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PubMed2005

Amphiphilic hydrogel nanoparticles. Preparation, characterization, and preliminary assessment as new colloidal drug carriers.

Inverse emulsion photopolymerization of acrylated poly(ethylene glycol)-bl-poly(propylene glycol)-bl-poly(ethylene glycol) and poly(ethylene glycol) was successfully employed to prepare stable, cross-linked, amphiphilic nanoparticles. Even at low emulsifier concentrations (2%) and high water-to-hexane weight ratios (35/65), the stability of the inverse emulsion allowed for the formation of well-defined colloidal material. Inverse emulsion characteristics and polymerization conditions could be controlled to vary the size of the nanoparticles between 50 and 500 nm. The presence of hydrophobic nanodomains within these otherwise hydrophilic nanoparticles was verified by using pyrene as a microenvironmentally sensitive probe. The hydrophobic poly(propylene glycol)-rich domains appear to be suitable for incorporation of hydrophobic drugs, encapsulating Doxorubicin up to 9.8% (w/w). We believe that the complex nano-architecture of these materials makes them a potentially interesting colloidal drug delivery carrier system and that the method should be useful for a number of amphiphilic macromolecular precursors.

Antineoplastic Agents↗
PubMed2005

Release and formation of surface-localized ionic clusters (SLICs) into phospholipid rafts from colloidal solutions during coalescence.

Stimuli-responsive behavior of phospholipids in the presence of ionic surfactants utilized in synthesis of MMA/nBA colloidal particles was investigated. Utilizing 1-myristoyl-2-hydroxy-sn-glycero-phosphocholine (MHPC) phospholipid, and sodium dioctyl sulfosuccinate (SDOSS) surfactant as dispersing media in H(2)O, narrow unimodal particle size distributions of methyl methacrylate (MMA)/n-butyl acrylate (nBA) copolymers were synthesized. The particle diameters were 154 nm when a SDOSS/MHPC mixture was used and 161 nm using MHPC as the only surface-stabilizing species. When such colloidal dispersions are exposed to 1.7, 3.3, and 6.7 mM aqueous CaCl(2) and KCl electrolyte solutions, surface-localized ionic clusters are generated at the film-air interface that may serve as lipid rafts composed of crystalline phases of MHPC deposited on poly(MMA)/nBA films. These studies illustrate that it is possible to control release and morphology developments of surface phospholipid rafts on artificial surfaces.

Colloids↗
PubMed2004

Deviation from the classical colloid filtration theory in the presence of repulsive DLVO interactions.

A growing body of experimental evidence suggests that the deposition behavior of microbial particles (e.g., bacteria and viruses) is inconsistent with the classical colloid filtration theory (CFT). Well-controlled laboratory-scale column deposition experiments were conducted with uniform model particles and collectors to obtain insight into the mechanisms that give rise to the diverging deposition behavior of microorganisms. Both the fluid-phase effluent particle concentration and the profile of retained particles were systematically measured over a broad range of physicochemical conditions. The results indicate that, in the presence of repulsive Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions, the concurrent existence of both favorable and unfavorable colloidal interactions causes significant deviation from the CFT. A dual deposition mode model is presented which considers the combined influence of "fast" and "slow" particle deposition. This model is shown to adequately describe both the spatial distribution of particles in the packed bed and the suspended particle concentration at the column effluent.

Colloids↗
PubMed2004

Colloid stability of lipid/polyelectrolyte decorated latex.

