Soft Matter (v.8, #18)

Front cover (4835-4835).

Inside front cover (4836-4836).

Contents list (4837-4848).

Beyond the lipid-bilayer: interaction of polymers and nanoparticles with membranes by Matthias Schulz; Adekunle Olubummo; Wolfgang H. Binder (4849-4864).
Membranes can be fabricated either from lipid or polymer molecules, leading to the formation of liposomes or polymersomes. In all types of liposomal membranes, the issue of phase separation plays a central role not only in the membrane-formation itself, but also in the resulting structural features taking place within or at the surface of such membranes. When nanoparticles or polymers interact with lipid membranes, the final morphology is strongly determined by the charge, composition and size of the interacting components, which in turn induce phase separation processes. The present review assembles investigations on lipid/polymer/nanoparticle interaction with the main focus directed towards model membrane systems published in the recent literature starting from ∼2005, providing a deeper and more thorough understanding of these complex interactions and their effects on membrane properties.

Direct observation of columnar liquid crystal droplets by A. A. Verhoeff; H. N. W. Lekkerkerker (4865-4868).
While the columnar liquid crystalline phase in suspensions of plate-like colloids is by now well-established, little is known about the pathway leading to the formation of this highly ordered, self-assembled structure. Here, we present direct observations of the morphology and structure of micrometer-sized droplets of the columnar phase formed in the nematic phase in suspensions of colloidal gibbsite plates. From polarized light microscopy and optical Bragg reflection measurements we deduce that these droplets consist of stacks of platelets in a hexagonal arrangement, forming a disk-shaped droplet. We discuss the relation of this droplet structure to the nucleation pathway of the columnar phase and to the anisotropic nematic–columnar interfacial tension.

Thermoresponsive oligoprolines by Feng Chen; Xiuqiang Zhang; Wen Li; Kun Liu; Yifei Guo; Jiatao Yan; Afang Zhang (4869-4872).
Monodispersed oligoprolines decorated covalently with hydrophobic units show characteristic thermoresponsive behavior with fast and sharp phase transitions at certain concentrations. The phase transition temperatures are dependent on the shape and location of the hydrophobic units, and can be also tuned via supramolecular host–guest interactions.

Supramolecular hydrogels based on antimycobacterial amphiphiles by Andreas Bernet; Marina Behr; Hans-Werner Schmidt (4873-4876).
Synthetic modification of antimycobacterial 4-alkoxy-anilines yields low molecular weight amphiphiles. The bioactivity is retained in these amphiphiles and shows alkyl chain length specificity. The self-assembly behaviour in aqueous media was investigated. It was found that several of these new compounds are capable of forming thermoreversible supramolecular hydrogels in alkaline aqueous media. The initial drug can be released from the hydrogel by thermal hydrolysis.

Magnesium ions and alginate do form hydrogels: a rheological study by Fuat Topuz; Artur Henke; Walter Richtering; Jürgen Groll (4877-4881).
Our study shows that magnesium ions which have so far been considered as non-gelling ions for alginate do induce alginate gelation. Rheology is used to examine effects of alginate chemical composition as well as alginate and magnesium ion concentration. Gelation in this system occurs at ca. 5–10 times higher concentration of ions than reported for calcium-based gels. Alginate network formation with magnesium ions is very slow and is typically accomplished within 2–3 hours. Gelation with magnesium ions is also strongly dependent on alginate chemical composition as the presence of long guluronic units privileges faster gel formation.

Thermal and electrical laser tuning in liquid crystal blue phase I by Alfredo Mazzulla; Gia Petriashvili; Mario Ariosto Matranga; Maria Penelope De Santo; Riccardo Barberi (4882-4885).
Thermal and electrical tuning of laser emission from optically pumped blue phase I of dye-doped short pitch cholesteric mixtures have been achieved. Temperature changes or applied electric field to the liquid crystal cells induce structural changes in the blue phase configuration, producing a shift of the photonic band gap. The emission tunability in a structure that in addition allows multidirectional emission may herald a new age of multipurpose laser sources. Furthermore, the reversibility of the effect points out the potential applications of these soft photonic self-assembled materials.

Fractional Brownian motion in crowded fluids by Dominique Ernst; Marcel Hellmann; Jürgen Köhler; Matthias Weiss (4886-4889).
Diffusion in crowded fluids, e.g. in the cytoplasm of living cells, has frequently been reported to show anomalous characteristics (so-called ‘subdiffusion’). Several random walk models have been proposed to explain these observations, yet so far an experimentally supported decision in favor of one of these models has been lacking. Here, we show that experimentally obtained trajectories in a prototypical crowded fluid show an asphericity that is most consistent with the predictions of fractional Brownian motion, i.e. an anti-correlated, anti-persistent generalization of normal Brownian motion that is related to the fluid's viscoelasticity.

