phase separation occurs. Rheology shows a typical solid-like response and mechanical recovery upon applying large deformations. CLSM and cryo-SEM highlight a colloidal structure, associated to the complex coacervates, of the oil/water interface and suggest a Pickering effect. These findings demonstrate the Pickering effect from PESC coacervates and the possibility to use biobased and biocompatible components, with application potential in cosmetics, food science, or oil recovery.

Study of Membrane Protein Monolayers Using Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS): Critical Dependence of Nanostructured Gold Surface Morphology.

Surface-enhanced infrared absorption spectroscopy (SEIRAS) is a powerful tool that allows studying the reactivity of protein monolayers at very low concentrations and independent from the protein size. In this study, we probe the surface's morphology of electroless gold deposition for optimum enhancement using two different types of immobilization adapted to two proteins. Independently from the mode of measurement (i.e., transmission or reflection) or type of protein immobilization (i.e., through electrostatic interactions or nickel-HisTag), the enhancement and reproducibility of protein signals in the infrared spectra critically depended on the gold nanostructured surface morphology deposited on silicon. Just a few seconds deviation from the optimum time in the nanoparticle deposition led to a significantly weaker enhancement. Scanning electron microscopy and atomic force microscopy measurements revealed the evolution of the nanostructured surface when comparing different deposition times. The optimal deposition time led to isolated gold nanostructures on the silicon crystal. Importantly, in the case of the immobilization using nickel-HisTag, the surface morphology is rearranged upon immobilization of linker and the protein. A complex three-dimensional (3D) network of nanoparticles decorated with the protein could be observed leading to the optimal enhancement. The electroless deposition of gold is a simple technique, which can be adapted to flow cells and used in analytical approaches.

Supramolecular tripeptide self-assembly initiated at the surface of coacervates by polyelectrolyte exchange.

Spatial control of supramolecular self-assembly can yield compartmentalized structures, a key feature for the design of artificial cells. Inducing self-assembly from and on compartments is still a challenge. Polyelectrolyte complex coacervates are simple model droplet systems able to reproduce the basic features of membrane-less organelles, appearing in cells. Here, we demonstrate the supramolecular self-assembly of a phosphorylated tripeptide, Fmoc-FFpY (Fmoc: fluorenyl-methoxycarbonyl; F: phenyl alanine, pY: phosphorylated tyrosine), on the surface of poly(l-glutamic acid)/poly(allylamine hydrochloride) (PGA/PAH) complex coacervate microdroplets. The phosphorylated peptides self-assemble, without dephosphorylation, through ion pairing between the phosphate groups of Fmoc-FFpY and the amine groups of PAH. This process provides spontaneous capsules formed by an amorphous polyelectrolyte complex core surrounded by a structured peptide/PAH shell. Similar fibrillar Fmoc-FFpY self-assembled structures are obtained at the interface between the peptide solution and a PGA/PAH polyelectrolyte multilayer, a complex coacervate in the thin film or "multilayer" format. In contact with the peptide solution, PAH chains diffuse out of the coacervate or multilayer film and complex with Fmoc-FFpY at the solution interface, exchanging any PGA with which they were associated. Self-assembly of Fmoc-FFpY, now concentrated by complexation with PAH, follows quickly.

Surface Triggered Self-Assembly of Fmoc-Tripeptide as an Antibacterial Coating.

In western countries, one patient on twenty will develop a nosocomial infection during his hospitalization at health care facilities. Classical antibiotics being less and less effective, this phenomenon is expanding year after year. Prevention of bacteria colonization of implantable medical devices constitutes a major medical and financial issue. In this study, we developed an antibacterial coating based on self-assembled Fmoc-tripeptide. Fmoc-FFpY peptides (F: phenylalanine; Y: tyrosine; p: PO4 2-) are dephosphorylated enzymatically into Fmoc-FFY by action of alkaline phosphatase functionalized silica nanoparticles (NPs@AP), previously deposited on a surface. Fmoc-FFY peptides then self-assemble through π-π stacking interactions, hydrogen bonds and hydrophobic interactions adopting ß-sheets secondary structures. The obtained hydrogel coatings show fibrillary structures observed by cryo-scanning electron microscopy with a thickness of few micrometers. At low concentration (≤0.5 mg.mL-1), self-assembled Fmoc-FFY has a superior antibacterial activity than Fmoc-FFpY peptide in solution. After 24 h of incubation, Fmoc-FFY hydrogel coatings fully inhibit the development of Gram-positive Staphylococcus aureus (S. aureus). The antibacterial effect is maintained on an in vitro model of repetitive infection in the case of S. aureus. This coating could serve in infections were Gram positive bacteria are prevalent, e.g., intravascular catheter infections. This work gives new insights toward the design of an alternative antimicrobial coating.

Tuning the Chiroptical Properties of Elongated Nano-objects via Hierarchical Organization.

Chiral materials appear as excellent candidates to control and manipulate the polarization of light in optical devices. In nanophotonics, the self-assembly of colloidal plasmonic nanoparticles gives rise to strong resonances in the visible range, and when such organizations are chiral, a strong chiroplasmonic effect can be observed. In the present work, we describe the optical properties of chiral artificial nanophotonic materials, Goldhelices, which are hierarchically organized by grazing incidence spraying. These Goldhelices are made by plasmonic nanoparticles (gold) grafted onto helical templates made from silica nanohelices. A comparison of oriented versus non-oriented surfaces has been performed by Mueller matrix polarimetry, showing the importance of the organization of the Goldhelices regarding their interaction with light. Moreover, mono- versus multilayer photonic films are created, and the measured optical properties are discussed and compared to simulations.

Effect of Alkyl Side Chain Length on Doping Kinetics, Thermopower, and Charge Transport Properties in Highly Oriented F4TCNQ-Doped PBTTT Films.

Doping of polymer semiconductors such as poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2- b]thiophene) (PBTTT) with acceptor molecules such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is widely used to tune the charge transport and thermoelectric (TE) properties in thin films. However, the mechanism of dopant insertion in the polymer matrix, insertion kinetics, and the ultimate doping levels reached have been investigated only marginally. This contribution addresses the effect of alkyl side chain length on the doping mechanism of a series of PBTTTs with linear side chains ranging from n-octyl to n-octyldecyl. The study focuses on thin films oriented by high-temperature rubbing and sequentially doped in F4TCNQ solution. Structure-property correlations are established as a function of side chain length by a combination of transmission electron microscopy, polarized UV-vis-NIR spectroscopy, and charge transport/thermopower measurements. Intercalation of F4TCNQ into the layers of side chains results in the expansion of the lattice along the side chains and the contraction along the π-stacking direction for all polymers. The extent of lattice expansion decreases with the increasing side chain length. UV-vis-NIR spectroscopy demonstrates integer charge transfer for all investigated PBTTTs. The doping kinetics and the final doping level depend on both the side chain length and packing. Highly disordered n-octyl and crystalline n-octyldecyl side chain layers tend to hamper dopant diffusion in the side chain layers contrary to n-dodecyl side chains that can host the highest proportion of dopants. Consequently, the best TE properties are observed for C12-PBTTT films. Alignment of the polymers significantly enhances the TE performance by increasing the charge conductivity and the thermopower along the rubbing direction. Aligned films of C12-PBTTT show charge conductivities of 193 S cm-1 along the rubbing direction and power factors of approximately 100 µW m-1 K-2 versus a few µW m-1 K-2 for nonoriented films.

Enzyme-assisted self-assembly within a hydrogel induced by peptide diffusion.

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.