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Showing papers in "Soft Matter in 2009"


Journal ArticleDOI
TL;DR: In this paper, the hierarchical structure of the Lotus leaf has been recreated to characterize the influence of hierarchical roughness on superhydrophobicity and adhesion, and a flat surface, microstructured Lotus leaf replica and a micropatterned Si replica were fabricated.
Abstract: The superhydrophobic and self-cleaning leaves of Lotus (Nelumbo nucifera, Gaertn.) have been used as a model for the development of artificial biomimetic surfaces. The hierarchical structure of the Lotus leaf has been recreated to characterize the influence of hierarchical roughness on superhydrophobicity and adhesion. Hierarchical structures were fabricated by a fast and precise molding of the Lotus leaf microstructure, and self-assembly of the natural Lotus wax deposited by thermal evaporation to create the wax tubules nanostructures. Tubule formation was initiated by exposure of the specimens to a solvent vapor phase at a selected temperature. In order to study the influence of structures at different scale sizes on superhydrophobicity, a flat surface, microstructured Lotus leaf replica and a micropatterned Si replica, and a nanostructure were fabricated. Static contact angle, contact angle hysteresis, tilt angle and adhesive forces were measured. The data show that microstructures and nanostructures lead to superhydrophobicity, whereas hierarchical structures further improve this property and show low contact angle hysteresis, superior to that of the natural Lotus leaves.

605 citations


Journal ArticleDOI
TL;DR: This review will survey the current techniques for controlling cell aggregation, proliferation and extracellular matrix deposition, as well as approaches to generating shape-controlled tissue modules, and highlight techniques utilized to create macroscale engineered biological tissues from modular microscale units.
Abstract: Tissue engineering creates biological tissues that aim to improve the function of diseased or damaged tissues. To enhance the function of engineered tissues there is a need to generate structures that mimic the intricate architecture and complexity of native organs and tissues. With the desire to create more complex tissues with features such as developed and functional microvasculature, cell binding motifs and tissue specific morphology, tissue engineering techniques are beginning to focus on building modular microtissues with repeated functional units. The emerging field known as modular tissue engineering focuses on fabricating tissue building blocks with specific microarchitectural features and using these modular units to engineer biological tissues from the bottom up. In this review we will examine the promise and shortcomings of “bottom-up” approaches to creating engineered biological tissues. Specifically, we will survey the current techniques for controlling cell aggregation, proliferation and extracellular matrix deposition, as well as approaches to generating shape-controlled tissue modules. We will then highlight techniques utilized to create macroscale engineered biological tissues from modular microscale units.

530 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a review of recent publications on the synthesis of responsive hydrogel thin films and hybrid films with entrapped nanoparticles and reagents by the chemical crosslinking of reactive polymers, layer-by-layer deposition, and block-copolymer self-assembly.
Abstract: In this brief review we address a range of interesting applications and prospects of responsive hydrogel thin films for the fabrication of “smart” responsive surfaces, membranes, sensors with various transduction mechanisms, micro/nanoactuators, and capsules. We show that hydrogel thin films compete with grafted polymers and demonstrate strong advantages for the fabrication of robust multifunctional and multiresponsive surfaces. This article reviews recent publications on the synthesis of responsive hydrogel thin films and hybrid films with entrapped nanoparticles and reagents by the chemical crosslinking of reactive polymers, layer-by-layer deposition, and block-copolymer self-assembly, as well as examining those publications to determine a range of applications.

525 citations


Journal ArticleDOI
TL;DR: The recent advances in the preparation and application of ‘smart’ and functional block copolymer vesicles such as those which respond to external stimuli to afford a change in structure, morphology or controlled release event are presented.
Abstract: Polymer vesicles prepared by self-assembly techniques have attracted increasing scientific interest in recent years. This is as a result of their numerous potential applications such as tunable delivery vehicles, for the templating of biomineralization, as nanoreactors and as scaffolds for biological conjugation. Presented in this review are the recent advances in the preparation and application of ‘smart’ and functional block copolymer vesicles such as those which respond to external stimuli to afford a change in structure, morphology or controlled release event. In this Highlight, we first give an overview of the structure of polymer vesicles, followed by a summary of the methods used for their preparation. We then focus on recently developed intelligent polymer vesicles which can respond to the application of external stimuli such as a change in temperature, pH or redox to afford novel nanomaterials. The potential applications of these materials are explored with specific focus on the functionalization of various domains of the polymer vesicles. Finally, the current limitations in the preparation and application of polymer vesicles are explored as are the challenges facing the development of these nanostructures towards real-world applications.

