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The behavior of single linear chains on a substrate is a well-studied area of polymer science. Herein, one of the most essential issues is the interaction of the chains with the substrate, which determines both macromolecular conformations near the substrate and adhesive properties of polymer materials. However, very little is known about the effect of macromolecular architecture on adhesion. In particular, there was no assessment of the effect of chain branching on the adhesion force. On the other hand, an essential progress in macromolecular chemistry allows the synthesis of various macromolecular architectures, including star-, comb-like, etc., in a very precise way. They are widely used in numerous applications. In particular, synthetic peptides are currently an integral part of many systems for biomedical purposes including bioglues, for which the adhesion force is a fundamental property. In this study, we conducted force experiments on the desorption of star-like pentapeptide chains from a solid substrate using an atomistic model of computer simulations. The cases of a linear chain and four- and eight-armed stars were considered. We have shown that the presence of branching enhances the adsorption strength under a fixed mass of the macromolecules. The force needed for chain desorption was shown to be linearly dependent on the branching degree.

Understanding the adsorption features of polymer microgels with different chemical compositions and structures is crucial in studying the mechanisms of respective emulsion stabilization. Specifically, the use of stimuli-responsive particles can introduce new properties and broaden the application range of such complex systems. Recently, we demonstrated that emulsions stabilized by microgels composed of interpenetrating networks (IPNs) of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA) exhibit higher colloidal stability upon heating compared to PNIPAM homopolymer and other relevant PNIPAM-based copolymer counterparts. In the present work, using pendant drop tensiometry, we studied the evolution of water-tetradecane interfacial tension during the adsorption of PNIPAM-PAA IPN particles, comparing them with single-network P-(NIPAM-co-AA) and PNIPAM microgels. The results showed that, despite having the same chemical composition, copolymer particles exhibit completely different adsorption behavior in comparison to other microgel architectures. The observed disparity can be attributed to the nonuniform distribution of charged acrylic acid groups within the P-(NIPAM-co-AA) network obtained through precipitation polymerization. Oppositely, the presence of IPN architecture provides a uniform distribution of different monomers inside respective microgels. Additionally, hydrogen bonding between PNIPAM and PAA subchains appears to reduce the electrostatic energy barrier, enhancing the ability of IPN particles to successfully cover the liquid interface. Overall, our findings confirm the efficiency of using PNIPAM-PAA IPN microgels for the preparation of oil-in-water emulsions and their stability, even when the temperature rises above the lower critical solution temperature of PNIPAM.

Hypothesis: While albumin-coated microbubbles are routine contrast agents for ultrasound imaging, their short duration of contrast enhancement limits their use, yet can be improved by incorporating protein-copolymer hybrids into microbubble shells. The incorporation of N-vinyl-2-pyrrolidone and acrylic acid copolymer (P(VP-AA)) has been shown to enhance the performance of bovine serum albumin (BSA)-coated microbubbles. However, the impact of the copolymer structural properties on key microbubble characteristics (i.e., concentration, mean diameter and acoustic response) remains poorly understood. Therefore, we hypothesize that the copolymer structure affects its capacity to form micelle-like nanoaggregates, protein-copolymer hybrids, and microbubble shells, ultimately influencing the physicochemical and acoustic properties of the microbubbles., Experiments: Here we evaluate the production and performance of BSA@P(VP-AA) microbubbles synthesized using a series of P(VP-AA) copolymers with -C 8 H 17 and -C 18 H 37 end groups and molecular weight cutoffs between 3.5 and 15 kDa. Both simulation and experimental data demonstrate that interactions between BSA and the copolymers significantly influence the performance of the resulting microbubbles across the library of 60 formulations., Findings: The introduction of -C 8 H 17 terminated copolymers into microbubble shells resulted in up to 200-fold higher concentration, 7-fold greater acoustic response, and 5-fold longer ultrasound contrast enhancement compared to plain BSA microbubbles. The enhanced acoustic performance was sustained during in vivo cardiac ultrasound imaging, without altering liver accumulation after copolymer introduction. These findings underscore how optimizing copolymer structure (specifically the terminal end group and molecular weight) can tailor the formation and performance of protein-copolymer-coated microbubbles, offering valuable insights for designing ultrasound contrast agents., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The adsorption of ellipsoidal colloidal particles on liquid interfaces induces interfacial deformation, resulting in anisotropic interface-mediated interactions and the formation of superstructures. Soft prolate-shaped microgels at the air-water interface offer an ideal model for studying spontaneous capillary-driven self-assembly due to their tunable aspect ratio, controlled functionality, and softness. These microgels consist of a polystyrene core surrounded by a cross-linked, fluorescently labeled poly([Formula: see text]-isopropylmethylacrylamide) shell. By uniaxially stretching the particles embedded in polyvinyl alcohol films, the aspect ratio [Formula: see text] can be finely adjusted. [Formula: see text] was found to vary from 1 to 8.8 as estimated in their swollen conformation at 20 ° C from confocal laser scanning microscopy. The spontaneous interfacial self-assembly at the air-water interface is investigated through fluorescence microscopy, theoretical calculations, and computer simulations. A structural transition occurs from a seemingly random assembly for small aspect ratios to compact clusters, which transform into a side-to-side assembly forming long chains for high aspect ratios. The influence of the poly([Formula: see text]-isopropylmethacrylamide) shell on the assembly indicates a significant [Formula: see text]-dependent microgel deformation. This deformation, in turn, determines the average distance between the particles. Consequently, capillary-driven self-assembly of soft anisotropic colloids becomes a powerful mechanism for structuring interfaces and designing microstructured materials., Competing Interests: Competing interests statement:The authors declare no competing interest.

Thin films made of deformable micro- and nano-units, such as biological membranes, polymer interfaces, and particle-laden liquid surfaces, exhibit a complex behavior during drying, with consequences for various applications like wound healing, coating technologies, and additive manufacturing. Studying the drying dynamics and structural changes of soft colloidal films thus holds the potential to yield valuable insights to achieve improvements for applications. In this study, interfacial monolayers of core-shell (CS) microgels with varying degrees of softness are employed as model systems and to investigate their drying behavior on differently modified solid substrates (hydrophobic vs hydrophilic). By leveraging video microscopy, particle tracking, and thin film interference, this study shed light on the interplay between microgel adhesion to solid surfaces and the immersion capillary forces that arise in the thin liquid film. It is discovered that a dried replica of the interfacial microstructure can be more accurately achieved on a hydrophobic substrate relative to a hydrophilic one, particularly when employing softer colloids as opposed to harder counterparts. These observations are qualitatively supported by experiments with a thin film pressure balance which allows mimicking and controlling the drying process and by computer simulations with coarse-grained models., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

The swelling and collapse of responsive nanogels on a planar lipid bilayer are studied by means of mesoscopic computer simulations. The effects of molecular weight, cross-linking density, and adhesion strength are examined. The conditions for collapse-mediated engulfing by the bilayer are found. In particular, the results show that at low hydrophobicity level the increase in the nanogel softness decreases the engulfing rate. On the contrary, for stronger hydrophobicity level the trend changes to the opposite one. At the same time, when the cross-linking density is too low or the adhesion strength is too high the nanogel deformation at the membrane suppresses the engulfing regardless of the network swelling ratio. Finally, for comparative reasons, the behavior of the nanogels is also studied at the solid surface. These results may be useful in the design of soft particles capable of tuning of their elasticity and porosity for successful intracellular drug delivery., (© 2024 Wiley‐VCH GmbH.)

