Rheological analysis of the structural properties effecting the percutaneous absorption and stability in pharmaceutical organogels

This study presents the organogels of glyceryl monostearate emulsifiers and coconut oil as an alternative for developing the traditional organogels. We investigated how the emulsifier type affects the semisolid consistency and the drug release. In these aspects we compared glyceryl monostearate organogels (GMSO) to commercially available references, while studying the effect of the individual constituents on the structural and functional properties.Rheology provided indirect information on the structure, relevant from an application point of view. We observed that glyceryl monostearate as an organogelator results in a network with elastic nature and moderate crosslink energy. The products had low viscosity and low yield value which means practically an easily spreadable pharmaceutical dosage form with soft consistency.Modelling the percutaneous absorption in vitro, we observed that the diffusion of the piroxicam incorporated was significantly affected by the thermodynamical potency of piroxicam, which was favoured by the emulsifier. The glyceryl monostearate enhanced the partition of the suspended drug, resulting in higher drug release.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Rheological properties of fresh cement pastes and clinker reactivity

This paper presents research results concerning the influence of clinker reactivity on rheological properties of cement pastes at early stages of hydration (lasting less than one hour). The research was carried out on clinkers synthesized in a laboratory, on non-alkaline cements and cements containing in-built alkalis (sodium, potassium) in the clinker phase.The clinker reactivity was estimated from the flow curves and stress changes in time occurring in clinker pastes while maintaining constant measurement parameters. It was found that the effectiveness of gypsum as a setting controller depends on clinker reactivity. Increased clinker reactivity is accompanied by a decreased consistency of a cement paste.The research results indicate that decreased reactivity of clinkers containing inbuilt alkalis is connected with decreased setting controlling effectiveness of added gypsum. This is manifested by a consistency increase of such system at early stages of hydration.     

In situ biosynthesized silver nanoparticle-incorporated synthesized zeolite A using Orthosiphon aristatus extract for in vitro antibacterial wound healing

The capability of synthesized zeolite A (SZ) to immobilize Ag ions (Ag-SZ) and Ag nanoparticles (AgNp-SZ) were comparatively studied. A novel approach of in situ biosynthesized AgNP-incorporated synthesized zeolite A (AgNp-SZ) was synthesized at an optimum volume of 0.4 mL of the Orthosiphon aristatus (O. aristatus) leaves plant extract (5%) using an in situ approach. In comparison, Ag-SZ was produced by loading the synthesized zeolite with Ag ions. All synthesized materials were characterized for their morphologies and physicochemical properties. The characterization analyses validate that the biosynthesized AgNP (<100 nm) using O. aristatus leaves extract was incorporated into the zeolite A. The antibacterial testing confirmed that these materials have antibacterial activity against Escherichia coli ATCC 11229 and Staphylococcus aureus ATCC 6538. MIC/MBC analysis demonstrated that in 0.9% saline solution, AgNP-SZ had higher antibacterial activity than Ag-SZ. The in vitro cell viability and migration assays were further examined towards human skin fibroblast cells HSF 1184. Results show that the materials are not cytotoxic to HSF 1184, and the biosynthesized AgNP-SZ promotes cell migration and proliferation higher than Ag-SZ. This research proved that the biocompatible antibacterial wound healing agent of AgNP-SZ can be synthesized using an in situ approach where the reduction process of Ag ions in the zeolite A can be performed using plant extract.     

弯曲动脉的血流动力学数值分析

利用计算流体力学的理论和方法对弯曲动脉中的血流动力学进行数值分析，是研究心血管疾病流体动力学机理的一种行之有效的方法。本文将升主动脉、主动脉弓和降主动脉联系起来作为弯曲动脉几何模型，给出了血液流动的边界条件以及计算条件。根据生理脉动流条件，对狗的弯曲动脉几何模型内发展中的血液流动进行了有限元数值模拟，并利用可视化方法对血液流动的轴向速度、二次流、壁面切应力等计算结果进行了分析。研究结果表明，在弯管内侧壁处，同时存在主流方向和二次流方向的回流，此处容易形成涡流。弯管内侧壁比外侧壁的壁面切应力具有更强的脉动性。     

