Colloidal Systems (colloidal + system)

Distribution by Scientific Domains

Selected Abstracts

A three-scale computational model of reactive pollutant transport in smectitic clays

Márcio A. Murad
Abstract A three-scale model of dual-porosity type is proposed to describe contaminant transport in swelling clays. The swelling medium is characterized by three separate length scales (nano, micro and macro) and two levels of porosity (micro- and macro-pores). At the nanoscale the medium is composed of charged clay particles saturated by a binary monovalent aqueous electrolyte solution occupying the micro-pores. At the intermediate (micro) scale the two-phase system is represented in a homogenized fashion with averaged microscopic equations governing the behaviour of the clay clusters (or aggregates) regarded a two-phase mixture composed of clay particles and electrolyte solution. At the macroscale, the microscale mixture of clay clusters is homogenized with the bulk solution containing non-electrolyte species lying in the macro-pore system. The resultant macroscopic picture appears governed by a dual-porosity model wherein the clay clusters act as sources/sinks of mass to the macro-pore system. Under a local equilibrium assumption between the clay clusters and macro-pores, a quasi-steady version of the dual-porosity model is derived. This framework combined with a three-scale picture of the colloidal system allows to provide nanoscopic representations for the retardation coefficient, governing the instantaneous adsorption/desorption of the ionic species in the micro-pores, in terms of the local behaviour of the electrical double layer potential which satisfies a Poisson,Boltzmann-type problem at the nanoscale. Copyright © 2006 John Wiley & Sons, Ltd. [source]

The dynamic behavior of magnetic colloids in suspension

Tina Autenrieth
The dynamic behavior of magnetic colloidal particles in suspension is investigated. The particles of the core,shell colloid consist of a cobalt ferrite core embedded in a silica shell and are stabilized by surface charges. As the suspension is strongly opaque to visible light, it can not be probed by dynamic light scattering techniques as a result of strong multiple scattering as well as absorption effects. Therefore, the static and dynamic behavior is probed with small-angle X-ray scattering and X-ray photon correlation spectroscopy (XPCS), respectively. Using XPCS, we are able to study the diffusion coefficient of an opaque colloidal system as a function of the scattering vector. In this paper, we report on the behavior of the colloidal system in the absence of an external magnetic field, meaning that the magnetic moments of the particles are oriented randomly. We find no evidence for magnetic interactions in the static data, while the dynamic XPCS data deviate very significantly from the predictions of model calculations. [source]

PLGA nanospheres for the ocular delivery of flurbiprofen: Drug release and interactions

E. Vega
Abstract Poly(D,L -lactide- co -glycolide) nanospheres incorporating flurbiprofen were prepared by the solvent displacement technique for purposes of assessing (i) drug,polymer physicochemical interactions, (ii) flurbiprofen release from the polymer matrix and (iii) eye permeation of the drug formulated in the colloidal system. The resulting nanospheres were on average 200,300 nm in size and bore a negative charge (,-potential around ,25 mV). They were shown by atomic force microscopy and transmission electron microscopy to be spherical and regular in shape. Thermal methods, infrared spectroscopy and X-ray diffraction showed that the drug was dispersed inside the particles. These tests evidenced an eutectic mixture meaning more widespread dispersion of the drug in the polymer system. Entrapped flurbiprofen was released in vitro from the polymer system by dissolution and diffusion in high drug loaded nanospheres, whereas those with a lesser load showed only diffusion. The ex vivo corneal permeation study showed that flurbiprofen-loaded nanospheres enhanced drug penetration by about twofold over commercial eye drops containing poly(vinyl alcohol) and by about fourfold over flurbiprofen in pH 7.4 phosphate buffer. The corneal hydration level of each cornea was determined to evaluate potential corneal damage. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:5306,5317, 2008 [source]

