Superhydrophobic polyimide films with a hierarchical topography : combined replica molding and layer-by-layer assembly

Artificial superhydrophobic surfaces with a hierarchical topography were fabricated by using layer-by-layer assembly of polyelectrolytes and silica nanoparticles on microsphere-patterned polyimide precursor substrates followed with thermal and fluoroalkylsilane treatment. In this special hierarchical topography, micrometer-scale structures were provided by replica molding of polyamic acid using two-dimensional arrays of polystyrene latex spheres as templates, and nanosized silica particles were then assembled on these microspheres to construct finer structures at the nanoscale. Heat treatment was conducted to induce chemical cross-linking between polyelectrolytes and simultaneously convert polyamic acid to polyimide. After surface modification with fluoroalkylsilane, the as-prepared highly hydrophilic surface was endowed with superhydrophobicity due to the bioinspired combination of low surface energy materials and hierarchical surface structures. A superhydrophobic surface with a static water contact angle of 160 degrees and sliding angle of less than 10 degrees was obtained. Notably, the polyimide microspheres were integrated with the substrate and were mechanically stable. In addition, the chemical and mechanical stability of the polyelectrolyte/silica nanoparticle multilayers could be increased by heat-induced cross-linking between polyelectrolytes to form nylon-like films, as well as the formation of interfacial chemical bonds.

Organic Solvent-Based Graphene Oxide Liquid Crystals: A Facile Route toward the Next Generation of Self-Assembled Layer-by-Layer Multifunctional 3D Architectures

We introduce soft self-assembly of ultralarge liquid crystalline (LC) graphene oxide (GO) sheets in a wide range of organic solvents overcoming the practical limitations imposed on LC GO processing in water. This expands the number of known solvents which can support amphiphilic self-assembly to ethanol, acetone, tetrahydrofuran, N-dimethylformamide, N-cyclohexyl-2-pyrrolidone, and a number of other organic solvents, many of which were not known to afford solvophobic self-assembly prior to this report. The LC behavior of the as-prepared GO sheets in organic solvents has enabled us to disperse and organize substantial amounts of aggregate-free single-walled carbon nanotubes (SWNTs, up to 10 wt %) without compromise in LC properties. The as-prepared LC GO-SWNT dispersions were employed to achieve self-assembled layer-by-layer multifunctional 3D hybrid architectures comprising SWNTs and GO with unrivalled superior mechanical properties (Young’s modulus in excess of 50 GPa and tensile strength of more than 500 MPa).

Layer-by-layer assembly of silica nanoparticles on 3D fibrous scaffolds : enhancement of osteoblast cell adhesion, proliferation, and differentiation

Silica nanoparticles were applied onto the fiber surface of an interbonded three-dimensional polycaprolactone fibrous tissue scaffold by an electrostatic layer-by-layer self-assembly technique. The nanoparticle layer was found to improve the fiber wettability and surface roughness. Osteoblast cells were cultured on the fibrous scaffolds to evaluate the biological compatibility. The silica nanoparticle coated scaffold showed enhanced cell attachment, proliferation, and alkaline phosphatase activities. The overall results suggested that interbonded fibrous scaffold with silica nanoparticulate coating could be a promising scaffolding candidate for various applications in bone repair and regeneration.

Development of a sustained release solid dispersion using swellable polymer by melting method

PURPOSE: This study is to design a sustained release solid dispersion using swellable polymer by melting method. METHODS: Polyethylene glycol 6000 (PEG 6000) and hydroxypropyl methylcellulose 4000 (HPMC 4000) were used in solid dispersion for not only enhancing drug dissolution rate but also sustaining drug release. HPMC 4000 is a common swellable polymer in matrix sustained release dosage form, but could not be used in preparation of solid dispersion by melting method. However, the current study utilized the swelling capability of HPMC 4000 accompanied by the common carrier PEG 6000 in solid dispersion to accomplish the goal. RESULTS: While PEG 6000 acted as a releasing stimulant carrier and provided an environment to facilitate the swelling of HPMC 4000, this swellable polymer could act as a rate-controlling agent. This greatly assisted the dissolution enhancement by changing the crystalline structure of drug to more amorphous form and creating a molecular interaction. CONCLUSIONS: These results suggested that this useful technique can be applied in designing a sustained release solid dispersion with many advantages.