Three types of coatings (contact-based, release-based, and combined coatings with both contact-based and release-based actions) were prepared and tested for the ability to inactivate SARS-CoV-2. In these coatings, quaternary ammonium surfactants were used as active agents since quaternary ammonium compounds are some of the most commonly used disinfectants. To provide contact-based action, the glass and silicon surfaces with covalently attached quaternary ammonium cationic surfactant were prepared using a dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride modifier. Surface modification was confirmed by attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and contact angle measurements. The grafting density of the modifier was estimated by XPS and elemental analysis. To provide release-based action, the widely used quaternary ammonium cationic disinfectant, benzalkonium chloride (BAC), and a newly synthesized cationic gemini surfactant, C18-4-C18, were bound non-covalently to the surface either through hydrophobic or electrostatic interactions. Virus titration revealed that the surfaces with combined contact-based and release-based action and the surfaces with only release-based action completely inactivate SARS-CoV-2. Coatings containing only covalently bound disinfectant are much less effective; they only provide up to 1.25 log10 reduction in the virus titer, probably because of the low disinfectant content in the surface monolayer. No pronounced differences in the activity between the flat and structured surfaces were observed for any of the coatings under study. Comparative studies of free and electrostatically bound disinfectants show that binding to the surface of nanoparticles diminishes the activity. These data indicate that SARS-CoV-2 is more sensitive to the free disinfectants.

Microbubbles (MB) are widely used as contrast agents for ultrasound (US) imaging and US-enhanced drug delivery. Polymeric MB are highly suitable for these applications because of their acoustic responsiveness, high drug loading capability, and ease of surface functionalization. While many studies have focused on using polymeric MB for diagnostic and therapeutic purposes, relatively little attention has thus far been paid to improving their inherent imaging and drug delivery features. This study here shows that manipulating the polymer chemistry of poly(butyl cyanoacrylate) (PBCA) MB via temporarily mixing the monomer with the monomer-mimetic butyl cyanoacetate (BCC) during the polymerization process improves the drug loading capacity of PBCA MB by more than twofold, and the in vitro and in vivo acoustic responses of PBCA MB by more than tenfold. Computer simulations and physisorption experiments show that BCC manipulates the growth of PBCA polymer chains and creates nanocavities in the MB shell, endowing PBCA MB with greater drug entrapment capability and stronger acoustic properties. Notably, because BCC can be readily and completely removed during MB purification, the resulting formulation does not include any residual reagent beyond the ones already present in current PBCA-based MB products, facilitating the potential translation of next-generation PBCA MB., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Emulsions have become a crucial product form in various industries in modern times. Expanding the class of substances used to stabilize emulsions can improve their stability or introduce new properties. Particularly, the use of stimuli-responsive microgels makes it possible to create "smart" emulsions whose stability can be controlled by changing any of the specified stimuli. Thus, finding new ways to stabilize emulsions may broaden their application. In this work, for the first time, we applied microgels based on interpenetrating polymeric networks (IPNs) of poly( N -isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) as stabilizing agents for "oil-in-water" emulsions. We have demonstrated that emulsions stabilized by such soft particles can remain colloidally stable for an extended period, even after being heated up to 40 °C, which is above the lower critical solution temperature (LCST) of PNIPAM. On the contrary, the emulsions stabilized by PNIPAM homopolymer microgels were broken upon heating. To understand the stabilization mechanism of the emulsions, mesoscopic computer simulations were performed to study the IPN microgels at the liquid-liquid interface. The simulations demonstrated that when the first subnetwork (PNIPAM) collapses, the particle adopts a flattened core-shell morphology with a highly swollen PAA-rich shell and a collapsed PNIPAM-rich core. Unlike its PNIPAM homopolymer counterpart, the IPN microgel maintains its three-dimensional shape, which provides stability to the microgel-based emulsions over a wide range of temperatures. Our combined findings could be useful in developing new approaches to emulsions' storage, biphasic catalysis, and lubrication of mechanisms in various operating and climatic conditions.

The progress of the pillar[5]arene chemistry allowed us to set out a new concept on application of the supramolecular assemblies to create antimicrobial films with variable surface morphologies and biological activities. Antibacterial films were derived from the substituted pillar[5]arenes containing nine pharmacophoric guanidine fragments and one thioalkyl substituent. Changing the only thioalkyl fragment in the macrocycle structure made it possible to control the biological activity of the resulting antibacterial coating. Pretreatment of the surface with aqueous solution of the amphiphilic pillar[5]arenes reduced the biofilm thickness by 56 ± 10% of Gram-positive Staphylococcus aureus in the case of the pillar[5]arene containing a thiooctyl fragment and by 52 ± 7% for the biofilm of Gram-negative Klebsiella pneumoniae in the case of pillar[5]arene containing a thiooctadecyl fragment. Meanwhile, the cytotoxicity of the synthesized macrocycles was examined at a concentration of 50 μg/mL, which was significantly lower than that of bis-guanidine-based antimicrobial preparations.

The use of linear supercharged unfolded polypeptides (SUPs) and oppositely charged surfactants in aqueous solution has demonstrated impressive adhesive properties. These substances possess biocompatibility, biodegradability and other necessary properties for practical application as a biomedical glue in wound repair. The success of these substances, coupled with limited knowledge about such systems, provides hope for enhancing the performance of the final product. One potential approach involves altering the topology of the polypeptide chain. In this article, we conduct a comparative analysis to examine the behavior of the ring and linear chains of a polypeptide in aqueous solution. This analysis utilizes full-atomic computer modeling to monitor the properties of the chains. We investigate the temperature dependence of the shape and size of individual polypeptides in the solution, as well as the formation of complexes via mixing the polypeptide chains with oppositely charged sodium dodecylbenzene sulfonate (SDBS) surfactant molecules in a stoichiometric ratio. Additionally, we explore the cohesive properties of the resulting complex through power experiments involving the extraction of single polypeptide chains out of the SUP-SDBS complexes.