518 citations


Journal ArticleDOI
TL;DR: This manuscript aims to highlight recent advances in the interface between biology and nanomedicine with the emphasis on nanogels as carriers for controlled drug delivery.
Abstract: Nanosized hydrogels (nanogels) have attracted considerable attention as multifunctional polymer-based drug delivery systems. Their versatility is demonstrated both in drug encapsulation and drug release. Nanogels can be designed to facilitate the encapsulation of diverse classes of bioactive compounds. With optimization of their molecular composition, size and morphology, nanogels can be tailor-made to sense and respond to environmental changes in order to ensure spatial and stimuli-controlled drug release in vivo. This manuscript aims to highlight recent advances in the interface between biology and nanomedicine with the emphasis on nanogels as carriers for controlled drug delivery.

450 citations


Journal ArticleDOI
TL;DR: The most promising approaches to make stimuli-responsive polymer vesicles that permit the controlled release of encapsulated contents are reviewed.
Abstract: Polymer vesicles, commonly called polymersomes, are spherical shell structures in which an aqueous compartment is enclosed by a bilayer membrane made from amphiphilic block copolymers. Compared to liposomes, their low molecular weight analogues, polymersomes have many superior properties (higher toughness, better stability, tailorable membrane properties), which make them attractive candidates for applications including encapsulation, drug delivery, nanoreactors and templates for micro- or nano-structured materials. Many potential applications require the ability to control the release of substances encapsulated in the interior compartment and/or in the hydrophobic core of membrane. To address this goal, polymersomes have to be developed in which a specific stimulus destabilises the vesicle structure. In this article we review the most promising approaches to make stimuli-responsive polymer vesicles that permit the controlled release of encapsulated contents. Stimuli including hydrolysis, oxidation, reduction, pH, temperature and light are discussed and their effect on the chemical and physical structure of the amphiphilic copolymers is also described.

428 citations


Journal ArticleDOI
TL;DR: It is shown that by coarse-grained simulation in combination with an efficient backmapping methodology one can obtain well-equilibrated long time- and large length-scale atomistic structures of polymeric melts or biomolecular aggregates which can be used for comparison to experimental data.
Abstract: Many physical phenomena and properties of soft matter systems such as synthetic or biological materials are governed by interactions and processes on a wide range of length- and time-scales. Computer simulation approaches that are targeted at questions in these systems require models which cover these scales and the respective levels of resolution. Multiscale simulation methods combine and systematically link several simulation hierarchies so that they can address phenomena at multiple levels of resolution. In order to reach the mesoscopic time- and length-scales important for many material properties, methods that bridge from the atomistic (microscopic) to a coarser (mesocopic) level are developed. Here, we review coarse-grained simulation models that are linked to a higher resolution atomistic description. In particular, we focus on structure-based coarse-graining methods which are used for a variety of soft matter problems – ranging from structure-formation in amorphous polymers to biomolecular aggregation. It is shown that by coarse-grained simulation in combination with an efficient backmapping methodology one can obtain well-equilibrated long time- and large length-scale atomistic structures of polymeric melts or biomolecular aggregates which can be used for comparison to experimental data. Methodological aspects are addressed such as the question of the time-scales and dynamics in the different simulation hierarchies and an outlook to future challenges in the area of resolution exchange approaches and adaptive resolution models is presented.