Performance modeling and analysis of blood flow in elastic arteries

Nomenclature　　τ　　wallshearstressγshearrateτy yieldstressηc Cassonviscosityktheconsistencyindexnnon_Newtonianindexτp shearstressofthepthelementωangularvelocityRvessel’sradiusCwavespeedM　　magneticparameter (Hartmannnumber)u,w　velocitycomponentinther_andz_directions,respectivelyP　　pressureα　　unsteadinessparameter k , R meanparametersTp relaxationtimeofthepthelementρ densityIntroductionTheimportancetoatherogenesisofarterialflowphenomenasuchasflowseparation ,recirculationands…     

The effects of blood viscoelasticity on the pulse wave in arteries

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Rheological properties and percolation in suspensions of multiwalled carbon nanotubes in polycarbonate

This paper is concerned with several issues related to the rheological behavior of polycarbonate/multiwalled carbon nanotube nanocomposites. The composites were prepared by diluting a masterbatch of 15 wt.% nanotubes using melt-mixing method, and the dispersion was analyzed by SEM, TEM, and AFM techniques. To understand the percolated structure, the nanocomposites were characterized via a set of rheological, electrical, and thermal conductivity measurements. The rheological measurements revealed that the structure and properties were temperature dependent; the percolation threshold was significantly lower at higher temperature suggesting stronger nanotube interactions. The nanotube networks were also sensitive to the steady shear deformation particularly at high temperature. Following preshearing, the elastic modulus decreased markedly suggesting that the nanotubes became more rigid. These results were analyzed using simple models for suspensions of rod-like particles. Finally, the rheological, electrical, and thermal conductivity percolation thresholds were compared. As expected, the rheological threshold was smaller than the thermal and electrical threshold.     

Rheological properties of lightly crosslinked carboxy copolymers in aqueous solutions

The rheological properties of a series of lightly crosslinked carboxy copolymers in aqueous solutions have been evaluated in steady shear and dynamic oscillatory modes. Viscosity profiles and the behavior of storage modulus are related to the chemical composition of the copolymers and their crosslinking density. A maximum in viscosity and in storage modulus which depends on the type of crosslinking agent used is explained by a combination of a chain entanglement mechanism and a closely-packed spheres model. The recovery of viscosity and storage modulus after shearing is very fast and is related to the very fast rearrangement of the microgel structure as a function of time.     

Rheological properties of oil paints and their flow instabilities in blade coating

Painters express their ideas and emotions by making use of oil paints, tools, and painting techniques. Their artworks appear on the surface, which depend on colors, tools, and the sensuous touch of the painters. From the scientific viewpoint, it is determined by the rheological properties of oil paints and their flow behavior while the external force is applied to oil paints. It means that the artists know through learning or by instinct that the oil paints have different rheological properties according to the color, and that various surfaces can be generated by changing the operating conditions. In this study, we measured the rheological properties of oil paints and investigated their flow behavior when the flow was applied. Flow instability was visualized, and the coating window was analyzed, which was supposed to mimic the painting process of the artists. We could understand that oil paints are similar in ingredients, rheological properties, and flow characteristics to industrial coating process. One important thing to note is that the painting is a process to pursue heterogeneity that is generated by the touches of the artists, while the coating process in industry is a process to pursue homogeneity so as to get defect-free surface with high productivity.     

Rheological properties of network models with configuration-dependent creation and loss rates

A numerical stochastic approach allows the exact solution of the convection equation arising in network theories. We now want to show the flexibility and the limits of this approach by studying the rheological properties of different kinds of models.     

