Effect of curing on water diffusivities in acrylate free films as measured via a sorption technique

Studies were performed to investigate the effect of curing on the diffusion coefficients of water, as measured via the sorption technique, in acrylate polymeric films. The mathematical model selected for obtaining diffusion constants from the vapor-phase sorption studies was derived from the longtime Fourier equation used for diffusion into a planar sheet. For Eudragit NE films, the diffusion coefficients of water decreased continuously until a constant minimum value was reached. Diffusion coefficients in Eudragit RS films decreased initially but increased beyond 4 hours of curing at 70δC and 90°C. This latter result suggested the possible evaporation of plasticizer, which also results in a more dramatic increase in glass transition temperature with curing for the Eudragit RS free film in comparison to the Eudragit NE free film. Such loss of plasticizer could also lead to the formation of molecular-scale channels within the films, which would result in increased film permeability. To verify this proposed explanation, the amounts of triethyl citrate plasticizer in Eudragit RS free films were determined using Fourier-transform infrared spectrophotometry. An optimal curing condition was predicted for Eudragit NE and Eudragit RS films based upon the curing conditions at which a minimum value of the diffusion coefficient was reached. Published: August 31, 2007     

The free energy of a liquid when viewed as a population of overlapping clusters

The expression of the free energy of a liquid in terms of an explicit decomposition of the particle configurations into local coordination clusters is examined. We argue that the major contribution to the entropy associated with structural fluctuations arises from the local athermal constraints imposed by the overlap of adjacent coordination shells. In the context of the recently developed Favoured Local Structure model [Soft Matt. 11, 3322 (2015)], we derive explicit expressions for the structural energy and entropy in the high-temperature limit, compare this approximation with simulation data and consider the extension of this free energy to the case of spatial inhomogeneity in the distribution of local structures.     

Impact of high-pressure processing on diffusion in polyethylene based on molecular dynamics simulation

Abstract

The impact of high-pressure processing (HPP) on dissusion of antioxidant butylated hydroxytoluene (BHT) in polyethylene (PE) was discussed via the molecular dynamics method. Furthermore, the glass transition temperatures (T_g), the accessible free volumes of PE and the diffusion coefficients of BHT in PE at different HPP treatments were calculated, and the diffusion trajectories of the BHT molecules in PE were also presented. Finally, the diffusion mechanism of BHT in PE under HPP was analyzed based on the aforementioned simulation results. The results show that the T_g of PE increases under high pressure while the fractional free volume (FFV) reduces, and the diffusion coefficient decreases with the pressure on the rise. The diffusion trajectories of BHT in PE under HPP indicate that the BHT molecules are trapped and slowly wriggle in a narrow path among PE molecular chains due to the extreme high pressure. However, the high temperature has an opposite effect on the diffusion behavior of BHT in PE compared with high pressure. As the temperature rises, the FFV of PE and the diffusion coefficient of BHT in PE are elevated. This study is helpful to the research of high-pressure food safety and packaging migration.     

Near-Infrared Analysis of Hydrogen-Bonding in Glass- and Rubber-State Amorphous Saccharide Solids

Near-infrared (NIR) spectroscopic analysis of noncrystalline polyols and saccharides (e.g., glycerol, sorbitol, maltitol, glucose, sucrose, maltose) was performed at different temperatures (30–80°C) to elucidate the effect of glass transition on molecular interaction. Transmission NIR spectra (4,000–12,000 cm⁻¹) of the liquids and cooled-melt amorphous solids showed broad absorption bands that indicate random configuration of molecules. Heating of the samples decreased an intermolecular hydrogen-bonding OH vibration band intensity (6,200–6,500 cm⁻¹) with a concomitant increase in a free and intramolecular hydrogen-bonding OH group band (6,600–7,100 cm⁻¹). Large reduction of the intermolecular hydrogen-bonding band intensity at temperatures above the glass transition (T _g) of the individual solids should explain the higher molecular mobility and lower viscosity in the rubber state. Mixing of the polyols with a high T _g saccharide (maltose) or an inorganic salt (sodium tetraborate) shifted both the glass transition and the inflection point of the hydrogen-bonding band intensity to higher temperatures. The implications of these results for pharmaceutical formulation design and process monitoring (PAT) are discussed.     