Surface-active polymers have important applications as effective and responsive emulsifiers, foaming agents, and coatings. In this contribution, we explore the impact of the polymer architecture on the behavior at oil-water interfaces by comparing different poly( N -isopropylacrylamide) (pNIPAM)-based systems, namely, monolayers of linear and star-shaped macromolecules, ultralow cross-linked, regular cross-linked, and hollow microgels. Compression isotherms were determined experimentally as well as by computer simulations. The latter provides information about the conformational changes of the individual macromolecules as well as the interfacial properties of the monolayer, including the surface structure and the density distribution of an ensemble of interacting macromolecules near an interface. Surprisingly, the isotherms of the linear polymer, of the star polymer, and of the ultralow cross-linked microgel have an identical shape that differs from the isotherms of regular and hollow microgels. We introduced the mass fraction of adsorbed polymer, which gives a measure of the polymer segments contributing to the isotherm in relation to the most flexible architecture, i.e., the linear polymer, and allows a comparison of polymers with different architectures. The data demonstrate that increasing the number of cross-links leads to a significantly lower amount of polymer in the proximity of the interface as the increase in cross-linker reduces the deformability or softness of the polymers at the interface. The volume fraction profiles along the normal to the interface are essentially different in the microgel monolayers as compared to those in the linear and star polymer. The profiles through the microgel contact line and their growth upon initial compression are similar to those of the linear chains. Herewith, the profiles through the center of mass practically do not change upon compression. Therefore, the initial growth in the microgel surface pressure reveals the polymer-like behavior and is related to the deformation of the peripheral part of the microgel. Further compression of the microgel monolayer leads to 3D interactions of the microgels within the aqueous side of the interface and soft colloid-like behavior.

Monolayers of polymer microgels with a spherical cavity adsorbed at the liquid-liquid interface were studied using mesoscopic computer simulations. One liquid, named water, was always considered as a good solvent, while the microgel solubility in the second liquid, named oil, was varied. The symmetric and asymmetric cases of vanishing and the strong differences in solubility between the network particles and the liquids were considered. The simulations provided us with an insight into the shape and volume changes of the microgels upon compression, making it possible to relate the response of the individual network with the collective order and structure of the monolayer. Similar to regular microgels, the compression of the monolayer of hollow particles led to a decrease in lateral sizes accompanied by shape transformation from a flattened to a nearly spherical shape. However, the presence of a cavity filled with solvent caused some unique differences in the behavior of the system. The adsorption pathway of hollow microgels at the liquid interface predefines: (a) the position of the particles with respect to the interface and (b) the structure of the monolayer. A striking discovery is that in the symmetric case of similar solubility of the microgel in both liquids, it is possible to produce a monolayer in which one part of the network faces the aqueous phase and the other part faces the oil phase. The polymer concentration profiles plotted along the normal to the interface reveal a redistribution of polymeric mass of the microgels relative to the interface, distinguishing between the microgels whose cavities are filled with water and oil, respectively. Moreover, the ratio between the microgels faced in water and oil does not change upon compression and predetermines the response and order of the monolayer.

Hypothesis: Recently, it has become possible to synthesize hollow polyelectrolyte nano- and microgels. The shell permeability can be controlled by external stimuli, while the cavity can serve as a storage place for guest molecules. However, there is a lack of a detailed understanding at the molecular level regarding the role of the network topology, inhomogeneities of the distribution of cross-links, and the impact of the electrostatics on the structural response of hollow microgel to external stimuli. To bridge these gaps, molecular dynamics (MD) of computer simulations are used., Experiments: Here, we propose a fresh methodology to create realistic hollow microgel particles in silico. The technique involves a gradual change in the average local length of subchains depending on the distance to the center of mass of the microgel particles resulting in the microgels with a non-uniform distribution of cross-linking species. In particular, a series of microgels with (i) a highly cross-linked inner part of the shell and gradually decreased cross-linker concentration towards the periphery, (ii) microgels with loosely cross-linked inner and outer parts, as well as (iii) microgels with a more-or-less homogeneous structure, have been created and validated. Counterions and salt ions are taken into account explicitly, and electrostatic interactions are described by the Coulomb potential., Findings: Our studies reveal a strong dependence of the microgel swelling response on the network topology. Simple redistribution of cross-links plays a significant role in the structure of the microgels, including cavity size, microgel size, fuzziness, and extension of the inner and outer parts of the microgels. Our results indicate the possibilities of qualitative justification of the structure of the hollow microgels in the experiments by measuring the relative change in the size of the sacrificial core to the size of the cavity and by estimation of a power law function, [Formula: see text] , of the hydrodynamic radius of the hollow microgels as a function of added salt concentration., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The copolymer sequence can be considered as a new tool to shape the resulting system properties on demand. This perspective is devoted to copolymers with "partially segregated" (or nonblocky) sequences. Such copolymers include gradient copolymers and copolymers with random sequences as well as copolymers with precisely controlled sequences. We overview recent developments in the synthesis of these systems as well as new findings regarding their properties, in particular, self-assembly in solutions and in melts. An emphasis is put on how the microscopic behavior of polymer chains is influenced by the chain sequences. In addition to that, a novel class of approaches allowing one to efficiently tackle the problem of copolymer chain sequence design─data driven methods (artificial intelligence and machine learning)─is discussed.

Polymer microgels have proven to be highly promising macromolecular objects for a wide variety of applications. In particular, the soft particles of an anisotropic (rod-like) shape are of special interest because of their potential use in tissue engineering or materials design. However, a little is known about the physical behavior of such microgels in solution, which inspired us to study them using mesoscopic computer simulations. For single networks, depending on the solvent quality, the dimensional characteristics were obtained for microgels of different molecular weight, crosslinking density and aspect ratio. In particular, the conditions for the rod-to-rod (preserving the nonspherical shape) and rod-to-sphere collapse were found. In addition, the effect of the liquid-crystalline (LC) ordering was demonstrated for the ensemble of rod-like microgels at different swelling ratios, and the influence of microgel aspect ratio on the volume fraction of the LC transition was shown., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Polymer hydrogels are known to be efficient absorbents of various aqueous solutions. Along with the hydrophilicity of the polymer network, the presence of specific functional groups is required for the absorption of respective solutes. Alternatively, a selective uptake can be realized without any specific attraction of solutes to the network, which is shown in this paper. By combining experimental and simulation approaches, we demonstrated that thermoresponsive poly( N -isopropylacrylamide) gels and microgels in compositionally strongly asymmetric water/1-octanol mixtures selectively uptake the minor (1-octanol) component. Initially swollen in water, the gels substitute water by the organic solvent upon the addition of its small fraction into aqueous solution. In turn, for microgels, it was shown that the single particles could absorb the amount of the organic liquid more than two times higher than their mass while preserving the colloidal stability. At the same time, the accumulation of 1-octanol in the networks "switches off" the temperature response. The mesoscopic computer simulations revealed a physical reason and molecular picture of the phenomenon. Absorption of the minor component by the gels is caused by the decrease in water/1-octanol interfacial tension due to the formation of the dense polymer layer at the interface. The simulations allowed tracking the evolution of the size and the internal structure of the single microgels with changing 1-octanol concentration.

