Advances in Colloid and Interface Science (v.207, #C)

This review reports on the latest developments in the field of magnetic nanocomposites, with a special focus on the potentials introduced by the incorporation of magnetic nanoparticles into polymer and supramolecular matrices. The general notions and the state of the art of nanocomposite materials are summarized and the results reported in the literature over the last decade on magnetically responsive films, capsules and gels are reviewed. The most promising concepts that have inspired the design of magneto-responsive nanocomposites are illustrated through remarkable examples where the integration of magnetic nanoparticles into organic architectures has successfully taken to the development of responsive multifunctional materials.Display Omitted
Keywords: Magnetic nanoparticle; Nanocomposite; Film; Capsule; Gel;

Emerging methods for the fabrication of polymer capsules by Jiwei Cui; Martin P. van Koeverden; Markus Müllner; Kristian Kempe; Frank Caruso (14-31).
Hollow polymer capsules are attracting increasing research interest due to their potential application as drug delivery vectors, sensors, biomimetic nano- or multi-compartment reactors and catalysts. Thus, significant effort has been directed toward tuning their size, composition, morphology, and functionality to further their application. In this review, we provide an overview of emerging techniques for the fabrication of polymer capsules, encompassing: self-assembly, layer-by-layer assembly, single-step polymer adsorption, bio-inspired assembly, surface polymerization, and ultrasound assembly. These techniques can be applied to prepare polymer capsules with diverse functionality and physicochemical properties, which may fulfill specific requirements in various areas. In addition, we critically evaluate the challenges associated with the application of polymer capsules in drug delivery systems.Display Omitted
Keywords: Nanoparticles; Polymer architecture; Assembly; Layer-by-layer; Drug delivery; Nanotechnology;

Liposomes have been extensively investigated as possible carriers for diagnostic or therapeutic agents due to their unique properties. However, liposomes still have not attained their full potential as drug and gene delivery vehicles because of their insufficient morphological stability. Recently, a super-stable and freestanding hybrid liposomal cerasome (partially ceramic- or silica-coated liposome) has drawn much attention as a novel drug delivery system because its atomic layer of polyorganosiloxane surface imparts higher morphological stability than conventional liposomes and its liposomal bilayer structure reduces the overall rigidity and density greatly compared to silica nanoparticles. Cerasomes are more biocompatible than silica nanoparticles due to the incorporation of the liposomal architecture into cerasomes. Cerasomes combine the advantages of both liposomes and silica nanoparticles but overcome their disadvantages so cerasomes are ideal drug delivery systems. The present review will first highlights some of the key advances of the past decade in the technology of cerasome production and then review current biomedical applications of cerasomes, with a view to stimulating further research in this area of study.Display Omitted
Keywords: Cerasomes; Liposomes; Drug delivery; Silica nanoparticles; Controlled release;

Fatty acids can self-assemble under various shapes in the presence of amines or cationic components. We assemble and compare these types of self-assembly leading toward a catanionic system either with a cationic surfactant or with an amine component playing the role of counter-ion. First, we focus on the molar ratio as a key driving parameter. Known and yet un-known values from other quantities governing the colloidal properties of these systems such as structural surface charge, osmotic pressure, molecular segregation, rigidity, in plane colloidal interactions and melting transition are discussed. We include also recent results obtained on the interfacial and foaming properties of these systems. We will highlight the specificity of these self-assemblies leading to unusual macroscopic properties rich of robust applications.Display Omitted
Keywords: Fatty acid self-assembly; Catanionic system; Counter-ion; Molar ratio; Surface charge;

Microcapsule mechanics: From stability to function by Martin P. Neubauer; Melanie Poehlmann; Andreas Fery (65-80).
Microcapsules are reviewed with special emphasis on the relevance of controlled mechanical properties for functional aspects. At first, assembly strategies are presented that allow control over the decisive geometrical parameters, diameter and wall thickness, which both influence the capsule's mechanical performance. As one of the most powerful approaches the layer-by-layer technique is identified. Subsequently, ensemble and, in particular, single-capsule deformation techniques are discussed. The latter generally provide more in-depth information and cover the complete range of applicable forces from smaller than pN to N. In a theory chapter, we illustrate the physics of capsule deformation. The main focus is on thin shell theory, which provides a useful approximation for many deformation scenarios. Finally, we give an overview of applications and future perspectives where the specific design of mechanical properties turns microcapsules into (multi-)functional devices, enriching especially life sciences and material sciences.Display Omitted
Keywords: Microcapsules; Mechanical characterization; Shell theory; Layer-by-layer; Drug delivery;

