Disentangling Origins of Adhesive Bonding at Interfaces between Epoxy/Amine Adhesive and Aluminum.

Joining metals by adhesive bonding is essential in widespread fields such as mobility, dentistry, and electronics. Although adhesive technology has grown since the 1920s, the roles of interfacial phenomena in adhesive bonding are still elusive, which hampers the on-demand selection of surface treatment and adhesive types. In the present study, we clarified how chemical interactions and mechanical interlocking governed adhesive bonding by evaluating adhesion properties at the interfaces between epoxy/amine adhesive and two kinds of Al adherends: a flat aluminum hydroxide (AlxOyHz) and technical Al plate with roughness. Spectroscopic and microscopical data demonstrate that the protonation of the amino groups in an amine hardener converts Al(OH)3 on the AlxOyHz surface to AlO(OH). The interfacial protonation results in an interfacial dipole layer with positive charges on the adhesive side, whose electrostatic interaction increases the interfacial fracture energy. The double cantilever beam tests for the flat AlxOyHz and technical Al substrates clarify that the mechanical interlocking originating from the surface roughness further increases the fracture energy. This study disentangles the roles of the chemical interactions and mechanical interlocking occurring at the epoxy adhesive/Al interface in the adhesion mechanism.

Amidoamine Oxide Surfactants as Low-Molecular-Weight Hydrogelators: Effect of Methylene Chain Length on Aggregate Structure and Rheological Behavior.

Rheology control is an important issue in many industrial products such as cosmetics and paints. Recently, low-molecular-weight compounds have attracted considerable attention as thickeners/gelators for various solvents; however, there is still a significant need for molecular design guidelines for industrial applications. Amidoamine oxides (AAOs), which are long-chain alkylamine oxides with three amide groups, are surfactants that act as hydrogelators. Here, we show the relationship between the length of methylene chains at four different locations of AAOs, the aggregate structure, the gelation temperature Tgel, and the viscoelasticity of the formed hydrogels. As seen from the results of electron microscopic observations, the aggregate structure (ribbon-like or rod-like) can be controlled by changing the length of methylene chain in the hydrophobic part, the length of methylene chain between the amide and amine oxide groups, and the lengths of methylene chains between amide groups. Furthermore, hydrogels consisting of rod-like aggregates showed significantly higher viscoelasticity than those consisting of ribbon-like aggregates. In other words, it was shown that the gel viscoelasticity could be controlled by changing the methylene chain lengths at four different locations of the AAO.

Role of Chemical Functionality in the Adhesion of Aluminum and Isotactic Polypropylene.

In the direct melt bonding of isotactic polypropylene (iPP) to aluminum (Al), the blending of a small amount of maleic anhydride-grafted PP (PPgMA) with iPP was found to induce a dramatic improvement of the strength of adhesion. The effect of blending PPgMA was, however, limited, maximizing at ∼20 wt % PPgMA. Incorporation of larger amounts of PPgMA reduced the strength of adhesion. We studied the mechanism of adhesion between Al and iPP by incorporating chemical functionality to the polymer side. The fracture surfaces produced by peeling off the interfaces were investigated by replicating the surface topographic features on a platinum thin film and analyzing them by scanning transmission electron microscopy (STEM) as well as by reconstructing three-dimensional (3D) surface structures with STEM tomography. The replica-STEM technique enabled us to visualize PP surface crystalline lamellar structures and their deformation upon the failure in 3D. We found that polymer/metal interfaces produced surface features in the failure that were similar to those associated with failure of entanglement-based polymer/polymer adhesion via chain pullout. A fractography study by replica-STEM suggested that the formation of a low-molecular-weight layer with low crystallinity at the interfacial region was responsible for the improvement of adhesion. The adhesion strength depended on the toughness of the "soft layer" and did not depend on the chemical bonding between PPgMA and Al. The interfacial chemical reaction between MA and the Al surface yielded PP with a grafted carboxylic acid (-COOH) group, which may have been excluded from the PP crystalline lamellae. We concluded that chemical bonding was not the primary reason for the improvement of adhesion, but it was necessary to induce the segregation of PPgMA in the interfacial region and the formation of the soft layer.

Toughness and Durability of Interfaces in Dissimilar Adhesive Joints of Aluminum and Carbon-Fiber-Reinforced Thermoplastics.