420 citations


Journal ArticleDOI
TL;DR: In this article, the effect of aspect ratio of particles on the stability of both water-in-oil and oil-inwater emulsions is investigated experimentally, and the results demonstrate that interfaces with controlled surface rheology, as obtained by using shape induced capillary forces and packing effects, can be used for the rational design of Pickering emulsion and other types of high interface materials.
Abstract: Pickering–Ramsden emulsions and other forms of particle stabilized soft materials have received quite some attention recently because of the relative ease of formulation and the possibility to create novel materials. There is, however, a clear need for approaches that are versatile and efficient. In the present work the effect of aspect ratio of particles on the stability of both water-in-oil and oil-in-water emulsions is investigated experimentally. Two types of non-spherical particles are used. Hydrophobic prolate ellipsoids with aspect ratios ranging from 1 to 9 are obtained by stretching polystyrene latex particles. Hydrophilic spindle type hematite particles have been synthesized with aspect ratios ranging from 1 to 6. A strong dependence of emulsion stability on the aspect ratio of the particles is observed. Optical as well as cryogenic scanning electron microscopy are used to visualize the droplet morphology and particulate structure and reveal fairly densely packed monolayers of ellipsoids, consistent with the mechanism of limited coalescence. Yet stable emulsions are only obtained for particles with a sufficient aspect ratio. Surface rheology on planar monolayers demonstrates the pronounced effect of aspect ratio on the surface moduli. The magnitude of the interfacial viscoelastic properties is shown to strongly depend on the aspect ratio at a given surface coverage. This is most probably due to an increased effective coverage and the occurrence of strong attractive shape induced capillary interactions. The dependence of the surface rheological properties on the aspect ratio of the particles rationalizes the observed emulsion stability as the surface rheological properties play a role in the coalescence process. The results demonstrate that interfaces with controlled surface rheology, as obtained by using shape induced capillary forces and packing effects, can be used for the rational design of Pickering emulsions and other types of high interface materials.

386 citations


Journal ArticleDOI
TL;DR: Different SA modalities are discussed: energy driven, entropy-driven, templated, and field-directed; non-equilibrium SA is discussed as a route to reconfigurable (“adaptive”) materials, and its connection to biological systems is emphasized.
Abstract: Self-assembly (SA) is the process in which a system's components—be it molecules, polymers, colloids, or macroscopic particles—organize into ordered and/or functional structures without human intervention. The main challenge in SA research is the ability to “program” the properties of the individual pieces such that they organize into a desired structure. Although a general strategy for doing so is still elusive, heuristic rules can be formulated that guide design of SA under various conditions and thermodynamic constraints. This Review examines SA in both the equilibrium and non-equilibrium/dynamic systems and discusses different SA modalities: energy driven, entropy-driven, templated, and field-directed. Non-equilibrium SA is discussed as a route to reconfigurable (“adaptive”) materials, and its connection to biological systems is emphasized.

381 citations


Journal ArticleDOI
TL;DR: In this paper, a generic approach to produce homogeneous and reproducible hydrogels from low molecular weight hydrogelators using the controlled hydrolysis of glucono-δ-lactone (GdL) was demonstrated.
Abstract: We demonstrate a generic new approach to produce homogeneous and reproducible hydrogels from low molecular weight hydrogelators using the controlled hydrolysis of glucono-δ-lactone (GdL). GdL slowly hydrolyses in water to give gluconic acid, which controllably lowers the pH. This hydrolysis is slower than the rate of dissolution; hence uniform pH change throughout the sample is possible. This results in homogeneous hydrogels that are unaffected by their shear or mixing history. A further advantage of this method is that it allows the gelation process to be monitored, giving further insight into the mechanism by which gelation occurs.

367 citations


Journal ArticleDOI
TL;DR: In this article, the authors focus on the characterization of superhydrophobic surfaces, models for the movement of drops, transitions between the Cassie and Wenzel states, and the behavior of super hydrophobic materials under condensation.
Abstract: Surface roughness has a profound influence on the wetting properties of a material. This fact is especially true with respect to the wetting of superhydrophobic surfaces. As a result of a special surface structure, a drop of water brought into contact with such a material forms an almost perfect sphere and even a very slight tilting of the superhydrophobic object is sufficient to cause the drop to roll off. For the description of the behavior of drops on rough surfaces two theories, namely those of Cassie and Wenzel, are often employed. However, it is currently becoming well established that both models explain the wetting behavior more from a qualitative or practical point of view rather than giving a quantitative description. For a prediction of actual contact angles, a more complex description is required that, next to thermodynamics, takes into account the kinetics of wetting. In this article, we focus on a few key aspects of superhydrophobic wetting, namely the characterization of superhydrophobic surfaces, models for the movement of drops, transitions between the Cassie and Wenzel states, and the behavior of superhydrophobic materials under condensation.

