Wurster coating studies

More recently, Andersson et al. reported in 1999 the possibility to predict pellet coating thickness with an error as low as 2.2 pm [39]. Lee et al. [40] reported very good agreement between actual measurements and NIR-predicted pellet film thickness for the real-time monitoring and endpoint determination of the coating endpoint. 

Pharmaceutical and medical applications of near-infrared spectroscopy 

Worts and T. Schaefer, Control of Fluidized Bed Granulation V Factors Affecting Granule Growth, Arch. Pharm. Chem. Set. Ed., 6,1 (1978). 

Davies and A. Grant, Air-Conditioning-Generated Noise in a Near-Infrared Spectrometer Caused by Fluctuations in Atmospheric Water Vapor, Appl. Spectrosc., 41, 7 (1987). 

Ellis and J. Bath, Modifications in the Near Infra-Red Absorption Spectra of Protein and of Light and Fleavy Water Molecules When Water Is Bound to Gelatin,/. Chem. Phys., 6,723 (1938). 

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Properly balanced fluidization is critical to successful Wurster coating. This fluidization includes critical aspects of the down-bed, up-bed, and expansion chamber regions. The dynamics of airflow and particle flow are complex and have been the subject of several studies. The critical elements include the following three points ... 

Effective product and process optimization play a prominent role in any successful scale-up study. As an illustration, this case study summarizes the initial development, and subsequent scale-up, of a Wurster process designed to facilitate the application of an aqueous ethylcellulose dispersion to drug-loaded pellets. At the same time, it was intended to deal, up front, with some of the idiosyncrasies of such a coating system that often influence the functionality of the final dosage form. 

During studies of particle and gas flow patterns in traditional Wurster coaters it was found that flow patterns were dominated by the particles rather than the gas. This explains why sometimes, in spite of the well defined flow, uniform coating is difficult to control. To overcome this problem, a precision Wurster coater was developed [B.97]. 

The real coating process in the studied Wurster coater apparatus with the bed mass of 3 kg contains about 21.8x10 particles with the size of 550 im. Unfortunately, the numerical effort for the calculation of the DPM model increases with increasing the number of simulated particles. The DPM model is unable to represent this number of particles, at least with the actually available computing power. However, the number of particles can be reduced by conservation of the particle and fluid dynamics in the simulated apparatus and its real geometry. In this work a scaling approach proposed by Link et al. (2009) and extended by Sutkar et al. (2013) has been used, in which the scahng of the particle size was carried out. Due to the size increase, the adequate properties of sohd and gas phase have been adapted to keep the dimensionless numbers Archimedes At) and Reynolds Re) and the velocities of minimal fluidization and elutriation constant. 

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