Air Suspension

Air suspension is a common technique to utilize fluidized bed systems for selecting the particle materials, which can be developed for coating the nanoparticles to realizing the micro/nanoencapsulation of drug products and food particles. This technique has been used widely in the pharmaceutical/food industry for production of core material and for film coating.

A review examined advances in the commercial production of microencapsulated drug products [516]. Factors influencing drug selection were considered with particular reference to the design of controlled drug delivery systems. The formulation of both aqueous and nonaqueous coating materials was discussed with examples of common problems encountered in applied coatings. Methods of core production were considered with emphasis on spheronization procedures. Pan and air suspension techniques, together with modification, were discussed. Local average velocity of a particle cloud in an air suspension by cross-correlation of two attenuated laser beams was measured [517].

The characterization of microcapsules containing drugs was reviewed with particular emphasis on sustained-release products produced commercially by pan or air-suspension coating and intended for oral administration [518]. After considering aspects of the core and coating, various technologies used to assess microcapsules were discussed such as optical and spectroscopic evaluation, particle size analysis, filling into hard gelatin capsules, and disintegration, dispersion, and dissolution testing. The in vivo testing of microcapsules and correlation with in vitro data was considered.

Fluidized bed systems were used in the pharmaceutical industry for production of core material and for film coating [519]. Top spray coaters produced batches of fine, coated particles in excess of 500 kg. Wurster bottom spray equipment was used to manufacture pellets as well as to coat products ranging from powders to tablets.

Within the framework of the mechanics of heterogeneous media undergoing phase transformations, a mathematical model was proposed for describing a mixture of gas and liquid (solid) metal particles. The differences between the velocities and temperatures of the phases and the nonequi-librium nature of the phase transition were considered [520]. The problem of the structure of a shock wave in an air suspension of melting particles was solved.

A controlled release preparation of salbutamol may improve patient compliance, minimize side effects, and be valuable in the treatment of nocturnal asthma by extending drug action throughout the night. A controlled release pellet preparation of salbutamol via the air suspension technique was formulated [521].

The influence of spatial nonuniformity in the distribution of chemically inert particles in a screening layer on the process of interrupting the propagation of a heterogeneous-detonation wave was studied numerically within the framework of the equations of motion of a three-velocity, three-temperature, unipressure continuum [522]. The distribution of flame-quenching particles in the layer can affect significantly the extinguishing of combustion waves in a monofuel-air suspension.

Nonpareil cores were spray-coated with a chlorpheni-ramine maleate (an alkylamine antihistamine) layer and a Eudragit(R) NE30D overcoat in a Wurster air-suspension apparatus [523]. In vitro dissolution drug release was a function of polymer membrane thickness.

A varied description was presented of the fluid bed process for coating or air-suspension coating with emphasis on the most efficient batch fluid bed apparatus (the Wurster system) and the ideal continuous fluid bed [524]. Phenomena involved in the process of coating fluidized solid particles were studied. The problem of the application of this technology to coat food particles, in terms of feasibility and profitability, was discussed.

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