Novel temperature-responsive polymer brushes with carbohydrate residues facilitate selective adhesion and collection of hepatocytes

Temperature-responsive glycopolymer brushes were designed to investigate the effects of grafting architectures of the copolymers on the selective adhesion and collection of hypatocytes. Homo, random and block sequences of N-isopropylacrylamide and 2-lactobionamidoethyl methacrylate were grafted on glass substrates via surface-initiated atom transfer radical polymerization. The galactose/lactose-specific lectin RCA₁₂₀ and HepG2 cells were used to test for specific recognition of the polymer brushes containing galactose residues over the lower critical solution temperatures (LCSTs). RCA₁₂₀ showed a specific binding to the brush surfaces at 37 °C. These brush surfaces also facilitated the adhesion of HepG2 cells at 37 °C under nonserum conditions, whereas no adhesion was observed for NIH-3T3 fibroblasts. When the temperature was decreased to 25 °C, almost all the HepG2 cells detached from the block copolymer brush, whereas the random copolymer brush did not release the cells. The difference in releasing kinetics of cells from the surfaces with different grafting architectures can be explained by the correlated effects of significant changes in LCST, mobility, hydrophilicity and mechanical properties of the grafted polymer chains. These findings are important for designing ‘on–off’ cell capture/release substrates for various biomedical applications such as selective cell separation.     

Facile synthesis of α-Fe2O3 nanodisk with superior photocatalytic performance and mechanism insight

Intrinsic short hole diffusion length is a well-known problem for α-Fe₂O₃ as a visible-light photocatalytic material. In this paper, a nanodisk morphology was designed to remarkably enhance separation of electron-hole pairs of α-Fe₂O₃. As expected, α-Fe₂O₃ nanodisks presented superior photocatalytic activity toward methylene blue degradation: more than 90% of the dye could be photodegraded within 30 min in comparison with a degradation efficiency of 50% for conventional Fe₂O₃ powder. The unique multilayer structure is thought to play a key role in the remarkably improved photocatalytic performance. Further experiments involving mechanism investigations revealed that instead of high surface area, ·OH plays a crucial role in methylene blue degradation and that O^·2− may also contribute effectively to the degradation process. This paper demonstrates a facile and energy-saving route to fabricating homogenous α-Fe₂O₃ nanodisks with superior photocatalytic activity that is suitable for the treatment of contaminated water and that meets the requirement of mass production.     

Identifying and rationalizing the morphological,structural, and optical properties of [... formula ...]-Ag2MoO4 microcrystals,and the formation process of Ag nanoparticles on their surfaces: combining experimental data and first-principles calculations

We present a combined theoretical and experimental study on the morphological, structural, and optical properties of β-Ag₂MoO₄ microcrystals. β-Ag₂MoO₄ samples were prepared by a co-precipitation method. The nucleation and formation of Ag nanoparticles on β-Ag₂MoO₄ during electron beam irradiation were also analyzed as a function of electron beam dose. These events were directly monitored in real-time using in situ field emission scanning electron microscopy (FE-SEM). The thermodynamic equilibrium shape of the β-Ag₂MoO₄ crystals was built with low-index surfaces (001), (011), and (111) through a Wulff construction. This shape suggests that the (011) face is the dominating surface in the ideal morphology. A significant increase in the values of the surface energy for the (011) face versus those of the other surfaces was observed, which allowed us to find agreement between the experimental and theoretical morphologies. Our investigation of the different morphologies and structures of the β-Ag₂MoO₄ crystals provided insight into how the crystal morphology can be controlled so that the surface chemistry of β-Ag₂MoO₄ can be tuned for specific applications. The presence of structural disorder in the tetrahedral [MoO₄] and octahedral [AgO₆] clusters, the building blocks of β-Ag₂MoO₄, was used to explain the experimentally measured optical properties.     