In this research, we studied, in detail, the behavior of common PNIPAM microgels, obtained through surfactant-free precipitation polymerization, in a number of organic solvents. We showed that many of the selected solvents serve as good solvents for the PNIPAM microgels and that the size and architecture of the microgels depend on the solvent chosen. Expanding the range of solvents used for PNIPAM microgel incubation greatly enhances the possible routes for microparticle functionalization and modification, as well as the encapsulation of water-insoluble species. In this demonstration, we successfully encapsulated water-insoluble Sudan III dye in PNIPAM microgels and prepared the aqueous dispersions of such composite-colored microparticles.

Soft colloidal macromolecular structures with programmable chemical functionalities, size, and shape are important building blocks for the fabrication of catalyst systems and adaptive biomaterials for tissue engineering. However, the development of the easy upscalable and template-free synthesis methods to obtain such colloids lack in understanding of molecular interactions that occur in the formation mechanisms of polymer colloids. Herein, a computer simulation-driven experimental synthesis approach based on the supramolecular self-assembly followed by polymerization of tailored pyrazole-modified monomers is developed. Simulations for a series of pyrazole-modified monomers with different numbers of pyrazole groups, different length and polarity of spacers between pyrazole groups and the polymerizable group are first performed. Based on simulations, monomers able to undergo π-π stacking and guide the formation of supramolecular bonds between polymer segments are synthesized and these are used in precipitation polymerization to synthesize anisotropic microgels. This study demonstrates that microgel morphologies can be tuned from spherical, raspberry-like to dumbbell-like by the increase of the pyrazole-modified monomer loading, which is concentrated at periphery of growing microgels. Combining experimental and simulation results, this work provides a quantitative and predictive approach for guiding microgel design that can be further extended to a diversity of colloidal systems and soft materials with superior properties., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Densely grafted comb-like macromolecules (bottlebrushes) with alternating solvophobic and solvophilic side chains were studied in a selective solvent and at the liquid interface using mesoscopic computer simulations. The effects of backbone length and copolymer composition were considered. While self-assembly in solution revealed only spherical aggregates for all ar-chitectures studied, adsorption onto the liquid interface in particular cases resulted in morpho-logical changes, with worm-like aggregates or a continuous monolayer observed. In turn, the compression of macromolecules at the interface also leads to morphological transitions, includ-ing the formation of a mesh-like percolated structure. The obtained results may be useful for the preparation of solid nanoparticles of anisotropic shape or nanostructured ultra-thin copolymer films.

In this study, we propose computer simulations of charged cylindrical microgels. The effects of cross-linking density, aspect ratio, and fraction of charged groups on the microgel swelling and collapse with a variation in the solvent quality were studied. The results were compared with those obtained for equivalent neutral cylindrical microgels. The study demonstrated that microgels' degree of swelling strongly depends on the fraction of charged groups. Polyelectrolyte microgels under adequate solvent conditions are characterized by a larger length and thickness than their neutral analogues: the higher the fraction of charged groups, the longer their length and greater their thickness. Microgels' collapse upon solvent quality decline is characterized by a decrease in length and non-monotonous behavior of its thickness. First, the thickness decreases due to the attraction of monomer units (beads) upon collapse. The further thickness increase is related to the surface tension, which tends to reduce the anisotropy of collapsed objects (the minimum surface energy is known to be achieved for the spherical objects). This reduction is opposed by the network elasticity. The microgels with a low cross-linking density and/or a low enough aspect ratio reveal a cylinder-to-sphere collapse. Otherwise, the cylindrical shape is preserved in the course of the collapse. Aspect ratio as a function of the solvent quality (interaction parameter) demonstrates the maximum, which is solely due to the electrostatics. Finally, we plotted radial concentration profiles for network segments, their charged groups, and counterions.

The construction of biomembranes that faithfully capture the properties and dynamic functions of cell membranes remains a challenge in the development of synthetic cells and their application. Here a new concept for synthetic cell membranes based on the self-assembly of amphiphilic comb polymers into vesicles, termed ionic combisomes (i-combisomes) is introduced. These combs consist of a polyzwitterionic backbone to which hydrophobic tails are linked by electrostatic interactions. Using a range of microscopies and molecular simulations, the self-assembly of a library of combs in water is screened. It is discovered that the hydrophobic tails form the membrane's core and force the backbone into a rod conformation with nematic-like ordering confined to the interface with water. This particular organization resulted in membranes that combine the stability of classic polymersomes with the biomimetic thickness, flexibility, and lateral mobility of liposomes. Such unparalleled matching of biophysical properties and the ability to locally reconfigure the molecular topology of its constituents enable the harboring of functional components of natural membranes and fusion with living bacteria to "hijack" their periphery. This provides an almost inexhaustible palette to design the chemical and biological makeup of the i-combisomes membrane resulting in a powerful platform for fundamental studies and technological applications., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Polymer microgels synthesized in silico were studied at a liquid-liquid interface via mesoscopic computer simulations and compared to microgels with ideal (diamond-like) structure. The effect of crosslinkers reactivity ratio on the single particle morphology at the interface and monolayer behavior was examined. It was demonstrated that single particles deform into an explicit core-corona morphology when adsorbed at the interface. An increase in the crosslinker reactivity ratio decreased both the deformation ratio and the ratio between the core and corona sizes. Meanwhile, the compression of microgel monolayers revealed the existence of five distinct interparticle contact regimes, which have been observed experimentally in the literature. The crosslinker reactivity ratio appeared to define the compression range in these regimes and the sharpness of the transition between them. In particular, the higher the crosslinker reactivity ratio, the smaller the corona, and in turn, the narrower the range of the intermediate regime comprising both core-core and corona-corona contacts. The obtained results demonstrate that the more realistic model of microgels synthesized via precipitation polymerization allows for a more accurate prediction of the properties of the microgels at a liquid-liquid interface in comparison to the conventional diamond-like lattice model.

Peptide receptor radionuclide therapy is used to treat solid tumors by locally delivering radiation. However, due to nephro- and hepato-toxicity, it is limited by its dosage. To amplify radiation damage to tumor cells, radiolabeled nanogels can be used. We show that by tuning the mechanical properties of nanogels significant enhancement in circulation half-life of the gel could be achieved. We demonstrate why and how small changes in the mechanical properties of the nanogels influence its cellular fate. Nanogels with a storage modulus of 37 kPa were minimally phagocytosed by monocytes and macrophages compared to nanogels with 93 kPa modulus. Using PET/CT a significant difference in the blood circulation time of the nanogels was shown. Computer simulations affirmed the results and predicted the mechanism of cellular uptake of the nanogels. Altogether, this work emphasizes the important role of elasticity even for particles that are inherently soft such as nano- or microgels., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The structures of a molecular brush in a good solvent are investigated using synchrotron small-angle X-ray scattering in a wide range of concentrations. The brush under study, P i POx 239 - g -P n PrOx 14 , features a relatively long poly(2-isopropenyl-2-oxazoline) (P i POx) backbone and short poly(2- n -propyl-2-oxazoline) (P n PrOx) side chains. As a solvent, ethanol is used. By model fitting, the overall size and the persistence length as well as the interaction length and interaction strength are determined. At this, the interplay between form and structure factor is taken into account. The conformation of the molecular brush is traced upon increasing the solution concentration, and a rigid-to-flexible transition is found near the overlap concentration. Finally, the results of computer simulations of the molecular brush solutions confirm the experimental results.