Cylinder-to-gyroid phase transition in a rod–coil diblock copolymer by Shih-Hsiang Lin; Chun-Chih Ho; Wei-Fang Su (4890-4893).
In this communication, the morphology of well-defined P3DDT-b-PMMA with a 65.2% PMMA coil volume fraction is revealed as a hexagonally packed cylinder structure by X-ray scattering experiments after thermal annealing. Upon heating, an order-to-order transition (OOT) between cylindrical and gyroidal structures is observed at temperatures above 170 °C. The evolution of the cylinder to the gyroid occurs while the crystalline structure of the P3DDT block disappears, suggesting the conformation of the P3DDT-b-PMMA at high temperatures is similar to coil–coil block copolymers. The phenomena reported here can provide a different viewpoint of the self-assembly behaviors of poly(3-alkylthiophene)-containing rod–coil block copolymers. The novel rare gyroid structure of this rod–coil copolymer is useful to fabricate long sought of bicontinuous structure for highly efficient polymer solar cells.

Texture defects in lipid membrane domains by Jes Dreier; Jonathan Brewer; Adam Cohen Simonsen (4894-4904).
Important aspects of lateral organization in biomembranes can be addressed in model systems. Recently, it has become clear from polarized fluorescence imaging and X-ray scattering that gel domains in bilayers may contain orientational texture related to the tilted acyl chains. Such internal structure of domains can be imaged in polarized 2-photon fluorescence microscopy using the Laurdan probe that aligns with the lipids. By imaging intensity variations as a function of the polarization angle, we map the lateral variations within domains. A Fourier analysis of the signal enables the texture to be obtained in single pixels. Here we show that gel domains display a complex pattern containing line defects and a pair of |m| = 1/2 point disclinations in the domain center. We perform a detailed image analysis of the line and point defects using gradient calculations. In contrast to results from Langmuir monolayers, the membrane texture vary radially and is continuous in the center and segmented near the periphery. A possible explanation is that bilayer domains are grown thermally whereas Langmuir monolayer domains grow isothermally upon compression. The defect lines show significant variation in the angle jump across the lines. We simulate the structure of the central disclination pair and the fit to the experimental data yields an offset angle of 60.5°± 6.5°. This indicates that the central defect has a conserved structure with an intermediate character between bend and splay.

Hierarchical gecko-inspired nanohairs with a high aspect ratio induced by nanoyielding by Dong Yun Lee; Dae Ho Lee; Seung Goo Lee; Kilwon Cho (4905-4910).
We present a simple method for fabricating hierarchical polymeric nanohairs using a multi-branched anodic aluminum oxide (AAO) template prepared by two-step anodization and barrier layer thinning processes. Combined with nanohair yielding of a polymeric material during peeling-off from the hydrophobically modified AAO template, elongated hierarchical nanohairs with a high aspect ratio were fabricated without fiber collapse, which showed excellent adhesive and frictional properties compared to other structures such as single-level nanohairs and hierarchical nanohairs with a low aspect ratio. Furthermore, this surface showed remarkable superhydrophobic properties similar to those of natural gecko foot hairs.

Dual signal glucose reporter based on inverse opal conducting hydrogel films by Lu Jin; Yuanjin Zhao; Xing Liu; Youli Wang; Baofen Ye; Zhuoying Xie; Zhongze Gu (4911-4917).
A novel glucose responsive hydrogel film possessing inverse opal structure and conducting property was developed, based on the principle of enzyme-catalytic redox reaction. The film can report glucose concentration via optical and electrochemical signals, respectively. To fabricate the sensor film, SiO2 crystalline colloidal array was utilized as a sacrificed template to endow the polyacrylamide(PAAm) hydrogel with non-closed-packed inverse opal structure, then conductive polymer (CP) poly(3,4-ethylenedioxythiophene) PEDOT was in situ chemically oxypolymerized to form interpenetrated network (IPN) within the hydrogel. The supporting matrix was activated by partial hydrolysis of amide groups on the backbone, to serve as bonding sites for glucose oxidase (GOx) and ion responsive elements. The changes in the hydrogel microenvironment caused by the catalytic product of glucose induced shrinkage of the hydrogel and a corresponding blue shift of the reflection peak of the film. Meanwhile, the hydrogel acted as a flexible amperometric electrode to sense current change. Linear response upon concentration of glucose ranged from 1 mM to 12 mM. Glucose was exhibited optically and electrically confirming a mutual regulation capacity to achieve better anti-interference performance.