Many degenerative diseases such as Alzheimer's and Parkinson's involve proteins that have a tendency to misfold and aggregate eventually forming amyloid fibers. This review describes the use of monolayers, bilayers, supported membranes, and vesicles as model systems that have helped elucidate the mechanisms and consequences of the interactions between amyloidogenic proteins and membranes. These are twofold: membranes favor the formation of amyloid structures and these induce damage in those membranes. We describe studies that show how interfaces, especially charged ones, favor amyloidogenic protein aggregation by several means. First, surfaces increase the effective protein concentration reducing a three-dimensional system to a two-dimensional one. Second, charged surfaces allow electrostatic interactions with the protein. Anionic lipids as well as rafts, rich in cholesterol and gangliosides, prove to play an especially important role. Finally, these amphipathic systems also offer a hydrophobic environment favoring conformational changes, oligomerization, and eventual formation of mature fibers. In addition, we examine several models for membrane permeabilization: protein pores, leakage induced by extraction of lipids, chaotic pores, and membrane tension, presenting illustrative examples of experimental evidence in support of these models. The picture that emerges from recent work is one where more than one mechanism is in play. Which mechanism prevails depends on the protein, its aggregation state, and the lipid environment in which the interactions occur.Display Omitted
Keywords: Membrane model systems; Amyloid aggregation; Membrane-assisted fibrillogenesis; Membrane permeabilization; Amyloid toxicity;

Interactions in lipid stabilised foam films by José Luis Toca-Herrera; Nadejda Krasteva; Hans-Joachim Müller; Rumen Krastev (93-106).
The interaction between lipid bilayers in water has been intensively studied over the last decades. Osmotic stress was applied to evaluate the forces between two approaching lipid bilayers in aqueous solution. The force–distance relation between lipid mono- or bilayers deposited on mica sheets using a surface force apparatus (SFA) was also measured. Lipid stabilised foam films offer another possibility to study the interactions between lipid monolayers. These films can be prepared comparatively easy with very good reproducibility. Foam films consist usually of two adsorbed surfactant monolayers separated by a layer of the aqueous solution from which the film is created. Their thickness can be conveniently measured using microinterferometric techniques. Studies with foam films deliver valuable information on the interactions between lipid membranes and especially their stability and permeability. Presenting inverse black lipid membrane (BLM) foam films supply information about the properties of the lipid self-organisation in bilayers. The present paper summarises results on microscopic lipid stabilised foam films by measuring their thickness and contact angle. Most of the presented results concern foam films prepared from dispersions of the zwitterionic lipid 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC) and some of its mixtures with the anionic lipid — 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DMPG).The strength of the long range and short range forces between the lipid layers is discussed. The van der Waals attractive force is calculated. The electrostatic repulsive force is estimated from experiments at different electrolyte concentrations (NaCl, CaCl2) or by modification of the electrostatic double layer surface potential by incorporating charged lipids in the lipid monolayers. The short range interactions are studied and modified by using small carbohydrates (fructose and sucrose), ethanol (EtOH) or dimethylsulfoxide (DMSO). Some results are compared with the structure of lipid monolayers deposited at the liquid/air interface (monolayers spread in Langmuir trough), which are one of most studied biomembrane model system. The comparison between the film thickness and the free energy of film formation is used to estimate the contribution of the different components of the disjoining pressure to the total interaction in the film and their dependence on the composition of the film forming solution.Display Omitted
Keywords: Foam films; Lipids; Electrostatc interaction; van der Waals interaction; Hydrophilic interaction; DLVO theory;