Anisotropic, submicrometer-sized particles are versatile systems providing interesting features in creating ordering in two-dimensional systems. Combining hard ellipsoids with a soft shell further enhances the opportunities to trigger and control order and alignment. In this work, we report rich 2D phase behavior and show how softness affects the ordering of anisotropic particles at fluid oil-water interfaces. Three different core-shell systems were synthesized such that they have the same elliptical hematite-silica core but differ with respect to thickness and stiffness of the soft microgel shell. Compression isotherms, the shape of individual core-shell microgels, and their 2D order at a decane-water interface are investigated by means of the Langmuir-Blodgett technique combined with ex-situ atomic force microscopy (AFM) imaging as well as dissipative particle dynamics (DPD) simulations. We show how the softness, size, and anisotropy of the microgel shell affect the side-to-side vs tip-to-tip ordering of anisotropic hybrid microgels as well as the alignment with respect to the direction of compression in the Langmuir trough. A large, soft microgel shell leads to an ordered structure with tip-to-tip alignment directed perpendicular to the direction of compression. In contrast, a thin and harder microgel shell leads to side-to-side ordering orientated parallel to the compression direction. In addition, the thin and harder microgel shell induces clustering of the microgels in the dilute state, indicating the presence of strong capillary interactions. Our findings highlight the relevance of softness for the complex ordering of anisotropic hybrid microgels at interfaces.

Microgels, cross-linked polymers with submicrometer size, are ideal soft model systems. While spherical microgels have been studied extensively, anisotropic microgels have hardly been investigated. In this study, we compare the interfacial deformation and assembly of anisotropic core-shell and hollow microgels. The core-shell microgel consists of an elliptical core of hematite covered with a thin silica layer and a thin shell made of poly( N -isopropylacrylamide). The hollow microgels were obtained after a two-step etching procedure of the inorganic core. The behavior of these microgels at the oil-water interface was investigated in a Langmuir-Blodgett trough combined with ex situ atomic force microscopy. First, the influence of the architecture of anisotropic microgels on their spreading at the interface was investigated experimentally and by dissipative particle dynamic simulations. Hereby, the importance of the local shell thickness on the lateral and longitudinal interfacial deformation was highlighted as well as the differences between the core-shell and hollow architectures. The shape of the compression isotherms as well as the dimensions, ordering, and orientation of the microgels at the different compressions were analyzed. Due to their anisotropic shape and stiffness, both anisotropic microgels were found to exhibit significant capillary interactions with a preferential side-to-side assembly leading to stable microgel clusters at low interfacial coverage. Such capillary interactions were found to decrease in the case of the more deformable hollow anisotropic microgels. Consequently, anisotropic hollow microgels were found to distribute more evenly at high surface pressure compared to stiffer core-shell microgels. Our findings emphasize the complex interplay between the colloid design, anisotropy, and softness on the interfacial assembly and the opportunities it therefore offers to create more complex ordered interfaces.

Amphiphilic miktoarm star copolymers with one long solvophobic arm (a "stem") and several short solvophilic arms (the "leaves") were studied in a selective solvent using mesoscopic computer simulations. The conventional morphologies (spherical, cylindrical and vesicular) as well as the mixed ones were obtained. However, the resulting diagram of states appeared to be different from the diagram of the linear diblock copolymer with the analogous composition. Namely, the increase of the number of leaves at fixed solvophobic-solvophilic ratio leads to the transition from the vesicles to the cylinders, while the latter ones eventually transform into spherical micelles in the case of highly branched copolymers. The observed effect appears due to the increase of the interfacial area between the collapsed and swollen blocks per single macromolecule. In turn, the increase of the solvent selectivity shifts the stability region of the cylindrical micelles to the region of more symmetric copolymer composition. Meanwhile, the compatibility between the blocks has a weak effect on the resulting morphology. Finally, it was found that the increase in the number of leaves and the simultaneous decrease in their length results in the localization of higher amount of solvophilic segments near the core-solvent interface, which in the case of cylindrical micelles significantly affects the shape of the aggregates making them thinner and longer., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The development of biomedical glues is an important, yet challenging task as seemingly mutually exclusive properties need to be combined in one material, i.e. strong adhesion and adaption to remodeling processes in healing tissue. Here, we report a biocompatible and biodegradable protein-based adhesive with high adhesion strengths. The maximum strength reaches 16.5 ± 2.2 MPa on hard substrates, which is comparable to that of commercial cyanoacrylate superglue and higher than other protein-based adhesives by at least one order of magnitude. Moreover, the strong adhesion on soft tissues qualifies the adhesive as biomedical glue outperforming some commercial products. Robust mechanical properties are realized without covalent bond formation during the adhesion process. A complex consisting of cationic supercharged polypeptides and anionic aromatic surfactants with lysine to surfactant molar ratio of 1:0.9 is driven by multiple supramolecular interactions enabling such strong adhesion. We demonstrate the glue's robust performance in vitro and in vivo for cosmetic and hemostasis applications and accelerated wound healing by comparison to surgical wound closures.

Complex coacervation enables important wet adhesion processes in natural and artificial systems. However, existed synthetic coacervate adhesives show limited wet adhesion properties, non-thermoresponsiveness, and inferior biodegradability, greatly hampering their translations. Herein, by harnessing supramolecular assembly and rational protein design, we present a temperature-sensitive wet bioadhesive fabricated through recombinant protein and surfactant. Mechanical performance of the bioglue system is actively tunable with thermal triggers. In cold condition, adhesion strength of the bioadhesive was only about 50 kPa. By increasing temperature, the strength presented up to 600 kPa, which is remarkably stronger than other biological counterparts. This is probably due to the thermally triggered phase transition of the engineered protein and the formation of coacervate, thus leading to the enhanced wet adhesion bonding., (© 2021 Wiley-VCH GmbH.)

