65 research outputs found
Slow sedimentation and deformability of charged lipid vesicles
The study of vesicles in suspension is important to understand the
complicated dynamics exhibited by cells in vivo and in vitro. We developed a
computer simulation based on the boundary-integral method to model the three
dimensional gravity-driven sedimentation of charged vesicles towards a flat
surface. The membrane mechanical behavior was modeled using the Helfrich
Hamiltonian and near incompressibility of the membrane was enforced via a model
which accounts for the thermal fluctuations of the membrane. The simulations
were verified and compared to experimental data obtained using suspended
vesicles labelled with a fluorescent probe, which allows visualization using
fluorescence microscopy and confers the membrane with a negative surface
charge. The electrostatic interaction between the vesicle and the surface was
modeled using the linear Derjaguin approximation for a low ionic concentration
solution. The sedimentation rate as a function of the distance of the vesicle
to the surface was determined both experimentally and from the computer
simulations. The gap between the vesicle and the surface, as well as the shape
of the vesicle at equilibrium were also studied. It was determined that
inclusion of the electrostatic interaction is fundamental to accurately predict
the sedimentation rate as the vesicle approaches the surface and the size of
the gap at equilibrium, we also observed that the presence of charge in the
membrane increases its rigidity
El colesterol - una molécula con mala reputación
Es natural que el colesterol no sea visto con vuenos ojos por la población en general, y se podría decir, sin miedo a equivocarse, que esta molécula se ha ganado una muy mala reputación. Sin embargo, en este artículo intentamos presentar el colesterol desde otra pespectiva, la de una molécula exquisitamente diseñada con una función fisiolólgica sencial: regular la organización y complejidad de las membranas celulares, fomentando la diversidad funcional de los diferentes sistemas celulares del organism
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