From terpyridine-based assemblies to metallo-supramolecular polyelectrolytes (MEPEs) by Guntram Schwarz; Iris Haßlauer; Dirk G. Kurth (107-120).
Introducing metal ion coordination as bonding motive into polymer architectures provides new structures and properties for polymeric materials. The metal ions can be part of the backbone or of the side-chains. In the case of linear metallo-polymers the repeat unit bears at least two metal ion receptors in order to facilitate metal-ion induced self-assembly. If the binding constants are sufficiently high, macromolecular assemblies will form in a solution. Likewise, polymeric networks can be formed by metal ion induced crosslinking. The metal ion coordination sites introduce dynamic features, e.g. for self-healing or responsive materials, as well as additional functional properties including spin-crossover, electro-chromism, and reactivity. Terpyridines have attracted attention as receptors in metallo-polymers due to their favorable properties. It is well suited to assemble linear rigid-rod like metallo-polymers in case of rigid ditopic ligands. Terpyridine binds a large number of metal ions and are readily functionalized giving rise to a plethora of available ligands as components in metallo-polymers. By the judicious choice of the metal ions, the design of the ligands, the counter ions and the boundary conditions of self-assembly, the final structure and properties of the resulting metallo-polymers can be tailored at all length scales. Here, we review recent activities in the area of metallo-polymers based on terpyridines as central metal ion receptors.Display Omitted
Keywords: Terpyridine; Self-assembly; Metallo-supramolecular coordination polyelectrolytes; Metallo-polymers; Metal ion coordination;

The knowledge of surface shear rheology is important to understand and model flow in systems where interfaces are present: multiphase flow, wetting, foaming and others. The topic has been investigated for more than 100 years, but the knowledge accumulated is still partial. The experimental devices used for the measurement of the viscoelastic parameters are delicate to operate and the response of the monolayers is complex, usually non-linear and time dependent. Furthermore, it is difficult to decouple from the response of the bulk liquid. Important discrepancies between microscopic and macroscopic methods were reported and remain to be clarified. The knowledge of shear properties does not suffice in general to achieve proper descriptions of the flow behavior and measurements of compression properties are needed as well. This paper presents examples taken from the literature and discusses the current level of understanding.Left: Interfacial stress as a function of strain for the DTAB–DNA surface layers; the frequency used is 1 Hz. The line has a slope 1 and indicates a linear regime. The horizontal arrows mark the onset of deviation to linearity, and correspond to the yield stress. Right: Brewster angle microscopy (BAM) picture of a sheared and fractured layerDisplay Omitted
Keywords: Surface shear rheology; Monolayers; Surface of water;

Serum albumin in 2D: A Langmuir monolayer approach by Nicholas F. Crawford; Roger M. Leblanc (131-138).
Understanding of protein interaction at the molecular level raises certain difficulties which is the reason a model membrane system such as the Langmuir monolayer technique was developed. Ubiquitous proteins such as serum albumin comprise 50% of human blood plasma protein content and are involved in many biological functions. The important nature of this class of protein demands that it be studied in detail while modifying the experimental conditions in two dimensions to observe it in all types of environments. While different from bulk colloidal solution work, the two dimensional approach allows for the observation of the interaction between molecules and subphase at the air–water interface. Compiled in this review are studies which highlight the characterization of this protein using various surroundings and also observing the types of interactions it would have when at the biomembrane interface. Free-energy changes between molecules, packing status of the bulk analyte at the interface as well as phase transitions as the monolayer forms a more organized or aggregated state are just some of the characteristics which are observed through the Langmuir technique. This unique methodology demonstrates the chemical behavior and physical behavior of this protein at the phase boundary throughout the compression of the monolayer.Display Omitted
Keywords: Human serum albumin; Bovine serum albumin; Langmuir monolayer; Langmuir–Blodgett films; Mixed monolayers;