The toughness and the durability under a high humidity condition of the interfaces in dissimilar adhesive joints of carbon-fiber-reinforced thermoplastic with a polyamide-6 matrix and Al alloy were evaluated by two test methods, in which a tensile opening load was applied to the specimens to cleave the interfaces apart in two different ways. In the double cantilever beam (DCB) test, the specimens were continuously pulled apart at a constant velocity, while in the wedge test, the specimens are pulled apart at a constant displacement. The crack growth along the interface in the DCB test was dynamically monitored with the assistance of mechanoluminescence for the accurate detection of the phenomena at the crack tip. The wedge test was employed for the evaluation of the durability of the interfaces under high humidity conditions. It was found that the adhesive joints were failed by various failure modes depending on the surface pretreatment and environmental conditions. Throughout the work, discussion was made concerned with the interfacial structures and the adhesion mechanism of dissimilar adhesive joints.

Immortalization of human hepatocytes from biliary atresia with CDK4R24C, cyclin D1, and TERT for cytochrome P450 induction testing.

Hepatocytes are an important tool for in vitro toxicology testing. In addition to primary cultures, a limited number of immortalized cell lines have been developed. We here describe a new cell line, designated as HepaMN, which has been established from a liver associated with biliary atresia. Hepatocytes were isolated from a liver of 4-year-old girl with biliary atresia and immortalized by inoculation with CSII-CMV-TERT, CSII-CMV-Tet-Off, CSII-TRE-Tight-cyclin D1 and CSII-TRE-Tight-CDK4R24C (mutant CDK4: an INK4a-resistant form of CDK4) lentiviruses at the multiplicity of infection of 3 to 10. HepaMN cells exhibited morphological homogeneity, displaying hepatocyte-like phenotypes. Phenotypic studies in vivo and in vitro revealed that HepaMN cells showed polarized and functional hepatocyte features along with a canalicular cell phenotype under defined conditions, and constitutively expressed albumin and carbamoyl phosphate synthetase I in addition to epithelial markers. Since HepaMN cells are immortal and subcloned, kinetics and expression profiles were independent of population doublings. HepaMN cells showed increased CYP3A4 expression after exposure to rifampicin, implying that their close resemblance to normal human hepatocytes makes them suitable for research applications including drug metabolism studies.

Alkylated cage silsesquioxane forming a long-range straight ordered hierarchical lamellar nanostructure.

An alkylated cage silsesquioxane (1), targeting for a new class of bottom-up-type fabricating materials, was successfully synthesized, and its self-assembled structure is described and discussed herein. Through this, it was found that the intermolecular interaction of long alkyl chains of 1 could be manipulated by thermal annealing to form a long-range straight ordered hierarchical lamellar structure with a periodicity of around 5 nm. Subsequent transmission electron microscopy (TEM) clearly identified polyhedral oligomeric silsesquioxane (POSS) molecules of 1 arranged in a highly ordered fashion, with a "head-to-head" type bilayered structure. The observation of a sublayer structure measuring approximately 0.4 nm in width was attributed to the highly regular packing of isobutyl groups in POSS molecules identified by TEM analysis. Moreover, the formation of a long-range straight structure with sharp interfacial boundaries, which is difficult to achieve with traditional diblock copolymers, is considered to be of significant importance to developing new practical applications of self-assembled nanostructures.

A novel planar polarity gene pepsinogen-like regulates wingless expression in a posttranscriptional manner.

BACKGROUND: Planar cell polarity (PCP) originally referred to the coordination of global organ axes and individual cell polarity within the plane of the epithelium. More recently, it has been accepted that pertinent PCP regulators play essential roles not only in epithelial sheets, but also in various rearranging cells. RESULTS: We identified pepsinogen-like (pcl) as a new planar polarity gene, using Drosophila wing epidermis as a model. Pcl protein is predicted to belong to a family of aspartic proteases. When pcl mutant clones were observed in pupal wings, PCP was disturbed in both mutant and wild-type cells that were juxtaposed to the clone border. We examined levels of known PCP proteins in wing imaginal discs. The amount of the seven-pass transmembrane cadherin Flamingo (Fmi), one of the PCP "core group" members, was significantly decreased in mutant clones, whereas neither the amount of nor the polarized localization of Dachsous (Ds) at cell boundaries was affected. In addition to the PCP phenotype, the pcl mutation caused loss of wing margins. Intriguingly, this was most likely due to a dramatic decrease in the level of Wingless (Wg) protein, but not due to a decrease in the level of wg transcripts. CONCLUSIONS: Our results raise the possibility that Pcl regulates Wg expression post-transcriptionally, and PCP, by proteolytic cleavages.

