Polyelectrolyte-induced aggregation of liposomes: a new cluster phase with interesting applications

Abstract

Different charged colloidal particles have been shown to be able to self-assemble, when mixed in an aqueous solvent with oppositely charged linear polyelectrolytes, forming long-lived finite-size mesoscopic aggregates. On increasing the polyelectrolyte content, with the progressive reduction of the net charge of the primary polyelectrolyte-decorated particles, larger and larger clusters are observed. Close to the isoelectric point, where the charge of the adsorbed polyelectrolytes neutralizes the original charge of the particles' surface, the aggregates reach their maximum size, while beyond this point any further increase of the polyelectrolyte-particle charge ratio causes the formation of aggregates whose size is progressively reduced. This re-entrant condensation behavior is accompanied by a significant overcharging. Overcharging, or charge inversion, occurs when more polyelectrolyte chains adsorb on a particle than are needed to neutralize its original charge so that, eventually, the sign of the net charge of the polymer-decorated particle is inverted. The stability of the finite-size long-lived clusters that this aggregation process yields results from a fine balance between long-range repulsive and short-range attractive interactions, both of electrostatic nature. For the latter, besides the ubiquitous dispersion forces, whose supply becomes relevant only at high ionic strength, the main contribution appears due to the non-uniform correlated distribution of the charge on the surface of the polyelectrolyte-decorated particles ('charge-patch' attraction). The interesting phenomenology shown by these system has a high potential for biotechnological applications, particularly when the primary colloidal particles are bio-compatible lipid vesicles. Possible applications of these systems as multi-compartment vectors for the simultaneous intra-cellular delivery of different pharmacologically active substances will be briefly discussed.

Interaction between like-charged polyelectrolyte-colloid complexes in electrolyte solutions: A Monte Carlo simulation study in the Debye–Hückel approximation

“…When a patch attraction is present but the complexes are not neutral, the competition between the residual repulsive interaction and the shorter ranged attraction determines a potential barrier, whose strength depends on the balancing between these two components. The presence of such barrier justifies [30] the aggregation behavior observed in several colloid-polyelectrolyte systems regulated by the amount of added polyelectrolyte chains [2,19,25,31,[42][43][44][45]58]. By adding a 'steric' contribution to the inter-particle potential, due to the overlapping of PE-layers, we recover the complete effective interaction between the decorated macroions.…”

“…In an attempt to reproduce what occurs experimentally when some oppositely charged polyelectrolyte is added to a colloidal aqueous suspension [2], we started simulating the formation of a decorated particle. A colloidal particle was located at the center of a cubic Once a single complex, a pd-particle, was formed, we duplicated the whole structure (bare colloid + adsorbed PE chains) simply by translation.…”

“…Understanding complexation of linear polyelectrolyte chains with oppositely charged particles has high potential for applications in nanoscience and bio-technology [2][3][4][5][6][7]. In a number of technological processes and biological systems, linear polyelectrolytes associate with a range of different nanoscopic particles or supramolecular assemblies, including inorganic particles, protein assemblies, micelles and liposomes, forming in aqueous media charged colloidal suspensions.…”

Origin of insulating weak-ferromagnetic phase in ultra-thin La0.67Sr0.33MnO3 films on SrTiO3 substrate

“…4 middle panel. Since the overlap between d3z 2 and dx 2 -y 2 orbitals is quite small the t z-x must be far less than the t (0.6-0.7 eV) in bulk LSMO. 26 And U S is about 4 eV as shown in Fig. 2(c).…”

Electric Properties of Carboxymethyl Cellulose

“…The change of uel sign from positive to negative indicates over-equivalent adsorption of CMC and predominant exposition of the polyelectrolyte charges. The steep slope of the curve before the isoelectric point reflects the well known fact that all added polyelectrolyte is adsorbed on the surface at low polymer concentration; that is a characteristic of polyelectrolyte adsorption on an oppositely charged surface [55,56]. The plateau at high CCMC reflects the saturated adsorption because electrostatic repulsion of already recharged surface and the CMC macromolecules.…”