Design of innovated lipid-based floating beads loaded with an antispasmodic drug: in-vitro and in-vivo evaluation

Context: Drotaverine hydrochloride (DRT) is used to treat gastrointestinal spasms accompanied with diarrhoea. Hence, the drug suffers from brief residence in the highly moving intestine during diarrhoea which leads to poor bioavailability and frequent dosing.

Objective: This study aimed to extend DRT residence in the stomach.

Methods: Calcium alginate floating beads were prepared using sodium alginate, isopropylmyristate (oil), and Gelucire® 43/01 (lipid) adopting emulsion gelation technique. The beads were evaluated for their floating ability, DRT entrapment efficiency and in-vitro release. Gelucire® 43/01 /oil-based beads of the selected formula were coated using ethylcellulose and different plasticizers as polyethylene glycol 400 and triethyl citrate to retard the drug release. The coated beads were re-characterized. Finally, the best formulae were investigated for their in-vivo floating ability in dogs besides their delivery to the systemic circulation compared to drug powder in human volunteers.

Results: Incorporation of Gelucire® 43/01 to oil-based beads enhanced the in-vitro performance of the beads. Coated beads prepared using drug:sodium alginate ratio of 1:3 (w/w), 20% (w/v) isopropylmyristate, 20% (w/v) Gelucire® 43/01 showed promising in-vitro performance. The beads floated for 12?h in the dogs’ stomach and produced three-fold increase of the total amount of DRT absorbed within 24?h compared to that of DRT powder.

Conclusions: Gelucire® 43/01 /isopropylmyristate-based calcium alginate floating beads coated with ethylcellulose using either PEG 400 or TEC as plasticizers proved to be a successful dosage form in extending DRT release.     

Glass Transition and Delocalization in a Binary Hard-Sphere Mixture

Abstract

The glass transition of a disparate-size binary liquid and the delocalization of small particles in a glassy matrix are studied within a mode-coupling theory. The density-relaxation functions together with their long-time limits are investigated by solving space- and time-dependent mode-coupling equations numerically. We focus our attention on the effective-potential fluctuations produced by the glassy matrix, which the small particles will experience when they move through the matrix. It is found that in a strongly localized state the spatial correlations of effective-potential fluctuations are well represented by a Gaussian function. For the small particles with a long localization length, on the other hand, the effective potential is no longer Gaussian, reflecting the structure of the glassy matrix established by the big particles. The time-dependence of the effective potential is also investigated.     

阿胶,新阿胶,黄明胶,马皮胶,杂皮胶的质量对比研究：Ⅰ.氨基酸分析

本文用835-50型氨基酸自动分析仪测定了阿胶、新阿胶、黄明胶、马皮胶和杂皮胶中游离氨基酸和总氨基酸的含量,并计算出游离氨基酸、总氨基酸按侧链基团分类和按医药用途分类的相对含量。结果表明,各种氨基酸含量一般以驴皮胶为较高,但与其他几种胶比较并无显著差异,似可以猪皮马皮、牛皮代替驴皮。这也说明,单从氨基酸的含量来鉴别胶的种类和质量似乎不可行。     

Solute-specific effects of osmotic stress on Staphylococcus aureus

AIM: To determine if cell death from osmotic stress is because of lack of sufficient energy to maintain cell metabolism. Additionally, the solute-specific effect of five humectants on bacterial osmoregulation and cell survival was examined. METHODS AND RESULTS: Staphylococcus aureus was placed into 84% relative humidity (RH) broth (five humectants used individually). ATP, ADP and cell viability measurements were determined over time. The results indicate that ATP is not the limiting factor for cell survival under excessive osmotic stress. Although the same RH was achieved with various humectants, the rates of cell death varied greatly as did the sensitivities of the cell populations to osmotic stress. CONCLUSIONS: The results from this study provide strong evidence that mechanisms of osmotic inactivation depend on the solute. The molecular mobility of the system may be an important means to explain these differences. SIGNIFICANCE AND IMPACT OF THE STUDY: By bringing together an understanding of solute-specific effects, microbial physiology and genetics, the mechanisms of inactivation of micro-organisms by solute-specific osmotic stress may be elucidated, and this knowledge may then be exploited to ensure the production of high quality, safe foods.     