Soft matter at solid-liquid interfaces plays an important role in multiple scientific disciplines as well as in various technological fields. For microgels, representing highly interesting soft matter systems, we demonstrate that the preparation method, i.e. the way how the microgel is applied to the specific surface, plays a key role. Focusing on the three most common sample preparation methods (spin-coating, drop-casting and adsorption from solution), we performed a comparative study of the deformation behavior of microgels at the solid-liquid interface on three different surfaces with varying hydrophilicities. For in situ visualization of the deformation of pNIPMAM microgels, we conducted highly sensitive 3D super resolution fluorescence microscopy methods. We furthermore performed complementary molecular dynamics simulations to determine the driving force responsible for the deformation depending on the surface and the deposition method. The combination of experiments and simulations revealed that the simulated equilibrium structure obtained after simulation of the completely dry microgel after deposition is retained after rehydration and subsequent fluorescent imaging.

The role of electrostatics on the interfacial properties of polyelectrolyte microgels has been discussed controversially in the literature. It is not yet clear if, or how, Coulomb interactions affect their behavior under interfacial confinement. In this work, we combine compression isotherms, atomic force microscopy imaging, and computer simulations to further investigate the behavior of pH-responsive microgels at oil-water interfaces. At low compression, charged microgels can be compressed more than uncharged microgels. The in-plane effective area of charged microgels is found to be smaller in comparison to uncharged ones. Thus, the compressibility is governed by in-plane interactions of the microgels with the interface. At high compression, however, charged microgels are less compressible than uncharged microgels. Microgel fractions located in the aqueous phase interact earlier for charged than for uncharged microgels because of their different swelling perpendicular to the interface. Therefore, the compressibility at high compression is controlled by out-of-plane interactions. In addition, the size of the investigated microgels plays a pivotal role. The charge-dependent difference in compressibility at low compression is only observed for small but not for large microgels, while the behavior at high compression does not depend on the size. Our results highlight the complex nature of soft polymer microgels as compared to rigid colloidal particles. We clearly demonstrate that electrostatic interactions affect the interfacial properties of polyelectrolyte microgels.

Arborescent copolymers with a core-shell-corona (CSC) architecture were synthesized and the topology of the molecules was challenged (constrained) through intramolecular interactions, resulting in phase separation breaking the symmetry of radial density. The inner poly(2-vinylpyridine) shell of these arborescent polystyrene- g -[poly(2-vinylpyridine)- b -polystyrene] molecules can self-assemble by binding metallic salts and acids in apolar and intermediate-polarity solvents. Upon loading with HAuCl 4 , the characteristics of the polymer templates govern the "loading sites" of the metal within the molecules. Unique morphologies were observed for the metal-loaded G0-G4 arborescent copolymers investigated, namely, spherical, toroidal, raspberry-like, spherical nanocage, and a new worm-in-sphere morphology. The reason for the emergence of such morphologies is the interplay among intramolecular interactions of unlike polymer segments, solvent selectivity, the entropic elasticity of the arborescent substrate, and phase segregation induced by coordination with the charged metallic species. Meanwhile, the stability of the arborescent molecules against aggregation provides intramolecular phase segregation with imposed "confined" geometry and thus leads to nonconventional morphologies. Furthermore, the size of the arborescent molecules is much smaller than that of other known particles (droplets) serving as confined geometries. Computer simulations were used to model the mesostructure of the arborescent copolymers, to demonstrate the influence of solvent selectivity, together with HAuCl 4 loading, on the evolution of the morphology of the macromolecules., Competing Interests: The authors declare no competing financial interest.

It is known that microgels can serve as soft, permeable and stimuli-responsive alternative of solid colloidal particles to stabilize oil-water emulsions. The driving force for the adsorption of the microgels on interface of two immiscible liquids is a shielding of unfavorable oil-water contacts by adsorbed subchains, that is, the decrease of the surface tension between the liquids. Such phenomenon usually proceeds if volume fractions of the two liquids are comparable with each other and the microgel concentration is not high enough. The natural question arises: what is going on with the system in the opposite case of strongly asymmetric mixture (one of the liquids (oil) has a very small fraction) or high microgel concentration (the overall volume of the microgels exceeds the volume of the minor oil component)? Here we demonstrate that the microgels uptake the oil whose concentration within the microgels can be orders of magnitude higher than outside, leading to the additional microgel swelling (in comparison with the swelling in water). Thus, the microgels can serve as scavengers and concentrators of liquids dissolved in water. At first glance, this effect seems counterintuitive. However, it has a clear physical reason related to the incompatibility of oil and water. Absorption of the oil by microgels reduces unfavorable oil-water contacts by microgel segments: the microgels have a higher concentration of the segments at the periphery, forming a shell. The microgels with uptaken oil are stable toward aggregation at very small oil concentration in the mixture. However, an increase in the oil concentration can lead to aggregation of the microgels into dimers, trimers, and so on. The increasing concentration of oil mediates the attraction between the microgels: the oil in the aggregates appears to be localized in-between the microgels instead of their interior, which is accompanied by the release of the elastic stress of the microgels. A further increase in the oil concentration results in a growth of the size of the oil droplets between the microgels and the number of the microgels at the droplet's periphery, that is, the emulsion is formed.

Monolayers of polymer microgels adsorbed at the liquid interfaces were studied by dissipative particle dynamics simulations. The results demonstrated that the compressibility of the monolayers can be widely tuned by varying the cross-linking density of the microgels and their (in)compatibility with the immiscible liquids. In particular, the compression of the monolayers (increase of 2D concentration of the microgels) leads to the decrease of their lateral size. Herewith, the shape of the individual soft particles gradually changes from oblate (diluted 2D system) to nearly spherical (compressed monolayer). The polymer concentration profiles plotted along the normal to the interface reveal a nonmonotonous shape with a sharp maximum at the interface. This is a consequence of the shielding effect: saturation of the interface by monomer units of the subchains is driven by minimization of unfavorable contacts between the immiscible liquids and is opposed by elasticity of the network. The decrease of the interfacial tension upon concentration (compression) of the monolayer is quantified. It has been demonstrated that the interfacial tension significantly differs if the solubility of the polymer chains of the microgel network in the liquids changes. These results correlate well with experimental data. The examination of the microgels' crystalline ordering in monolayers demonstrated a nonmonotonous dependency on the compression degree (microgel concentration). Finally, the worsening of the solvent quality leads to the collapse of the microgels in monolayer and nonmonotonous behavior of the interfacial tension.