Biological applications of LbL multilayer capsules: From drug delivery to sensing by Loretta Laureana del Mercato; Marzia Maria Ferraro; Francesca Baldassarre; Serena Mancarella; Valentina Greco; Ross Rinaldi; Stefano Leporatti (139-154).
Polyelectrolyte multilayer (PEM) capsules engineered with active elements for targeting, labeling, sensing and delivery hold great promise for the controlled delivery of drugs and the development of new sensing platforms. PEM capsules composed of biodegradable polyelectrolytes are fabricated for intracellular delivery of encapsulated cargo (for example peptides, enzymes, DNA, and drugs) through gradual biodegradation of the shell components. PEM capsules with shells responsive to environmental or physical stimuli are exploited to control drug release. In the presence of appropriate triggers (e.g., pH variation or light irradiation) the pores of the multilayer shell are unlocked, leading to the controlled release of encapsulated cargos. By loading sensing elements in the capsules interior, PEM capsules sensitive to biological analytes, such as ions and metabolites, are assembled and used to detect analyte concentration changes in the surrounding environment. This Review aims to evaluate the current state of PEM capsules for drug delivery and sensing applications.Display Omitted
Keywords: Layer-by-Layer; Polymer capsules; Drug delivery; Cancer therapy; Biosensing; Optical reporters;

In the past decade, mesoporous silica nanoparticles (MSNs) as nanocarriers have showed much potential in advanced nanomaterials due to their large surface area and pore volume. Especially, more and more MSNs based nanodevices have been designed as efficient drug delivery systems (DDSs) or biosensors. In this paper, lipid, protein and poly(NIPAM) coated MSNs are reviewed from the preparation, properties and their potential application. We also introduce the preparative methods including physical adsorption, covalent binding and self-assembly on the MSNs' surfaces. Furthermore, the interaction between the aimed cells and these molecular modified MSNs is discussed. We also demonstrate their typical applications, such as photodynamic therapy, bioimaging, controlled release and selective recognition in biomedical field.Display Omitted
Keywords: Lipids; Protein; Poly(NIPAM); Mesoporous silica nanoparticles; Biomedical application;

Controllable metal-enhanced fluorescence in organized films and colloidal system by Qianling Cui; Fang He; Lidong Li; Helmuth Möhwald (164-177).
In recent years, considerable efforts have been devoted to better understand the unique emission properties of fluorophores enhanced by the localized surface plasmon resonance of metal nanoparticles (NPs), due to the widespread applications of fluorescence techniques. It is demonstrated by experiment and theoretical calculation that the enhancement efficiency strongly depends on the morphology of the metal NPs, the spectral overlap between metal and fluorophores, the separation distance between them, and other factors. Among these aspects to be considered are suitable spacer material and assembling methods to control the spatial arrangement of plasmonic NPs and fluorophore with proper optical properties and interactions. In this contribution, we provide a brief overview on recent progress of metal-enhanced fluorescence in organized films and colloidal systems.Display Omitted
Keywords: Fluorescence; Self-assembly; Multilayers; Nanoparticles; Polyelectrolytes;

Polymer multilayered hollow microspheres prepared by layer-by-layer (LbL) self-assembly attract more and more interest due to their unique application, especially as drug delivery system (DDS). Unfortunately, the multilayered hollow microspheres assembled via weak linkages could fuse and/or aggregate in high ionic strength media or strong acidic or basic media. This severely restricts the practical applications of the multilayered hollow microspheres as DDS in human physiological medium. In the present work, the progress in stabilization of the multilayered hollow microspheres is reviewed, with emphasis on the assembling process and their crosslinking mechanism.Display Omitted
Keywords: Multilayered hollow microspheres; Layer-by-layer self-assembly; Stabilization; Stimuli-responsive; Drug delivery system;

Clay nanotube encapsulation for functional biocomposites by Yuri Lvov; Artem Aerov; Rawil Fakhrullin (189-198).
Natural halloysite clay nanotubes with 50 nm outer- and 15 nm inner- diameters are described as miniature vehicles for sustained release of drugs and proteins. The release time may be adjusted from 10 to 200 h with the tube surface polymeric coating. An explanation of sustained release through locking electrical potential at the nanotube ends is suggested. These biocompatible ceramic tubes may be also used for architectural construction of nanoshells on microbes through alternation with polycations to enhance the intrinsic properties of biological cells. Halloysite nanotubes (pristine or drug-loaded) are well mixable with polar and low-polar polymers allowing for functional biocomposites with enhanced mechanical strength, adhesivity and slow release of drugs or other chemical agents. Halloysite is nontoxic abundantly available from natural deposit material which does not require exfoliation or other complicated energy consuming processing.Display Omitted
Keywords: Halloysite clay nanotubes; Nanosafety; Sustained release; Drugs; Enzymes; Microbial shells;