Cohesin controls planar cell polarity by regulating the level of the seven-pass transmembrane cadherin Flamingo.

Planar cell polarity (PCP) refers to the coordination of global organ axes and individual cell polarity in vertebrate and invertebrate epithelia. Mechanisms of PCP have been best studied in the Drosophila wing, in which each epidermal cell produces a single wing hair at the distal cell edge, and this spatial specification is mediated by redistribution of the core group proteins, including the seven-pass transmembrane cadherin Flamingo/Starry night (Fmi/Stan), to selective plasma membrane domains. Through genetic screening, we found that a mutation of the SMC3 gene caused dramatic misspecification of wing hair positions. SMC3 protein is one subunit of the cohesin complex, which regulates sister chromatid cohesion and also plays a role in transcriptional control of gene expression. In the SMC3 mutant cells, Fmi appeared to be upregulated by a posttranscriptional mechanism(s), and this elevation of Fmi was at least one cause of the PCP defect. In addition to the PCP phenotype, the loss of the cohesin function affected wing morphogenesis at multiple levels: one malformation was loss of the wing margin, and this was most likely a result of downregulation of the homeodomain protein Cut. At the cellular level, apical cell size and hexagonal packing were affected in the mutant wing. Dysfunction of cohesin in humans results in Cornelia de Lange syndrome (CdLS), which is characterized by various developmental abnormalities and mental retardation. Our analysis of cohesin in epithelia may provide new insight into cellular and molecular mechanisms of CdLS.

Preparation and characterization of imogolite/DNA hybrid hydrogels.

Imogolite is one of the clay minerals contained in volcanic ash soils. The novel hybrid hydrogels were prepared from imogolite nanofibers and DNA by utilizing strong interaction between the aluminol groups on imogolite surface and phosphate groups of DNA. The hybrid hydrogels of imogolite and DNA were prepared in various feed ratios, and their physicochemical properties and molecular aggregation states were investigated in both dispersion and gel states. The maximum DNA content in the hybrid gels was shown in equivalent molar ratio of imogolite and DNA. The physical properties of the hybrid gels were changed by varying DNA blend ratios. In the dispersion state, the hybrid gels showed a fibrous structure of imogolite, whereas a continuous network structure was observed in pure imogolite, indicating that the hybrid with DNA enhanced the dispersion of imogolite. In the gel state, DNA and imogolite nanofibers formed a 3D network structure.

The seven-pass transmembrane cadherin Flamingo controls dendritic self-avoidance via its binding to a LIM domain protein, Espinas, in Drosophila sensory neurons.

Members of the Flamingo cadherin family are required in a number of different in vivo contexts of neural development. Even so, molecular identities downstream from the family have been poorly understood. Here we show that a LIM domain protein, Espinas (Esn), binds to an intracellular juxtamembrane domain of Flamingo (Fmi), and that this Fmi-Esn interplay elicits repulsion between dendritic branches of Drosophila sensory neurons. In wild-type larvae, branches of the same class IV dendritic arborization neuron achieve efficient coverage of its two-dimensional receptive field with minimum overlap with each other. However, this self-avoidance was disrupted in a fmi hypomorphic mutant, in an esn knockout homozygote, and in the fmi/esn trans-heterozygote. A functional fusion protein, Fmi:3eGFP, was localized at most of the branch tips, and in a heterologous system, assembly of Esn at cell contact sites required its LIM domain and Fmi. We further show that genes controlling epithelial planar cell polarity (PCP), such as Van Gogh (Vang) and RhoA, are also necessary for the self-avoidance, and that fmi genetically interacts with these loci. On the basis of these and other results, we propose that the Fmi-Esn complex, together with the PCP regulators and the Tricornered (Trc) signaling pathway, executes the repulsive interaction between isoneuronal dendritic branches.

Golden Goal collaborates with Flamingo in conferring synaptic-layer specificity in the visual system.

Neuronal connections are often organized in layers that contain synapses between neurons that have similar functions. In Drosophila, R7 and R8 photoreceptors, which detect different wavelengths, form synapses in distinct medulla layers. The mechanisms underlying the specificity of synaptic-layer selection remain unclear. We found that Golden Goal (Gogo) and Flamingo (Fmi), two cell-surface proteins involved in photoreceptor targeting, functionally interact in R8 photoreceptor axons. Our results indicate that Gogo promotes R8 photoreceptor axon adhesion to the temporary layer M1, whereas Gogo and Fmi collaborate to mediate axon targeting to the final layer M3. Structure-function analysis suggested that Gogo and Fmi interact with intracellular components through the Gogo cytoplasmic domain. Moreover, Fmi was also required in target cells for R8 photoreceptor axon targeting. We propose that Gogo acts as a functional partner of Fmi for R8 photoreceptor axon targeting and that the dynamic regulation of their interaction specifies synaptic-layer selection of photoreceptors.

