Energy release rate along a kinked path

Considering anti‐plane elasticity we provide an existence result for the energy release rate along a piecewise C^{1, 1} path that admits a kink. We provide two representations: an asymptotic one in terms of the stress intensity factor and an integral one in terms of the Eshelby tensor. Both the formulas make use of an implicit coefficient, depending on the kink angle and obtained by a minimum problem. Copyright © 2010 John Wiley & Sons, Ltd.     

Functional film of ethylene vinyl acetate and co‐polyamide compound containing “Nisin” active substance

This study deals with flexible films incorporating nisin for antibacterial active packaging purposes. A novel approach was used to gain control over nisin release profile from a thermoplastic film in order to enhance its antibacterial efficiency. This approach involves polymer blends of ethylene vinyl acetate copolymer and co‐polyamide at various ratios. It was shown that the release profile of an antibacterial substance from active packaging to foodstuff is a key factor concerning the antibacterial efficiency. Samples of 400[μm] were produced by using a laboratory twin screw compounder and a laboratory hot press. Samples were characterized for their migration kinetics, molecular interactions, mechanical properties, and water swelling properties. Antibacterial activity tests show that nisin incorporated films reduced bacterial count by different extents. Listeria ATCC 33090 was used as target bacteria (data not shown). Nisin migration profile to water medium was determined by Lowry's protocol. Scanning electron microscopy images and thermal analysis indicated that no significant molecular interactions occurred. Furthermore, droplet and co‐continues like morphology were seen at different polymer blend ratios. Osmotic pressure driven release mechanism appears to be the dominant migration mechanism, and diffusion kinetics was dominant. Results show that morphology of the polymer blend matrix alters the diffusion coefficient. In addition, water swelling characterization of different samples was done in order to reveal the relations with the diffusion coefficient. It seems that there is an inverse resemblance between water swelling and the diffusion coefficient trends.     

One step synthesis,characterization of F127-Mn+-chlorpyrifos mesoporous silica for sustained release system with pH sensitivity

The triblock copolymer F127 (molecular formula (EO)₁₀₆(PO)₇₀(EO)₁₀₆) was adopted as template with TMOS as the silica source. They were hydrolyzed by acidic aqueous solution in which chlorpyrifos (CH) and metal ions (Mⁿ⁺) were introduced to the products to construct "F127-Mⁿ⁺-CH" coordination structure in one step. Different sustained release systems were prepared through changing the composition of acidic aqueous solution added during the preparation. The characterization results confirmed the coordination interaction existing among metal ions, mesoporous silica and chlorpyrifos. It was also proved that the chlorpyrifos loaded in the sustained release system existed as amorphous state. According to SEM and TEM observation, the pore of the material presented as face-centered cage-type cubic structure with IM-3M symmetry similar to SBA-16 which is in accordance with N₂ adsorption isotherms. The as-synthesized system showed significant pH sensitivity in the sustained release process indicating that the sustained release system can be well stored in neutral environment and activated while sprayed into earth in acid or basic environment. Their sustained release curves can be described by Korsmeyer-Peppas equation in neutral while accords with Higuchi under acid or basic environment.     

Controlled Release of an Antihypertensive Drug through Interpenetrating Polymer Network Hydrogel Tablets of Tamarind Seed Polysaccharide and Sodium Alginate

The application of interpenetrating polymer network (IPN) hydrogel tablets of tamarind seed polysaccharide and sodium alginate for controlled release of a water-soluble antihypertensive drug, propranolol HCl (PPL), was investigated. The IPN tablets loaded with PPL or PPL–resin complex (resinate) were prepared by a wet granulation/covalent cross-linking method. Fourier Transform Infrared Spectroscopic confirmed the cross-linking reaction and IPN formation, while X-ray Diffraction and Scanning Electron Microscopy studies confirmed the amorphous dispersion of the drug within the IPN tablets. The plain drug PPL showed complete release within 1 h, while drug release from the resinate was prolonged for 2.5 h and the IPN matrices showed drug release up to 24 h. The drug release rate from the IPN matrices was affected by polymer concentration and cross-linking time; the higher the cross-linking time, the slower was the drug release. The drug release mechanism was found to be of a non-Fickian type.     

Fabrication and sustained release properties of porous hollow silica nanoparticles

MCM-41-type mesoporous silica nanospheres(MSN) have been prepared using n-cetyltrimethylammonium bromide(CTAB) as a soft template.The pseudo-moire' rotational pattern inside the MSN results in many interior defects.Hollow mesoporous silica(HMS) spheres were synthesized by solvent extraction of the template from MSN.The morphology and structure of MSN and HMS were studied by TEM,XRD and nitrogen sorption techniques.A model drug,bromocresol green dye,was packed inside different regions of HMS through impregna...     