Layer-by-layer structured membranes of silk fibroin and polyethylenimine on electrospun silk fibroin nanofibers

Self-assembled silk fibroin (SF)-polyethylenimine (PEI) multilayered films were fabricated on ethanol treated electrospun SF nanofibrous substrates via the electrostatic layer-by-layer (LBL) adsorption. The film coated membranes were characterized using scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectrophotometer (XPS). The SEM images showed that the multilayers of SF-PEI were formed on the surface of the ethanol treated SF nanofibres. The characteristics such as the fiber shape and porous structure were well maintained as the number of the coated SF-PEI bilayers was less than five. However, obvious adhesive substances and blocked pores were observed on the surface of the fibers as the number of bilayers of SF-PEI increased to six. Furthermore, the obvious core-shell structures were observed by TEM. The thickness of five SF-PEI bilayers was approximately 80nm. Additionally, the XPS results also revealed that the SF-PEI multilayer composite membranes formed. The adsorption mainly depended on a simple electrostatic interaction between the layers of SF and PEI. These SF-PEI multilayer assembled nanofibrous membranes could be a promising material for use as a sensor, gene delivery agent and scaffolds.

Effect of heat-treatment atmosphere on the bond strength of apatite layer on Ti substrate

Objectives
The purpose of this study was to investigate the bond strength of apatite layer on titanium (Ti) substrate coated by biomimetic method and to improve the bonding of apatite layer to Ti substrate by optimizing the alkali heat-treatment process.

Methods
Ti plates pre-treated with an alkali solution of 10 M sodium hydroxide (NaOH) were heat-treated at 600 °C for 1 h at different atmospheres: in air and in vacuum. A dense apatite layer formed on top of the sodium titanate layer after soaking the alkali and heat-treated Ti samples in simulated body fluid (SBF) for up to 3 weeks. The bond strengths of the sodium titanate layer on Ti substrate, and apatite layer on the sodium titanate layer, were measured, respectively, by applying a tensile load. The fracture sites were observed with a scanning electron microscope (SEM).

Results
The apatite layer on the substrate after alkali heat-treatment in air achieved higher bond strength than that on the substrate after alkali heat-treatment in vacuum. It was found that the interfacial structure between the sodium titanate and Ti substrate has a significant influence on the bond strength of the apatite layer.

Significance
It is advised that titanium implants can achieve better osseointegration under load-bearing conditions by depositing an apatite layer in vivo on a Ti surface subjected to alkali and heat-treated in air.

Influence of fill gap on flexural strength of parts fabricated by curved layer fused deposition modeling

Rapid Prototyping Techniques (RPT) have evolved over the last decade. Novel RP techniques are being developed to improve the overall properties of parts manufactured using RPT. One such technique is the Curved layer fused deposition modeling (CLFDM) which has been developed based on the conventional Fused Deposition Modeling (FDM) technique. The CLFDM technique has gained significant amount of attention as a result of its advantages such as increased flexural strength, reduction of the stair-stepping effect and the reduction in the number of layers, especially for thin shell-like structures. This paper studies the effects of fill gap (FG) on flexural strength and bead dimension, middle-plane cross section profiles and the fracture surface and compares the results to parts made using the traditional planar layer-by-layer approach. Also, in the end some meaningful and interesting future study areas both in hardware design and software development for the CLFDM are proposed.

Determination of cashmere and wool fibre scale frequency by analysing diameter profiles with fast fourier transform

This paper describes a potentially faster and cheaper method of determining fibre scale frequencies. The method uses the single fibre analyser (SIFAN) to  determine the along the fibre diameter profile. This information is then analysed by the Fast Fourier Transform technique using computer software. The paper shows the close association between the mean scale frequencies determined by this method and the traditional approach using SEM.