Powder X-Ray Reference Patterns of Sr2RGaCu2Oy (R = Pr,Nd, Sm,Eu, Gd,Dy, Ho,Er, Tm,and Y)

X-Ray Rietveld refinements were conducted on a series of eleven lanthanide phases, Sr₂RGaCu₂O_y (2112 phase, R = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, and Yb) that are structurally related to the high T_c superconductor Ba₂YCu₃O₇ (213). In the 2112 structure, instead of square planar Cu-O chains, tetrahedral GaO4 chains were found to run in a zig-zag fashion along the diagonal of the basal 213 ab-direction. Reference powder patterns for these compounds were prepared by using the Rietveld decomposition technique. The unit cell volume of these compounds follows the expected trend of the lanthanide contraction. The lattice parameters range from a = 22.9694(3) Å, b = 5.5587(2) Å, and c = 5.44743(7) Å for R = Pr, to a = 22.8059(2) Å, b = 5.46031(5) Å, and c = 5.37773(5) Å for R = Yb. An electon diffraction study of the Sm- and Er-analogs showed characteristic diffuse streaks along the b-axis, suggesting some disorder within the GaO₄ chains.     

Ba(OH)2 Equilibria in the System Ba-O-H-F,With Application to the Formation of Ba2YCu3O6.5 + x From BaF2-Precursors

The ex situ process for fabricating Ba₂YCu₃O_{6.5 + x} superconducting tapes from BaF₂- based precursors involves a hydration/oxidation reaction at ≈730 °C to 750 °C generally written as: (2BaF2+Y+3Cu)(amorphous)+(2H2O+2.25O2)(g)→Ba2YCu3O6.5+x(s)+4HF(g).However, microscopic observations of partially processed films suggest the presence of a transient liquid phase during conversion. Alternatively, the conversion reaction can be rewritten as the sum of several intermediate steps, including the formation of a barium hydroxide liquid: (BaF2)(amorphous)+2H2O(g)→Ba(OH)2(liq)+2HF(g).To evaluate the possibility of a hydroxide liquid conversion step, thermodynamic calculations on the stability of Ba(OH)₂(liq) have been completed from 500 °C to 900 °C at 0.1 MPa p_total. Based on currently available data, the calculated phase diagrams suggest that a viable hydroxide reaction path exists in the higher part of this temperature range. The calculations indicate that Ba(OH)₂(liq) may be stable at log p_H2O (Pa) values from ≈4 to 5, provided log p_HF (Pa) values can be maintained below 0 to −1. Limited experimental confirmation is provided by results of an experiment on BaF₂(s) at 815 °C, 0.1 MPa p_H2O, in which essentially all F at the surface was replaced by O. It is therefore possible that processing routes exist for producing Ba₂YCu₃O_{6.5 + x} based on the presence of a Ba(OH)₂ liquid, which might have an effect on conversion rates and texturing in the superconducting film.     

Synthesis of nanoparticle CT contrast agents: in vitro and in vivo studies

Water-soluble and biocompatible D-glucuronic acid coated Na₂WO₄ and BaCO₃ nanoparticles were synthesized for the first time to be used as x-ray computed tomography (CT) contrast agents. Their average particle diameters were 3.2 ± 0.1 and 2.8 ± 0.1 nm for D-glucuronic acid coated Na₂WO₄ and BaCO₃ nanoparticles, respectively. All the nanoparticles exhibited a strong x-ray attenuation. In vivo CT images were obtained after intravenous injection of an aqueous sample suspension of D-glucuronic acid coated Na₂WO₄ nanoparticles, and positive contrast enhancements in the kidney were clearly shown. These findings indicate that the nanoparticles reported in this study may be promising CT contrast agents.     

Leaf surface structures enable the endemic Namib desert grass Stipagrostis sabulicola to irrigate itself with fog water

The Namib grass Stipagrostis sabulicola relies, to a large degree, upon fog for its water supply and is able to guide collected water towards the plant base. This directed irrigation of the plant base allows an efficient and rapid uptake of the fog water by the shallow roots. In this contribution, the mechanisms for this directed water flow are analysed. Stipagrostis sabulicola has a highly irregular surface. Advancing contact angle is 98° ± 5° and the receding angle is 56° ± 9°, with a mean of both values of approximately 77°. The surface is thus not hydrophobic, shows a substantial contact angle hysteresis and therefore, allows the development of pinned drops of a substantial size. The key factor for the water conduction is the presence of grooves within the leaf surface that run parallel to the long axis of the plant. These grooves provide a guided downslide of drops that have exceeded the maximum size for attachment. It also leads to a minimum of inefficient drop scattering around the plant. The combination of these surface traits together with the tall and upright stature of S. sabulicola contributes to a highly efficient natural fog-collecting system that enables this species to thrive in a hyperarid environment.     