The colloid stability of supramolecular assemblies composed of the synthetic cationic lipid dioctadecyldimethylammonium bromide (DODAB) on carboxymethyl cellulose (CMC) supported on polystyrene amidine (PSA) microspheres was evaluated via turbidimetry kinetics, dynamic light scattering for particle sizing, zeta-potential analysis, and determination of DODAB adsorption on CMC-covered particles. At 0.1 g L(-1) CMC and 2 x 10(11) PSA particles/mL, CMC did not induce significant particle flocculation, and a vast majority of CMC-covered single particles were present in the dispersion so that this was the condition chosen for determining DODAB concentration (C) effects on particle size and zeta potentials. At 0.35 mM DODAB, charge neutralization, maximal size, and visible precipitation indicated extensive flocculation and minimal colloid stability for the DODAB/CMC/PSA assembly. At 0.1 g L(-1) CMC, isotherms of high affinity for DODAB adsorption on CMC-covered particles presented a plateau at a limiting adsorption of 700 x 10(17) DODAB molecules adsorbed per square meter PSA which was well above bilayer deposition on a smooth particle surface. The polyelectrolyte layer on hydrophobic particles was swelled and fluffy (ca. 11-nm hydrodynamic thickness), and maximal adsorption of DODAB lipid onto this layer produced a compressed composite cationic film with 20 mV of zeta potential and about 10-nm mean thickness. The assembly of cationic lipid/CMC layer/polymeric particle was stable only well above charge neutralization of the polyelectrolyte by the cationic lipid, at relatively large lipid concentrations (at and above 1 mM DODAB) with charge neutralization leading to extensive particle aggregation.

Adsorption↗
PubMed2004

Sensing capabilities of colloidal gold modified with a self-assembled monolayer of a glucose-carrying polymer chain on a glass substrate.

A disulfide-carrying polymer with pendent glucose residues (poly(2-methacryloyloxyethyl D-glucopyranoside)) was obtained by using a benzyl N,N-diethyldithiocarbamoyl derivative which shows the abilities of initiation, chain transfer, and termination (iniferter). The disulfide-carrying polymer was accumulated on a colloidal Au-immobilized glass substrate, and the usefulness of the polymer as a sensing element of concanavalin A (Con A) was examined by using a UV-visible spectrophotometer with the help of surface plasmon resonance. The sensor showed a concentration-dependent specific binding of Con A with a detection limit of 1.9 nM, and furthermore, it had a very high stability at high ionic strength. The polymer-coated device examined here was not only useful as a simple biosensor chip but is also expected to expand our knowledge of interfacial phenomena by introducing various functional polymers on colloidal Au.

Adsorption↗
PubMed2004

Formation of a supramolecular gel between alpha-cyclodextrin and free and adsorbed PEO on the surface of colloidal silica: effect of temperature, solvent, and particle size.

Aqueous solutions of alpha-cyclodextrin (alpha-CD) complex spontaneously with poly(ethylene oxide) (PEO), forming a supramolecular structure known as pseudopolyrotaxane. We have studied the formation of the complex obtained from the threading of alpha-CD onto PEO, both free in solution and adsorbed on colloidal silica. The kinetics of the reaction were studied by gravimetric methods and determined as a function of temperature and solvent composition for the PEO free in solution. PEO was then adsorbed on the surface of colloidal silica particles, and the monomers were displaced by systematically varying the degree of complexation, the concentration of particles, and the molecular weight of the polymer. The effect of the size of the silica particles on the yield of the reaction was also studied. With the adsorbed PEO, the complexation was found to be partial and to take place from the tails of the polymer. The formation of a gel network containing silica at high degrees of complexation was observed. Small-angle X-ray and neutron scattering experiments were performed to study the configuration of the polymeric chains and confirmed the partial desorption of the polymer from the surface of the silica upon complexation.

Adsorption↗
PubMed2005

Relationship between interfacial forces measured by colloid-probe atomic force microscopy and protein resistance of poly(ethylene glycol)-grafted poly(L-lysine) adlayers on niobia surfaces.

Adsorbed layers of "comb-type" copolymers consisting of PEG chains grafted onto a poly(l-lysine) (PLL) backbone on niobium oxide substrates were studied by colloid-probe AFM in order to characterize the interfacial forces associated with coatings of varying architectures (PEG/PLL ratios and PEG chain lengths) and their relevance to protein resistance. The steric and electrostatic forces measured varied substantially with the architecture of the PLL-g-PEG copolymers. Varying the ionic strength of the buffer solutions enabled discrimination between electrostatic and steric-entropic contributions to the net interfacial force. For high PEG grafting densities the steric component was most prominent, but at low ionic strengths and high grafting densities, a repulsive electrostatic surface force was also observed; its origin was assigned to the niobia charges beneath the copolymer, as insufficient protonated amine groups in the PLL backbone were available for compensation of the oxide surface charges. For lower grafting densities and lower ionic strengths there was a substantial attractive electrostatic contribution arising from interaction of the electrical double layer arising from the protonated amine groups, with that of the silica probe surface (as under low ionic strength conditions, the electrical double layer was thicker than the PEG layer). For these PLL-g-PEG coatings the net interfacial force can thus be a markedly varying superposition of electrostatic and steric-entropic contributions, depending on various factors. The force curves correlate with protein adsorption data, demonstrating the utility of AFM colloid-probe force measurements for quantitative analysis of surface forces and how they determine interfacial interactions with proteins. Such characterization of the net interfacial forces is essential to elucidate the multiple types of interfacial forces relevant to the interactions between PLL-g-PEG coatings and proteins and to advance interpretation of protein adsorption or repellence beyond the oversimplified steric barrier model; in particular, our data demonstrate the importance of an ionic-strength-dependent minimum PEG layer thickness to screen the electrostatic interactions of charged interfaces.