Thermoresponsive copolymer microgels based on the biocompatible monomer N-vinylcaprolactam (VCL) and the hydrophobic comonomer 4-tert-butylcyclohexylacrylate (TBCHA) with highly tunable comonomers ratio were for the first time synthesized by miniemulsion polymerization. Their physical properties in aqueous solution and at the solid interface were characterized using dynamic light scattering (DLS), atomic force microscopy (AFM) and dissipative particle dynamics (DPD) simulations. The results show a significant decrease of the swelling rate of the obtained microgels with an increase of the amount of the hydrophobic comonomer. In the case when the fraction of TBCHA is equal or higher than the fraction of VCL, the microgels become almost insensitive to the temperature changes, and the amount of water inside the microgels appeared to be diminishingly small. In the opposite case, if the VCL fraction is major, the copolymer microgels preserve their softness and deformability while being adsorbed onto a solid surface. At the same time, all samples have shown a good colloidal stability and a low polydispersity in size. Thus, the presented polymerization technique is applicable for the fabrication of microgels using hydrophobic monomers, which are not accessible by conventional precipitation polymerization. We demonstrate that the mechanical properties and the temperature-responsiveness of the copolymer microgels can be precisely adjusted by the content of the hydrophobic comonomer., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The structure of complexes formed by oppositely charged polyelectrolytes and adsorbed layers on charged surfaces is sensitive to low-molecular-weight salt. Furthermore, if the concentration exceeds some threshold value, the complexes and adsorbed chains can be "dissolved". This is due to the screening of the electrostatic interactions between charged units. In the current paper, we perform a comparative analysis of "dissolution" (dissociation) of complexes and layers upon addition of salt. For this, the conventional Brownian dynamics of computer simulations is used. We demonstrate that the complex based on linear chains dissociates at lower salt concentration than that required for desorption of equivalent chains from an oppositely charged surface. The physical reason is the difference in the symmetry of the electric field, which binds the chains into the complex (layer). In the salt-free regime, the intensity of the electric field (and attractive force) between two linear chains decays with the distance R between them, like for two spherical objects, ∼ R -2 , if R is bigger than the characteristic size of the chain. On the contrary, the attractive force of the chain to the infinite surface does not depend on the distance to the surface (the electric field is constant). Therefore, if attractive forces in the condensed states of the two systems are equal, one needs to add more salt to screen the constant force than the decaying one. The computer simulation results on the adsorption of the chains were compared with the experimental data obtained for adsorption of cationic poly(4-vinylpyridine) on the surface of anionic liposomes. Good quantitative agreement was achieved.

Exploring and controlling chemical reactions in compartments opens new platforms for designing bioinspired catalysts and energy-autonomous systems. Aqueous polymer networks or hydrogels serve as a perfect model for biological tissues, allowing systematic investigations of chemical transformations in compartments. Herein, we report the synthesis of a versatile, colloidal microgel catalyst containing covalently bound l-proline as an organocatalyst. The key finding of our work is that the catalytic activity can be tuned by adjusting the distribution of the organocatalyst in the microgel network as well as the properties of the solvent. We demonstrate that l-proline groups integrated into microgels enable the reaction of 4-nitrobenzaldehyde and cyclohexanone in a heterogeneous reaction mixture in which free l-proline is not active. By controlling the localization of the l-proline groups within the microgel network (core or corona), the rate of the aldol reaction in homogenous and heterogeneous reaction mixtures can be modulated. Furthermore, microgels with covalently attached catalysts can be recycled and reused in sequential catalytic runs without deterioration of the catalyst performance in terms of activity and selectivity. The internal structure of the microgel in heterogeneous reaction mixtures was studied by computer simulations., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli-responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus-like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self-assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus-like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The authors demonstrate how the size and structure of the cavity of hollow charged microgels may be controlled by varying pH and ionic strength. Hollow charged microgels based on N-isopropylacrylamide with ionizable co-monomers (itaconic acid) combine advanced structure with enhanced responsiveness to external stimuli. Structural advantages accrue from the increased surface area provided by the extra internal surface. Extreme sensitivity to pH and ionic strength due to ionizable moieties in the polymer network differentiates these soft colloidal particles from their uncharged counterparts, which sustain a hollow structure only at cross-link densities sufficiently high that stimuli sensitivity is reduced. Using small-angle neutron and light scattering, increased swelling of the network in the charged state accompanied by an expanded internal cavity is observed. Upon addition of salt, the external fuzziness of the microgel surface diminishes while the internal fuzziness grows. These structural changes are interpreted via Poisson-Boltzmann theory in the cell model., (© 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We investigate soft, temperature-sensitive microgels at fluid interfaces. Though having an isotropic, spherical shape in bulk solution, the microgels become anisotropic upon adsorption. The structure of microgels at interfaces is described by a core-corona morphology. Here, we investigate how changing temperature across the microgel volume phase transition temperature, which leads to swelling/deswelling of the microgels in the aqueous phase, affects the phase behavior within the monolayer. We combine compression isotherms, atomic force microscopy imaging, multiwavelength ellipsometry, and computer simulations. At low compression, the interaction between adsorbed microgels is dominated by their highly stretched corona and the phase behavior of the microgel monolayers is the same. The polymer segments within the interface lose their temperature-sensitivity because of the strong adsorption to the interface. At high compression, however, the portions of the microgels that are located in the aqueous side of the interface become relevant and prevail in the microgel interactions. These portions are able to collapse and, consequently, the isostructural phase transition is altered. Thus, the temperature-dependent swelling perpendicular to the interface ("3D") affects the compressibility parallel to the interface ("2D"). Our results highlight the distinctly different behavior of soft, stimuli-sensitive microgels as compared to rigid nanoparticles.

Solid-liquid interfaces play an important role for functional devices. Hence, a detailed understanding of the interaction of soft matter objects with solid supports and of the often concomitant structural deformations is of great importance. We address this topic in a combined experimental and simulation approach. We investigated thermoresponsive poly( N -isopropylmethacrylamide) microgels (μGs) at different surfaces in an aqueous environment. As super-resolution fluorescence imaging method, three-dimensional direct stochastical optical reconstruction microscopy (dSTORM) allowed for visualizing μGs in their three-dimensional (3D) shape, for example, in a "fried-egg" conformation depending on the hydrophilicity of the surface (strength of adsorption). The 3D shape, as defined by point clouds obtained from single-molecule localizations, was analyzed. A new fitting algorithm yielded an isosurface of constant density which defines the deformation of μGs at the different surfaces. The presented methodology quantifies deformation of objects with fuzzy surfaces and allows for comparison of their structures, whereby it is completely independent from the data acquisition method. Finally, the experimental data are complemented with mesoscopic computer simulations in order to (i) rationalize the experimental results and (ii) to track the evolution of the shape with changing surface hydrophilicity; a good correlation of the shapes obtained experimentally and with computer simulations was found.