Fabrication and characterization of transparent superhydrophilic/superhydrophobic silica nanoparticulate thin films

The realization of transparent and superhydrophilic/superhydrophobic surfaces by silica nanoparticulate thin films was exploited in this work. An aqueous electrostatic layer-by-layer assembly process was utilized to fabricate nanoparticulate thin films with adhesion/body/top layer structure on glass substrates by using SiO₂ nanoparticles and polyelectrolytes. The effects of volume ratio of differently sized silica nanoparticle solutions for the body layer deposition on transmittance in visible light region and surface wettability of the nanoparticulate thin films were systematically studied. The experimental results revealed that both optical transparency and superhydrophobicity/superhydrophilicity can be achieved on the same SiO₂ nanoparticulate thin film by using appropriate volume ratios of differently sized silica nanoparticle solutions for body layer deposition, and with and without silane treatment in the fabrication process. The high contrast of wettability that can be achieved by this way suggests the possibility of the creation of superhydrophilic/superhydrophobic patterning and superhydrophilic-superhydrophobic gradient on the same surfaces.     

Synthesis of monodisperse spherical core-shell SiO2-SrAl2Si2O8: Eu2+ phosphors by hydrothermal homogeneous precipitation method

Nanocrystalline SrAl₂Si₂O₈ :Eu²⁺ phosphor layers were coated on nonaggregated, monodisperse and spherical SiO₂ particles using a hydrothermal homogeneous precipitation. After annealing at 1100 °C, core-shell SiO₂@SrAl₂Si₂O₈ :Eu²⁺ particles were obtained. They were characterized with x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy and photoluminescence techniques. XRD analysis confirmed the formation of SiO₂ @SrAl₂Si₂O₈ :Eu²⁺ particles; it indicated that the SrAl₂Si₂O₈ :Eu²⁺ shells on SiO₂ particles consisted of hexagonal crystallites. The core-shell phosphors obtained are well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the coated layer is approximately 20–40 nm. Under ultraviolet excitation (361 nm), the particles emit blue light at about 440 nm due to the Eu²⁺ ions in their shells.     

Effect of surface metrology on the wettability of SiO2 nanoparticle coating

In this work, we fabricated an array of model hydrophobic surfaces with controlled roughness to establish a correlation between surface structure and observed hydrophobicity. SiO₂ nanoparticles of different sizes (7, 12, 14 and 40 nm) were layer-by-layer spin-coated on glass supports to study the effect of surface roughness on wettability evaluated by water contact angles. The hydrophobicity of one-layer structured surfaces improved with an increase in particle size. Deposition of bigger nanoparticles on top of smaller ones, generating double-layer structures, resulted in rougher surfaces with higher hydrophobicity. A strong correlation between the size ratio of deposited nanoparticle combinations and roughness was observed. Based on these correlations, it is now possible to tune surface roughness and subsequent wettability by controlling the sizes of the nanoparticle layers.     

Anatomy of a negative feedback loop: the case of IκBα

The magnitude, duration and oscillation of cellular signalling pathway responses are often limited by negative feedback loops, defined as an ‘activator-induced inhibitor’ regulatory motif. Within the NFκB signalling pathway, a key negative feedback regulator is IκBα. We show here that, contrary to current understanding, NFκB-inducible expression is not sufficient for providing effective negative feedback. We then employ computational simulations of NFκB signalling to identify IκBα molecular properties that are critical for proper negative feedback control and test the resulting predictions in biochemical and single-cell live-imaging studies. We identified nuclear import and nuclear export of IκBα and the IκBα–NFκB complex, as well as the free IκBα half-life, as key determinants of post-induction repression of NFκB and the potential for subsequent reactivation. Our work emphasizes that negative feedback is an emergent systems property determined by multiple molecular and biophysical properties in addition to the required ‘activator-induced inhibitor’ relationship.     