Adsorption↗
PubMed2005

Molecular dynamics simulation of the structural configuration of binary colloidal monolayers.

Molecular dynamics simulations of binary colloidal monolayers, i.e., monolayers consisting of mixtures of two different particle sizes, are presented. In the simulations, the colloid particles are located at an oil-water interface and interact via an effective dipole-dipole potential. In particular, the influence of the particle ratio on the configurations of the binary monolayers is investigated for two different relative interaction strengths between the particles, and the pair correlation functions corresponding to the binary monolayers are calculated. The simulations show that the binary monolayers can only form two-dimensional crystals for certain particle ratios, for example, 2:1, 6:1, etc., while, for example, for a particle ratio of 7:1 the monolayers are found to be in a disordered, glassy state. The calculations also reveal that in analogy to the Wigner lattice the configurations are very sensitive to the relative interaction strength between the particles but not to the absolute magnitude of the interaction strength, even when particle size effects are taken into account. Consequently, it is argued that a comparison between the calculated configurations and actual binary particle monolayer systems could provide useful information on the relative interaction strength between large and small particles. Possible mechanisms giving rise to disparities in the interaction strength between large and small particles are described briefly.

Colloids↗
PubMed2005

Biomimetic particles: optimization of phospholipid bilayer coverage on silica and colloid stabilization.

The effect of ionic strength and pH on phosphatidylcholine (PC) adsorption from vesicles on silica nanoparticles was investigated over a range of NaCl concentrations (0.1-150 mM) at pH 6.3 and 7.4 from determination of adsorption isotherms, colloid stability, particle sizing, and zeta-potentials. At and above 10 mM ionic strength, pH 6.3, high-affinity adsorption isotherms with limiting adsorption indicative of one-bilayer deposition on each silica particle were obtained. At 10 mM ionic strength, adsorption isotherms indicated lower affinity between PC and silica at pH 7.4 than at pH 6.3, suggesting a role of hydrogen bonding between silanol on silica and phosphate on PC in promoting bilayer deposition at low pH. Under conditions where high affinity and bilayer deposition were achieved, silica sedimentation documented from photographs was absent, suggesting particle stabilization induced by bilayer coverage. However, at physiological (150 mM NaCl) or close to physiological ionic strength (140 mM NaCl), the large colloid stability similarly achieved at pH 6.3 or 7.4 suggested the major role of van der Waals attraction between the PC bilayer vesicle and silica particle in determining bilayer deposition. The effect of increasing ionic strength was increasing van der Waals attraction, which caused PC vesicle disruption with bilayer deposition and bilayer-induced silica stabilization.

Adsorption↗
PubMed2005

On the effect of Ca2+ and La3+ on the colloidal stability of liposomes.

This work deals with the effect of Ca2+ and La3+ on the colloidal stability of phosphatidylcholine (PC) liposomes in aqueous media. As physical techniques, nephelometry, photon correlation spectroscopy, electrophoretic mobility, and surface tension were used. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek theory. Changes in the size of liposomes and high polydispersity values were observed as La3+ concentration increases, suggesting that this cation induces the aggregation of liposomes. However, changes in polydispersity were not observed with Ca2+, suggesting a coalescence mechanism or fusion of liposomes. The stability factor (W), calculated from the nephelometry measurements indicated that aggregation/fusion occurs at a critical concentration (c.c.) of 0.3 and 0.7 M for La3+ and Ca2+, respectively. To gain a better insight into the interaction mechanism between the liposomes and the studied ions, the interaction between PC monolayers and Ca2+ and La3+ was studied. Changes in the surface area per lipid molecule (A0) in the monolayer at the c.c. values were found for both ions, with a more pronounced effect in the case of Ca2+. This corresponds with a larger reduction of the steric repulsive interaction between the headgroups at the phospholipid membrane (pi(head)). The experimental result validates the hypothesis made on the liposome fusion in the presence of Ca2+ and liposome aggregation in the presence of La3+. These aggregation mechanisms have also been confirmed by transmission electron microscopy.

