Use Of Colloidal Particles Research Articles

Dramatic droplet deformation through interfacial particles jamming

Droplets of one fluid in a second, immiscible fluid are typically spherical in shape due to the interfacial tension between the two fluids. Shear forces can lead to droplet deformation when they are subjected to flow, and these effects can be further modified when the droplet is stabilized by a surfactant due to a flow-induced gradients in the surfactant concentration. An alternative method of stabilizing droplets is through the use of colloidal particles, whose stabilization behavior is intrinsically different from molecular surfactants. Under the same flow condition, a gradient of particle concentration can result in the jamming of particles in regions with a high packing density, making the interface solid-like, albeit only under compression and not tension. However, how this asymmetry in the surfactant properties alters the droplet shape under shear is unknown. Here, we show that shear of particle-stabilized droplets can lead to a remarkable array of shape deformations as the droplets flow through a constrained microchannel. The shear-induced migration of particles on the surface results in the formation of an elastic shell at the back of the droplet, which can wrinkle and invaginate, ultimately leading to a unique core-shell structure. The shapes depend on the Peclet number of the flow, reflecting the balance of shear forces that drive the particles and diffusion that randomizes them. These findings highlight the consequences of the asymmetry in the forces between the particles and provide a unique method to controllably create droplets with a vast array of different shapes.

Stabilization of a Pickering Emulsion by Nanoparticles of Eudragit RSPO and Pol-epsilon Caprolactone: Contact Angle Measurement and Surface Tension Studies

The use of colloidal particles to prepare and stabilize emulsions, known as "Pickering emulsions “, has aroused growing interest in recent years. Pickering and Ramsden demonstrated at the beginning of the last century the feasibility of surfactant-free emulsions, in presence of these emulsions is called "Pickering Emulsions". This concept of emulsions stabilized by solid particles is experiencing renewed interest nowadays given the many advantages it offers good stability, environmental protection, user safety, and particle varieties.
 The first part is devoted to the synthesis of Eudragit RSPO and pol epsilon-caprolactone nanoparticles and their characterization. The characterization of the nanoparticles is performed by dynamic light scattering and geometry. The understanding of the interfacial behavior of these nanoparticles and their associated stabilization mechanisms for emulsions was carried out. The second part of the study investigated the formulation and stabilization of the emulsion using the washed suspension containing the nanoparticles as the only stabilizer. The objective of this part is to stabilize and characterize the formulated emulsions. Droplet size determination and microscopy were performed using a Zeiss optical microscope. The direction of the formulated emulsions was determined by conductimetry. In conclusion, Pickering emulsions stabilized solely by Eudragit RSPO and Poly-epsilon Caprolactone nanoparticles appear to be highly effective innovative drug carriers, opening new doors as potential drug delivery systems.

Rational Surface Engineering of Colloidal Drug Delivery Systems for Biological Applications.

The use of colloidal particles as drug delivery carriers holds a great promise in terms of improvement of traditional treatment and diagnosis of human diseases. Nano- and microsized particles of a different composition including organic and inorganic materials can be fabricated with a great control over size, shape and surface properties. Nevertheless, only some few formulations have surpassed the benchtop and reached the bedside. The principal obstacle of colloidal drug delivery systems is their poor accumulation in target tissues, organs and cells, mainly by efficient sequestration and elimination by the mononuclear phagocytic system. Recent evidence suggests that, besides size, the surface character of colloidal systems is the most determinant design parameter that may ultimately guarantee successful biological performance. To approach these issues, materials designers and engineers can make use of multiple strategies and tools to finely modulate the particles' surface towards highly efficient and biocompatible materials. In this article, we provide an overview of the most relevant colloidal drug delivery systems, a summary of the available literature regarding the effects of surface charge, hydrophobicity and softness on biological response, and finally, we review the key points of surface modification strategies with organic, inorganic and biological materials.

