Different Microtubule Structures Assembled by Kinesin Motors.

The microtubule-kinesin system is used to form microtubule-based structures via microtubule gliding motility. On the kinesin-coated surface, the microtubules can be easily assembled into stable micro- and nanostructures like circles and microtubule bundles using the streptavidin-biotin system. Furthermore, these microtubules structures can still retain performance with kinesin motor movement in spite of different velocities. Collisions bear responsibility for the majority of events leading to circle formation. By taking advantage of biological substances, some micro- or nanostructures, which are difficult to fabricate by artificial processes, can be easily obtained.

Elastic to Plastic Deformation in Uniaxially Stressed Polylelectrolyte Multilayer Films.

Polyelectrolyte multilayer (PEM) are thin polymeric films produced by alternating adsorption of positively and negatively charged polyelectrolytes (PE) on a substrate. These films are considered drug delivery agents as well as coating material for implants, due to their antibiofouling and biologically benign properties. For these reasons the film mechanical properties as well as response to mechanical stress are important measurement parameters. Especially intriguing is the correlation of the mechanical properties of PEM on macroscopic level with the structure of PEM on molecular level, which is addressed here for the first time. This study investigates PEM from PDADMA/PSS produced by spraying technique with neutron and X-ray reflectometry. Reflectometry technique provides precise information on thickness and density (i.e., electron density or scattering length density, respectively), and, this way, allows to conclude on changes in film composition. Thus, neutron and X-ray reflectometry technique is suitable to investigate the overall and the internal transformations, which PEM films might undergo upon exposure to mechanical load. During uniaxial elongation two regimes of PEM-deformation can be observed: An elastic regime at small elongations (below ca. 0.2%), which is characterized by a reversible change of film thickness, and a plastic regime with a permanent change above this limit. Both regimes have in common, that the mechanical load induces an increase of the film thickness, which is accompanied by an uptake of water from the surrounding atmosphere. The strain causes a molecular rearrangement within the PEM-structure of stratified layers, which, even in elastic regime, is permanent, although the thickness change remains reversible.

A Two-Dimensional Polymer Synthesized at the Air/Water Interface.

A trifunctional, partially fluorinated anthracene-substituted triptycene monomer was spread at an air/water interface into a monolayer, which was transformed into a long-range-ordered 2D polymer by irradiation with a standard UV lamp. The polymer was analyzed by Brewster angle microscopy, scanning tunneling microscopy measurements, and non-contact atomic force microscopy, which confirmed the generation of a network structure with lattice parameters that are virtually identical to a structural model network based on X-ray diffractometry of a closely related 2D polymer. The nc-AFM images highlight the long-range order over areas of at least 300×300 nm2 . As required for a 2D polymer, the pore sizes are monodisperse, except for the regions where the network is somewhat stretched because it spans over protrusions. Together with a previous report on the nature of the cross-links in this network, the structural information provided herein leaves no doubt that a 2D polymer has been synthesized under ambient conditions at an air/water interface.

Anisotropic Self-Assembly of Organic-Inorganic Hybrid Microtoroids.

Toroidal structures based on self-assembly of predesigned building blocks are well-established in the literature, but spontaneous self-organization to prepare such structures has not been reported to date. Here, organic-inorganic hybrid microtoroids synthesized by simultaneous coordination-driven assembly of amphiphilic molecules and hydrophilic polymers are reported. Mixing amphiphilic molecules with iron(III) chloride and hydrophilic polymers in water leads, within minutes, to the formation of starlike nanostructures. A spontaneous self-organization of these nanostructures is then triggered to form stable hybrid microtoroids. Interestingly, the toroids exhibit anisotropic hierarchical growth, giving rise to a layered toroidal framework. These microstructures are mechanically robust and can act as templates to host metallic nanoparticles such as gold and silver. Understanding the nature of spontaneous assembly driven by coordination multiple non-covalent interactions can help explain the well-ordered complexity of many biological organisms in addition to expanding the available tools to mimic such structures at a molecular level.

Self-Regulated Ion Permeation through Extraction Membranes.