Journal ArticleDOI
TL;DR: In this article, electrorheological (ER) materials in state-of-the-art polymeric particles and their various nanocomposites with clay, mesoporous inorganics and carbon nanotubes along with their potential application are reported.
Abstract: This highlight aims to report electrorheological (ER) materials in state-of-the art polymeric particles and their various nanocomposites with clay, mesoporous inorganics and carbon nanotubes along with their potential application. ER fluids, suspensions of these particles having higher dielectric constant or electrical conductivity than the low-viscosity fluids in which they are suspended, are currently regarded as a smart/intelligent material, because their structural and rheological properties can be systematically tuned by controlling electric field strengths. In this highlight, various conducting polymers, including polyaniline, polypyrrole, poly(p-phenylene), poly(naphthalene quinone) and copolyaniline, are introduced and different types of polymer nanocomposites are emphasized. Flow curves for shear stress of the ER fluids are also examined.

Journal ArticleDOI
TL;DR: The recent contributions of polyelectrolyte microcapsules in the biomedical field, comprising in vitro and in vivodrug delivery as well as their applications as biosensors are reviewed.
Abstract: In this paper we review the recent contributions of polyelectrolyte microcapsules in the biomedical field, comprising in vitro and in vivodrug delivery as well as their applications as biosensors.

Journal ArticleDOI
TL;DR: This review summarizes the salient biological and biophysical features of this system and describes the current understanding of swarming motility.
Abstract: Bacterial swarming is an example of dynamic self-assembly in microbiology in which the collective interaction of a population of bacterial cells leads to emergent behavior. Swarming occurs when cells interact with surfaces, reprogram their physiology and behavior, and adapt to changes in their environment by coordinating their growth and motility with other cells in the colony. This Review summarizes the salient biological and biophysical features of this system and describes our current understanding of swarming motility. We have organized this Review into four sections: (1) The biophysics and mechanisms of bacterial motility in fluids and its relevance to swarming. (2) The role of cell/molecule, cell/surface, and cell/cell interactions during swarming. (3) The changes in physiology and behavior that accompany swarming motility. (4) A concluding discussion of several interesting, unanswered questions that is particularly relevant to soft matter scientists.

Journal ArticleDOI
TL;DR: In this paper, it was shown that sheets of protomolecules stack to form onion-like nanostructures and inter-sheet spacings within these structures are between 3.7 and 4.0, consistent with non-covalent π-π stacking in heteroaromatic systems.
Abstract: The melanins are an important class of multifunctional bio-macromolecules with fascinating and potentially useful electronic and optoelectronic properties. They are one of the last major bio-macromolecular systems where we do not know how the constituent molecules organise. This knowledge gap hinders attempts to map their properties and function and is a particular issue in understanding their roles in human photoprotection and melanoma cancer. In this article we provide strong and direct evidence of supramolecular organisation in both natural and synthetic eumelanins. Using low voltage–high resolution transmission electron microscopy (LVHRTEM) we show that sheets of protomolecules stack to form onion-like nanostructures. The inter-sheet spacings within these structures are between 3.7 and 4.0 A consistent with non-covalent π–π stacking in heteroaromatic systems. This type of arrangement has previously been suggested by reciprocal space scattering studies, but our real-space microscopic analysis provides the definitive evidence and dimensions. Furthermore, we show that key photophysical properties of melanin related to their role as photoprotectants are derived from the system's primary chemical structure rather than supramolecular organisation. We now have a framework for the secondary structure of melanins upon which biologically relevant structure–function relationships can be built and new bio-inspired optoelectronic materials and multifunctional coatings can be designed and realised.