In situ forming hydrogels of new amino hyaluronic acid/benzoyl-cysteine derivatives as potential scaffolds for cartilage regeneration by Fabio Salvatore Palumbo; Giovanna Pitarresi; Calogero Fiorica; Pietro Matricardi; Antonella Albanese; Gaetano Giammona (4918-4927).
A new chemical strategy is described to link ethylenediamino (EDA) groups to primary hydroxyl groups of hyaluronic acid (HA) and the obtained derivatives have been characterized by 1H-NMR and 13C-NMR analyses. Such HA–EDA derivatives have been exploited to control the functionalization degree in benzoyl-cysteine (BC) groups, chosen as moieties able to allow both self-assembling in aqueous media and an oxidative crosslinking. In particular, the kinetics of oxidation of thiol groups in HA–EDA–BC derivatives has been studied in Dulbecco's Phosphate Buffer Solution (DPBS) pH 7.4 by colorimetric assays and rheological measurements. Mechanical properties of chemical hydrogels obtained after oxidative crosslinking have been evaluated by using two different concentration values (1 and 1.5% w/v) of HA–EDA–BC. These hydrogels show a dense interconnected fibrillar structure similar to the extracellular matrix of soft tissue and a resistance to chemical and enzymatic hydrolysis. Therefore, the potential suitability of HA–EDA–BC hydrogels as scaffolds for cartilage regeneration has been preliminarily assessed using primary human chondrocytes and evaluating their viability and ability to produce extracellular collagen.

Triple-shape memory effect of covalently crosslinked polyalkenamer based semicrystalline polymer blends by José M. Cuevas; Raquel Rubio; Lorena Germán; José M. Laza; José L. Vilas; Matilde Rodriguez; Luis M. León (4928-4935).
Triple-shape memory polymers are developed by blending and crosslinking two semicrystalline polymers (poly(cyclooctene), PCO, and polyethylene, PE) towards creating two pronounced segregated crystalline domains within a covalently crosslinked network. The key thermo-mechanical properties of a series of a polyalkenamer and a polyolefin based polymer blends are characterised using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Furthermore, the versatile multi-shape memory functionality is demonstrated, and main shape memory response is evaluated by performing consecutive thermo-mechanical bending experiments based on a two-step programming process and subsequent progressive thermal recovery. The proposed approach, thanks to the excellent achieved shape memory properties, as well as the possibility of tailoring the thermo-mechanical response, is presented as a versatile method to increase the potential applications of these thermo-active materials by designing optimal compositions.

Fast relaxation and elasticity-related properties of trehalose-glycerol mixtures by Devin Averett; Marcus T. Cicerone; Jack F. Douglas; Juan J. de Pablo (4936-4945).
Molecular dynamics simulations are used to investigate basic fast relaxation properties and thermo-physical properties of trehalose-glycerol mixtures over a wide composition range and for a temperature range from above to below the glass transition temperature, Tg. An important aspect of the present work is that we employ a revised force field that yields glycerol densities that agree much better with experiment than those formerly used in models of these mixtures. This optimized molecular model provides a platform for more refined simulation studies of this class of protein drug preservative matrix materials. For temperatures below Tg, the inverse of the Debye–Waller factor, <u2>−1, exhibits a maximum near a 30% relative glycerol mass concentration. This local ‘stiffening’ effect, in conjunction with a reduction of Tg by glycerol, indicates that glycerol is an antiplastizer of trehalose at intermediate concentrations, a finding consistent with dielectric measurements on trehalose-glycerol mixtures in which moisture has been carefully excluded from the samples. We also find that the shear modulus of these materials C11 increases progressively with glycerol concentration. The Boson peak, which provides one of the most experimentally accessible fast dynamics properties of glass-forming liquids, is also calculated for trehalose-glycerol glasses as a function of glycerol concentration. The change in the Boson peak intensity with glycerol concentration is found to be consistent with a reduction of fragility of glass formation with the addition of glycerol, an effect that previous simulation studies of coarse grain models have linked to antiplasticization. We also find general agreement with a recently proposed relation between the fast beta relaxation time τβ and the local amplitude of atomic motion on picosecond timescales, <u2>.1 The implications of our simulations and their interpretation in terms of physics of glass formation are briefly discussed in the context of protein stabilization.