Separation of rare earth compounds from water into an organic phase in practical cases requires the use of specific ion binding ligands in high concentrations. These tend to form complex liquid crystalline phases preferentially at ion-rich locations inside a pertraction membrane. They form a blocking layer above an ion concentration threshold, which is experimentally characterized. It is shown to limit the flux through the membrane, which is studied for the application of rare earth recycling, an example being the phase transfer of Nd from water into organic phase. This feedback leads to a stationary membrane permeation rate that can be modeled without any free parameters in very good agreement with experiment. The ion-specific formation and dissolution of the blocking layer, a feature found also in nature, and its control suggest further studies to enhance permeation as well as its selectivity control.

Self-Assembled Injectable Peptide Hydrogels Capable of Triggering Antitumor Immune Response.

Self-assembled peptide hydrogels are particularly appealing for drug delivery, tissue engineering, and antitumor therapy due to various advantageous features including excellent biocompatibility and biodegradability, defined molecular and higher organized structures, and easy availability. However, the poor mechanical and rheological properties of assembled peptide hydrogels cause difficulties in injection, thus limiting further applications. Herein, injectable peptide-based hydrogels with tunable mechanical and rheological properties were obtained by combination with a positively charged poly peptide (poly-l-lysine, PLL). Electrostatic coupling between PLL and a self-assembling dipeptide (Fmoc-FF) provides a smart switch to enable the fibrous hydrogels to be shear-thinning and self-healing, thus leading to the formation of supramolecular hydrogels with rheological properties suitable for injection. The latter can be flexibly adjusted by merely varying the concentration or the molecular weight of the polypeptide to satisfy a variety of requirements in biological applications. The hydrogels, consisting of helical nanofibers stabilized with disulfide bonds, are prepared and further injected for antitumor therapy. The results demonstrate that the helical fibrous hydrogel, without the addition of antigens, immune regulatory factors, and adjuvants, can activate T cell response and efficiently suppress tumor growth. Therefore, injectable hydrogels self-assembled by a combination of small peptides and biomacromolecules present a great potential for biomedical applications, especially for development of a new type of immuno-responsive materials toward antitumor therapy.

Ultrasonic Mastering of Filter Flow and Antifouling of Renewable Resources.

Inadequate access to pure water and sanitation requires new cost-effective, ergonomic methods with less consumption of energy and chemicals, leaving the environment cleaner and sustainable. Among such methods, ultrasound is a unique means to control the physics and chemistry of complex fluids (wastewater) with excellent performance regarding mass transfer, cleaning, and disinfection. In membrane filtration processes, it overcomes diffusion limits and can accelerate the fluid flow towards the filter preventing antifouling. Here, we outline the current state of knowledge and technological design, with a focus on physicochemical strategies of ultrasound for water cleaning. We highlight important parameters of ultrasound for the delivery of a fluid flow from a technical perspective employing principles of physics and chemistry. By introducing various ultrasonic methods, involving bubbles or cavitation in combination with external fields, we show advancements in flow acceleration and mass transportation to the filter. In most cases we emphasize the main role of streaming and the impact of cavitation with a perspective to prevent and remove fouling deposits during the flow. We also elaborate on the deficiencies of present technologies and on problems to be solved to achieve a wide-spread application.

Effect of Cavitation Bubble Collapse on the Modification of Solids: Crystallization Aspects.

This review examines the concepts how cavitation bubble collapse affects crystalline structure, the crystallization of newly formed structures, and recrystallization. Although this subject can be discussed in a broad sense across the area of metastable crystallization, our main focus is discussing specific examples of the inorganic solids: metal, intermetallics, metal oxides, and silicon. First, the temperature up to which ultrasound heats solids is discussed. Cavitation-induced changes in the crystal size of intermetallic phases in binary AlNi (50 wt % of Ni) alloys allow an estimation of local temperatures on surfaces and in bulk material. The interplay between atomic solid-state diffusion and recrystallization during bubble collapses in heterogeneous systems is revealed. Furthermore, cavitation triggered red/ox processes at solid/liquid interfaces and their influence on recrystallization are discussed for copper aluminum nanocomposites, zinc, titanium, magnesium-based materials, and silicon. Cavitation-driven highly nonequilibrium conditions can affect the thermodynamics and kinetics of mesoscopic phase formation in heterogeneous systems and in many cases boost the macroscopic performance of composite materials, notably in catalytic alloy and photocatalytic semiconductor oxide properties, corrosion resistance, nanostructured surface biocompatibility, and optical properties.