Calcium↗
PubMed2005

Colloidal particles coated and stabilized by DNA-wrapped carbon nanotubes.

Single-walled carbon nanotubes (SWNTs) are dispersed in water via wrapping with short segments of single-stranded DNA (ssDNA). Small angle neutron scattering suggests a power-law exponent that is consistent with clustered nanotubes and hence marginal stability. The SWNT-ssDNA complex is used to stabilize dispersions of hydrophilic colloidal particles with the nanotubes adhered to the surface of the colloids. Near-infrared fluorescence microscopy demonstrates the interfacial band-gap fluorescence of these SWNT-coated particles, suggesting potential routes to novel platforms and applications.

Colloids↗
PubMed2006

Phospholipid-assisted synthesis of stable F-containing colloidal particles and their film formation.

This letter illustrates for the first time the preparation of p-methyl methacrylate/n-butyl acrylate/heptadecafluorodecyl methacrylate (p-MMA/nBA/FMA) colloidal dispersions containing up to 15% w/w FMA, which is accomplished by the utilization of biologically active phospholipids (PLs) and ionic surfactants. The use of monomer-starved conditions during emulsion polymerization and the utilization of 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), sodium dodecyl sulfate (SDS), and phosphoric acid bis(tridecafluoro-octyl) ester ammonium salt (FSP) as surfactants, which function as transfer and dispersing agents, facilitate a suitable environment for the polymerization of p-MMA/nBA/FMA colloidal dispersions that exhibit nonspherical particle morphologies. Such nonspherical particles upon coalescence form phase-separated films with unique surface properties.

Biocompatible Materials↗
PubMed2006

Formation of spherical nanostructures by the controlled aggregation of gold colloids.

Stable suspensions of size-uniform spherical assemblies of 5-8 nm gold colloids in toluene are readily obtained by cross linking the colloidal particles using alkanedithiols within a defined range of gold-dithiol molar ratios. The assemblies are very stable and remain suspended in toluene for several months without significant aggregation. These porous gold spheres can be further organized into hierarchically assembled relatively linear chains by the addition of ethanol.

Gold Colloid↗
PubMed2006

Three-dimensional centimeter-sized colloidal silica crystals formed by addition of base.

Three-dimensional (3D) centimeter-sized colloidal crystals can be spontaneously formed simply by dropping a NaOH solution (10 mM, approximately 10 microL) into an aqueous dispersion of dilute charged colloidal silica (particle diameter 110 nm, particle volume fraction phi = 0.023, 3-4 mL). The charge number of the silica particle increases with pH. Upon adding the NaOH solution, first, sub-millimeter-sized polycrystals are formed in the upper part of the sample due to charge-induced crystallization. The local phi value in the crystal region becomes nonuniform. The crystals with a high phi value accumulate at the bottom of the cell and then grow upward as columnar crystals. The crystal widths increase discontinuously with the growth, and in some cases, 3D centimeter-sized crystals are formed. The centimeter-sized crystals are also obtainable by the controlled diffusion of the base from its dilute reservoir. The present findings may prove valuable in the fabrication of large 3D single-crystalline photonic materials.

Colloids↗
PubMed2005

Monodispersed spherical colloids of Se@CdSe: synthesis and use as building blocks in fabricating photonic crystals.