A three-dimensional polymer scaffolding material exhibiting a zero Poisson's ratio by Pranav Soman; David Y. Fozdar; Jin Woo Lee; Ameya Phadke; Shyni Varghese; Shaochen Chen (4946-4951).
Poisson's ratio describes the degree to which a material contracts (expands) transversally when axially strained. A material with a zero Poisson's ratio does not transversally deform in response to an axial strain (stretching). In tissue engineering applications, scaffolding having a zero Poisson's ratio (ZPR) may be more suitable for emulating the behavior of native tissues and accommodating and transmitting forces to the host tissue site during wound healing (or tissue regrowth). For example, scaffolding with a zero Poisson's ratio may be beneficial in the engineering of cartilage, ligament, corneal, and brain tissues, which are known to possess Poisson's ratios of nearly zero. Here, we report a 3D biomaterial constructed from polyethylene glycol (PEG) exhibiting in-plane Poisson's ratios of zero for large values of axial strain. We use digital micro-mirror device projection printing (DMD-PP) to create single- and double-layer scaffolds composed of semi-re-entrant pores whose arrangement and deformation mechanisms contribute to the zero Poisson's ratio. Strain experiments prove the zero Poisson's behavior of the scaffolds and that the addition of layers does not change the Poisson's ratio. Human mesenchymal stem cells (hMSCs) cultured on biomaterials with zero Poisson's ratio demonstrate the feasibility of utilizing these novel materials for biological applications which require little to no transverse deformations resulting from axial strains. Techniques used in this work allow Poisson's ratio to be both scale-independent and independent of the choice of strut material for strains in the elastic regime, and therefore ZPR behavior can be imparted to a variety of photocurable biomaterials.

Self-assembly mechanisms of silk protein nanostructures on two-dimensional surfaces by Nicholas E. Kurland; Joydip Kundu; Shilpa Pal; Subhas C. Kundu; Vamsi K. Yadavalli (4952-4959).
Self-assembly processes are ubiquitous in natural systems, and their study can provide insight into the harnessing of unique properties for engineering of new materials from the bottom up. Models for diffusion-limited assembly behavior have shown that structures formed have a characteristic fractal dimensionality that is smaller than the embedding space or the lattice. Typically however, these processes have only been studied via theoretical and computational tools, with relatively few natural systems having been reported to approach the limiting conditions assumed. Sericin, a protein critical to silk macrostructure, displays the remarkable ability to self-assemble through different modes of classical and non-universal diffusion-limited aggregation to produce radially-branched dendritic architectures. We report on the characterization of these assemblies by pure proteins from different species of silkworms in the absence of any charge shielding or modulation by salts. It is shown how physical differences between colloidal systems can yield remarkable changes in branching architectures from proteins that are functionally similar. This represents a novel system for fundamental and applied studies of particle aggregation and the development of biomaterials based on self-similarity at multiple length scales.

From compact to fractal crystalline clusters in concentrated systems of monodisperse hard spheres by Chantal Valeriani; Eduardo Sanz; Peter N. Pusey; Wilson C. K. Poon; Michael E. Cates; Emanuela Zaccarelli (4960-4970).
We address the crystallization of monodisperse hard spheres in terms of the properties of finite-size crystalline clusters. By means of large scale event-driven molecular dynamics simulations, we study systems at different packing fractions ϕ ranging from weakly super-saturated state points to glassy ones, covering different nucleation regimes. We find that such regimes also result in different properties of the crystalline clusters: compact clusters are formed in the classical nucleation theory regime (ϕ≤ 0.54), while a crossover to fractal, ramified clusters is encountered upon increasing packing fraction (ϕ≥ 0.56), where nucleation is more spinodal-like. We draw an analogy between macroscopic crystallization of our clusters and percolation of attractive systems to provide ideas on how the packing fraction influences the final structure of the macroscopic crystals. In our previous work (Phys. Rev. Lett., 2011, 106, 215701), we have demonstrated how crystallization from a glass (at ϕ > 0.58) happens via a gradual (many-step) mechanism: in this paper we show how the mechanism of gradual growth seems to hold also in super-saturated systems just above freezing showing that static properties of clusters are not much affected by dynamics.