MHz Ultrasound Induced Roughness of Fluid Interfaces.

The interface between two fluids is never flat at the nanoscale, and this is important for transport across interfaces. In the absence of any external field, the surface roughness is due to thermally excited capillary waves possessing subnanometric amplitudes in the case of simple liquids. Here, we investigate the effect of ultrasound on the surface roughness of liquid-gas and liquid-liquid interfaces. Megahertz (MHz) frequency ultrasound was applied normal to the interface at relatively low ultrasonic pressures (<0.6 MPa), and the amplitudes of surface fluctuations have been measured by light reflectivity and ellipsometry. We found a dramatic enhancement of surface roughness, roughly linear with intensity, with vertical displacements of the interface as high as 50-100 nm. As a consequence, the effective contact area between two fluids can be increased by ultrasound. This result has a clear impact for enhancing interface based processes such as mass or heat transfer.

Ultrasonically treated liquid interfaces for progress in cleaning and separation processes.

Ultrasound and acoustic cavitation enable ergonomic and eco-friendly treatment of complex liquids with outstanding performance in cleaning, separation and recycling of resources. A key element of ultrasonic-based technology is the high speed of mixing by streams, flows and jets (or shock waves), which is accompanied by sonochemical reactions. Mass transfer across the phase boundary with a great variety of catalytic processes is substantially enhanced through acoustic emulsification. Encapsulation, separation and recovery of liquids are fast with high production yield if applied by ultrasound. Here we discuss the state of knowledge of these processes by ultrasound and acoustic cavitation from a perspective of a physico-chemical model in order to predict and control the outcome. We focus on the physical interpretation and quantification of ultrasonic parameters and properties of liquids to understand the chemistry of liquid/liquid interfaces in acoustic fields. The roles of thermodynamic enthalpy and entropy (incl. Laplace and osmotic pressure) in the context of sonochemical reactions (separation, catalysis, degradation, cross-linking, ion exchange and phase transfer) are outlined. The synergy of ultrasound and electric fields or continuous flow chemistry for cleaning and separation via emulsification is highlighted by specific strategies involving polymers and ultrasonic membranes.

Molecular and mesoscale mechanism for hierarchical self-assembly of dipeptide and porphyrin light-harvesting system.

A multi-scale theoretical investigation of dipeptide-porphyrin co-assembly systems has been carried out to establish such understanding, where two different types of the dipeptides, dilysine (KK(3+)) and diphenylalanine (FF(+)) are compared on tuning the porphyrin organization. Density functional theory results reveal that the electrostatic attraction between different functional groups has significantly strengthened the hydrogen bonds between them, which are considered as the driving force of the self-assembly at the molecular level. All-atom molecular dynamics (MD) simulation further indicates that the formation of the core-shell nanorods is driven and stabilized by the hydrophobic interaction between dipeptides and negatively charged porphyrin (H2TPPS(2-)), where the packed porphyrins stay inside as the core of the nanorods and the hydrophilic groups (amino- and carboxyl-groups) as the shell. With stronger hydrophobicity, FF(+) is more likely to insert into the porphyrin aggregates and build crosslinks than KK(3+). Moreover, dissipative particle dynamics (DPD) simulation suggests equilibrium morphologies with different dipeptides, where KK(3+)-H2TPPS(2-) assembled in fiber bundles, whereas FF(+)-H2TPPS(2-) assembled as microspheres, corresponding to the different packing behavior in MD simulations. The consistency of these results at different scales is discussed. The method used in this work could be extended for studying similar issues in hierarchical self-assembly of building blocks such biomaterials.

Simple Peptide-Tuned Self-Assembly of Photosensitizers towards Anticancer Photodynamic Therapy.