In this work, we studied the behavior of charged microgels at a liquid-liquid interface by means of dissipative particle dynamics simulations with explicit electrostatic interactions; the liquids represent polar and nonpolar solvents like water and oil. The effect of the fraction of charged groups and both solvents qualities on the microgel size, shape, degree of immersion into different liquids, and 2D ordering of the microgels at the interface is studied. For the case of both athermal solvents, we demonstrated that increasing the fraction of charged units results in significant swelling of the microgel inside the polar liquid and a dramatic drop in the number of adsorbed monomer units. For the case of a bad nonpolar solvent for the polyelectrolyte microgels, they easily get detached from the surface into the polar solvent. When the opposite case of a bad polar solvent is considered (like high temperatures for thermosensitive PNIPAM- or PVCL-based microgels), the microgels demonstrate a decrease of the swelling perpendicular to the interface at low χ-values, and they start to swell into the nonpolar liquid at high χ-values. Two approaches for accounting for different dielectric permittivity of the liquids were considered: implicit and explicit ones; we obtained that the results of the two approaches were always in qualitative agreement. However, the explicit model is necessary to correctly reproduce the physics of the phenomena in certain regimes, in particular, when the charged molecules move through the interface of two liquids. Finally, the microgels ordering was studied at the liquid-liquid interface. We found that even at rather low fraction of charged monomer units the microgels exhibit an almost ideal hexagonal packing even though the average distance between the microgels centers is significantly larger than the microgel diameter, while uncharged microgels positions were completely random. This implies that the interfacial ordering can be controlled by using pH-sensitive monomer units in the microgel structure.

Active colloidal catalysts inspired by glutathione peroxidase (GPx) were synthesized by integration of catalytically active selenium (Se) moieties into aqueous microgels. A diselenide crosslinker (Se X-linker) was successfully synthesized and incorporated into microgels through precipitation polymerization, along with the conventional crosslinker N,N'-methylenebis(acrylamide) (BIS). Diselenide bonds within the microgels were cleaved through oxidation by H 2 O 2 and converted to seleninic acid whilst maintaining the intact microgel microstructure. Through this approach catalytically active microgels with variable amounts of seleninic acid were synthesized. Remarkably, the microgels exhibited higher catalytic activity and selectivity at low reaction temperatures than the molecular Se catalyst in a model oxidation reaction of acrolein to acrylic acid and methyl acrylate., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this work, we investigated the phase behavior of melts of block-copolymers with one charged block by means of dissipative particle dynamics with explicit electrostatic interactions. We assumed that all the Flory-Huggins χ parameters were equal to 0. We showed that the charge- correlation attraction solely can cause microphase separation with a long-range order; a phase diagram was constructed by varying the volume fraction of the uncharged block and the electrostatic interaction parameter λ (dimensionless Bjerrum length). The obtained phase diagram was compared to the phase diagram of "equivalent" neutral diblock-copolymers with the non-zero χ-parameter between the beads of different blocks. The neutral copolymers were constructed by grafting the counterions to the corresponding co-ions of the charged block with further switching off the electrostatic interactions. Surprisingly, the differences between these phase diagrams are rather subtle; the same phases in the same order are observed, and the positions of the order-disorder transition ODT points are similar if the λ-parameter is considered as an "effective" χ-parameter. Next, we studied the position of the ODT for lamellar structure depending on the chain length N . It turned out that while for the uncharged diblock copolymer the product χ cr N was almost independent of N , for the diblock copolymers with one charged block we observed a significant increase in λ cr N upon increasing N . This can be attributed to the fact that the counterion entropy prevents the formation of ordered structures, and its influence is more pronounced for longer chains since they undergo the transition to ordered structures at smaller values of λ, when the electrostatic energy becomes comparable to k b T . This was supported by studying the ODT in diblock-copolymers with charged blocks and counterions cross-linked to the charged monomer units. The ODT for such systems was observed at significantly lower values of λ, with the difference being more pronounced at longer chain lengths N . The fact that the microphase separation is observed even at zero Flory-Huggins parameter can be used for the creation of "high-χ" copolymers: The incorporation of charged groups (for example, ionic liquids) can significantly increase the segregation strength. The diffusion of counterions in the obtained ordered structures was studied and compared to the case of a system with the same number of charged groups but a homogeneous structure; the diffusion coefficient along the lamellar plane was found to be higher than in any direction in the homogeneous structure., Competing Interests: The authors declare no conflict of interest.

Amphiphilic microgels adsorbed at an oil-water interface were studied by means of dissipative particle dynamics (DPD) simulations. The hydrophobic (A) and hydrophilic (B) monomer units in the polymer network are considered to be randomly distributed. Effects of the crosslinking density, interfacial tension between the liquids, their selectivity as solvents towards species A and B, and the degree of incompatibility between the A and B units on the internal microgel structure and distribution of the liquids are considered. The most important predictions are that (i) two immiscible liquids can homogeneously be mixed within the microgels and (ii) the adsorbed microgels contain a high fraction of the liquids (they are swollen at the interface). Simultaneous fulfillment of these two conditions can have a high impact on the design of new and efficient catalytic systems. In particular, such microgels can mix immiscible reactants dissolved in water and oil and trigger chemical reactions in the presence of a catalyst embedded into the microgel.

Nanogels and microgels are soft, deformable, and penetrable objects with an internal gel-like structure that is swollen by the dispersing solvent. Their softness and the potential to respond to external stimuli like temperature, pressure, pH, ionic strength, and different analytes make them interesting as soft model systems in fundamental research as well as for a broad range of applications, in particular in the field of biological applications. Recent tremendous developments in their synthesis open access to systems with complex architectures and compositions allowing for tailoring microgels with specific properties. At the same time state-of-the-art theoretical and simulation approaches offer deeper understanding of the behavior and structure of nano- and microgels under external influences and confinement at interfaces or at high volume fractions. Developments in the experimental analysis of nano- and microgels have become particularly important for structural investigations covering a broad range of length scales relevant to the internal structure, the overall size and shape, and interparticle interactions in concentrated samples. Here we provide an overview of the state-of-the-art, recent developments as well as emerging trends in the field of nano- and microgels. The following aspects build the focus of our discussion: tailoring (multi)functionality through synthesis; the role in biological and biomedical applications; the structure and properties as a model system, e.g., for densely packed arrangements in bulk and at interfaces; as well as the theory and computer simulation.

A striking discovery in our work is that the distribution of ionizable groups in polyampholyte microgels (random and core-shell) controls the interactions with the captured proteins. Polyampholyte microgels are capable to switch reversibly their charges from positive to negative depending on pH. In this work, we synthesized differently structured polyampholyte microgels with controlled amounts and different distribution of acidic and basic moieties as colloidal carriers to study the loading and release of the model protein cytochrome c (cyt-c). Polyampholyte microgels were first loaded with cyt-c using the electrostatic attraction under pH 8 when the microgels were oppositely charged with respect to the protein. Then the protein release was investigated under different pH (3, 6, and 8) both with experimental methods and molecular dynamics simulations. For microgels with a random distribution of ionizable groups complete and accelerated (compared to polyelectrolyte counterpart) release of cyt-c was observed due to electrostatic repulsive interactions. For core-shell structured microgels with defined ionizable groups, it was possible to entrap the protein inside the neutral core through the formation of a positively charged shell, which acts as an electrostatic potential barrier. We postulate that this discovery allows the design of functional colloidal carriers with programmed release kinetics for applications in drug delivery, catalysis, and biomaterials.