Capillary bond between rod-like particles and the micromechanics of particle-laden interfaces by L. Botto; L. Yao; R. L. Leheny; K. J. Stebe (4971-4979).
Rod-like microparticles assemble by capillarity at fluid interfaces to make distinctively different microstructures depending on the details of the particle shape. Ellipsoidal particles assemble in side-to-side orientations to form flexible chains, whereas cylinders assemble end-to-end to form rigid chains. To understand these differences, we simulate the near-field capillary interactions between pairs of rod-like particles subject to bond-stretching and bond-bending deformations. By comparing ellipsoids, cylinders, and cylinders with smooth edges, we show that geometric details dramatically affect the magnitude and shape of the capillary energy landscape. We relate this energy landscape to the mechanics of the chains, predicting the flexural rigidity for chains of ellipsoids, and a complex, non-elastic response for chains of cylinders. These results have implications in the design of particle laden interfaces for emulsion stabilization and encapsulation, and for oriented assembly of anisotropic materials.

Influence of film casting method on block copolymer ordering in thin films by Xiaohua Zhang; Jack F. Douglas; Ronald L. Jones (4980-4987).
We study the orientation of the cylinder phase of the block copolymer (BCP) poly(styrene-block-methylmethacrylate) (PS-b-PMMA) in thin spun-cast films having a range of film thicknesses and temperatures and compare to our earlier observations on flow-coated films of the same BCP under similar thermodynamic conditions. As in our former measurements on flow-coated films, morphology maps of our spun-cast BCP films reveal distinct ordering regimes where the cylinders orient predominantly perpendicular or parallel to the interface and an ‘intermediate’ regime where these morphologies are mixed. However, we find that the locations of these morphology lines in the temperature–film thickness plane are greatly influenced by the method of film formation. We hypothesize that the slow solvent evaporation of the flow-coated films leads to films having higher residual stresses than spun-cast films because of a relatively inhibited transport of the solvent out of the film during drying, and annealing measurements on both types of cast films provide supporting evidence that the BCP surface morphology change is associated with residual stresses within the films. Contrary to our initial expectations, spun-cast films showed little sensitivity to film casting speed so that residual stress effects associated with the comparatively violent fluid flow conditions of spin-casting appear to be small. Instead, residual stresses arising from slow film evaporation appear to be implicated. Residual stress effects arising during the course of film casting and drying are relevant to other fabrications involving cast polymer films, such as in organic photovoltaic devices where flow-coating or similar industrial film casting method is normally employed for film formation.

DNA with amphiphilic counterions: tuning colloidal DNA with cyclodextrin by Azat Bilalov; Jonas Carlstedt; Elena Krivtsova; Björn Lindman; Ulf Olsson (4988-4994).
DNA compaction in vitro can be controlled by lipids. Cyclodextrins can disperse lipids in the form of water soluble inclusion complexes, thus tuning their self-assembly. To progress in the fundamental understanding of double-stranded (ds) DNA–lipid–cyclodextrin interactions, the aqueous phase behavior of a cationic surfactant (dodecyltrimethylammonium, DTA)–dsDNA compound in the presence of cyclodextrin (hydroxypropyl-β-cyclodextrin, HPβCD, or β-cyclodextrin, βCD) was investigated. βCD has a low water solubility due to the formation of stable crystals. The more hydrophobic HPβCD, on the other hand, is highly water soluble because the bulky HP substitution destabilizes the crystalline state. Both βCD and HPβCD form strong inclusion complexes with DTA, with an essentially infinite binding constant, and the DNA self-assembly behavior is controlled by the molar ratio R = [DTA]/[CD], in addition to the DNA concentration. DTA–DNA can be solubilized in the isotropic liquid phase of water and HPβCD when R≤ 1. This phase is micelle free and from the sharp phase boundary at R = 1 it is concluded that HPβCD does not associate with DNA, only with DTA. Increasing the DTA–DNA concentration, keeping R < 1, leads to the formation of a liquid crystal with 2D hexagonally ordered DNA. With a further increase of the DTA–DNA and R > 1.5–2, a second, novel, anisotropic phase is formed that we identify as having a tetragonal lattice. In this phase, the DNA duplexes are still parallel but with a simple square rather than a hexagonal packing. The periodicity in the direction of the DNA duplexes is coupled to the DNA pitch length, 3.3 nm. With βCD, the phase behavior is less rich because of the poor water solubility of the cyclodextrin. Here, only a very small hexagonal phase region is formed in the center of the ternary phase diagram, with R≈ 1.

