Biomedical subjects

A Buguin

Publications and source records attributed to A Buguin.

8 recordsLinked to original sources

PubMed2006

Homophilic interactions between cadherin fragments at the single molecule level: an AFM study.

We report measurements of the adhesion forces between single E-cadherin fragments anchored on solid surfaces. These fragments consist of the two outermost extracellular domains of the protein. The specificity of the measured rupture forces was demonstrated by Ca2+ exchange experiments. Two series of experiments were performed using two linkers of different rigidity and length. We find that the pull-off force is distributed with a maximum value independent of the linker and logarithmically dependent on the velocity of separation of the two surfaces. Our dynamical results are compatible with previous flow chamber experiments performed with the same fragments and can be compared from a different perspective with previously reported AFM experiments on the full-length extracellular domain of the VE-cadherin. Interestingly, using a rigid linker, we have been able for the first time to evidence the deformation of the cadherin molecule under mechanical stress, a piece of information not accessible with more classical grafting strategies.

Cadherins↗

PubMed2006

Cascade of shocks in inertial liquid-liquid dewetting.

We study the inertial dewetting of water films (A) (thickness e) deposited on highly hydrophobic liquid substrates (B). On these ideal surfaces, thin films can be made which dewet at large velocities obeying under those conditions the Culick law for the bursting of soap films. The rim collecting the water film can become coupled to the surface waves characterized by a surface tension gamma(B) upstream of the rim (coated substrate) and gamma = gamma(B) downstream, where the water film has dried. Upon decreasing the thickness, we observe a sequence of two hydraulic shocks during the dewetting inducing gravity waves behind the rim, and capillary waves ahead.

Journal Article↗

PubMed2006

Motions induced by asymmetric vibrations. The solid/solid case.

We discuss theoretically the motions of a coin on a horizontally vibrating plate, with dry friction between the coin and the plate. As first noticed by Daniel and Chaudhury in a different situation (droplets on a plate), when the periodic acceleration gamma(t) imposed by the plate is unsymmetrical, the coin can move macroscopically with a certain drift velocity V. We analyse here: (a) the vibration threshold below which V=0, and the generic behavior expected just above threshold; (b) the limiting behavior at very high amplitudes, where V should become independent of the amplitude; (c) the complications due to small, macroscopic inhomogeneities on the supporting plate.

Journal Article↗

PubMed2005

Triplon modes of puddles.

Free fluctuations of the contact line of large drops ("puddles") of wavelength lambda > kappa(-1), the capillary length, cannot be seen on a solid substrate because even a small but finite hysteresis is enough to block these slow modes. We show here that vertical vibrations of the substrate (at frequency omegaE, acceleration Lambda) above a threshold amplitude Lambda(c) release the line and excite contour oscillations (triplons). We observe harmonic modes and parametric excitations at omegaE/2. We construct the phase diagram (Lambda, omegaE) of these subharmonic modes and we study their growth dynamics: they slow down near the threshold of the contour instability.

Journal Article↗

PubMed2004

Vibrated sessile drops: transition between pinned and mobile contact line oscillations.

We study the effects of vertical vibrations on non-wetting large water sessile drops flattened by gravity. The solid substrate is characterized by a finite contact angle hysteresis (10-15 degrees). By varying the frequency and the amplitude of the vertical displacement, we observe two types of oscillations. At low amplitude, the contact line remains pinned and the drop presents eigen modes at different resonance frequencies. At higher amplitude, the contact line moves: it remains circular but its radius oscillates at the excitation frequency. The transition between these two regimes arises when the variations of contact angle exceed the contact angle hysteresis. We interpret different features of these oscillations, such as the decrease of the resonance frequencies at larger vibration amplitudes. The hysteresis acts as "solid" friction on the contour oscillations, and gives rise to a stick-slip regime at intermediate amplitude.

Biophysics↗

PubMed2003

Formation of adhesive contacts: spreading versus dewetting.

A soft bead (radius Rb) is pressed with a force F against a hydrophobic glass plate through a water drop ("wet" JKR set-up). We observe with a fast camera the growth of the contact zone bridging the rubber bead to the glass. Depending on the approach velocity V, two regimes are observed: i) at large V a liquid film is squeezed at the interface and dewets by nucleation and growth of a dry contact; ii) at low velocities, the bead remains nearly spherical. As it comes into contact, the rubber bead spreads on the glass with a characteristic time (in the range of one millisecond) tau approximately eta Rb2/F, where eta is the liquid viscosity. The laws of spreading are interpreted by a balance of global mechanical and viscous forces.

Computer Simulation↗

PubMed2002

Rectified motion of colloids in asymmetrically structured channels.

We set micron size particles into macroscopic motion by submitting them to a low frequency electric field (of zero mean value) in a microfabricated channel exhibiting a topological ratchet-like local polarity. Rectification is induced by the coupling between electrophoresis, electroosmosis, and dielectrophoresis. The macroscopic velocities of the particles are functions of the electric field and of the geometry of the channel; they strongly depend on their size which opens the way to potential separations.

Journal Article↗

PubMed2002

Wetting transitions at soft, sliding interfaces.

We observe (by optical interferometry) the contact of a rubber cap squeezing a nonwetting liquid against a plate moving at velocity U. At low velocities, the contact is dry. It becomes partially wet above a threshold velocity V(c1), with two symmetrical dry patches on the rear part. Above a second velocity V(c2), the contact is totally wet. This regime U>V(c2) corresponds to the hydroplaning of a car (decelerating on a wet road). We interpret the transitions at V(c1), V(c2) in terms of a competition between (a) liquid invasion induced by shear (b) spontaneous dewetting of the liquid (between nonwettable surfaces).

Journal Article↗