Surfactant coated particles

The main formulation challenge with HFA pMDI has been the poor solubility of the surfactants that were used in CFC products. Most pMDI formulations are suspensions of fine powder in propellant, and in order to obtain acceptable dose uniformity these suspensions usually require surfactants to stabilize them. The inability to use conventional surfactants has therefore led to a range of diverse formulation approaches. These encompass drug solubilization using cosolvents (Qvar is an example), new surfactants, coating particles with surfactant, and particle engineering (Fig. 3). However, as is the case with most... 

The reduced cytotoxicity of surfactant-coated particles may be related to a suppression of surface free radical activity (141) by surfactant. Natural surfactant is capable of scavenging hydrogen peroxide (H2O2), the oxygen free radicals (O and OH ), and radical species derived from peroxynitrite (142). In the process, peroxidation of unsaturated lipids in surfactant and degradation of surfactant pro-... 

BAM showed bright regions due to the Ag particles and dark regions occupied primarily by oleic acid (Fig. 10b). TEM showed monolayer domains of surfactant-coated silver particles within regions of oleic acid. Vertical transfer onto quartz plates of up to eight layers with good linearity was reported. 

By performing in situ the polymerization of acrylamide in water/AOT/toluene microemulsions, clear and stable inverse latexes of water-swollen polyacrylamide particles stabilized by AOT and dispersed in toluene have been found [192-194], It was shown that the final dispersions consist of two species of particles in equilibrium, surfactant-coated polymer particles (size about 400 A) with narrow size distribution and small AOT micelles (size about 30 A). 

The longtime stabihty of surfactant-coated Pd nanoparticles in w/o microemulsions has been investigated. It has been proven that under suitable conditions, the use of the functionalized surfactant Pd(AOT)2 allows very stable nanosize Pd particles to be obtained and to finely control their average size [229],... 

In the flotation process, surfactant-coated mineral particles float to the surface of the mixture, where they become trapped in the froth. The gangue settles to the bottom. 

Solution phase chemical synthesis is a convenient way for making surfactant coated magnetic nanoparticles, as described in various reviews [12-18]. Monodisperse Co nanoparticles with standard deviation less than 10% are synthesized by decomposition of Co2(CO)8 [19-22] or Co(rj3-C8Hi3X n4-C8Hi2) [23] and reduction of cobalt salt [24,25] in the presence of oleic acid and trialkylphosphine, or trialkylphosphine oxide, or alkylamine. Monodisperse iron nanoparticles are normally prepared from decomposition of Fe(CO)5 [26-28]. However, metallic iron-based particles from this decomposition procedure are difficult to characterize due to the chemical instability. A recent synthesis using decomposition of Fe[NSiMe3)2]2 offers a promising approach to monodisperse Fe nanocrystals [29]. 

Flexible macromolecules, such as proteins, and small molecules, such as surfactants, are amphipathic and may form a layer at the oil-water interface. These molecules may also partly stabilize emulsions by forming a physical barrier to close contact, thereby reducing the attractive van der Waals forces to ineffective levels (Dalgleish, 1989). Repulsion can arise in either of two ways and physico-chemical calculations are available for both mechanisms in oil-in-water systems. Either the approaching protein-coated particles will tend to compress or alternatively interpenetrate the adsorbed protein layer on adjacent particles. The optimum structure of the stabilizing protein will be dealt with in the section on protein as an ingredient. 

This method has been employed to measure the critical wetting surface tensions of particles of sulfur, silver iodide, methylated glass beads, quartz, paraffin-wax-coated coal, and surfactant-coated pyrite. Generally. Fuerstenau and coworkers [106-115] found that the film flotation technique is sensitive to the surface hydrophobicity and the heterogeneity of the particles. It was found that particle size, particle shape, particle density, film flotation time, and the nature of the wetting liquids have negligible effects on the results of film flotation. But the liquid and the solid particles used in the experiments must not have any chemical interactions. 

Pelletier, S. and Lucy, C.A. Fast and high-resolution ion chromatography at high pH on short columns packed with 1.8 /an surfactant-coated silica reverse-phase particles. 

The sol-gel process is used to prepare dense, spherical particles of ThOa and (Th,U)02 for sphere-pac and coated-particle fuels. The thoria is dispersed in water from nitrate solutions by slow heating and steam denitration to form a stable sol from which spherical particles are produced. The sol droplets are injected at the top of a tapered glass column containing an upward flow of 2-ethylhexarol (2-EH). The water from the sol particles is slowly extracted by suspension in the 2-EH, and the gelled spheres drop out of the column. Coalescence of the particles is prevented with surfactants in the 2-EH. The sol-gel spheres are dried in steam and Ar at 220°C and sintered in H2 at ISOO C. 

The adsorption or incorporation of molecules, such as surfactants and polymers, can create a steric repulsion that prevents aggregation [288-290]. This can also increase suspension stability, important for metered-dose inhaler formulations [291]. Lung surfactant coating on the surface of poly(lactic-co-glycolic) acid microparticles has been shown to dramatically improve dry powder aerosol performance by reducing particle-particle interactions [134,292],... 

The use of nanoparticles for oral appHca-tion is an intensively studied concept for the delivery of poorly soluble drugs, as discussed above. Particle uptake has been known for more than 50 years via M-cells as specialized phagocytic enterocytes, but also via lymphoid tissue and normal intestinal enterocytes [75, 76]. The kinetics of particle uptake and translocation depend on biopharmaceutical parameters like accessibility through the mucus and contact with the enterocytes, as well as on the physical properties of the particle like its size, particle charge, surfactant coating and, sometimes, targeting devices. 

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