Igor L. Radtchenko

Polyelectrolyte multilayer capsule permeability control

Abstract The permeability properties of hollow polyelectrolyte multilayer capsules for different substances were investigated as a function of pH and salt concentration. Capsules were prepared by layer-by-layer (LBL) adsorption of oppositely charged polyelectrolytes onto the surface of melamine formaldehyde and CdCO3 particles followed by core removal. It was shown that the capsules are closed at a pH value of 8 and higher, but at a pH lower than 6 the macromolecules permeate into the capsule interior. For low molecular weight molecules capsules, templated on CdCO3 cores were found to be less permeable than MF-derived capsules. The open and closed states of the capsule wall are reversible. It provides thus an opportunity to encapsulate different materials into polyelectrolyte capsules.

Micron-scale hollow polyelectrolyte capsules with nanosized magnetic Fe3O4 inside

Two novel methods for imparting magnetic properties to the hollow polyelectrolyte capsules were proposed. The first one includes the impregnation of the capsules with pre-formed Fe3O4 magnetite nanoparticles; the second approach is based on selective synthesis of magnetic Fe3O4 inside the polyelectrolyte capsules filled with polycations. Synthesized Fe3O4 core/polyelectrolyte shell composites were characterized by transmission electron microscopy (TEM) and WAXS techniques. Perspectives of the usage of hollow polyelectrolyte capsules as microreactors for spatially restricted inorganic synthesis were demonstrated.

A novel method for encapsulation of poorly water-soluble drugs: precipitation in polyelectrolyte multilayer shells

A novel method to include poorly water-soluble substances into the polyelectrolyte capsules of defined size, stability, composition and affinity properties is proposed. Encapsulation explores the polarity gradient across the capsule wall. Capsules creation makes use of electrostatic interaction and can involve many substances as layer constituents, such as synthetic polyelectrolytes, proteins, nucleic acids, lipids and multivalent dyes. Using capsules made of synthetic polyelectrolytes as a model system was demonstrated how to prepare, to measure and to use this gradient for low molecular weigh materials encapsulation.

Incorporation of macromolecules into polyelectrolyte micro- and nanocapsules via surface controlled precipitation on colloidal particles

Abstract A novel approach to incorporate different polymers into micro- and nanocapsules fabricated by means of layer-by-layer (LbL) adsorption of oppositely charged polyelectrolytes on colloidal particles is proposed. This method comprises two stages. At first, the polymers, which are supposed to be incorporated, precipitate on the surface of colloidal particles. This can be done either by complexation of polyelectrolytes with multivalent ions or by adding miscible non-solvents. Then stable LbL assembled polyelectrolyte shells are formed. After core decomposition the inner polymer molecules are released from the wall but captured by the outer shell and floating in the capsule interior. The possibilities to encapsulate a wide class of charged and non-charged polymers were demonstrated on such examples as sodium poly(styrene sulfonate) as a polyanion, poly(allylamine hydrochloride) as a polycation and Dextrane as non-charged water soluble polymer.

Artificial cell based on lipid hollow polyelectrolyte microcapsules channel reconstruction and membrane potential measurement

A new model system as an artificial cell based on hollow polyelectrolyte microcapsules (HPM), fabricated by step-wise adsorption of polyelectrolytes and phospholipids, was proposed. To demonstrate the feasibility of the functioning of HPM coated with lipid layers as a model biosystem, the membrane permeability for ions and the channel reconstruction were examined by measuring the membrane potential as one of the most important cell parameters. The membrane potential was measured by confocal microscopy using the potentiometric fluorescent dye tetramethylrhodamine ethyl ester perchlorate (TMRE). The influence of the lipid composition (phosphatidylcholine – DPPC-HPM, phosphatidylcholine/phosphatidic acid 9/1–(DPPC/DPPA)-HPM) and metal cations (Na+, K+, Ca2+) on the membrane potential was shown. Addition of DPPA was found to lead to an increase of the negative membrane potential value. To investigate the ion-transport activity of the lipid-HPM, the ion channel-forming peptides valinomycin and gramicidin were used. The selectivity of the valinomycin and gramicidin channels for K+ and for K+, and Na+ ions, respectively, and the tolerance for Ca2+ ions is evidence that lipid-HPM functions as an artificial cell.

Molecular-dynamics simulations and x-ray analysis of dye precipitates in the polyelectrolyte microcapsules

The precipitate of the Disperse Red-1 dye in bulk and in confined microsized volumes was investigated by x-ray powder diffraction and molecular-dynamics simulations. The diffraction patterns exhibited two different precipitation regimes: In bulk when dye molecules form a distinct crystallite structure and inside polyelectrolyte capsules with a diameter up to 8 μm when the precipitate presumably represents a very fine polycrystalline powder. The latter result was further supported by molecular-dynamics simulations carried out for up to 640 dye molecules in the NVT ensemble. Calculations have also shown that effects of confined geometry and steric restrictions arising due to encapsulated polyelectrolyte molecules can not prohibit dye nucleation and subsequent crystallization. However, nonspecific interactions between Disperse Red-1 and encapsulated polyelectrolyte could cause the onset of heterogeneous nucleation resulting in formation of a fine polycrystalline powder. The formation process was directly obs...