Journal ArticleDOI
Abstract: Since the first reported thermal phase transition of poly(N-isopropylacrylamide) by Heskin in 1968, this unique polymer has continued to gain popularity. Because of their potential applications in the field of biomedical science, various responsive polymeric systems, such as those induced by pH, salt, co-solvent, thermal, light, electric and magnetic field, have been synthesized and studied. This review reports on recent developments (over the last 10 years) of thermo- and photo-responsive homopolymers, copolymers, microgels, hydrogels and polymer brushes at interfaces, where the synthesis, physicochemical properties, and potential applications are highlighted. Although homopolymers and microgels undergo phase transitions upon the application of external stimuli, block copolymers, however, self-assemble into different nanostructures. Such reversible phase transitions and self-assembly behaviors have generated many robust structures that can be applied in coating industries, personal/home care, petroleum, drug/protein/DNA delivery and separation processes.

Journal ArticleDOI
TL;DR: In this article, a new class of hydrogelators based on synthetic self-assembling N-terminally Boc-protected tripeptides has been developed, which can be potentially utilized for the treatment of waste-water and the organic dyes (Rhodamine B, Reactive Blue 4 and Direct Red 80) that are widely used in textile industries.
Abstract: A new class of hydrogelators based on synthetic self-assembling N-terminally Boc-protected tripeptides has been developed. A series of five tripeptides have been synthesized to study their self-assembling behavior in aqueous medium. Three of them form thermoreversible translucent gels at basic pH (pH 11.5–13.5). These hydrogels were characterized by FT-IR spectroscopy, circular dichroism (CD), small angle X-ray diffraction analysis (SAXRD), field-emission scanning electron microscopic (FE-SEM), transmission electron microscopic (TEM) and atomic force microscopic (AFM) studies. These hydrogels can be potentially utilized for the treatment of waste-water and the organic dyes (Rhodamine B, Reactive Blue 4 and Direct Red 80) that are widely used in textile industries can be efficiently removed. Moreover, peptide gelators can be recovered very easily just by changing the pH of the medium.

Journal ArticleDOI
TL;DR: Magnetic Janus particles are assembled into novel staggered chain structures under the action of magnetic and electric fields, which can result in permanent structures, which could be disassembled on demand by remote demagnetization as discussed by the authors.
Abstract: Magnetic Janus particles are assembled into novel staggered chain structures under the action of magnetic and electric fields. The magnetic assembly can result in permanent structures, which could be disassembled on demand by remote demagnetization.

Journal ArticleDOI
TL;DR: Why it is attractive to load the microbubbles with drugs is described and recent attempts made in the design of drug loaded microbubble are discussed.
Abstract: Ultrasound imaging is widely used in both diagnosis of diseases and pregnancy follow-up. As ultrasound imaging is a harmless, cheap and portable technique, ultrasound guided drug delivery is gaining more and more attention in the drug delivery field. To be effective, in most cases, ultrasonic drug delivery makes use of microbubbles. This highlight describes why it is attractive to load the microbubbles with drugs and discusses recent attempts made in the design of drug loaded microbubbles.

