Microparticle | EPFL Graph Search

Microparticles are particles between 0.1 and 100 μm in size. Commercially available microparticles are available in a wide variety of materials, including ceramics, glass, polymers, and metals. Microparticles encountered in daily life include pollen, sand, dust, flour, and powdered sugar. Microparticles have a much larger surface-to-volume ratio than at the macroscale, and thus their behavior can be quite different. For example, metal microparticles can be explosive in air. Microspheres are spherical microparticles, and are used where consistent and predictable particle surface area is important. In biological systems, a microparticle is synonymous with a microvesicle, a type of extracellular vesicle (EV). Alternative definitions for size Mathematical: as the term "micro" refers to 10^{-6}, the range for micro would then be 10^{-7.5} to 10^{-4.5}, or roughly 31.6 nm to 31.6 micrometers. However, general acceptance considers parti

Automated microfluidic sorting of mammalian cells labeled with magnetic microparticles for those that efficiently express and secrete a protein of interest

Niamh Harraghy, Etienne Lançon, Nicolas Mermod, Amar Rida

We developed a method for the fast sorting and selection of mammalian cells expressing and secreting a protein at high levels. This procedure relies on cell capture using an automated microfluidic device handling antibody-coupled magnetic microparticles and on a timed release of the cells from the microparticles after capture. Using clinically compatible materials and procedures, we show that this approach is able to discriminate between cells that truly secrete high amounts of a protein from those that just display it at high levels on their surface without properly releasing it. When coupled to a cell colony imaging and picking device, this approach allowed the identification of CHO cell clones secreting a therapeutic protein at high levels that were not achievable without the cell sorting procedure. Biotechnol. Bioeng. 2017;114: 1791-1802. (c) 2017 Wiley Periodicals, Inc.

Wiley2017

Separation of magnetic microparticles in segmented flow using asymmetric splitting regimes

Matteo Cornaglia, Martinus Gijs

A magnetic microparticle-based bioassay requires the separation of the microparticles from the sample matrix, after the microparticles have specifically captured the target of interest. For the implementation of such an assay in water-in-oil droplet segmented flow microfluidics, the particles must be separated from the aqueous sample droplets during a purification step. Current magnetic separation methods pose limits to purification, as only a limited part of the sample volume is removed in the purification step. Combining asymmetric droplet splitting in a T-junction-shaped microfluidic channel with magnetic separation, as induced by a permanent magnet positioned close to the microfluidic channel, is a promising and elegant solution for extracting the magnetic microparticles. However, retaining a high separation efficiency is a challenge and yet untried. In this paper, we describe a microfluidic and magnetic setup to separate superparamagnetic microparticles from the sample droplets, removing up to 90 % of the original sample volume in a single purification step, while keeping the separation efficiency constant. First, the conditions for particle aggregation, attraction and immobilization are determined and used to predict good separation conditions. Second, the magnetic forces at the splitting zone on the microfluidic chip are simulated for different permanent magnet positions and orientations; hereafter, the most promising setups are experimentally realized in polydimethylsiloxane microchannels, tested and the results considering different splitting regimes compared.

Springer Heidelberg2015

Interaction of polyelectrolytes with oppositely charged surfaces

Vesela Malinova

Despite progress during the last decade, the behavior of charged macromolecules, polyelectrolytes, including their interactions is not yet completely understood. In particular, interactions with oppositely charged surfaces, which play a significant role in many practical applications and are of central importance in life processes, need more investigation. This situation has motivated the selection of the topic of this doctoral thesis. The study is dedicated to interactions of positively charged polyelectrolytes with negatively charged surfaces considering two types of surfaces, flat amphiphile monolayers and porous surfaces of microspheres. The research aimed at quantitative evaluation of the influence of macromolecular dimensions, chemical structure, electrostatic parameters, and surface characteristics on the adsorption process. As a prerequisite, a series of poly(vinylbenzyltrialkylammonium chloride) model polyelectrolytes has been synthesized. The characteristics were five defined contour lengths with three different types of substituents at the quaternary ammonium group each in addition to uniform charge density and narrow chain length distribution. The final polyelectrolytes were the quaternization products of precursors synthesized by controlled radical polymerization. Two experimental techniques were employed to quantify the influence of chemical, macromolecular, and electrostatic parameters as well as geometrical characteristics on the adsorption of polyelectrolytes on porous microsphere surfaces. These were adsorption on microspheres suspended in aqueous phase and microspheres packed in a chromatography column. During the first technique the total surface comes immediately in contact with the polyelectrolyte molecules, whereas the second technique followed the rules of chromatography. For the first time, the contour length of the polyelectrolyte, the Debye length, the pore dimensions, as well as the chemical structure were likewise considered in a comprehensive study to describe the interaction of polyelectrolytes with well-characterized porous surfaces. A polyelectrolyte charge to surface charge ratio was defined and served to classify different adsorption behavior. Three models have been proposed to illustrate the adsorption behavior based on experimental findings and model calculations. The first one identifies the Debye length in addition to the contour length as dominating parameter, which decides whether a polyelectrolyte molecule can enter a pore or not. The second quantifies the influence of the contour length. Finally, the third describes the concentration influence on the type of molecule organization, layer formation, on the outer surface or inside of pores with diameters exceeding considerably the contour length. For amphiphile monolayer, for the first time, the influence of chain length and substituent at the quaternary ammonium group on the adsorption process was quantified. Based on the surface pressure, pressure-area and pressure-time isotherms measured, a model describing the monolayer arrangement on polyelectrolyte solutions was proposed. A second model correlates the increase of the area per amphiphile molecule and the decrease of the surface pressure with the size and hydrophobicity of the substituents. In addition chain length influence was evident. The results of the thesis contribute to progress in basic research in the field of polyelectrolytes, while also an impact on technical applications such as surface modification, chromatographic processes or improvement of materials is expected. Precise data for comparison with theoretical model calculations are provided, which were not available before.

EPFL2005

Interaction of polyelectrolytes with oppositely charged surfaces

Vesela Malinova

EPFL2005