Biomedical subjects

Yan Levin

Publications and source records attributed to Yan Levin.

8 recordsLinked to original sources

PubMed2007

The renormalized jellium model for spherical and cylindrical colloids.

Starting from a mean-field description for a dispersion of highly charged spherical or (parallel) rodlike colloids, we introduce the simplification of a homogeneous background to include the contribution of other polyions to the static field created by a tagged polyion. The charge of this background is self-consistently renormalized to coincide with the polyion effective charge, the latter quantity thereby exhibiting a nontrivial density dependence, which directly enters into the equation of state through a simple analytical expression. The good agreement observed between the pressures calculated using the renormalized jellium and Monte Carlo simulations confirms the relevance of the renormalized jellium model for theoretical and experimental purposes and provides an alternative to the Poisson-Boltzmann cell model since it is free of some of the intrinsic limitations of this approach.

Colloids↗

PubMed2006

Smoluchowski equation and the colloidal charge reversal.

Smoluchowski equation and the Monte Carlo simulations are used to study the conditions leading to the reversal of the electrophoretic mobility. Zeta (zeta) potential is identified with the diffuse potential at the shear plane which, we argue, must be placed at least one ionic diameter away from the colloidal surface. For sufficiently strongly charged colloids, zeta potential changes sign as a function of the multivalent electrolyte concentration, resulting in a reversal of the electrophoretic mobility. This behavior occurs even for very small ions of 4 A diameter as long as the surface charge density of the colloidal particles is sufficiently large and the concentration of 1:1 electrolyte is sufficiently low.

Chemistry, Physical↗

PubMed2004

Effective charge of colloidal particles.

A new dynamical definition of the effective colloidal charge, especially suitable for the Monte Carlo and Molecular-dynamics simulations, is proposed. It is shown that for aqueous colloidal suspensions containing monovalent counterions the "dynamical" effective charge agrees perfectly with the "statistical" effective charge calculated using the Alexander prescription. In the case of multivalent ions, the effective charge behaves in a qualitatively different way from the predictions of the Poisson-Boltzmann theory.

Journal Article↗

PubMed2004

Rupture of a liposomal vesicle.

We discuss pore dynamics in osmotically stressed vesicles. A set of equations which govern the liposomal size, internal solute concentration, and pore diameter is solved numerically. We find that dependent on the internal solute concentration and vesicle size, liposomes can stay pore free, nucleate a short-lived pore, or nucleate a long-lived pore. The phase diagram of pore stability is constructed, and the different scaling regimes are deduced analytically.

Computer Simulation↗

PubMed2004

Two rubber balloons: phase diagram of air transfer.

Two identical rubber balloons are partially inflated with air (to different extent) and connected by a hose with a valve. It is found that depending on initial balloon volumes, when the valve is opened the air will flow either from the larger (fuller) balloon to the smaller (emptier) balloon, or from the smaller balloon to the larger one. The phenomenon is explained in terms of the nonideal rubber elasticity of balloons. The full phase diagram for the air flow dynamics is constructed.

Journal Article↗

PubMed2004

Renormalized jellium model for charge-stabilized colloidal suspensions.

We introduce a renormalized jellium model to calculate the equation of state for charged colloidal suspensions. An almost perfect agreement with Monte Carlo simulations is found. Our self-consistent approach naturally allows to define the effective charge of particles at finite colloidal density. Although this quantity may differ significantly from its counterpart obtained from the standard Poisson-Boltzmann cell approach, the osmotic pressures for both models are in good agreement. We argue that by construction, the effective charge obtained using the jellium approximation is more appropriate to the study of colloidal interactions. We also discuss a possibility of a fluid-fluid critical point and show how our equation of state can be used to shed light on the surprising results found in recent sedimentation experiments.

Journal Article↗

PubMed2002

Thermodynamics of ionic microgels.

We present a theory of dilute aqueous suspensions of microgel particles. It is found that as the number of charged monomers in the polymer network composing mesoscopic gel increases, the particles undergo a swelling transition. Depending on the hydrophobicity of the polymer, this transition can be either continuous or discontinuous. Furthermore, similar to charge stabilized colloidal particles, we find that the electrophoretic mobility of the microgel is controlled by an effective charge. Unlike the colloids, however, for which the effective charge grows asymptotically with the logarithm of the bare charge, the effective charge of an ionic microgel scales as Z(eff) approximately Z0.5. The findings are in good agreement with the experimental measurements.

Journal Article↗

PubMedDate not supplied

Linear DNA low efficiency transfection by liposome can be improved by the use of cationic lipid as charge neutralizer.

A plasmid expressing the beta-galactosidase enzyme was used to transfect Vero cells in order to evaluate the efficiency of a liposome-mediated transfection by circular and linear DNA. The results obtained showed a low rate of transfection by linear DNA:liposome complexes. To explore whether the structure of the complexes was interfering with the transfection, atomic force microscopy (AFM) was used. It has confirmed the difference between the linear and circular condensates: whereas the circular DNA:liposome complexes presented compact spherical or cylindrical structures of about 100-800 nm, the linear DNA showed pearl necklace-like structures, with pearls varying from 250 to 400 nm. On the basis of the theory proposed by Kuhn et al. (1999), low concentrations of cationic amphihile were used to neutralize or reverse the DNA charge in order to improve the transfection efficiency of the linear DNA. Using this method, we were able to obtain the expression of the transgene without an associated toxicity observed with the linear DNA liposome delivery.

Animals↗