Patterning of J-aggregated dyes using directed self-assembly on micro- and nanopatterned templates fabricated from phase-separated mixed Langmuir-Blodgett films.

We report a useful technique for the deposition of dyes in the form of J-aggregates using directed self-assembly on the micro- and nanopatterned templates fabricated from the phase-separated mixed Langmuir-Blodgett (LB) films. The patterns of the mixed LB films can be tuned by adjusting the intermolecular interactions between the film-forming molecules. We used the mixed LB films containing silane coupling agent for the fabrication of micro- and nanopatterned templates, taking advantage of the difference between the surface free energy of the patterned regions and that of the self-assembled monolayers of the silane coupling agent. Atomic force microscopy showed that dyes were deposited by casting, spin-coating and the LB technique in accordance with the patterns of the original mixed LB films. Emission spectroscopy revealed that J-aggregates were formed in the patterned films. We succeeded in obtaining nanopatterns of a cyanine dye in the form of J-aggregates on the templates.

Contamination-free transmission electron microscopy for high-resolution carbon elemental mapping of polymers.

Specimen contamination induced by electron beam irradiation has long been a serious problem for high-resolution imaging and analysis by a transmission electron microscope (TEM). It creates a deposition of carbonaceous compounds on a region under study, causing the loss of resolution. We developed a method to reduce the beam-induced specimen contamination by cleaning a TEM with activated oxygen radicals. The hydrocarbon contaminants accumulated inside the microscope's chamber can be etched away by gentle chemical oxidation without causing any damage to the microscope. The "contamination-free TEM" can effectively suppress the deposition of carbon-rich products on a specimen and therefore enables us to perform high-resolution carbon elemental mapping by energy-filtering transmission electron microscopy (EFTEM). In this study, we investigated the structure of polymer brushes immobilized on a silica nanoparticle (SiNP), of which molecular weight, length, and density of the brushes had been characterized in detail. The isolated particle showed the stretched formations of the polymer chains growing from the surface, while the densely distributed particles showed the connection of the polymer chains between neighboring particles. Moreover, the polymer brush layer and the surface initiator could be differentiated from each other by the component-specific contrast achieved by electron spectroscopic imaging (ESI). The contamination-free TEM can allow us to perform high-resolution carbon mapping and is expected to provide deep insights of soft materials' nanostructures.

Global gene expression changes including drug metabolism and disposition induced by three-dimensional culture of HepG2 cells-Involvement of microtubules.

Constitutive upregulation and a higher degree of induction of drug metabolism and disposition-related genes were found in a three-dimensional HepG2 culture. The upregulated genes are believed to be regulated by different regulatory factors. Global gene expression analysis using the Affymetrix GeneChip indicated that altered expression of microtubule-related genes may change the expressed levels of drug metabolizing and disposition genes. Stabilization of microtubule molecules with docetaxel, a tubulin-stabilizing agent, in the two-dimensional culture showed gene expression patterns similar to those found in the three-dimensional culture, indicating that the culture environment affects drug metabolism functions in HepG2 cells.

Core-shell structures of silica-organic pigment nanohybrids visualized by electron spectroscopic imaging.

Energy-filtering electron transmission spectroscopy observation has been achieved to elucidate the nanostructures of powdery nanohybrids, which were produced by the dry mechanical milling of organic pigments and silica nanoparticles. The hybrids possess core-shell structures, irrespective of the levels of aggregation of primary particles, whereas hollow sites of aggregates of primary silica particles were filled with the pigment, leading to the locally concentrated distribution of the pigment to reduce the surface areas of the hybrids. The results imply that nanohybridization is referred to as the buildup method, although mechanical tools and procedures are quite the same as those for the conventional breakdown method.

Locating a silane coupling agent in silica-filled rubber composites by EFTEM.

