Microparticles dispersion system

Moreover, stearic acid is a common constituent in enteric coating for its plasticity and stability in stomach. Occasionally, it is used as binder agent especially in melt pelletization. In addition to be a traditional biomedical material, which has been used for thousands of years, stearic acid also plays an important role in newly developed drug delivery system, like microparticle dispersion system which is usually used for sustained drug delivery. Stearic acid is a vital ingredient candidate for nanoparticle and microsphere preparation. 

Although stearic acid is a traditional pharmaceutical auxiliary, we can also find its place in new drug delivery system, like microparticle dispersion system, which has been extensively studied in recent decades. 

General examples of this system are polymer micelles, microsphere, nanoparticles, liposomes, etc. The microparticle dispersion system has the following advantages ... 

The carrier materials of many microparticle dispersion systems are usually synthesized polymers whose accumulation in vivo could cause possible toxicity. In contrast, stearic acid is a better material for microparticle dispersion system due to its biocompatibility and nontoxicity. Generally, as solid lipid with the above advantages, stearic acid can be used for preparation of solid lipid nanopartical (SLN), which is supposed to be more stable than emulsion or liposome due to solid form of stearic acid at room temperature. 

In the microparticle-disperse system, microparticles having large surface area, e.g., silica gel for column chromatography (ca. 50-pm... 

Figure 7.3 shows the two-beam photon-force measurement system using a coaxial illumination photon force measurement system. Two microparticles dispersed in a liquid are optically trapped by two focused near-infrared beams ( 1 pm spot size) of a CW Nd YAG laser under an optical microscope (1064 nm, 1.2 MWcm , lOOX oil-immersion objective, NA = 1.4). The particles are positioned sufficiently far from the surface of a glass slide in order to neglect the interaction between the particles and the substrate. Green and red beams from a green LD laser (532 nm, 21 kWcm ) and a He-Ne laser (632.8 nm, 21 kW cm ) are introduced coaxially into the microscope and slightly focused onto each microparticle as an illumination light (the irradiated area was about 3 pm in diameter). The sizes of the illumination areas for the green and red beams are almost the same as the diameter of the microparticles (see Figure 7.4). The back scattered light from the surface of each microparticle is...

W Im-Emsap, R Bodmeier. In vitro drug release from in situ forming microparticle (ISM)-systems with dispersed drug. AAPS PharmSci Supplement 2(4), AAPS Annual Meeting Abstracts, 2000. 

The drug dosage form may also be affected by food. For example, enteric-coated tablets may stay in the stomach for a longer period of time because food delays stomach emptying. If the enteric-coated tablet does not reach the duodenum rapidly, drug release and subsequent systemic drug absorption are delayed. In contrast, enteric-coated beads or microparticles disperse in the stomach, are less affected by food, and demonstrate more consistent drug absorption from the duodenum. 

Solid heterogeneous catalysts are typical finely dispersed systems. Depending on the manufacturing method, the porous stmcture of catalyst grain is formed by numerous microparticles or nanoparticles bound together. The diameter of these particles varies from a few nanometers to... 

FIGURE 2.43. Schematic representation of an electrocatalytic system consisting of dispersed catalytically active microparticles in a polymeric matrix, (a) Microparticles dispersed in an electronically conducting polymer matrix, (b) Electron relay complex/catalytic microparticle dispersion in an ionically conducting polymer matrix. 

Expressions for the Flux j and Mechanistic Indicators for Microheterogeneous Catalysis at Conducting Polymer/Dispersed Microparticle Composite Systems... 

This lecture is intended to demonstrate qualitative aspects of various many-body phenomena like deposition, fracturing, aggregation, crystallization, melting and vortices using model systems of uniform microparticles dispersed in water or ferrofluid. The particles are confined to monolayers between glass plates allowing direct microscopic observations of local structure and movement of individual particles. 

Following the evaporation of water from the lipid nanodispersion applied to the skin surface, lipid particles form an adhesive layer, applying occlusion to the surface [17,40]. Therefore, the hydration of the stratum comeum may increase, which can facilitate drug penetration into deeper skin strata and even systemic availability of the drug. Occlusive effects are strongly related to particle size. Nanoparticles have turned out 15-fold more occlusive than microparticles [17], and particles smaller than 400 nm in a dispersion containing at least 35% high-crystallinity lipid proved to be most potent [41]. 

There is a wealth of literature on transport and kinetics in microhetero-geneous catalytic systems [175,176], the influence of particle size [177], and complicated situations in which both catalytic microparticles and electron-transfer mediators are dispersed in a polymer matrix [176-179]. The designs and uses of this type of flow-through sensors have been thoroughly reviewed [180,181]. 

Different architectures, such as block copolymers, crosslinked microparticles, hyperbranched polymers and dendrimers, have emerged (Fig. 7.11). Crosslinked microparticles ( microgels ) can be described as polymer particles with sizes in the submicrometer range and with particular characteristics, such as permanent shape, surface area, and solubility. The use of dispersion/emulsion aqueous or nonaqueous copolymerizations of formulations containing adequate concentrations of multifunctional monomers is the most practical and controllable way of manufacturing micro-gel-based systems (Funke et al., 1998). The sizes of CMP prepared in this way vary between 50 and 300 nm. Functional groups are either distributed in the whole CMP or are grafted onto the surface (core-shell, CS particles). 

Controlled crosslinking of cationic starches improves performance in microparticle-containing papermaking systems.84-86 Superior performance over cationic potato starch was achieved with crosslinked cationic or amphoteric waxy maize, tapioca or potato starch in microparticle systems when the starch cooking was optimized to produce the proper colloidal dispersions.86... 

The pioneer in this field was Speiser, who developed nanopellets for peroral administration [7], These nanopellets were produced by dispersing melted lipids with high-speed mixers or with ultrasound. A relatively large amount of microparticles was present in these formulations, which might not be a serious problem for peroral administration, but they exclude an intravenous injection. Lipospheres, produced by high-shear mixing or ultrasound, were developed by Domb and represent similar systems [8-10], They also contain large amounts of microparticles. 

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