Monodispersed spherical core-shell colloids of Se@Ag(2)Se have been exploited as a chemical template to synthesize Se@CdSe core-shell particles using a cation-exchange reaction. A small amount of tributylphosphine could facilitate the replacement of Ag(+) by Cd(2+) in methanol at 50 degrees C to complete the conversion within 150 min. The orthorhombic structure of beta-Ag(2)Se changed to a well-defined wurtzite lattice for CdSe. The CdSe shells could be converted back to beta-Ag(2)Se by reacting with AgNO(3) in methanol at room temperature. Because of the uniformity in size and high refractive index associated with the Se@CdSe core-shell colloids, they could serve as a new class of building blocks to fabricate photonic crystals with wide and strong stop bands.

Cadmium Compounds↗
PubMed2007

Ordered binary arrays of Au nanoparticles derived from colloidal lithography.

By using angle-resolved colloidal lithography and O2-plasma etched bilayers of hexagonally packed spheres as templates, we succeeded in fabrication of highly ordered binary arrays of gold nanoparticles with varied shapes, for instance, with a shuttlecock-like shape composed of a small crescent-shaped nanoparticle and a big fan-shaped one. The size and shape of both small and big nanoparticles obtained were manipulated by the plasma etching period and the incidence angle of Au vapor flow. The subsequent thermal annealing led to binary arrays of round Au nanoparticles with a rather narrow distribution in terms of size and shape. Our approach should pave a simple and versatile colloidal way to form binary nanoparticle arrays, holding immense promise for technical applications such as nanoelectronics and nanophotonics.

Colloids↗
PubMed1997

Stability of nystatin in mouthrinses; effect of pH temperature, concentration and colloidal silver addition, studied using an in vitro antifungal activity.

Alkaline low concentration nystatin mouthrinses extemporanely prepared can be used to treat oropharyngeal candidiasis in immunodeficient patients. However, their expiration dates are not distinctly determined. The stability of nystatin, added (as Mycostatine) at a concentration of 14,400 U/ml in 10-4N hydrochloric acid, purified water and 1.4% injectable sodium hydrogen carbonate with or without 0.002% colloidal silver (an antiseptic agent added because of its known antifungal potency) was studied after storage in tinted glass bottles at 5 degrees C and 22 degrees C over 11 days, and compared with reconstituted 100,000 U/ml aqueous Mycostatine oral suspension. At 2, 4, 7, 9, and 11 days after preparation. Samples were tested for pH, microbial contamination, and assayed by an in vitro microbiological test. Neither significant variation of pH nor microbial contamination were in evidence. Nystatin 14400 U/ml maintained at least 90% of its initial concentration for 4 days in acid at both temperatures, for 7 days (5 degrees C) and 4 days (22 degrees C) in aqueous and alkaline environments, for 9 days (5 degrees C) and 7 days (22 degrees C) in 1.4% injectable sodium hydrogen carbonate containing colloidal silver which showed an antifungal potency. The 100,000 U/ml aqueous Mycostatine oral suspension was stable for 9 days and 4 days at 5 degrees C and 22 degrees C respectively. An ambulant patient can keep a low concentration alkaline antifungal mouthrinse at home for a week at 5 degrees C.

Antifungal Agents↗
PubMed2001

Monitoring the intragastric distribution of a colloidal drug carrier model by magnetic resonance imaging460.

PURPOSE: Monitoring the distribution of drugs or drug delivery systems in the human gastrointestinal tract is an important prerequisite for the design of orally administered drugs. We investigated the intragastric distribution of a colloidal drug delivery system (liposomes containing the contrast agent Gd-DOTA) by magnetic resonance imaging. METHODS: Following ingestion of a liquid or a solid meal, gastric distribution of liposomes released from a capsule and the fat component of the solid meal were tracked in 7 healthy subjects for 90 min. Liposomes were identified in gastric content by the increased signal intensity provided by the encapsulated Gd-DOTA. RESULTS: With the liquid meal, liposomes initially formed a layer on the surface before distributing in 86 +/- 2% of gastric content (maximum distribution volume) within 42 +/- 6 min. With the solid meal, maximum distribution (7 +/- 1%, reached within 24 +/- 6 min) was confined to a small volume in the fundus without forming a layer, suggesting that distribution was related to the accessible liquid compartment. Fat distribution was inhomogeneous and concentrated in the fundus. CONCLUSIONS: Intragastric distribution of a colloidal drug carrier model, such as Gd-DOTA-filled liposomes, varies between meals of different composition. These differences can be monitored in three dimensions in humans by MRI.

Adult↗