Vibrational spectroscopy for probing molecular-level interactions in organic films mimicking biointerfaces by Diogo Volpati; Pedro H.B. Aoki; Priscila Alessio; Felippe J. Pavinatto; Paulo B. Miranda; Carlos J.L. Constantino; Osvaldo N. Oliveira (199-215).
Investigation into nanostructured organic films has served many purposes, including the design of functionalized surfaces that may be applied in biomedical devices and tissue engineering and for studying physiological processes depending on the interaction with cell membranes. Of particular relevance are Langmuir monolayers, Langmuir–Blodgett (LB) and layer-by-layer (LbL) films used to simulate biological interfaces. In this review, we shall focus on the use of vibrational spectroscopy methods to probe molecular-level interactions at biomimetic interfaces, with special emphasis on three surface-specific techniques, namely sum frequency generation (SFG), polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and surface-enhanced Raman scattering (SERS). The two types of systems selected for exemplifying the potential of the methods are the cell membrane models and the functionalized surfaces with biomolecules. Examples will be given on how SFG and PM-IRRAS can be combined to determine the effects from biomolecules on cell membrane models, which include determination of the orientation and preservation of secondary structure. Crucial information for the action of biomolecules on model membranes has also been obtained with PM-IRRAS, as is the case of chitosan removing proteins from the membrane. SERS will be shown as promising for enabling detection limits down to the single-molecule level. The strengths and limitations of these methods will also be discussed, in addition to the prospects for the near future.The use of vibrational spectroscopy techniques, including sum-frequency generation (SFG), polarization-modulated infrared reflection-absorption (PM-IRRAS) and Surface Enhanced Raman Scattering (SERS), is reviewed for the study of biointerfaces.Display Omitted
Keywords: Thin nanostructured films; Vibrational spectroscopy; Cell-membrane models; Surface functionalization; Biomolecules; Biointerfaces;

Self-assembled chitin nanofibers and applications by Marco Rolandi; Ranieri Rolandi (216-222).
Self-assembled natural biomaterials offer a variety of ready-made nanostructures available for basic science research and technological applications. Most natural structural materials are made of self-assembled nanofibers with diameters in the nanometer range. Among these materials, chitin is the second most abundant polysaccharide after cellulose and is part of the exoskeleton or arthropods and mollusk shells. Chitin has several desirable properties as a biomaterial including mechanical strength, chemical and thermal stability, and biocompatibility. However, chitin insolubility in most organic solvents has somewhat limited its use. In this research highlight, we describe recent developments in producing biogenic chitin nanofibers using self-assembly from a solution of squid pen β-chitin in hexafluoroisopropanol. With this solution based assembly, we have demonstrated chitin-silk composite self-assembly, chitin nanofiber fabrication across length-scales, and manufacturing of chitin nanofiber substrates for tissue engineering.Display Omitted
Keywords: Chitin; Chitosan; Nanofiber; Self-assembly; Chitin nanofiber ink;