A silane coupling agent (SA) was added to silica/rubber composites at different mixing temperatures and the formation of a coupling layer at the silica/rubber interface was investigated by energy-filtering transmission electron microscopy. Bis(triethoxysilypropyl)tetrasulfane (TESPT), which was used as the SA, reacted with the silanol groups on the silica surface and with styrene-butadiene rubber to form an interfacial coupling layer. The silicon and sulfur elemental distributions were analyzed by electron energy loss spectroscopy (EELS) and elemental mapping. The amount of TESPT trapped in the rubber matrix could be qualitatively estimated by EELS, and the in situ formed coupling layer could be characterized by elemental mapping. The result indicated that the formation of the coupling layer was affected by the mixing temperature. The technique described here will contribute to the study of interface-property relationships and the evaluation of the role of SAs in polymeric composites.

Self-assembled lamellar nanostructures of wholly aromatic rod-rod-type block molecules.

Wholly aromatic rod-rod type di- and triblock molecules, oligo(ether sulfone)-b-oligo(ether ketone)s (OES-OEK), were synthesized to study a solid-state self-assembled nanostructure. The OES and OEK segments in the block molecules form segregated crystalline domains. The energy-filtering transmission electron microscopy images revealed that the di- and triblock OES-OEK co-oligomers formed lamellar nanostructures with a periodicity of approximately 9 and 13 nm, respectively. [structure: see text].

Nanoimaging and spectroscopic analysis of rubber/ZnO interfaces by energy-filtering transmission electron microscopy.

Energy-filtering transmission electron microscopy (EFTEM) was employed for investigating interactions between rubber and ZnO particles in the accelerated vulcanization process. Combining elemental mapping and electron energy loss spectroscopy (EELS) by EFTEM enabled the characterization of the interfaces with spatial resolutions of less than 10 nm and with high elemental detection sensitivity. We found that a sulfur- and zinc-rich compound was generated around ZnO particles, and that product was then revealed to be ZnS-generated as a byproduct in the accelerated vulcanization process. Through this study, it is indicated that the accelerated vulcanization with ZnO does not occur uniformly in the rubber matrix; it occurs locally around ZnO particles at a higher reaction rate, implying that the rubber network structure is not uniform on the nanoscale.

Tunable metallization by assembly of metal nanoparticles in polymer thin films by photo- or electron beam lithography.

The technique of patterning of surfaces with metal-rich structures on micro- or nanoscales was developed by assembling metal nanoparticles into a thin film of polymer in a controllable way. Palladium (Pd) nanoparticles were incorporated into a thin film of poly(methyl methacrylate) (PMMA) using palladium (II) bis(acetylacetonato), Pd(acac)(2), as a precursor vaporized in a nitrogen atmosphere. Depending upon its dose, the irradiation of a PMMA film by UV light or an electron beam (EB) enhances its reducing capability against Pd(acac)(2). This dependency on dose can be used to control the formation and assembly of Pd nanoparticles. Using this technique, binary patterns consisting of metal-rich and metal-poor regions in the polymer film can be created simply by irradiating the surface of the polymer through a binary photomask. Besides the creation of binary patterns, it is also possible to create grayscale patterns where the density of Pd nanoparticles can be tuned to provide shades of gray by the use of light with continuously modulated intensity. Because the electron beam also enhances the reducing power of PMMA against Pd(acac)(2), it is thus possible to obtain highly metallized films with nanoscale pattern features. The PMMA film can be selectively removed by oxygen plasma treatment or by pyrolysis. Thus, highly metallized surfaces with binary or grayscale patterns can be obtained by selective removal of the PMMA films. The metallized regions possess relatively high resistivity against CF(4) plasma compared to the bare silicon surface; therefore, the metallized surface patterns can be transferred onto the underlying silicon substrate by CF(4) plasma treatment. Because of the nanosize effect of metal nanoparticles, the thermal treatment at 900 degrees C, which is significantly lower than the melting temperature of the bulk Pd, yields continuous metallic features by binding the assembled nanoparticles.

Characterization of polymer-adhesive interfaces on a nanometre scale by elemental mapping and image EELS using EFTEM.

Energy-filtering transmission electron microscopy (EFTEM) was applied for investigating interfaces between a polymer and an adhesive. The sample employed in this work is polybutylene terephtharate (PBT) sheets laminated with an epoxy adhesive. It was found that heat aging of the PBT at 180 degrees C in air for > 9 h prior to adhesion decreases the adhesion strength drastically. To investigate this unfavourable aging effect on the adhesion strength, we performed elemental mapping and image EELS using EFTEM. A weak boundary layer with a thickness of < 50 nm was visualized at the PBT-adhesive interface by elemental mapping in the sample subjected to the heat aging and image EELS revealed the origin of this layer. Thus, we clearly correlated the nanoscale interfacial structure with the adhesion strength by EFTEM.