A nanodispensing technique using specific atomic force microscope tips was used to pattern surfaces with liquids with sub-micron resolution, down to diameter spots of 70 nm. The experimental results revealed that spot sizes and linewidths are ruled by the dynamics of spreading of the liquid on the substrate. The feature size R follows a temporal evolution with two different regimes: it scales as R∼t0.26±0.04 at short times (smaller than 1 s) and then saturates to reach an equilibrium value at longer times. A model considering the spreading of liquid from a source, under constant pressure conditions, was developed. It leads to a R∼t1/4 power law for the early stage of spreading which accounts quantitatively for the non-conventional dynamics and for the influence of tip and substrate properties observed in the experiments. This study provides a precise understanding of the nanodispensing mechanism, useful to develop and improve the method. It also shows that this nanodispensing technique is a unique method to study liquid spreading at the sub-micron scale and down to the millisecond timescale.

Effective interactions between grafted nanoparticles in a polymer matrix by Dong Meng; Sanat K. Kumar; J. Matthew D. Lane; Gary S. Grest (5002-5010).
Molecular dynamics simulations were used to delineate the separation dependent forces between two polymer-grafted nanoparticles in a polymer melt, the associated potential of mean force (PMF), and the molecular origins of these forces. The nanoparticle radius (=5, in units of the size of the chain monomers) and grafted brush length (=10) were held constant, while the grafting density and the polymer matrix length were varied systematically in a series of simulations. We first show that simulations of a single nanoparticle do not reveal any signatures of the expected autophobic dewetting of the brush with increasing polymer matrix length. In fact, density distributions of the matrix and grafted chains around a single nanoparticle appear to only depend on the grafting density but not on the matrix chain length in the regime where autophobic dewetting is expected, i.e., when the matrix chain length is equal to or longer than the graft chain length. We thus conjecture that two nanoparticle simulations might be more illuminating in these situations. Indeed, the calculated forces between two nanoparticles in a melt show that increasing the matrix chain length from 10 to 70 causes the inter-nanoparticle potential of mean force (PMF) to go from purely repulsive to attractive with a well depth on the order of kBT. These results are purely entropic in origin and arise from a competition between brush-brush repulsion and an attractive inter-nanoparticle interaction caused by matrix depletion from the inter-nanoparticle zone. The matrix-induced Asakura-Oosawa type inter-nanoparticle attraction, which dominates at intermediate nanoparticle separations especially in the case of long matrix chains, is thus implicated as the essential player in the autophobic dewetting phenomenon, which drives phase separation in these situations.

Deformability-selective particle entrainment and separation in a rectangular microchannel using medium viscoelasticity by Seungyoung Yang; Sung Sik Lee; Sung Won Ahn; Kyowon Kang; Wooyoung Shim; Gwang Lee; Kyu Hyun; Ju Min Kim (5011-5019).
We report a new phenomenon that particles are selectively entrained along the corners of a straight rectangular microchannel according to their deformabilities under viscoelastic flows of a polymer solution. The mechanism behind this phenomenon is elucidated by the competition between the wall lift force induced by the particle deformability and the elastic force of the medium at the corners. On the basis of these findings, we devise a novel label-free deformability-selective cell-separation method, which achieves the high-purity separation of rigid particles and rigidified red blood cells (RBCs) from fresh RBCs in a single step, without any active components such as an electric force or sophisticated channel design. Furthermore, our novel method can be used directly to isolate white blood cells (WBCs) from diluted whole blood with a high enrichment ratio (>300) by utilizing difference in cell deformability.

Polymer surface texturing for direct inkjet patterning by atmospheric pressure plasma treatment by Jae Beom Park; Jae Yong Choi; Suk Han Lee; Yong Seol Song; Geun Young Yeom (5020-5026).
It would be beneficial if the substrate surface were treated to have hydrophobic properties, in order to keep the line pattern fine during the inkjet processing, while at the same time having improved adhesion properties on the substrate. In this study, a polyimide surface was textured using atmospheric pressure plasma treatment for fine line metal inkjet printing by micromasking the surface followed by etching the polyimide surface selectively. The water contact angle on the textured polyimide film was measured to be over 100 degrees, showing that the surface was hydrophobic. When the textured polyimide surface was printed on using an electro-hydro-dynamic inkjet for Ag line printing, not only fine line Ag printing, but also improved adhesion of Ag to the polyimide surface could be obtained while maintaining excellent resistivity. The improved adhesion properties in addition to the fine line patterning afforded by texturing the polyimide surface were caused by the increased surface contact area between the metal ink and the polyimide surface during the annealing of the Ag line.