Comparison between the behavior of different hydrophobic peptides allowing membrane anchoring of proteins by Mustapha Lhor; Sarah C. Bernier; Habib Horchani; Sylvain Bussières; Line Cantin; Bernard Desbat; Christian Salesse (223-239).
Membrane binding of proteins such as short chain dehydrogenase reductases or tail-anchored proteins relies on their N- and/or C-terminal hydrophobic transmembrane segment. In this review, we propose guidelines to characterize such hydrophobic peptide segments using spectroscopic and biophysical measurements. The secondary structure content of the C-terminal peptides of retinol dehydrogenase 8, RGS9-1 anchor protein, lecithin retinol acyl transferase, and of the N-terminal peptide of retinol dehydrogenase 11 has been deduced by prediction tools from their primary sequence as well as by using infrared or circular dichroism analyses. Depending on the solvent and the solubilization method, significant structural differences were observed, often involving α-helices. The helical structure of these peptides was found to be consistent with their presumed membrane binding. Langmuir monolayers have been used as membrane models to study lipid–peptide interactions. The values of maximum insertion pressure obtained for all peptides using a monolayer of 1,2-dioleoyl-sn-glycero-3-phospho-ethanolamine (DOPE) are larger than the estimated lateral pressure of membranes, thus suggesting that they bind membranes. Polarization modulation infrared reflection absorption spectroscopy has been used to determine the structure and orientation of these peptides in the absence and in the presence of a DOPE monolayer. This lipid induced an increase or a decrease in the organization of the peptide secondary structure. Further measurements are necessary using other lipids to better understand the membrane interactions of these peptides.Display Omitted
Keywords: Transmembrane hydrophobic peptide; Lecithin retinol acyltransferase; Retinol dehydrogenase; R9AP; Monolayer; Circular dichroism and infrared spectroscopy;

A bottom-up approach to understanding protein layer formation at solid–liquid interfaces by Mark Kastantin; Blake B. Langdon; Daniel K. Schwartz (240-252).
A common goal across different fields (e.g. separations, biosensors, biomaterials, pharmaceuticals) is to understand how protein behavior at solid–liquid interfaces is affected by environmental conditions. Temperature, pH, ionic strength, and the chemical and physical properties of the solid surface, among many factors, can control microscopic protein dynamics (e.g. adsorption, desorption, diffusion, aggregation) that contribute to macroscopic properties like time-dependent total protein surface coverage and protein structure. These relationships are typically studied through a top-down approach in which macroscopic observations are explained using analytical models that are based upon reasonable, but not universally true, simplifying assumptions about microscopic protein dynamics. Conclusions connecting microscopic dynamics to environmental factors can be heavily biased by potentially incorrect assumptions. In contrast, more complicated models avoid several of the common assumptions but require many parameters that have overlapping effects on predictions of macroscopic, average protein properties. Consequently, these models are poorly suited for the top-down approach. Because the sophistication incorporated into these models may ultimately prove essential to understanding interfacial protein behavior, this article proposes a bottom-up approach in which direct observations of microscopic protein dynamics specify parameters in complicated models, which then generate macroscopic predictions to compare with experiment. In this framework, single-molecule tracking has proven capable of making direct measurements of microscopic protein dynamics, but must be complemented by modeling to combine and extrapolate many independent microscopic observations to the macro-scale. The bottom-up approach is expected to better connect environmental factors to macroscopic protein behavior, thereby guiding rational choices that promote desirable protein behaviors.Display Omitted
Keywords: Adsorption; Desorption; Interfacial diffusion; Protein aggregation; Single-molecule;

Colloidal micro- and nano-particles as templates for polyelectrolyte multilayer capsules by Bogdan V. Parakhonskiy; Alexey M. Yashchenok; Manfred Konrad; Andre G. Skirtach (253-264).
Colloidal particles play an important role in various areas of material and pharmaceutical sciences, biotechnology, and biomedicine. In this overview we describe micro- and nano-particles used for the preparation of polyelectrolyte multilayer capsules and as drug delivery vehicles. An essential feature of polyelectrolyte multilayer capsule preparations is the ability to adsorb polymeric layers onto colloidal particles or templates followed by dissolution of these templates. The choice of the template is determined by various physico-chemical conditions: solvent needed for dissolution, porosity, aggregation tendency, as well as release of materials from capsules. Historically, the first templates were based on melamine formaldehyde, later evolving towards more elaborate materials such as silica and calcium carbonate. Their advantages and disadvantages are discussed here in comparison to non-particulate templates such as red blood cells. Further steps in this area include development of anisotropic particles, which themselves can serve as delivery carriers. We provide insights into application of particles as drug delivery carriers in comparison to microcapsules templated on them.Display Omitted
Keywords: Microcapsules; Colloidal particles; Templates; Polyelectrolytes; Multilayers;

