Powder dispersion

For the dispersion studies, all powders referred to as unexposed were 

Fluidized beds have also been used for generating suspensions of solid particles with diameters in the range of 0.5-40 gm. Air flows through the fluidized bed, which contains beads kept suspended by the motion of the air dust injected into the bed is broken up into small particles and carried out with the air flow (Raabe, 1976). 

A device such as an impactor or cyclone is frequently used at the exit of these dry powder dispersion devices to eliminate the large particles. A charge neutralizer is usually used to reduce the electrostatic charges on the dispersed particles. 

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Stages Powder dispersal Setting time Texture Flavour release Relative cost... 

Powders dispersed in liquids consist of agglomerates—a collection of aggregates—which in turn are composed of primary particles. Agglomerates... 

Dynamic Powder Disperser Lactose 12 Cartridge Gas assist Turbulence, shear force... 

Dispersions of finely divided solids in non-aqueous media have been important for paints, inks, reinforced polymers and lubricating oils, but with the development of liquid toner systems and "ultra-structure" processing of ceramics as fine powders dispersed in organic media, the understanding and optimization of such systems is more important than ever. 

Grind the oil and sample together until the solid is a fine powder dispersed throughout the oil. 

Adhesive mixtures require large carrier crystals to improve the handhng properties of the powders. Dispersion of the small drng particles over the larger carrier material should assure dose uniformity. However, the small dmg particles shonld be removed from the carrier material dnring inhalation, to render an aerosol clond of respirable particles. If the particles remain on the carrier, month or throat deposition of the drng will occur, which might decrease therapeutic efficacy or cause serious side-effects. 

There are a number of techniques for generating aerosols, and these are discussed in detail in the LBL report (1979) and in volumes edited by Willeke (1980) and Liu et al. (1984). We briefly review here the major methods currently in use these include atomizers and nebulizers, vibrating orifices, spinning disks, the electrical mobility analyzer discussed earlier, dry powder dispersion, tube furnaces, and condensation of vapors from the gas phase. 

The particle size distribution of each powder was determined using a Sympatec Helos/ Rodos laser diffraction particle size analyzer (Sympatec Inc., Princeton, New Jersey, U.S.A.) with dry powder dispersion capability. The powder dispersion pressure was varied between 0.5 and 2.0 bar (depending on the tendency for agglomeration) with direct feed into the dispersion funnel. The optical concentration was maintained in the range of 5% to 20%. The mean value of duplicate determinations is reported. 

At present, dry powder inhalers (DPIs) are not used as commonly in the United States as are pMDIs. DPIs have been the last pharmaceutical inhalation aerosol system developed. Although the concept of operation is readily envisioned for these devices, the development of an efficient dry powder dispersion device intended for lung delivery has been notoriously difficult. Most of these devices function by using interactive mixtures of fine drug particles (1-5 pm diameter) and carrier excipient particles (usually 75 200 pm). Some evidence suggests that DPI performance is dictated largely by the physicochemical properties of the excipients used (5). However, as will be discussed, the availability of different choices of excipients is very limited, particularly in the United States. 

An overview of potential excipient physicochemical factors that influence dry powder dispersion are summarized here. 

Hickey AJ. Phannaceutical inhalation aerosol powder dispersion an unbalancing act. Am Pharma Rev 2003 6(4) 106-110. 

I. The simplest method of accomplishing dispersion is by grinding the solid tor liquid) material with the liquid medium until particles of the required size arc ultimately obtained. The colloid mill (Pluuson. 1921) is used for such purpose, as in mixing paints and pastes, regenerating inilk from milk powder, dispersing cellulose in sodium... 

Figure 12. (a) Infrared spectrum of isooctyl thiogiycolate (b) infrared spectrum of isooctyl thioglycolate-treated Cu20 powder dispersed in a KBr pellet. 

The concise scientific definition of an aerosol refers specifically to a colloidal state of material suspended in a gas. However, the term has acquired an additional meaning in common household usage. In the commercial packaging field, the term aerosol now is synonymous with pressurized products that are released in a dispersed form from a can or a bottle. The discharge ranges from coarse fogs and mists to finely divided liquid or powder dispersions. 

Powder Dispersion. Low-dose formulations require a very small particle size to ensure dose content uniformity.12 This can create logistical challenges when particle size information is required. Small particles dissolve more quickly than larger ones therefore, if a liquid is used for a dispersing medium, the compound should be insoluble or nearly insoluble in that medium. 

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