Biomedical subjects

J Bibette

Publications and source records attributed to J Bibette.

18 recordsLinked to original sources

PubMed2006

Acceleration of the recognition rate between grafted ligands and receptors with magnetic forces.

When ligands and receptors are both attached on surfaces, because of the restriction of configurational freedom, their recognition kinetics may be substantially reduced as compared with freely diffusing species. In nature, this reduction may influence the efficiency of the capture and adhesion of circulating cells. Here we show that similar consequences are observed for colloids grafted with biomolecules that are used as probes for diagnostics. We exploit Brownian magnetic colloids that self-assemble into linear chains to show also that the resulting one-dimensional confinement considerably accelerates the recognition rate between grafted receptors and their ligands. We propose that because confinement significantly augments the colliding frequency, it also causes a large increase in the attempt frequency of the recognition. This work gives the basis of a rapid, homogeneous, and highly sensitive bioanalysis method.

Antibodies↗

PubMed2006

Irreversible shear-activated aggregation in non-Brownian suspensions.

We have studied the effect of shear on the stability of suspensions made of non-Brownian solid particles. We demonstrate the existence of an irreversible transition where the solid particles aggregate at remarkably low volume fractions (phi approximately 0.1). This shear-induced aggregation is dramatic and exhibits a very sudden change in the viscosity, which increases sharply after a shear-dependent induction time. We show that this induction time is related exponentially to the shear rate, reflecting the importance of the hydrodynamic forces in reducing the repulsive energy barrier that prevents the particles from aggregating.

Journal Article↗

PubMed2005

Magnetic force probe for nanoscale biomolecules.

We present a new technique to measure the mechanical properties of small biomolecules. This technique uses long range repulsive colloidal forces together with magnetic attraction as a force probing tool. The biomolecules are grafted between superparamagnetic particles, which are regularly spaced within long chains maintained by an external magnetic field. Varying the magnetic field results in compression or extension of the molecules between the particles. In order to demonstrate this technique we use, as a size controlled model molecule, a short double stranded DNA (151 base pairs) for which the force-extension law is determined and found in agreement with existing predictions.

Biopolymers↗

PubMed2005

Solid colloidal particles inducing coalescence in bitumen-in-water emulsions.

Silica particles are dispersed in the continuous phase of bitumen-in-water emulsions. The mixture remains dispersed in quiescent storage conditions. However, rapid destabilization occurs once a shear is applied. Observations under the microscope reveal that the bitumen droplets form a colloidal gel and coalesce upon application of a shear. We follow the kinetic evolution of the emulsions viscosity, eta, at constant shear rate: eta remains initially constant and exhibits a dramatic increase after a finite time, tau. We study the influence of various parameters on the evolution of tau: bitumen droplet size and volume fraction, silica diameter and concentration, shear rate, etc.

Journal Article↗

PubMed2003

Flexible magnetic filaments as micromechanical sensors.

We propose a new micromechanical approach to probe bending rigidity at molecular scale. Long flexible filaments made of magnetic colloids and linkers are shown to adopt under magnetic field a hairpin configuration. Measuring the hairpin curvature as a function of the field intensity and the linker length from diffracted light allows us to deduce the linker bending rigidity kappa. The technique is presented for two types of linkers: a spontaneously adsorbing polymer and a grafted biomolecular.

Acrylic Resins↗

PubMed2002

Double emulsions: how does release occur?

Water-in-oil-in-water double emulsions (W/O/W) consist of dispersed oil globules containing smaller aqueous droplets. These materials offer interesting possibilities for the controlled release of chemical species initially entrapped in the internal droplets. A better understanding of the stability conditions and release properties in double emulsions requires the use of model systems with a well-defined droplet size. In this paper, we use quasi-monodisperse double emulsions made of calibrated water droplets and oil globules to investigate the two mechanisms that are responsible for the release of a chemical substance (NaCl). (i) One is due to the coalescence of the thin liquid film separating the internal droplets and the globule surfaces. (ii) The other mechanism termed as 'compositional ripening' occurs without film rupturing; instead it occurs by diffusion and/or permeation of the chemical substance across the oil phase. By varying the proportions and/or the chemical nature of the surface active species it is possible to shift from one mechanism to the other one. We therefore study separately both mechanisms and we establish some basic rules that govern the behavior of W/O/W double emulsions.

Biopolymers↗

PubMed2001

Double emulsions: a tool for probing thin-film metastability.

We study the kinetics of the release of monodisperse water-in-oil-in-water double emulsions in the regime dominated by coalescence of the internal aqueous droplets onto the globule interface. By measuring the rate of release of adsorbed droplets, we directly determine the average lifetime of the thin film that forms between the small internal droplets and the globule surface. Therefore, the activation energy and the natural frequency of the hole nucleation process within the adhesive thin liquid films are unambiguously deduced.

Journal Article↗

PubMed2000

Viscous sintering phenomena in liquid-liquid dispersions.

We present experimental evidence for viscous sintering phenomena in a gel formed by highly viscous emulsion droplets. When a rupturing agent is added to the initially stable emulsion, a gel forms, which further contracts by preserving the geometry of the container. The initial stages of densification (up to 60%) follow very well the "cylindrical model" for viscous sintering, but deviate at the final stages of densification. The observed inverse dependence of the contraction rate on viscosity is consistent with the viscous sintering theory.

Journal Article↗

PubMed1996