Preparation of PLGA/Rose Bengal colloidal particles by double emulsion and layer-by-layer for breast cancer treatment

The use of colloidal particles (CPs) in the transport of drugs is developing rapidly thanks to its effectiveness and biosafety, especially in the treatment of various types of cancer. In this study Rose Bengal/PLGA CPs synthesized by double emulsion (W/O/W) and by electrostatic adsorption (layer-by-layer), were characterized and evaluated as potential breast cancer treatment. CPs were evaluated in terms of size, zeta potential, drug release kinetics and cell viability inhibition efficacy with the triple negative breast cancer cell line HCC70. The results showed that both types of CPs can be an excellent alternative to conventional cancer treatment by taking advantage of the enhanced permeation and retention (EPR) effect, manifested by solid tumors; however, the double emulsion CPs showed more suitable delivery times of up to 60% within two days, while layer-by-layer showed fast release of 50% in 90 min. Both types of CPs were capable to decrease cell viability, which encourage us to further testing in in vivo models to prove their efficacy and feasible use in the treatment of triple negative breast cancer.

Antireflective Coatings for Glass and Transparent Polymers.

Antireflective coatings (ARCs) are applied to reduce surface reflections. We review coatings that reduce the reflection of the surface of the transparent substrates float glass, polyethylene terephthalate, poly(methyl methacrylate), and polycarbonate. Three main coating concepts exist to lower the reflection at the interface of a transparent substrate and air: multilayer interference coatings, graded index coatings, and quarter-wave coatings. We introduce and discuss these three concepts, and zoom in on porous quarter-wave coatings comprising colloidal particles. We extensively discuss the four routes for introducing porosity in quarter-wave coatings through the use of colloidal particles, which have the highest potential for application: (1) packing of dense nanospheres, (2) integration of voids through hollow nanospheres, (3) integration of voids through sacrificial particle templates, and (4) packing of nonspherical nanoparticles. Finally, we address the remaining challenges in the field of ARCs, and elaborate on potential strategies for future research in this area.

Poly(2-oxazoline)-Based Microgel Particles for Neuronal Cell Culture.

An increasing number of in vivo and in vitro neuro-engineering applications are making use of colloidal particles as neuronal cell carriers. Recent studies highlight the shortcomings of commercial glass particles and stress the benefit of using soft microgel particles (MGPs) instead. This study describes first the fabrication of MGPs from telechelic poly(2-methyl-2-oxazoline)s (PMeOx) cross-linkers and hydrophilic neutral (hydroxyethyl)methacrylate (HEMA) or charged 2-methacryloxyethyltrimethylammonium (METAC) monomers by emulsion polymerization, and it discusses their ability to support cell growth. It establishes that uncharged copolymers lead to MGPs with nonfouling properties inappropriate for cell culture, and it provides a protocol to amend their surface properties to enable cell adhesion. Finally, it demonstrates that the introduction of positive charges by METAC is necessary to obtain surface properties suitable for neuronal cell development. Through the optimization of the PMeOx30 MGP properties, this work provides general guidelines to evaluate and tune MGP chemistry to obtain microcarriers for neuro-engineering applications.

Pickering interfacial catalysis for biphasic systems: from emulsion design to green reactions.

Pickering emulsions are surfactant-free dispersions of two immiscible fluids that are kinetically stabilized by colloidal particles. For ecological reasons, these systems have undergone a resurgence of interest to mitigate the use of synthetic surfactants and solvents. Moreover, the use of colloidal particles as stabilizers provides emulsions with original properties compared to surfactant-stabilized emulsions, microemulsions, and micellar systems. Despite these specific advantages, the application of Pickering emulsions to catalysis has been rarely explored. This Minireview describes very recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions with special emphasis on their assets and challenges for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.