Journal ArticleDOI
TL;DR: In this paper, the surface dilational elastic moduli of bubbles immersed in water and soap bubbles in air were measured using either image analysis or pressure measurements, and it was possible with this method to measure directly the Gibbs elasticity.
Abstract: We have measured the surface dilational elastic moduli of bubbles immersed in water and soap bubbles in air. The short time response was obtained by submitting the bubbles to a rapid expansion after which the surface tension evolution was monitored, using either image analysis or pressure measurements. It was possible with this method to measure directly the Gibbs elasticity. The longer time response was obtained by submitting the bubbles to low frequency oscillations. Experiments were performed with solutions of non-ionic surfactants, C12E6, C12G2, their 1:1 mixture, Pluronic F-68 and 127 and the surface elastic moduli were compared with the stability of foams made with these surfactants. The foams evolve with time, first by Ostwald ripening, controlled by the low frequency elasticity, and then by bubbles coalescence, controlled by the high frequency elasticity.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated quasi-ordered nanostructures of avian feather barbs which produce vivid non-iridescent colors and found that these unstable structures are locked in by the kinetic arrest of the β-keratin matrix, likely through the entanglement or cross-linking of supermolecular β-kibatin fibers.
Abstract: Some of the most vivid colors in the animal kingdom are created not by pigments, but by wavelength-selective scattering of light from nanostructures. Here we investigate quasi-ordered nanostructures of avian feather barbs which produce vivid non-iridescent colors. These β-keratin and air nanostructures are found in two basic morphologies: tortuous channels and amorphous packings of spheres. Each class of nanostructure is isotropic and has a pronounced characteristic length scale of variation in composition. These local structural correlations lead to strong backscattering over a narrow range of optical frequencies and little variation with angle of incidence. Such optical properties play important roles in social and sexual communication. To be effective, birds need to precisely control the development of these nanoscale structures, yet little is known about how they grow. We hypothesize that multiple lineages of birds have convergently evolved to exploit phase separation and kinetic arrest to self-assemble spongy color-producing nanostructures in feather barbs. Observed avian nanostructures are strikingly similar to those self-assembled during the phase separation of fluid mixtures; the channel and sphere morphologies are characteristic of phase separation by spinodal decomposition and nucleation and growth, respectively. These unstable structures are locked-in by the kinetic arrest of the β-keratin matrix, likely through the entanglement or cross-linking of supermolecular β-keratin fibers. Using the power of self-assembly, birds can robustly realize a diverse range of nanoscopic morphologies with relatively small physical and chemical changes during feather development.

Journal ArticleDOI
TL;DR: The results suggest that control over the mechanical properties of hydrogel NPs can be used to tailor the cellular uptake mechanism and kinetics of drug delivery.
Abstract: Uptake and intracellular trafficking of hydrogel nanoparticles (NPs) of N,N-diethyl acrylamide and 2-hydroxyethyl methacrylate crosslinked with N,N′-methylene-bis-acrylamide were studied with a RAW 264.7 murine macrophage cell line. Results show that the uptake rate, the mechanism of internalization and the concentration of internalized NPs are correlated to the NP Young modulus. Soft NPs are found to be internalized preferentially via macropinocytosis while the uptake of stiff NPs is mediated by a clathrin-dependent mechanism. NPs with an intermediate Young modulus exhibit multiple uptake mechanisms. The accumulation rate of the NPs into lysosomal compartments of the cell is also dependent on the NP elasticity. Our results suggest that control over the mechanical properties of hydrogel NPs can be used to tailor the cellular uptake mechanism and kinetics of drug delivery.

Journal ArticleDOI
TL;DR: In this paper, the effect of the adsorption of milk proteins at the oil-water interface on their digestibility in simulated gastrointestinal environment was investigated, and the degradation of β-Lg was significantly protected through simulated duodenal digestion as a result of a complex formed with the PC.
Abstract: We have studied the effect of the adsorption of milk proteins at the oil-water interface on their digestibility in simulated gastrointestinal environment. The investigations aimed to characterize how both the breakdown of the adsorbed proteins and the interactions with physiological surfactants, phosphatidylcholine (PC) and bile salts (BS), influence structural transformations of model, protein-stabilized food emulsions in the gastrointestinal track. Proteolysis of two contrasting proteins, β-casein (β-Cas) and β-lactoglobulin (β-Lg), was compared between the protein presented in solution or in emulsion, after adsorption at the oil-water interface. Digestion of β-Cas was faster when presented as an emulsion and led to the persistence of a 6 kD peptide not seen when the protein was presented in solution. Adsorption gave rise to a pepsin-susceptible form of β-Lg. Complex interactions were observed with PC introduced to the system in the vesicular form. Measurements of interfacial tension revealed that PC displaced the proteins from the oil droplets after only 30 s for β-Lg and 12 min for β-Cas, so that the gastric digestion largely took place in solution. Pepsinolysis of adsorbed β-Cas played a dominant role in emulsion destabilization. In contrast, collapse of β-Lg-stabilized emulsion under gastric conditions was mainly dependent on protein-PC interactions. β-Lg was significantly protected through simulated duodenal digestion as a result of a complex formed with the PC. In the absence of PC, the proteins were completely broken down after duodenal digestion, during which the duodenal surfactants, BS, displaced any remaining protein from the interface and governed the final structure of emulsion.