Peptide-tuned self-assembly of functional components offers a strategy towards improved properties and unique functions of materials, but the requirement of many different functions and a lack of understanding of complex structures present a high barrier for applications. Herein, we report a photosensitive drug delivery system for photodynamic therapy (PDT) by a simple dipeptide- or amphiphilic amino-acid-tuned self-assembly of photosensitizers (PSs). The assembled nanodrugs exhibit multiple favorable therapeutic features, including tunable size, high loading efficiency, and on-demand drug release responding to pH, surfactant, and enzyme stimuli, as well as preferable cellular uptake and biodistribution. These features result in greatly enhanced PDT efficacy in vitro and in vivo, leading to almost complete tumor eradication in mice receiving a single drug dose and a single exposure to light.

Mimicking Primitive Photobacteria: Sustainable Hydrogen Evolution Based on Peptide-Porphyrin Co-Assemblies with a Self-Mineralized Reaction Center.

Molecular evolution, with self-organization of simple molecules towards complex functional systems, provides a new strategy for biomimetic architectonics and perspectives for understanding the complex processes of life. However, there remain many challenges to fabrication of systems comprising different types of units, which interact with one another to perform desired functions. Challenges arise from a lack of stability, dynamic properties, and functionalities that reconcile with a given environment. A co-assembling fiber system composed of simple peptide and porphyrin is presented. This material is considered a prebiotic assembly of molecules that can be rather stable and flexibly self-functionalized with the assistance of visible light in a "prebiotic soup"; acidic (pH 2), hot (70 °C), and mineral-containing (Na(+) , Ti(4+) , Pt(2+) , and so forth) water. The co-assembled peptide-porphyrin fiber, with self-mineralized reaction centers, may serve as a primitive photobacteria-like cellular model to achieve light harvesting, energy transfer, and ultimately sustainable hydrogen evolution.

Light-Induced Water Splitting Causes High-Amplitude Oscillation of pH-Sensitive Layer-by-Layer Assemblies on TiO2.

We introduce a simple concept of a light induced pH change, followed by high amplitude manipulation of the mechanical properties of an adjacent polymer film. Irradiation of a titania surface is known to cause water splitting, and this can be used to reduce the environmental pH to pH 4. The mechanical modulus of an adjacent pH sensitive polymer film can thus be changed by more than an order of magnitude. The changes can be localized, maintained for hours and repeated without material destruction.

Optical heating and temperature determination of core-shell gold nanoparticles and single-walled carbon nanotube microparticles.

The real-time temperature measurement of nanostructured materials is particularly attractive in view of increasing needs of local temperature probing with high sensitivity and resolution in nanoelectronics, integrated photonics, and biomedicine. Light-induced heating and Raman scattering of single-walled carbon nanotubes with adsorbed gold nanoparticles decorating silica microparticles are reported, by both green and near IR lasers. The plasmonic shell is used as nanoheater, while the single-walled carbon nanotubes are Raman active and serve as a thermometer. Stokes and Anti-Stokes Raman spectra of single-walled carbon nanotubes serve to estimate the effective light-induced temperature rise on the metal nanoparticles. The temperature rise is constant with time, indicating stability of the adsorption density. The effective temperatures derived from Stokes and Anti-Stokes intensities are correlated with those measured in a heating stage. The resolution of the thermal experiments in our study was found to be 5-40 K.

The Influence of Long-Range Surface Forces on the Contact Angle of Nanometric Droplets and Bubbles.

For a droplet or a bubble of dimensions below 100 nm, long-range surface forces such as long-range van der Waals forces can compete with capillarity, which leads to a size dependence of the contact angle. This is discussed in this work, where we also show that the effect cannot simply be described by a normalized line tension. We calculate interfacial profiles for typical values of van der Waals forces and discuss the role of long-range surface forces on the contact angle of nanobubbles and nanodrops.

Periodic Precipitation Patterns during Coalescence of Reacting Sessile Droplets.

