Sterisch stabilisierte Vesikel

Mg2+-induced vesicles of tetradecyldimethylamine oxide and magnesium dodecyl sulfate

A Mg2+-induced vesicle phase was prepared from a mixture of tetradecyldimethylamine oxide (C14DMAO) and magnesium dodecyl sulfate [Mg(DS)2] in aqueous solution. Study of the phase behavior shows that at the appropriate mixing ratios, Mg2+-ligand coordination between C14DMAO and Mg(DS)2 results in the formation of molecular bilayers, in which Mg2+ can firmly bind to the head groups of the two surfactants. The area of the head group can be reduced because of the complexation. In this case, no counterions exist in aqueous solution because of the fixation of Mg2+ ions to the bilayer membranes. Therefore, the charges of the bilayer membranes are not shielded by salts. The birefringent solutions of Mg(DS)2 and C14DMAO mixtures consist of vesicles which were determined by transmission electron microscopy (TEM) images and rheological measurements. Magnesium oxide (MgO) nanoplates were obtained via the decomposition of Mg(OH)2 which were synthesized in Mg2+-induced vesicle phase which was used as the microreactor under the existence of ammonia hydroxide. The morphologies and structures of the obtained MgO nanoplates have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the crystal growth is along the (111) direction which can be affected by the presence of a vesicle phase having a fixation of Mg2+ ions to the bilayer membranes.

Disterolphospholipids: nonexchangeable lipids and their application to liposomal drug delivery

Extreme makeover of cholesterol: Cholesterol exchange is a major reason for the instability of liposomes in blood. The formation of a covalent hybrid between cholesterol and glycerophosphocholine preserves the bilayer-stabilizing effect of free cholesterol but prevents its transfer from the bilayer. Thus, disterolphospholipids (e.g. 1) are valuable new components for liposome formulation.

Effect of hydrophobically modified polymers on shear-induced multilamellar vesicles

The effects of polymer concentration, polymer molecular weight, and hydrophobe substitution level of modified poly(acrylic acid) polymers on the formation, size, and viscoelastic properties of shear-induced multilamellar vesicles (onions) are studied by rheology and light diffraction. The onions are close-packed, space-filling vesicles formed by shearing aqueous lamellar phases of C12E5 surfactant to produce phases with sufficient order and size uniformity (O(1-3 microm)) to diffract light. The addition of hydrophobically modified polymers enhances the rate of formation, uniformity, and stability independent of hydrophobe substitution level. Onion size decreases with increasing shear rate as observed for pure surfactant onion systems, but the shear-rate dependence is changed by the polymer. The onion phase has a plateau modulus that increases with polymer concentration but is independent of hydrophobe substitution level or molecular weight. The model presented by Panizza et al. that relates the plateau modulus of the onion phase to membrane rigidity and the compression modulus is consistent with independent measurements of membrane properties from SANS.

Multivalent Host-Guest Interactions between β-Cyclodextrin Self-Assembled Monolayers and Poly(isobutene-alt-maleic acid)s Modified with Hydrophobic Guest Moieties

Poly(isobutene-alt-maleic acid)s modified with p-tert-butylphenyl or adamantyl groups interact with beta-cyclodextrin self-assembled monolayers (beta-CD SAMs) by inclusion of the hydrophobic substituents in the beta-cyclodextrin cavities. The adsorption was shown to be strong, specific, and irreversible. Even with a monovalent competitor in solution, adsorption to the beta-CD SAMs was observed, and desorption proved impossible. The adsorbed polymer layer was very thin as evidenced by surface plasmon resonance spectroscopy and AFM. Apparently, all or most hydrophobic groups of the polymers were employed efficiently in multivalent binding, as was further supported by the absence of specific binding of beta-CD-modified gold nanoparticles to the polymer surface assemblies. Supramolecular microcontact printing of the polymers onto the beta-CD SAMs led to assembly formation in the targeted areas of the substrates.

Polymer-induced structural changes in lecithin/sodium dodecyl sulfate-based multilamellar vesicles

Aqueous concentrated lecithin mixtures (asolectin from soybean) show typical lamellar liquid crystalline behavior and the individual lamellae tend to form spherical supramolecular structures, i.e., multilamellar vesicles. When part of the lecithin is replaced by the anionic surfactant sodium dodecyl sulfate (SDS), the compact multilamellar vesicles disappear and the viscosity decreases. By adding poly(diallyldimethylammonium chloride) (PDADMAC) to the lecithin/SDS system, the formation of multilamellar vesicles can be induced again and the viscosity increases. However, one characteristic feature of these polymer-modified systems is a temperature-dependent phase transition from a compact multilamellar vesicle phase to a more swollen liquid crystalline phase. The polymer-modified multilamellar compact vesicles are of interest for utilization as new thermosensitive drug delivery systems.

Liposomes as drug carriers: a technological approach

Liposome researchers have created a hugh variety of liposomal drug carriers in the past thirty years mainly by small-scale laboratory techniques using more or less well defined raw materials. Only a few of these liposomal preparations have made their way to approved drugs for clinical use in humans so far. The review gives a critical literature survey over key technologies, which are used to evaluate an appropriate lipid formula and to prepare, size, load and sterilise liposomes. It also deals with quality and shelf stability aspects of liposomal drug carriers.

Influence of the surfactant concentration on the body distribution of nanoparticles

The rapid reticuloendothelial system (RES) uptake of nanoparticles after i.v. injection, especially by the liver, can be reduced and the body distribution can be altered by coating them with non-ionic surfactants. In the present work 2-14C-poly(methyl methacrylate) nanoparticles were coated with poloxamine 908 and polysorbate 80, and the influence of different surfactant concentrations on the body distribution was investigated. These surfactants were chosen because earlier studies showed that poloxamine 908 was very effective in decreasing the liver uptake and keeping the nanoparticles in circulation, whereas polysorbate 80 was the most effective surfactant to direct the particles to organs that do not belong to the RES. Above nanoparticles were injected i.v. to rats and the animals were sacrificed after 30 min. Below a surfactant concentration of 0.1% the nanoparticle preparations behaved like uncoated particles. At a 0.1% concentration a very sudden and significant change in the body distribution occurred with poloxamine 908. The liver concentration decreased from about 75% of the dose to 13% and stayed at this level at higher surfactant concentrations. This decrease was combined with a similar sudden complementary increase in blood and other organ and tissue concentrations. With polysorbate 80 the decrease in liver concentration and increase in the blood and the other organ levels was gradual and became important only above 0.5% surfactant concentration. The results indicate that the type of interaction and the strength of the adsorptive binding to the nanoparticles are different with different surfactants. This in turn leads to different body distribution patterns after i.v. injection of surfactant coated nanoparticles.