The use of highly brilliant synchrotron light sources in the middle of the 1980s for X-ray diffraction has revolutionized the research of condensed monolayers. Since then, monolayers gained popularity as convenient quasi two-dimensional model systems widely used in biophysics and material science. This review focuses on structures observed in one-component phospholipid monolayers used as simplified two-dimensional models of biological membranes. In a monolayer system the phase transitions can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction. Competing interactions between the different parts of the molecule are responsible for the different monolayer structures. These forces can be modified by chemical variations of the hydrophobic chain region, of the hydrophilic head group region or of the interfacial region between chains and head groups. Modifications of monolayer structures triggered by changes of the chemical structure of double-chain phospholipids are highlighted in this paper.Display Omitted
Keywords: GIXD (grazing incidence X-ray diffraction); Monolayers; Structures; Phospholipids; Chains; Head groups;

Layer-by-layer assembled polyelectrolyte capsules with well-controlled architectures and great versatility have been the subject of great interest, due to their unique advantages and tremendous potentials of being excellent candidates in multidisciplinary fields. UV light responsive microcapsules, as one class of the stimuli responsive capsules, possess the abilities to active their functionalities by responding to the UV stimulus remotely without requirement of direct contact or interaction. Therefore, any advances in this field will be of great value for the establishment of approaches to fabricate UV responsive polyelectrolyte capsules for desired uses. This review presents current development of UV responsive capsules, with emphasis on the underlying design strategies and their potential applications as delivery vesicles. In particular, UV-stimulated capsule functionalities, such as cargo encapsulation, release and combined multifunctionalities by the multilayers, have been addressed.Display Omitted
Keywords: Polyelectrolyte microcapsules; Stimuli responsive; Encapsulation; Release; UV irradiation;

We present a critical review of recent work related to the assembly of multicompartment liposome clusters using nucleic acids as a specific recognition unit to link liposomal modules. The asymmetry in nucleic acid binding to its non-self complementary strand allows the controlled association of different compartmental modules into composite systems. These biomimetic multicompartment architectures could have future applications in chemical process control, drug delivery and synthetic biology. We assess the different methods of anchoring DNA to lipid membrane surfaces and discuss how lipid and DNA properties can be tuned to control the morphology and properties of liposome superstructures. We consider different methods for chemical communication between the contents of liposomal compartments within these clusters and assess the progress towards making this chemical mixing efficient, switchable and chemically specific. Finally, given the current state of the art, we assess the outlook for future developments towards functional modular networks of liposomes.Display Omitted
Keywords: Lipid vesicles; DNA amphiphiles; Directed assembly; Compartmentalization; Bionanotechnology;

Porous CaCO3 vaterite microparticles have been introduced a decade ago as sacrificial cores and becoming nowadays as one of the most popular templates to encapsulate bioactive molecules. This is due to the following beneficial features: i) mild decomposition conditions, ii) highly developed surface area, and iii) controlled size as well as easy and chip preparation. Such properties allow one to template and design particles with well tuned material properties in terms of composition, structure, functionality — the parameters crucially important for bioapplications. This review presents a recent progress in utilizing the CaCO3 cores for the assembly of micrometer-sized beads and capsules with encapsulated both small drugs and large biomacromolecules. Bioapplications of all the particles for drug delivery, biotechnology, and biosensing as well as future perspectives for templating are addressed.Display Omitted
Keywords: CaCO3; Drug delivery; Microparticle; Encapsulation; Porous template;

About different types of water in swollen polyelectrolyte multilayers by Ralf Koehler; Roland Steitz; Regine von Klitzing (325-331).
The review addresses swelling of polyelectrolyte multilayers in water. Different models for the determination of the water content are compared. It is clearly shown that voids under dry conditions present cavities for water which contribute to the water content of the multilayer in the swollen state. This so-called “void water” does not lead to any changes in thickness but in scattering length density during swelling. The “swelling water” leads to both changes in scattering length density and in thickness. Depending on the preparation conditions like the type polymers, polymer charge density, ionic strength and type of salt the ratio of “void water” differs between 1 and 15 vol.% while the amount of “swelling water” is of several ten's of vol.%.Display Omitted
Keywords: Polyeletrolyte multilayers; Water content; Neutron reflectivity; Neutron reflectometry; Void water; Ion specific effects;