Development of formaldehyde-free agar/gelatin microcapsules containing berberine HCl and gallic acid and their topical and oral applications by Pik-Ling Lam; Kenneth Ka-Ho Lee; Stanton Hon-Lung Kok; Gregory Yin-Ming Cheng; Xiao-Ming Tao; Desmond Kwok-Po Hau; Marcus Chun-Wah Yuen; Kim-Hung Lam; Roberto Gambari; Chung-Hin Chui; Raymond Siu-Ming Wong (5027-5037).
The safety issues of biomedical applications have been a major concern in recent years. Drug delivery associated with microencapsulation technology has been focused on as microencapsulated drugs are believed to promote comparative therapeutic efficiency on human absorption and prolong the life cycle of drugs. The most commonly applied crosslinker is formaldehyde in a gelatin microencapsulation system, which is considerably toxic to the human body. To reduce the risks involved when using formaldehyde, agar was associated with gelatin as the wall matrix materials of microcapsules as it could crosslink with gelatin to give a gel network in the microcapsules formation. Here we report the development, characterization and safe use of agar–gelatin microcapsules. We further demonstrate that both oral and topical applications are possible using the berberine HCl and gallic acid loaded microcapsules respectively. Microcapsules containing both drugs were prepared combining the optimal parameters identified. The mean drug loading efficiency and the mean particle sizes of the berberine HCl loaded microcapsules were 78.16% and 16.75 μm respectively, while those of gallic acid loaded microcapsules were 70.28% and 21.98 μm respectively. The compositions and surface morphology of berberine HCl and gallic acid containing microcapsules were examined using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The in vitro controlled release models demonstrated that the drugs could be gradually released from the microcapsules. The minimum inhibitory concentrations (MICs) and anti-Staphylococcus aureus activity also proved that the berberine HCl loaded microcapsules exhibited better antibacterial activity towards Staphylococcus aureus when compared with those of the original drugs. The in vitro drug delivery model also demonstrated the delivery of berberine HCl from microcapsule treated textiles into nude mice skin. The in vivo mice disease model also showed that gallic acid loaded microcapsules were helpful in the treatment of acute liver and kidney toxicity after an overdose administration of acetaminophen. The development of agar–gelatin microcapsules was demonstrated to be an efficient, deliverable tool for both oral and topical applications.

How to make a cylinder roll uphill by Dipabali Hore; Abhijit Majumder; Subrata Mondal; Abhijit Roy; Animangsu Ghatak (5038-5042).
Slithering, crawling, slipping, and gliding are various modes of limbless locomotion that have been mimicked for micro-manipulation of soft, slender and sessile objects. A lesser known mode is rolling which involves periodic, asymmetric and lateral muscular deformations. Here we enable an elastomeric cylinder of poly(dimethylsiloxane) to roll on a substrate by releasing a small quantity of a solvent like chloroform, toluene, hexane, heptane and so on, which swells differentially a portion of the cylinder, but evaporates from the portion of it which remains exposed to the atmosphere. In a dynamic situation, this asymmetric swelling–shrinking cycle generates a torque which drives the cylinder to roll. The driving torque is strong enough that the cylinder can roll up an inclined plane, within a range of inclination, its velocity even increases. The cylinder can even drag a dead weight significantly larger, ∼8 to 10 times its own weight. A scaling law is derived for optimizing the rolling velocity.

Temperature-responsive inclusion complex of cationic PNIPAAM diblock copolymer and γ-cyclodextrin by Giuseppe Lazzara; Gerd Olofsson; Viveka Alfredsson; Kaizheng Zhu; Bo Nyström; Karin Schillén (5043-5054).
Aqueous mixtures of γ-cyclodextrin (γ-CD) and the thermosensitive cationic diblock copolymer poly(N-isopropylacrylamide)-b-poly(3-acrylamidopropyl)trimethylammonium chloride (PNIPAAM24-b-PAMPTAM(+)9) or the PNIPAAM homopolymer PNIPAAM47 have been investigated using various experimental methods. Solid γ-CD–polymer inclusion complexes (pseudopolyrotaxanes) form at ambient temperatures in fairly concentrated CD solutions. The NMR measurements showed that the stoichiometry of the inclusion complexes is close to two NIPAAM units per CD molecule. The cationic block of the copolymer is not incorporated into the CD cavity. Synchrotron radiation X-ray diffraction spectra of the solid inclusion complexes indicate a compact columnar structure of CD molecules threaded onto the PNIPAAM chains. In water, square-shaped cyclodextrin aggregates were found to co-exist with single cyclodextrin molecules. In mixed solutions of γ-CD and PNIPAAM24-b-PAMPTAM(+)9 these aggregates disintegrate with time as inclusion complexes are formed and the kinetics was studied using time-resolved static and dynamic light scattering and cryo-TEM. Steady-state fluorescence spectroscopy measurements reveal that the CD molecules dethread from the PNIPAAM chains upon increasing the temperature to 40 °C, which is above the lower critical solution temperature of PNIPAAM.