Dermal delivery of desmopressin acetate using colloidal carrier systems

Melkamu Getie
Recently, the transdermal route has received attention as a promising means to enhance the delivery of drug molecules, particularly peptides, across the skin. In this work, the skin penetration profiles of desmopressin acetate from a colloidal system (water-in-oil microemulsion) and an amphiphilic cream, a standard formulation, were determined using Franz diffusion cells and compared. In the case of the microemulsion, the total percentages of dose obtained from different skin layers (stratum corneum to subcutaneous tissue) were 3.30 ± 0.67, 7.37 ± 2.43 and 15.54 ± 2.72 at 30, 100 and 300 min, respectively. Similarly, 5.19 ± 0.96, 8.04 ± 0.97 and 14.4 ± 5.15% of the dose applied was extracted from the skin treated with the cream. About 6% of the applied dose reached the acceptor compartment from the microemulsion instead of 2% from the cream within 300 min. The concentration of drug that penetrated into the upper layers of the skin was higher from the cream than from the microemulsion at all time intervals. On the other hand, a higher amount of drug was found in the deeper skin layers and in the acceptor compartment from the microemulsion. [source]

Polyethylenimine-coated albumin nanoparticles for BMP-2 delivery

Sufeng Zhang
Abstract Nanoparticle (NP)-based delivery has gained importance for improving the potency of therapeutic agents. The bovine serum albumin (BSA) NPs, obtained by a coacervation process, was modified by electrostatic adsorption of cationic polyethylenimine (PEI) to NP surfaces for delivery of bone-inducing growth factor, bone morphogenetic protein-2 (BMP-2). Different concentrations of PEI were utilized for coating BSA NPs to stabilize the colloidal system and to control the release of BMP-2. The NPs were characterized by size and zeta potential measurements, as well as by Scanning Electron Microscopy and Atomic Force Microscopy. The encapsulation efficiency was typically >90% in all NP preparations. In vitro release kinetics showed that the PEI concentration used for coating the NPs efficiently controlled the release of BMP-2, demonstrating a gradual slowing, sustained release pattern during a 10-day study period. The bioactivity of the encapsulated BMP-2 and the toxicity of the NPs were examined by the alkaline phosphatase (ALP) induction assay and the MTT assay, respectively, using C2C12 cells. The results indicated that PEI was the primary determinant of NP toxicities, and BSA NPs coated with 0.1 mg/mL PEI demonstrated tolerable toxicity, retained the bioactivity of BMP-2, and efficiently slowed the release rate of BMP-2. We conclude that BMP-2 encapsulated in BSA NPs might be an efficient way to deliver the protein for in vivo bone induction. [source]

Forces between Surfactant-Coated ZnS Nanoparticles in Dodecane: Effect of Water,

Alig, R. Godfrey
Abstract The forces between mica surfaces confining solutions of spherical and rod-shaped ZnS nanoparticles (diameter ca. 5,nm) coated with hexadecylamine or octadecylamine surfactant in dodecane have been measured in the absence and after the introduction of trace amounts of water. Initially, or at very low water content, the water molecules cause the nanoparticles to aggregate and adsorb on the hydrophilic mica surfaces, resulting in a long-range exponentially decaying repulsive force between the surfaces. After longer times (>,20,h), water bridges nucleate and grow between the nanoparticles and mica surfaces, and attractive capillary forces then cause a long-range attraction and a strong (short-range) adhesion. It is found, as has previously been observed in nonaqueous bulk colloidal systems, that even trace amounts of water have a profound effect on the interactions and structure of nanoparticle assemblies in thin films, which in turn affect their physical properties. These effects should be considered in the design of thin-film processing methodologies. [source]

Experimental design comparison of studies evaluating doxorubicin nanoparticles in breast cancer therapy