Ultrathin organic semiconductor films — Soft matter effect by Tong Wang; Donghang Yan (332-346).
The growth of organic semiconductor thin films has been a crucial issue in organic electronics, especially the growth at the early stages. The thin-film phase has been found to be a common phenomenon in many organic semiconductor thin films, which is closely related with the weak van der Waals interaction between organic molecules, the long-range interaction between organic molecules and the substrate, as well as the soft matter characteristics of ultrathin films. The growth behavior and soft matter characteristics of the thin-film phase have great effects on thin film morphology and structure, for example, the formation and coalescence of grain boundaries, which further influences the performance of organic electronic devices. The understanding of thin-film phase and its intrinsic quality is necessary for fabricating large-size, highly ordered, continuous and defect-free ultrathin films. This review will focus on the growth behavior of organic ultrathin films, i.e., the level of the first several molecular layers, and provide an overview of the soft matter characteristics.Display Omitted
Keywords: Soft matter; Organic semiconductor; Ultrathin film; Thin film growth; Rod-like molecule;

Two-dimensional (2D) nanomaterials with the thickness at atomic level are promising candidates for a wide range of applications, and now reach the point to create diversified 2D architectures. The colloidal synthesis route is powerful to produce crystalline nanosheets, nanoribbons and nanoplatelets, and the self-assembly strategy is robust to integrate the functionalities of different nano-objects. In this review, we bridge the colloidal synthesis of nanosheets and the 2D self-assembly of nanoclusters (NCs) with the aim to further optimize the physical and chemical properties of 2D nanomaterials. Ultrasmall NCs, the intermediate for synthesizing nanosheets, are highlighted to show the similarity of 2D crystallization and 2D self-assembly. The modification of conventional 2D colloidal synthesis route greatly permits the controlled self-assembly of NCs into free-standing monolayers in colloidal solutions.The constructing of two-dimensional (2D) nanostructures by combining the colloidal synthesis of crystalline nanosheets and self-assembly strategy are summarized. Ultrasmall nanoclusters, the intermediates for synthesizing nanosheets, are highlighted to show the similarity of 2D crystallization and 2D self-assembly. The self-assembly strategy are powerful for preparing nanocluster monolayers with the thickness at atomic level.Display Omitted
Keywords: Nanocluster; Self-assembly; Monolayer; Colloidal synthesis; Nanosheet;

Self-assemblies of luminescent rare earth compounds in capsules and multilayers by Renjie Zhang; Juanjuan Shang; Jing Xin; Beibei Xie; Ya Li; Helmuth Möhwald (361-375).
This review addresses luminescent rare earth compounds assembled in microcapsules as well as in planar films fabricated by the layer-by-layer (LbL) technique, the Langmuir–Blodgett (LB) method and in self-assembled monolayers. Chemical precipitation, electrostatic, van der Waals interactions and covalent bonds are involved in the assembly of these compounds. Self-organized ring patterns of rare earth complexes in Langmuir monolayers and on planar surfaces with stripe patterns, as well as fluorescence enhancement due to donor–acceptor pairs, microcavities, enrichment of rare earth compounds, and shell protection against water are described. Recent information on the tuning of luminescence intensity and multicolors by the excitation wavelength and the ratio of rare earth ions, respectively, are also reviewed. Potential applications of luminescent rare earth complex assemblies serving as biological probes, temperature and gas sensors are pointed out.Self-assemblies of luminescent rare earth compounds in capsules and multilayersRenjie Zhang, Juanjuan Shang, Jing Xin, Beibei Xie, Ya Li, Helmuth MöhwaldDisplay Omitted
Keywords: Rare earth compounds; Microcapsules; Layer-by-layer (LbL); Langmuir–Blodgett (LB) films; Self-assembled monolayers (SAMs); Fluorescence;