Sol–gel matrices for controlled release: from macro to nano using emulsion polymerisation

By combining sol–gel technology with emulsion chemistry, it is possible to produce spherical particles with a designed microstructure based on a judicious choice of solvent/surfactant and sol–gel reaction parameters. When an active molecule is located in the aqueous droplet of a water-in-oil (W/O) emulsion, encapsulation occurs as the silicon precursors polymerise to build an oxide cage around the active species. By changing the solvent–surfactant combination, the particle size can be varied from 10 nm to 100 μm. The size of the particles is controlled by the size of the emulsion droplet, which acts as a nano-reactor for the sol–gel reaction. The release profiles can be tailored, independently of the particle size, by controlling the internal structure of the particles: pore volume, pore size, tortuosity, and surface chemistry (e.g. by introduction of trialkoxysilane). This can be easily achieved by controlling sol–gel processing parameters such as the water-to-alkoxide ratio, pH, alkoxide concentration, ageing, drying time and temperature. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Dynamic Structural Transformation of Resveratrol‐Modified Stearate Liposomes Led to a Spontaneous Drug Release System

A mono‐substituted resveratrol derivative, resveratrol‐modified stearate (RMS), was synthesized by selectively coupling of stearic acid to the monohroxyphenyl of resveratrol in order to enhance both the stability and bioavailability of resveratrol. The RMS self‐assembles into liposomes and a series of suprastructural transformations into metastable helical ribbon, linear wire‐like structures, and inert spherical nanoparticles were detected that may be induced by the hydrogen‐bonding interactions. As a model for drug‐release investigations, gold nanoparticles (AuNPs) were encapsulated successfully by RMS to generate vesicles and succeed to release AuNPs druing the transformation to a ribbon‐like metastable stucture at ambient temperature.     

Nanocomposites of TiO 2 and Siloxane Copolymers as Environmentally Safe Flame-Retardant Materials †

Composites of titanium dioxide (TiO₂) nanoparticles and biocatalytically synthesized dimethylsiloxane copolyamides were prepared, and their thermal and flame-retardant properties were investigated. The flammability properties such as heat release capacity and total heat release were measured from microscale cumbustion calorimetry (MCC). The thermal degradation temperatures, char yields, and the heat-release capacities of these nanocomposites were significantly improved over the pure polymers. The heat-release capacities of the siloxane copolymer nanocomposites with 20wt% of TiO₂ were found to be 167 and 129 J/g K, which is a 35% less than the pure polymers (260 and 194 J/g K, respectively). The SEM/EDAX surface-analysis studies on nanocomposite films and their char revealed that nanocrystalline-TiO₂ plays an important role in forming carbonaceous silicate char on the surface as a protective layer.     

Well‐defined thermoresponsive dendritic polyamide/poly(N‐vinylcaprolactam) block copolymers

The first‐ and second‐generation well‐defined thermoresponsive amphiphilic linear–dendritic diblock copolymers based on hydrophilic linear poly(N‐vinylcaprolactam) and hydrophobic dendritic aromatic polyamide have been synthesized via reversible addition fragmentation chain transfer polymerization of N‐vinylcaprolactam by employing dendritic chain‐transfer agents possessing a single dithiocarbamate moiety at the focal point. These linear–dendritic copolymers exhibit reversible temperature‐dependent phase transition behaviors in aqueous solution as characterized by turbidity measurements using UV–vis spectroscopy. Their lower critical solution temperatures depend on the generation of the dendritic aromatic polyamides and the concentrations of the copolymer solutions. These amphiphilic copolymers are able to form nanospherical micelles in the aqueous solution as revealed by fluorescent spectroscopy, dynamic light scattering, and transmission electron microscope (TEM). The core–shell structure of micelles has been proved by ¹H NMR analyses of the micelles in D2O. The micelles loaded with indomethacin as a model drug showed high‐drug loading capacity and thermoresponsive drug release behavior. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3240–3250     

Controlled Drug Release from Gelatin-Sodium Carboxymethylcellulose Interpenetrating Polymer Networks

Hydrogels of uncrosslinked gelatin, crosslinked gelatin (Gelx), and various compositions of semi-interpenetrating polymer network of cross-linked gelatin with uncross-linked sodium carboxymethylcellulose [Gelx-NaCMC] were investigated as potential matrices for substrate delivery. Simultaneous swelling behavior and controlled drug release under enzymatic conditions (erodible) were monitored for hydrogels of [Gelx-NaCMC] and Gelx. Results indicated a first order release indicating that the processes (rate of drug diffusion and degradation) do not follow the same kinetics.