The coalescence behavior of two sessile drops that contain different chemical reactants (cerium nitrate and oxalic acid) and its impact on the formation of the solid precipitate (cerium oxalate) are investigated. With different liquids, the surface tension difference in the moment of drop-drop contact can induce a Marangoni flow. This flow can strongly influence the drop-drop coalescence behavior and thus, with reacting liquids, also the reaction and its products (through the liquid mixing). In our study we find three distinctly different coalescence behaviors ("barrier", "intermediate", "noncoalescence"), in contrast to only two behaviors that were observed in the case of nonreacting liquids. The amount of liquid mixing and thus the precipitation rate are very different for the three cases. The "intermediate" case, which exhibits the strongest mixing, has been studied in more detail. For high oxalic acid concentrations, mainly needle-like aggregates, and for low concentrations, mainly flower-like precipitate morphologies are obtained. In a transition range of the oxalic acid concentration, both morphologies can be produced. With the applied coalescence conditions, the different aggregate particles are arranged and fixed in a precipitate raft in a regular, periodic line pattern. This confirms the drop-drop coalescence configuration as a convection-reaction-diffusion system, which can have stationary as well as oscillatory behavior depending on the system parameters.

From Beetles in Nature to the Laboratory: Actuating Underwater Locomotion on Hydrophobic Surfaces.

The controlled wetting and dewetting of surfaces is a primary mechanism used by beetles in nature, such as the ladybird and the leaf beetle for underwater locomotion.1 Their adhesion to surfaces underwater is enabled through the attachment of bubbles trapped in their setae-covered legs. Locomotion, however, is performed by applying mechanical forces in order to move, attach, and detach the bubbles in a controlled manner. Under synthetic conditions, however, when a bubble is bound to a surface, it is nearly impossible to maneuver without the use of external stimuli. Thus, actuated wetting and dewetting of surfaces remain challenges. Here, electrowetting-on-dielectric (EWOD) is used for the manipulation of bubble-particle complexes on unpatterned surfaces. Bubbles nucleate on catalytic Janus disks adjacent to a hydrophobic surface. By changing the wettability of the surface through electrowetting, the bubbles show a variety of reactions, depending on the shape and periodicity of the electrical signal. Time-resolved (µs) imaging of bubble radial oscillations reveals possible mechanisms for the lateral mobility of bubbles on a surface under electrowetting: bubble instability is induced when electric pulses are carefully adjusted. This instability is used to control the surface-bound bubble locomotion and is described in terms of the change in surface energy. It is shown that a deterministic force applied normal can lead to a random walk of micrometer-sized bubbles by exploiting the phenomenon of contact angle hysteresis. Finally, bubble use in nature for underwater locomotion and the actuated bubble locomotion presented in this study are compared.

Distorted colloidal arrays as designed template.

In this paper, a novel type of colloidal template with broken symmetry was generated using commercial, inductively coupled plasma reactive ion etching (ICP-RIE). With proper but simple treatment, the traditional symmetric non-close-packed colloidal template evolves into an elliptical profile with high uniformity. This unique feature can add flexibility to colloidal lithography and/or other lithography techniques using colloidal particles as building blocks to fabricate nano-/micro-structures with broken symmetry. Beyond that the novel colloidal template we developed possesses on-site tunability, i.e. the transformability from a symmetric into an asymmetric template. Sandwich-type particles with eccentric features were fabricated utilizing this tunable template. This distinguishing feature will provide the possibility to fabricate structures with unique asymmetric features using one set of colloidal template, providing flexibility and broad tunability to enable nano-/micro-structure fabrication with colloidal templates.

Laser-induced fast fusion of gold nanoparticle-modified polyelectrolyte microcapsules.

In this study we investigated the effect of laser-induced membrane fusion of polyelectrolyte multilayer (PEM) based microcapsules bearing surface-attached gold nanoparticles (AuNPs) in aqueous media. We demonstrate that a dense coating of the capsules with AuNPs leads to enhanced light absorption, causing an increase of local temperature. This enhances the migration of polyelectrolytes within the PEMs and thus enables a complete fusion of two or more capsules. The encapsulated substances can achieve complete merging upon short-term laser irradiation (30 s, 30 mW @ 650 nm). The whole fusion process is followed by optical microscopy and scanning electron microscopy. In control experiments, microcapsules without AuNPs do not show a significant capsule fusion upon irradiation. It was also found that the duration of capsule fusion is affected by the density of AuNPs on the shell - the higher the density of AuNPs the shorter the fusion time. All these findings confirm that laser-induced microcapsule fusion is a new type of membrane fusion. This effect helps to study the interior exchange reactions of functional microcapsules, micro-reactors and drug transport across multilayers.