Biomedical subjects

P Galatola

Publications and source records attributed to P Galatola.

16 recordsLinked to original sources

PubMed2005

Tube formation and spontaneous budding in a fluid charged membrane.

We determine the equations governing the equilibrium shape of an axially symmetric charged fluid membrane under the action of an external field. We consider that the charges are free to diffuse along the membrane, and we neglect the effect of screening counterions. By numerically integrating these equations for a membrane spread across a hole by a constant tension, we show that there exists a threshold electric field above which an infinitely long tube can be pulled. The threshold field for pulling a tube decreases as the surface charge density of the membrane increases, reaching zero at a finite critical value. Above this critical density of charge, the membrane spontaneously buds, in the absence of externally applied fields, because of the electrostatic repulsion of its charges.

Cell Surface Extensions↗

PubMed2002

Nonspontaneous surface-induced nematic phase.

By means of a Landau-de Gennes mean field model, we predict the existence of a nonspontaneous surface nematic phase in a smectogenic compound in contact with a suitable solid substrate. In the bulk the system does not show any nematic phase, the latter being solely induced by the substrate-liquid crystal interaction. Depending on the strength of the surface potential, a prewetting line, terminating at a critical point, may appear. For strong enough coupling, a new surface smectic phase can be induced, accompanied by a reentrant behavior. Our analysis might explain some recent experimental results [T. Moses, Phys. Rev. E 64, 010702(R) (2001)]: to validate it we suggest possible further experimental investigations.

Journal Article↗

PubMed2002

Analytical characterization of adhering vesicles.

We characterize vesicle adhesion onto homogeneous substrates by means of a perturbative expansion around the infinite adhesion limit, where curvature elasticity effects are absent. At first order in curvature elasticity, we determine analytically various global physical quantities associated with adhering vesicles: height, adhesion radius, etc. Our results are valid for adhesion energies above a certain threshold, that we determine numerically. We discuss the haptotactic force acting on a vesicle in the limit of weak adhesion gradients. We also propose a few methods for measuring adhesion energies and we suggest a possible way of determining the size of suboptical vesicles using controlled adhesion gradients.

Elasticity↗

PubMed2002

Exact calculations of the paranematic interaction energy for colloidal dispersions in the isotropic phase of a nematogenic material.

In a recent paper [Phys. Rev. E 61, 2831 (2000)], Borstnik, Stark, and Zumer have studied the stability of a colloidal dispersion of micron-sized spherical particles in the isotropic phase of a nematogenic material. Close to the nematic transition, the attraction due to a surface-induced paranematic order can yield flocculation. Their calculation of the nematic-mediated interaction was based on an ansatz for the order-parameter profile. We compare it with an exact numerical calculation, showing that their results are qualitatively correct. Besides, we point out that in the considered regime, the exact interaction is extremely well approximated by a simple analytical formula which is asymptotically exact.

Journal Article↗

PubMed2002

Anisotropic capillary interactions and jamming of colloidal particles trapped at a liquid-fluid interface.

We determine the capillary attraction and equilibrium configurations of particles trapped at a liquid-fluid interface due to the pinning of their contact line. We calculate analytically the asymptotic interaction energy between two particles and, numerically, the multibody energy landscape for up to four contacting particles. Our results are consistent with recent experiments. We show that a system composed of a large number of such particles behaves as a jammed system.

Journal Article↗

PubMed2001

Nematic-wetted colloids in the isotropic phase: pairwise interaction, biaxiality, and defects.

We calculate the interaction between two spherical colloidal particles embedded in the isotropic phase of a nematogenic liquid. The surface of the particles induces wetting nematic coronas that mediate an elastic interaction. In the weak wetting regime, we obtain exact results for the interaction energy and the texture, showing that defects and biaxiality arise, although they are not topologically required. We evidence rich behaviors, including the possibility of reversible colloidal aggregation and dispersion. Complex anisotropic self-assembled phases might be formed in dense suspensions.

Journal Article↗

PubMed1999

Coarse-graining analysis of the Berreman anchoring.

By means of a coarse-graining technique, we derive the effective anchoring energy of a nematic liquid crystal in contact with a macroscopically corrugated surface imposing a weak degenerate planar anchoring. For coarse-grained nematic director's profiles that vary only in the direction perpendicular to the average surface's plane, our results generalize those already known by including the anisotropy of the elastic constants. In the general case, on the contrary, we show that extra surface gradient terms appear that generally are not negligible.

Journal Article↗

PubMed1996