Synthesis of Hybrid Colloids Through the Growth of Polystyrene Latex Particles onto Methacryloxy methyl triethoxysilane - Functionalized Silica Particles

AbstractOne area of particular effort recently is the use of colloidal particles as precursors in engineering new materials. Nevertheless, these particles are nearly always spheres. This places limitations on the structures that can be built, especially in making photonic-bandgap materials. Therefore, it is a great challenge to create new colloids with an original shape, i.e. different from the sphere, in a controllable manner.We present here an original approach to create hybrid organic-inorganic colloidal particles with a perfect controlled shape. The synthetic route of these structures, which are composed of spherical silica spheres surrounded by a varying number of polystyrene beads, consists in the emulsion polymerization of styrene in presence of silica particles, which had been surface-modified by a coupling agent containing polymerizable groups.The influence of the size of the silica particle and of the nature of the coupling agent on the resulting colloidal particles morphologies was carefully analyzed. We show in particular that the number of growing polystyrene beads varies homogeneously with the diameter of the mineral spheres. A main advantage of this technique is also that we can precisely control the reaction time, allowing us to tune the final morphology of the hybrid structures. These colloidal assemblies are original building blocks for the elaboration of new functional materials.

The Feasibility of High Resolution, Multiple Labeling using Colloidal Particles of Similar Size but Different Shapes and Elemental Compositions

High resolution, quantitative cell labeling analysis for electron microscopy is typically accomplished using colloidal gold (cAu) particles which have a uniform diameter such that each particle conjugates no more than one ligand with monovalent specificity, such as an Fab antibody fragment. in this way, one particle labels exactly one target molecule. The corresponding particle size which satisfies this requirement, in the case of the Fab fragment, is 3-5nm. Under these constraints, multiple labeling cannot be performed using the standard cAu technology in which particles of various diameters are used such that each size corresponds to a unique label. Particles larger than 5nm may conjugate multiple Fab fragments, and thus a single particle may lable multiple target sites. Conversely, several particles smaller than 3nm may bind to a single Fab fragment so that several particles may label a single target molecule. Recent work in our lab has focused on the development of a labeling system which maintains the advantages of the standard cAu labeling technology, namely the use of electron-dense particles with excellent secondary and backscattered electron emission properties which make them readily detectable by both TEM and SEM, while at the same time offering greater versatility by permitting multiple labeling for high resolution, quantitative analysis. This novel labeling system makes use of colloidal particles which have unique and distinctive shapes, and composed of a variety of different metals including Au, Ag, Pt, Pd, Rh, and Ru. These elements all form stable aqueous colloidal suspensions, and the particles have surface charge properties similar to those of Au, permitting the adsorption of proteins and other ligands to them by the same conjugation techniques used with cAu (fig. 1).

Gravity effect on the electric field deposition of two-dimensional particle arrays

We developed a method for the deposition of colloidal particle layers in a horizontal electrophoretic cell. The particles accumulate on the surface of the (upper) working electrode. The particle nuclei increase in size to form islands, which are then bridged and converted into a dense array: monolayer or bilayer. Uniform coating of electroconductive glass by micrometer and submicrometer size latex particles of negative charge has been obtained. The transportation stage of the process is described theoretically. The use of colloidal particles made visible with an optical microscope also provides a new look inside electrode processes.

Biopharmaceutical aspects of lipid formulations of amphotericin B.

To improve the clinical utility of amphotericin B (AmpB), several lipid-based formulations have been developed. The biopharmaceutical aspects related to the parenteral use of colloidal lipid particles as carriers of AmpB are reviewed here. The first part of the review provides an introduction to the parenteral use of colloidal particles for chemotherapy by addressing the concept of a particulate drug carrier system, the pharmaceutical technological issues, and the biological factors governing the potential and limitations of lipid particles for effective drug delivery. The second part is devoted to AmpB lipid formulations. The pharmaceutical characteristics of the various industrially produced formulations, their pharmacokinetics and possible mechanisms of action, and potential future developments are described.

Use of colloidal particles to improve the biocatalytic activity of microorganisms.

Two cell-associated yeast enzyme systems have been shown to be influenced by the addition of biochemically inert colloidal particles to the growth medium. Titers of the alcohol oxidase enzyme system of Pichia pastoris and the β-glucosidase system of Candida wickerhamii were amplified up to 3-fold through the addition of small (5–10 g/l) amounts of commercial aluminum oxide particles. This discovery is of importance from an applied perspective as a means of increasing biocatalytic efficiency. As well, it provides a means of studying the physiological changes associated with cell sorption, independent of confounding influences such as diffusional limitations that are normally associated with film growth.