Farman A. Moayed
Background The unique properties of nanoparticles (NP) qualify these colloidal systems for a wide range of medical applications, including diagnosis and treatment. Particularly in cancer therapy, NP have significantly enhanced the potential of conventional imaging, radiotherapy, and chemotherapy and, consequently, offered new avenues for early interventions. So far, breast cancer has been one of the most studied cancer types with NP research, which can benefit the occupational breast cancer for the increasing number of women in the labor force in industry. Objectives The objective of this study is to compare the experimental designs of preclinical studies that assessed the effect of doxorubicin NP (DOX-NP) on the estrogen-dependent MCF-7 breast cancer cell line using a recently established quantitative Experimental Appraisal Instrument (ExpAI). Methods A systematic review of research articles published between August 2004 and August 2005 on NP and breast cancer treatment with doxorubicin was performed using various online databases and indexes available through the University of Cincinnati. Restrictive inclusion and exclusion criteria were defined leading to selection of four relevant articles that used comparable experimental designs. Critical appraisal of those studies was performed by five independent assessors using the ExpAI version 2.0 and the results were summarized in a table of evidence. Results The study design in the selected articles was either between groups or mixed, with sample sizes varying from n = 3,6, and the evaluation of the effect of DOX-NP either in vitro or in vivo. The cytotoxic drug doxorubicin was the input variable in all studies, whereas different end points such as pharmacokinetic parameters, cytotoxicity surrogates (e.g., growth inhibition, mitochondrial activity), and quantitative analysis of messenger RNA were used as output variables. Conclusions Although the articles assessed in this article were preclinical experimental studies, the results showed that doxorubicin NP drugs can be used effectively to enhance the delivery process in MCF-7 breast cancer cells by increasing the circulation time and targeting the tumor tissues. Considering the rising number of women in the labor force and the risk of occupational breast cancer, it can be concluded that DOX-NP may potentially be used as an effective anticancer drug on humans, but further research and studies are required to understand how DOX-NP drugs might react in the human body before using it on breast cancer patients. © 2008 Wiley Periodicals, Inc. [source]

The two-Yukawa model and its applications: the cases of charged proteins and copolymer micellar solutions

Sow-Hsin Chen
Charged and uncharged colloidal systems are known from experiment to display an extremely rich phase behavior, which is ultimately determined by the effective pair potential between particles in solution. As a confirmation, the recent striking observation of an equilibrium cluster phase in charged globular protein solutions [Stradner, Sedgwick, Cardinaux, Poon, Egelhaaf & Schurtenberger (2004). Nature, 432, 492,495] has been interpreted as the effect of competing short-range attractive and long-range repulsive interactions. The `two-Yukawa (2Y) fluid' model assumes an interparticle potential consisting of a hard core plus an attractive and a repulsive Yukawa tail. We show that this rather simple model can indeed explain satisfactorily the structural properties of diverse colloidal materials, measured in small-angle neutron scattering (SANS) experiments, including the cases of equilibrium cluster formation and soft-core repulsion. We apply this model to the analysis of SANS data from horse-heart cytochrome c protein solutions (whose effective potential can be modeled as a hard-sphere part plus a short-range attraction and a weaker screened electrostatic repulsion) and micellar solutions of a triblock copolymer (whose effective potential can be modeled as a hard-sphere part plus a repulsive shoulder and a short-range attraction). The accuracy of the 2Y model predictions is successfully tested against Monte Carlo simulations in both cases. [source]

Simultaneous light and small-angle neutron scattering on aggregating concentrated colloidal suspensions

Sara Romer
A new sample environment has been developed in order to perform light and small-angle neutron scattering (SANS) simultaneously on colloidal systems. The combination of SANS and diffusing wave spectroscopy (DWS) is of particular use in the high-concentration regime. DWS provides information on the local dynamic properties of the individual particles, whereas SANS gives access to the structural properties on similar length scales. The combination of both methods thus allows one to obtain structural and dynamic information over a very large range of length and time scales. Using this new setup, the onset of aggregation and the sol,gel transition in concentrated destabilized polystyrene sphere suspensions have been investigated. At the gel point, a dramatic change of the particle dynamics from diffusion to a subdiffusive arrested motion is observed. However, while the DWS measurements indicate that dramatic changes in the local dynamics occur over a long period, the SANS pattern quickly reaches its final appearance. The SANS experiments thus indicate that a fluid-like structure is arrested in the course of the gel formation. The data are found to be in good qualitative agreement with computer simulations. [source]

