Assessment of the effect of Cellets’ particle size on the flow in a Wurster fluid-bed coater via powder rheology

The main objective of this study was to investigate the effect of microcrystalline cellulose (MCC) spheres (Cellets) size effect on the powder properties to assess the possible impact of the Cellets’ size on the powder behaviour in the down-flow bed and horizontal transport zone when a Wurster fluid-bed coater is used. The particle size distribution of Cellets was determined using optical digital microscopy. Standard pharmacopoeia methods as bulk/tapped density and flow rate measured with gravitational funnel method as well as investigation of dynamic angle of repose and dynamic cohesivity index with a rotating drum tester (GranuDrum) and conditioned bulk density, basic flowability energy, specific energy, pressure drop, permeability and compressibility by powder rheometer (FT4 Powder Rheometer®), were employed to characterise the powder's properties of Cellets 90, 100, 200 and 350 (D50-size from 94 to 424 μm) alone or premixed with 0.5% w/w magnesium stearate. Specific powder rheology methods were proposed for characterisation of Cellets’ behaviour in down-flow bed, the horizontal transport and coating zone. The level of Cellets’ processability decreasing in the Wurster fluid-bed coater with decreasing of Cellets size (D50) from 425 to 94 μm was established with different powder rheology methods.