Structural and photocatalytic properties of TiO2/SiOx/TiOx multi-layer prepared by electron-beam evaporation method

TiO₂/SiO_x/TiO_x multi-layers on quartz glass were prepared by electron-beam evaporation method and their structural and photocatalytic properties were investigated. The photocatalytic activity of the TiO₂/SiO_x/TiO_x multi-layer was evaluated by the photodecomposition of methylene blue in aqueous solution. As the thickness of the SiO_x inter-layer increased, the surface roughness of the TiO₂/SiO_x/TiO_x multi-layer increased but the anatase crystallite size decreased. The TiO₂/SiO_x(80 nm)/TiO_x multi-layer exhibited excellent photocatalytic activity resulting from higher surface roughness and more trap levels in the SiO_x(80 nm) inter-layer.     

Can a Pressure Standard be Based on Capacitance Measurements?

We consider the feasibility of basing a pressure standard on measurements of the dielectric constant ϵ and the thermodynamic temperature T of helium near 0 °C. The pressure p of the helium would be calculated from fundamental constants, quantum mechanics, and statistical mechanics. At present, the relative standard uncertainty of the pressure u_r(p) would exceed 20 × 10⁻⁶, the relative uncertainty of the value of the molar polarizability of helium A_ϵ calculated ab initio. If the relativistic corrections to A_ϵ were calculated as accurately as the classical value is now known, a capacitance-based pressure standard might attain u_r(p) < 6 × 10⁻⁶ for pressures near 1 MPa, a result of considerable interest for pressure metrology. One obtains p by eliminating the density from the virial expansions for p and ϵ − 1. If ϵ − 1 were measured with a very stable, 0.5 pF toroidal cross capacitor, the small capacitance and the small values of ϵ − 1 would require state-of-the-art capacitance measurements to achieve a useful pressure standard.     

Bacterial adhesion onto nanopatterned polymer surfaces

Two-dimensional nanopore arrays, consisting of hydrophilic SiO₂-like holes within hydrophobic poly(hydroxymethylsiloxane) (PHMS) surfaces, were fabricated by using a colloidal template-assisted method. The pores typically were deep 2–3 nm and wide ∼100 nm, as measured by tapping mode AFM. The adhesion behaviour of Pseudomonas aeruginosa, i.e. a micrometer width cell, was investigated by Fluorescence Microscopy both onto the nanopatterned PHMS surfaces and the homogeneous corresponding substrates of unmodified PHMS as well as the SiO₂-like surfaces obtained by plasma modification of PHMS films. The nanostructured films were able to induce a general increase of adhered cells with respect to the unmodified hydrophobic surfaces and a spot grown of biofilm-like aggregates. The observed effects are discussed in terms of the surface free energy of the patterned films as well as of the homogeneity and total integrated area of the 2D nanopore array.     

Electrode effect on resistive switching of Ti-added amorphous SiOx films

Ti-added amorphous SiO_x films were sputter-deposited into stacks of Pt/SiO_x/Pt and Cu/SiO_x/Pt. Optimally prepared Pt/SiO_x/Pt exhibits unipolar resistive switching over 10² cycles, resistance ratio ∼ 10³, yet wide voltage distribution (2 ∼ 7 V for SET, 0.5 ∼ 1.5 V for RESET). Cu/SiO_x/Pt exhibit similar endurance, resistance ratio up to 10⁷, and SET and RESET voltages reduced to 1.8 ∼ 4.2 V and 0.5 ∼ 1 V, respectively. Cu diffusion into SiO_x at the virgin state may play a role in resistive switching of Cu/SiO_x/Pt stack besides of filament conduction. Ti-added amorphous SiO_x films incorporating Cu electrode shows potential for resistive memory.     