Colloidal soft matter as drug delivery system

Giulia Bonacucina
Abstract Growing interest is being dedicated to soft matter because of its potential in delivering any type of drugs. Since hydrophilic, lipophilic, small and big molecules can be loaded into these colloidal systems and administered through the parenteral or nonparenteral route, soft matter systems have been used to solve many biomedical and pharmaceutical problems. In fact, they make possible to overcome difficulties in the formulation and delivery of poorly water-soluble drug molecules, settle some stability issues typical of biological drug molecules, design parenteral sustained release forms and provide functionalized soft particles that are very effective in drug targeting. This review deals with the important role that colloids play in the drug delivery and targeting, with particular attention to the more currently used systems such as microemulsions, organogels, liposomes, micelles, and dendrimers. Though significant progress has been made in drug targeting, some challenges still remain. Further efforts will be required to better understand the characteristics of targets and to discover new ones. In-depth knowledge of the physico-chemical structure and properties of the systems used for targeting is fundamental for understanding the mechanism of interaction with the biological substrate and the consequent drug release. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1,42, 2009 [source]

Microemulsions as colloidal vehicle systems for dermal drug delivery.

Part V: Microemulsions without, with glycolipid as penetration enhancer
Abstract The aim of this study was to investigate the dermal administration of a highly hydrophilic model drug, diphenhydramine (DPH), in colloidal systems with an aqueous colloidal phase in the presence of a glycolipid (GL) as a penetration modifier. Dermal penetration of DPH, GL, and isopropylpalmitate (IPP) from ME systems without GL and with GL as well as from a hydrogel used as standard formulation were estimated in vitro using human skin. The penetration of the drug, the oil (IPP), and the GL was measured with highly sensitive HPLC, HPLC-MS, and GC-MS assays, respectively. It could be shown that penetration modifier GL is penetrating very fast, and to a high extent into and through the human skin. In contrast, the penetration of IPP used as oily phase in the ME is limited. When incorporated in the ME systems GL and DPH was accumulated in the viable epidermis and in the dermis. Using ME containing a penetration modifier such as GL, a slight additional enhancing effect could be observed, particularly concerning the penetration of DPH into the acceptor fluid when a highly hydrophilic drug such as DPH was applied. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:821,827, 2005 [source]

Aggregation and surface-enhanced Raman activity study of dye-coated mixed silver,gold colloids

Jinghuai Fang
Abstract The aggregate morphologies of silver, gold, and mixed silver,gold nanoparticles coated with fuchsine basic were directly investigated by means of transmission electron microscopy. It was found that the aggregation of silver and gold colloids induced by the adsorption of fuchsine basic displayed different aggregate characteristics. The adsorption of fuchsine basic in mixed silver and gold colloidal systems led to altered aggregation and surface-enhanced Raman scattering (SERS) enhancement behavior. A suitable ratio of mixed silver and gold colloids could form a favorable state of aggregation and significantly increase the SERS activity of mixed colloids compared with single silver and gold colloids. This is the first report of the SERS of fuchsine basic on mixed silver and gold colloids. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Estimation of Centres and Radial Intensity Profiles of Spherical Nano-Particles in Digital Microscopy

Mats Kvarnström
Abstract Control of the microscopic characteristics of colloidal systems is critical in a wealth of application areas, ranging from food to pharmaceuticals. To assist in estimating these characteristics, we present a method for estimating the positions of spherical nano-particles in digital microscopy images. The radial intensity profiles of particles, which depend on the distances of the particles from the focal plane of the light microscope and have no closed functional form, are modelled using a local quadratic kernel estimate. We also allow for the case where pixel values are censored at an upper limit of 255. Standard errors of centre estimates are obtained using a sandwich estimator which takes into account spatial autocorrelation in the errors. The approach is validated by a simulation study. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]