Rheological properties of branched polystyrenes: nonlinear shear and extensional behavior

Nonlinear shear and uniaxial extensional measurements on a series of graft-polystyrenes with varying average numbers and molar masses of grafted side chains are presented. Step-strain measurements are performed to evaluate the damping functions of the melts in shear. The damping functions show a decreasing dependence on strain with an increase in mass fraction of grafted side chains. Extensional viscosities of the melts of graft-polystyrenes exhibit a growing strain hardening with increasing average number of grafted side chains as long as the side branches have a sufficient molar mass to be entangled. Graft-polystyrenes with side arms below the critical molar mass M _c for entanglements of linear polystyrene but above the entanglement molar mass M _e of linear polystyrene (M _e < M _w,br < M _c) still show a distinct strain hardening. With decreasing molar mass of the grafted side chains (M _w,br < M _e) the nonlinear-viscoelastic properties of the graft-polystyrene melts approach the behavior for a linear polystyrene with comparable polydispersity.Electronic Supplementary Material Supplementary material is available for this article at     

Rheological properties and dispersion stability of magnetorheological (MR) suspensions

In the present article, the rheological responses and dispersion stability of magnetorheological (MR) fluids were investigated experimentally. Suspensions of magnetite and carbonyl iron particles were prepared as model MR fluids. Under an external magnetic field (H ₀) and a steady shear flow, the yield stress depends upon H ₀ ^3/2. The Yield stress depended on the volume fraction of the particle (φ) linearly only at low concentration and increased faster at high fraction. Rheological behavior of MR fluids subjected to a small-strain oscillatory shear flow was investigated as a function of the strain amplitude, frequency, and the external magnetic field. In order to improve the stability of MR fluid, ferromagnetic Co-γ-Fe₂O₃ and CrO₂ particles were added as the stabilizing and thickening agent in the carbonyl iron suspension. Such needle-like particles seem to play a role in the steric repulsion between the relatively large carbonyl iron particles, resulting in improved stability against rapid sedimentation of dense iron particles. Furthermore, the additive-containing MR suspensions exhibited larger yield stress, especially at higher magnetic field strength. Received: 4 April 2000 Accepted: 6 November 2000     

Investigation of third-grade non-Newtonian blood flow in arteries under periodic body acceleration using multi-step differential transformation method

In this paper, a non-Newtonian third-grade blood in coronary and femoral arteries is simulated analytically and numerically. The blood is considered as the thirdgrade non-Newtonian fluid under the periodic body acceleration motion and the pulsatile pressure gradient. The hybrid multi-step differential transformation method (Hybrid-MsDTM) and the Crank-Nicholson method (CNM) are used to solve the partial differential equation (PDE), and a good agreement between them is observed in the results. The effects of the some physical parameters such as the amplitude, the lead angle, and the body acceleration frequency on the velocity and shear stress profiles are considered. The results show that increasing the amplitude, A_g, and reducing the lead angle of body acceleration, φ, make higher velocity profiles on the center line of both arteries. Also, the maximum wall shear stress increases when A_g increases.     

Experimental Methods in Testing of Tissues and Implants*

Three experimental tasks are of primary interest in biomechanics: determination of the mechanical properties of biomaterials, including tissues and artificial materials; validation of the mechanical reliability of implantable devices; assessment of the compatibility of the mechanical properties of such devices with the surrounding biological environment. Due to the complexity of the in vivo conditions, most of these studies are performed on in vitro models. This contribution presents a review of some methods that are currently utilised at the Laboratory of Biological Structure Mechanics at the Politecnico of Milan.     

Two-phase non-linear model for blood flow in asymmetric and axisymmetric stenosed arteries

The pulsatile flow of a two-phase model for blood flow through axisymmetric and asymmetric stenosed narrow arteries is analyzed, treating blood as a two-phase model with the suspension of all the erythrocytes in the core region as the Herschel-Bulkley material and plasma in the peripheral layer as the Newtonian fluid. The perturbation method is applied to solve the resulting non-linear implicit system of partial differential equations. The expressions for various flow quantities are obtained. It is found that the pressure drop, plug core radius, wall shear stress increase as the yield stress or stenosis height increases. It is noted that the velocity increases, longitudinal impedance decreases as the amplitude increases. For asymmetric stenosis, the wall shear stress increases non-linearly with the increase of the axial distance. The estimates of the increase in longitudinal impedance to flow of the two-phase Herschel-Bulkley material are significantly lower than those of the single-phase Herschel-Bulkley material. The results show the advantages of two-phase flow over single-phase flow in small diameter arteries with stenosis.     