Theoretical aspects of charge correlations in θ-(BEDT-TTF)2X

A review is given on the theoretical studies of charge correlations in θ-(BEDT-TTF)₂X. Various studies show that within a purely electronic model on the θ-type lattice with on-site U and nearest neighbor V_p and V_c interactions, the diagonal stripe, c-axis three-fold, and the vertical stripe charge correlations are favored in the regime V_p<V_c, V_p∼V_c, and V_p>V_c, respectively. In the realistic parameter regime of V_p∼V_c, there is competition between the c-axis three fold state and diagonal stripe state. Since these are different from the experimentally observed a-axis three fold and the horizontal stripe charge correlations, additional effects have to be included in order to understand the experiments. The electron–lattice coupling, which tends to distort the lattice into the θ_d-type, is found to favor the horizontal stripe state, suggesting that the occurrence of this stripe ordering in the actual materials may not be of purely electronic origin. On the other hand, distant electron–electron interactions have to be considered in order to understand the a-axis three fold correlation, whose wave vector is close to the nesting vector of the Fermi surface. These studies seem to suggest that the minimal model to understand the charge correlation in θ-(BEDT-TTF)₂X may be more complicated than expected. Future problems regarding the competition between different types of charge correlations are discussed.     

Simple synthesis of ZrO2/SiOx core/shell nanofibers using ZrSi2 with gallium

ZrO₂/SiO_x core/shell nanofibers with diameter ~ 50 nm were synthesized by the thermal oxidation of ZrSi₂ substrates with gallium. The crystalline ZrO₂ cores were grown with amorphous SiO_x shells. It is proposed that the growth of crystalline ZrO₂ core was guided by the prior supersaturation of Zr species in the molten gallium film, whereas the amorphous SiO_x shell could be attributed to the deposition of SiO vapor on the surface of ZrO₂ core. In addition, the ZrO₂/SiO_x core/shell nanofibers show a wide visible photoluminescence (PL) emission at 480 nm, which should originate from the SiO_x shells.     

Composite SiOx/fluorocarbon plasma polymer films prepared by r.f. magnetron sputtering of SiO2 and PTFE

Composite films SiO_x/fluorocarbon plasma polymers were prepared by r.f. sputtering from two balanced magnetrons equipped with polytetrafluoroethylene (PTFE) and silica (SiO₂) targets. Argon was used as the working gas. The obtained films were characterised by means of XPS, RBS, FTIR, AFM, TEM, microhardness and static contact angle measurements. The obtained SiO_x/fluorocarbon plasma polymer films reveal different wettability (static contact angle of water ranges from 68° to 40°) and hardness (ranges from 720 to 3200 N/mm²) when the volume fraction ratio (filling factor) of SiO₂ changes from 0.01 to 0.7. The concentration of elements determined by RBS/ERDA varies strongly over this range of filling factors. The heterogeneous structure of the composite films is indicated by TEM at high SiO_x contents.     

High-pressure studies on Tc and crystal structure of iron chalcogenide superconductors

The superconducting transition temperature, T_c, in iron-based solids can be enhanced by applied pressure: T_c increases from 8 to 37 K for the 11-type FeSe when the pressure is raised from 0 to 4 GPa. High-pressure studies can elucidate the mechanism of superconductivity in such novel materials. In this paper, we present a high-pressure study of Fe(Se_1−xTe_x) and Fe(Se_1−xS_x). In the case of Fe(Se_1−xTe_x), the maximum T_c under high pressure did not exceed the T_c of FeSe, which can be attributed to the structural transition to the monoclinic phase. For Fe(Se_1−xS_x) (0 < x < 0.3), T_c exhibited a significant increase with pressure; however, the maximum T_c under high pressure did not exceed the T_c of FeSe. This may be due to the disorder induced by substituting S for Se, which is similar to the pressure effect on T_c for the 1111-type superconductor Ca(Fe_1−xCo_x)AsF. The T_c of Fe(Se_1−xS_x) showed a complex behavior below 1 GPa, first decreasing and then increasing with increasing pressure. From high-pressure x-ray diffraction measurements, the T_c (P) curve was correlated with the local structural parameter.