Journal ArticleDOI
TL;DR: In this article, the static and dilational properties of the gas-liquid interfaces of partially hydrophobic nanoparticles (fumed silica) were investigated, and it was shown that the Gibbs stability criterion E > γ/2 against foam coarsening is fulfilled.
Abstract: In an attempt to elucidate the remarkable stability of foams generated from dispersions of partially hydrophobic nanoparticles (fumed silica), we present investigations into the static and dilational properties of the gas–liquid interfaces of such dispersions. By relating the dynamic surface tension γ(t) and the dilational elasticity E measured using an oscillating bubble device, we confirm that the Gibbs stability criterion E > γ/2 against foam coarsening is fulfilled. We complement these studies using ellipsometry and Brewster angle microscopy, which provide evidence for a pronounced adsorption barrier for the particles and a network-like structure in the interface at sufficiently high concentrations. We observe this structure also in freely suspended films drawn from the same particle dispersions.

Journal ArticleDOI
TL;DR: In this paper, the authors fabricate onion-like multi-membrane hydrogels starting from a template gel-core to shells through a dynamic self-assembly method and investigate the influence of various factors on the formation of the complex system in detail.
Abstract: Multi-membrane hydrogels are newly promising carriers in biomedical fields. We fabricate alginate-based onion-like multi-membrane hydrogels starting from a template gel-core to shells through a dynamic self-assembly method, and investigate the influence of various factors on the formation of the complex system in detail. By precisely controlling the process of preparation, multi-layered hydrogels of different shapes either with or without defined internal space between separated layers can be prepared. And a pulse-like delivery of macromolecule has been achieved by this architecture.

Journal ArticleDOI
TL;DR: In this article, pressure is used as a physical-chemical parameter for studying the physicochemical and phase behavior of lipid self-assembly and the effect of other additives such as ions, cholesterol, and anaesthetics.
Abstract: Besides temperature, hydrostatic pressure has been used as a physical-chemical parameter for studying the energetics and phase behavior of membrane systems. First we review some theoretical aspects of lipid self-assembly. Then, the temperature and pressure dependent structure and phase behavior of lipid bilayers, differing in chain configuration, headgroup structure and composition as revealed by using thermodynamic, spectroscopic and scattering experiments is discussed. We also report on the lateral organization of phase-separated lipid membranes and model raft mixtures as well as the influence of peptide and protein incorporation on membrane structure and dynamics upon pressurization. Also the effect of other additives, such as ions, cholesterol, and anaesthetics is discussed. Furthermore, we introduce pressure as a kinetic variable. Applying the pressure-jump relaxation technique in combination with time-resolved synchrotron X-ray diffraction, the kinetics of various lipid phase transformations was investigated. Finally, also new data on pressure effects on membrane mimetics, such as surfactants and microemulsions, are presented.

Journal ArticleDOI
TL;DR: In this article, the effects of surfactant type and bubble surface mobility on foam rheological properties are discussed, focusing on the viscous friction between bubbles in steadily sheared foams, as well as between bubbles and confining solid wall.
Abstract: This paper is an overview of our recent understanding of the effects of surfactant type and bubble surface mobility on foam rheological properties. The focus is on the viscous friction between bubbles in steadily sheared foams, as well as between bubbles and confining solid wall. Large set of experimental results is reviewed to demonstrate that two qualitatively different classes of surfactants can be clearly distinguished. The first class is represented by the typical synthetic surfactants (such as sodium dodecylsulfate) which are characterised with low surface modulus and fast relaxation of the surface tension after a rapid change of surface area. In contrast, the second class of surfactants exhibits high surface modulus and relatively slow relaxation of the surface tension. Typical examples for this class are the sodium and potassium salts of fatty acids (alkylcarboxylic acids), such as lauric and myristic acids. With respect to foam rheology, the second class of surfactants leads to significantly higher viscous stress and to different scaling laws of the shear stress vs. shear rate in flowing foams. The reasons for these differences are discussed from the viewpoint of the mechanisms of viscous dissipation of energy in sheared foams and the respective theoretical models. The process of bubble breakup in sheared foams (determining the final bubble-size distribution after foam shearing) is also discussed, because the experimental results and their analysis show that this phenomenon is controlled by foam rheological properties.