Rheological and diffusion properties of a dextran-con A polymer in the presence of Insulin and Magnesium

Previous work carried out in our laboratories has focused on the formation and investigation of a dextran and concanavalin A (con A) based gel, which has the ability to alter its conformational structure in the presence and absence of free and terminal glucoses such that a gel–sol phase transition occurs. Here we report the diffusion and rheological investigations in to the effects of the addition of insulin and varyingconcentrations of magnesium chloride hexahydrate (Mg₂Cl₂6H₂O) at 20 and 37 °C. Rheological examination of glucose-sensitive (dextran-con A) gels were conducted using a cone and plate viscometer used in continual rotation and oscillatory modes. The results are interpreted in terms of the structure of the gel network and suggest rheological assessment provides an effective method of assessing the properties of gel systems. The subsequent testing of such formulations in in-vitro diffusion experiments revealed a reduction in the rate of diffusivity in the insulin marker, poly R-478 dye. The performance of this self-regulating drug delivery system has been examined and the addition of insulin and magnesium chloride may alter the way in which the gel operates as a drug delivery device and in the delivery of insulin. This may have implications for other ligands.     

A computer model of pulse wave and input impedance in human arteries

To predict the propagation of pressure and flow pulses in arterial system and the variation of vascular input impedance, a branched and tapered tube model is studied through one-dimensional transient flow analysis. Coupling the continuity and momentum equations yields a group of quasilinear hyperbolic partial differential equations which can be solved numerically by using the method of characteristics. Several boundary conditions of the arterial system are also simplified suitably. The propagation of the pulses of the arterial system and the vascular input impedance is calculated on computer by using the dimensions and the physiological data of the arterial system. The results point out that the pressure and flow pulses of the arterial system and the vascular input impedance produced by this theoretical model is consistent quite well with the experimental results published.     

Numerical studies of blood flow in healthy,stenosed, and stented carotid arteries

Numerical analysis of pulsatile blood flow in healthy, stenosed, and stented carotid arteries is performed with the aim of identifying hemodynamic factors in the initiation, growth, and the potential of leading to severe occlusions of a diseased artery. The Immersed Finite Element Method is adopted for this study to conveniently incorporate various geometrical shapes of arteries without remeshing. Our computational results provide detailed quantitative analysis on the blood flow pattern, wall shear stress, particle residence time, and oscillatory shear index. The analysis of these parameters leads to a better understanding of blood clot formation and its localization in a stenosed and a stented carotid artery. A healthy artery is also studied to establish a baseline comparison. This analysis will assist in developing treatments for diseased arteries and novel stent designs to reduce restenosis. Copyright © 2008 John Wiley & Sons, Ltd.     

Flat-jack tests and inverse analysis for the identification of stress states and elastic properties in concrete dams

In this paper an experimental-numerical method, centred on flat-jack tests, is presented for the identification of local stress states and possibly deteriorated elastic properties of concrete in existing dams. It is shown herein that the synergistic combination of new pattern of flat-jack experiment, computer simulation of the test (by conventional finite elements) and inverse analysis allows to exploit experimental data more effectively than by the traditional procedure, and to achieve more information on material properties. In fact, at suitably chosen locations on the free surface of the monitored dam, all the components of local (plane) stress state and the elastic moduli in two orthogonal directions (including shear stiffness) can be estimated by the proposed method. The inverse problem in point is formulated as a sequence of two parameter identifications, i.e. as a bilevel (in the sense of Stackelberg) mathematical programming problem. The solution in a stochastic context is achieved by means of a modified Bayes technique, allowing to obtain, in a “batch” (non sequential) way, parameter estimates endowed with a covariance matrix which quantifies their degrees of confidence and correlations. Dedicated to the memory of Professor Giulio Ceradini.