What's in a measure? A multi-method study of child sexual offenders' beliefs

The hypothesis that child sexual offenders (CSOs) hold distorted, offence-supportive beliefs is usually investigated using interview and questionnaire techniques. However, in light of various problems associated with the use of these techniques, researchers are increasingly turning to cognitive-experimental approaches. To date, no study has examined potential differences in the nature of the beliefs that are revealed using interview, questionnaire, and experimental methods. In this study, data is gathered using these three methods and the results triangulated. CSOs are interviewed and the content categorised into five belief types. CSOs and offender controls then complete a questionnaire measure of offence-supportive beliefs and an experimental task (Rapid Serial Visual Presentation-Modified, or RSVP-M), which uses sentence reading times to explore content held in cognitive structures. As hypothesised, CSOs showed evidence of holding distorted beliefs according to the interview and questionnaire measures. Against predictions, however, CSOs did not show evidence of holding distorted belief structures on the RSVP-M task. In fact, the three methods showed no agreement regarding the belief types each CSO was deemed to hold. These results raise important questions about the phenomena and potential artefacts measured by each method.

Photoreactive azido-containing silica nanoparticle/polycation multilayers : durable superhydrophobic coating on cotton fabrics

In this study, we report the functionalization of silica nanoparticles with highly photoreactive phenyl azido groups and their utility as a negatively charged building block for layer-by-layer (LbL) electrostatic assembly to produce a stable silica nanoparticle coating. Azido-terminated silica nanoparticles were prepared by the functionalization of bare silica nanoparticles with 3-aminopropyltrimethoxysilane followed by the reaction with 4-azidobenzoic acid. The azido functionalization was confirmed by FTIR and XPS. Poly(allylamine hydrochloride) was also grafted with phenyl azido groups and used as photoreactive polycations for LbL assembly. For the photoreactive silica nanoparticle/polycation multilayers, UV irradiation can induce the covalent cross-linking within the multilayers as well as the anchoring of the multilayer film onto the organic substrate, through azido photochemical reactions including C–H insertion/abstraction reactions with surrounding molecules and dimerization of azido groups. Our results show that the stability of the silica nanoparticle/polycation multilayer film was greatly improved after UV irradiation. Combined with a fluoroalkylsilane post-treatment, the photoreactive LbL multilayers were used as a coating for superhydrophobic modification of cotton fabrics. Herein the LbL assembly method enables us to tailor the number of the coated silica nanoparticles through the assembly cycles. The superhydrophobicity of cotton fabrics was durable against acids, bases, and organic solvents, as well as repeated machine wash. Because of the unique azido photochemistry, the approach used here to anchor silica nanoparticles is applicable to almost any organic substrate.

Preparation of nanoparticles by crosslinking folate conjugated chitosan with vanillin and its characterization

Functionalized chitosan (CS) were widely used as drug delivery system in the chemotherapy of various disease. In this work, folate (FA) was conjugated into chitosan molecular as targeting ligand based on Schiff reaction between –NH₂ group of CS and –COOH group of FA. And nanoparticles were made by emulsion method with vanillin novel cross-linking agent. The FA modified CS and its nanoparticles were characterized by Fourier transform spectroscopy (FT-IR), scanning electron microscope (SEM) and Zeta potential. SEM results confirmed the nanoparticles made from FA-CS conjugate were spherical in shape and were about 100 nm in size. Zeta potential analysis revealed that the nanoparticles were negatively charged with charge density of -7.73mV.

Self-assembled multimicellar vesicles via complexation of a rigid conjugated polymer with an amphiphilic block copolymer

A viable method of encapsulating block copolymer micelles inside vesicles using a conjugated polymer is reported in this study. Self-assembly and complexation between an amphiphilic block copolymer poly(methyl methacrylate)-b-poly(acrylic acid) (PMMA-b-PAA) and a rod-like conjugated polymer polyaniline (PANI) in aqueous solution were studied using transmission electron microscopy, atomic force microscopy and dynamic light scattering. The complexation and morphology transformation were driven by electrostatic interaction between PANI and the PAA block of the block copolymer. Addition of PANI to PMMA-b-PAA induced the morphology transformation from micelles to irregular vesicles through vesicles, thick-walled vesicles (TWVs) and multimicellar vesicles (MMVs). Among the observed morphologies, MMVs were observed for the first time. Morphology transformation was studied as a function of aniline/acrylic acid molar ratio ([ANI]/[AA]). Micelles were observed for the pure block copolymer, while vesicles and TWVs were observed at [ANI]/[AA] = 0.1 and 0.3, respectively. MMVs were observed at [ANI]/[AA] = 0.5 and irregular vesicles were observed for molar ratios at 0.7 and above. Clearly, a conjugated polymer like polyaniline can induce a morphology transformation even at its lower concentrations and produce complex morphologies.