Journal ArticleDOI
TL;DR: A novel process that utilizes different crosslinking mechanisms to provide gel environments that are either permissive or inhibitory to cellular spreading is developed, both to provide new insights into the relationships between gel structure and cell behavior, and for eventual tissue-engineering applications where spatial control over cells is desired.
Abstract: With advanced understanding of how manipulations in material chemistry and structure influence cellular interactions, material control over cellular behavior (e.g., spreading) is becoming increasingly possible. In this example, we developed a novel process that utilizes different crosslinking mechanisms to provide gel environments that are either permissive or inhibitory to cellular spreading. To accomplish this, a multi-acrylated macromer (i.e., acrylated hyaluronic acid) was first crosslinked with an addition reaction using a matrix metalloprotease (MMP) cleavable peptide containing thiol groups. When an adhesive peptide was also coupled to the network, this environment permitted the spreading of encapsulated human mesenchymal stem cells (hMSCs), whereas control systems did not. If all acrylates were not consumed during the initial crosslinking step, a photoinitiated radical polymerization could be used to crosslink the remaining acrylates and inhibit cellular spreading with the production of covalent barriers. Variations in the ratio of the two crosslink types in individual constructs controlled the degradation and mechanical properties of the hydrogels, as well as the degree of spreading of encapsulated cells. Cell spreading was further controlled spatially with the use of photomasks. Overall, this new technology is an exciting and potentially valuable tool, both to provide new insights into the relationships between gel structure and cell behavior, and for eventual tissue-engineering applications where spatial control over cells is desired.

Journal ArticleDOI
TL;DR: In this article, a detailed description of the drop shape and the (singular) distribution of the electric field in the vicinity of the contact line has been provided for dynamic electrowetting.
Abstract: Electrowetting is a versatile tool for manipulating typically submillimetre-sized drops in various microfluidic applications. In recent years the microscopic understanding of the electrowetting effect has substantially improved leading to a detailed description of the drop shape and the (singular) distribution of the electric field in the vicinity of the contact line. Based on these findings, novel quantitative models of contact angle saturation, the most important and longstanding fundamental problem in the field, have recently been developed. Future challenges arise in the context of dynamic electrowetting: neither the translational motion of drops nor the generation of internal flow patterns are currently well understood.

Journal ArticleDOI
TL;DR: In this article, the ability of nanoparticles (metallic, semiconductor and magnetic) assembly in various highly ordered superstructures is explored to explore the ability to modulate or enhance the overall behavior of the nanomaterials.
Abstract: The skill to use new synthetic routes to assemble nanoparticles (NPs) into advanced architectures for specific functions is a big challenge for the researchers. Controlled morphologies designed for generating 1-dimensional (1D) and 2-dimensional (2D) structures inspired by nature are one of the hot topics in nanoscience. The unique properties of individual nanocrystals upon assembly also provide the opportunity to modulate or enhance the overall behavior of the nanomaterials. New synthetic approaches will be discussed to explore the ability of the NP (metallic, semiconductor and magnetic) assembly in various highly ordered superstructures. The mechanism of NP assembly (non-covalent or covalent) with itself or by targeting polymers and biomolecules as linkers will also be illustrated. The topics will include new methods for construction of 1D nanowires and 2D nanosheets by spontaneous dipole–dipole interactions, air–water interface assembly and specific interactions using polymer and bio-templates. Use of polymers as templates for generating arrays of NPs or biomolecules (for investigating the intrinsic behavior of DNA or proteins in the assembly) opens the possibility of designing novel devices and hybrid materials. Once the desired superstructures have been fabricated and characterized, the corresponding materials can be further investigated for optical, magnetic, electronic and sensor applications.