A novel method to predict the glass transition of 70% glycerol aqueous solution

Vitrification has been used to successfully cryopreserve cells and tissues for over 60 years. Glass transition temperature (T _g) of the vitrification is a critical parameter, which has been investigated experimentally. In this study, an isothermal–isobaric molecular simulation (NPT-MD) is proposed to investigate the glass transition and T _g of such vitrification solution. The cohesive energy density, solubility parameter (δ) and bulk modulus of the solution during the process of the glass transition are investigated as well. The results indicate that these properties as functions of temperature can give a definite inflexion; thus, these properties can be used to predict T _g more accurately than the heat capacity (C _p ), density (ρ), volume (V) and radial distribution function (rdf). At the same time, the predicted values of T _g agree well with the experimental results. Therefore, molecular dynamics simulation is a potential method for investigating the glass transition and T _g of the vitrification solutions.     

The Frictional Coefficient of Bovine Knee Articular Cartilage

1 Introduction Cartilage has excellent biomechanical and tri- bological properties with low friction and minimum wear in diarthrodial joints throughout the lifetime of most people, and the lifetime of articular cartilage can be 40 years or longer. This has inspired material and bionic scientists to study the mechanism of such excellent tri- bological characteristics in order to develop artificial joints. Various mechanisms have been proposed to ex- plain the remarkable low friction behavior of…     

The Influence of Normal Load and Sliding Speed on Frictional Properties of Skin

The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carded out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s^-1 to 4 mm·s^-1, the friction coefficient increases and ＂stick-slip＂ phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was in- terpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.     

Glass Transition Temperatures Studied by MD Simulation of Some Alkali Metasilicates

Abstract

Molecular dynamics simulation of some alkali metasilicates (M₂SiO₃, M = Li, Na, K) was performed to compare glass transition temperatures, T_g , defined in various ways. The potential parameters derived from ab initio MO calculations were used and found to reproduce the inflection of V-T relation on cooling the system. The T_g defined by the inflection point corresponds well to that defined by geometrical changes of coordination polyhedra found in previous work. The self-diffusion coefficients of the alkali ions in higher temperature regions were shown to be related to the amount of free volume in these systems.     

阿胶、新阿胶、黄明胶、马皮胶、杂皮胶的质量对比研究——Ⅱ、微量元素分析

本文用电感耦合等离子体发射光谱法测定了对人体具有营养、生理及临床意义的27种微量元素。结果表明,各类胶中这些元素的含量均有一个比较狭小的变动范围,可供质量鉴别时参考。除杂皮胶有多种元素含量超出各自的变动范围之外,阿胶、新阿胶、黄明胶中各元素含量比较相近,似可用猪皮、牛皮代用驴皮。阿胶的补血作用可能与其含铁量较高有关,阿胶的止血作用可能与其含钙有关。     

Ketoprofen poly(lactide-co-glycolide) physical interaction

The aim of this work was to provide an understanding of the interaction occurring between ketoprofen and poly(lacticco-glycodic acid) (PLGA) that leads to polymer plasticization. Experimental glass transition temperature (Tg) values were fitted with the theoretical ones predicted by the Fox and Gordon-Taylor/Kelley-Bueche equations. PLGA films containing different amounts of ketoprofen (KET) were prepared by solvent casting and characterized by scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry evidenced that KET acted as a plasticizer in a similar biphasic way in both end-capped and uncapped PLGA. At KET contents of 20% to 35%, depending on the investigated polymer, the Tg was around 23°C. Higher KET amounts did not lower further the Tg, and the excess of drug was found to crystallize into the polymeric matrix. Experimental Tg's deviated negatively from the predicted ones probably because of hydrogen bonding. The FTIR spectra of the films, loaded with different amounts of KET, showed a shift to higher wavenumbers for the peaks at 1697 and 1655 cm⁻¹ confirming the presence of some interactions, probably hydrogen bonds between the ketoprofen carboxylic group and the PLGA carbonyl groups along the polymer backbone. The hydrogen bonding between KET and PLGA is probably responsible for KET plasticizing effect. KET behaving as a lubricant may disrupt polymer chain-chain interactions, removing additional barriers to bond rotation and chain mobility. Published: May 11, 2007