Synchrotron XRR study of soft nanofilms at the mica–water interface by Wuge H. Briscoe; Francesca Speranza; Peixun Li; Oleg Konovalov; Laurence Bouchenoire; Jan van Stam; Jacob Klein; Robert M. J. Jacobs; Robert K. Thomas (5055-5068).
We describe here the design of a liquid cell specific for synchrotron X-ray reflectometry (XRR) characterisation of soft matter nanofilms at the mica–water interface. The feature of the cell is a “bending mica” method: by slightly bending the mica substrate over an underling cylinder the rigidity of the mica sheet along the bending axis is enhanced, providing sufficient flatness along the apex of the cylinder as required by XRR measurements. Using this cell, we have performed XRR measurements for a number of systems and in this article we show example results: (1) a cationic surfactant, C16TAB; (2) a zwitterionic surfactant, C12H25PC; (3) a semi-fluorinated surfactant, F4H11(d)TAB; and (4) surface complex of an anionic fluorinated surfactant, CsPFN, and a positively charged polymer, PEI. For the data analysis we have taken into account the mica crystal truncation rod, i.e. the reflectivity from the mica substrate, and fitted the data with a custom Java™ based software package. Our results unravel detailed structural information of these soft nanofilms, indicating that this method is suitable for XRR measurements of a wide range of soft matter structures at the mica–water interface.

Triggered cell release from shellac–cell composite microcapsules by Shwan A. Hamad; Simeon D. Stoyanov; Vesselin N. Paunov (5069-5077).
We report the fabrication of novel shellac–cell composite microcapsules with programmed release of cells upon change of pH in a narrow range. The microcapsules were prepared from yeast cells as a model for probiotics combined with aqueous solution of ammonium shellac doped with a pH sensitive polyelectrolyte, like carboxymethyl cellulose or polyacrylic acid. The cell dispersions in aqueous ammonium shellac were spray-dried or spray co-precipitated to yield composite shellac–cell microcapsules in which the cells retained their viability even when treated with aqueous solutions of very low pH and subjected to mechanical stress. We demonstrate two types of triggered release of yeast cells from these microcapsules with pH trigger and cell growth trigger and evaluate the microcapsule disintegration rates. Depending on the type of the polyelectrolyte integrated in the shellac microcapsules they can be programmed to give very versatile responses ranging from slow cell release to explosive swelling and disintegration at higher pH or exposure to growth media. We show that the cells retain their viability following their release from the microcapsules into the aqueous solution. Such composite microcapsules could find applications in formulations for protection and delivery of probiotic and other cell cultures with programmed and triggered release of the encapsulated cells in cell implants, including stem cells and live vaccines.

Hydrophobically associated hydrogels based on acrylamide and anionic surface active monomer with high mechanical strength by Wenbo Li; Huiyong An; Ying Tan; Cuige Lu; Chang Liu; Pengchong Li; Kun Xu; Pixin Wang (5078-5086).
In this work, a physically cross-linked hydrogel (HA gels) with high mechanical strength is synthesized via micellar copolymerization of acrylamide (AAm) and an anionic surface active monomer (surfmer), sodium 9 or 10-acrylamidostearic acid (NaAAS) without any adscititious surfactant or chemical cross-linkers. SEM and DLS characterizations indicate that the surfmer formed multi-micellar aggregates with 80–90 nm diameters above its critical micelle concentration, and serve as a crosslinked-center to endow the obtained hydrogel a robust three-dimensional architecture. Compared with the chemically cross-linked hydrogel, HA gels exhibit unusual swelling–deswelling behavior in water and a pulsatile swelling–deswelling behavior is exhibited with alternating pH changes from 5 to 10 because the presence of carboxyl in the surfmer, demonstrating a smart characteristic of the hydrogel. Moreover, the presence of the surfmer greatly improve the mechanical properties of HA gels. A hydrogel containing 20% (mol/mol) surfmer shows a compression strength of 22.50 MPa at a strain of 90% and can be elongated to 13 times its original length. Furthermore, the HA gels show a significant hysteresis recovery after large deformation, underlying a serious energy-dissipation mechanism. This uncommon swelling behavior and mechanical properties of the HA gels result from its special characteristic of cross-linked units. A self-healing ability is expected for this physical hydrogel in future applications in biotechnology.

Back cover (5087-5088).