title: Air-dictated bottom spray process: impact of fluid dynamics on granule growth and morphology.
abstract: BACKGROUND
  Growing interest in the use of the less-explored bottom spray technique for fluidized bed granulation provided impetus for this study.
  
  
  OBJECTIVE
  The impact of fluid dynamics (air accelerator insert diameter; partition gap) and wetting (binder spray rate) on granule properties were investigated.
  
  
  METHODS
  In this 3(3) full factorial study, the results were fitted to a quadratic model using response surface methodology. The air velocity at the spray granulation zone for the investigated conditions was measured using a pitot tube.
  
  
  RESULTS
  Air accelerator insert diameter correlated to measured air velocity at the spray granulation zone and was found to not only dictate growth but also influence granule morphology. The partition gap was found to play important roles in regulating particle movement into the spray granulation zone and optimizing process yields, whereas binder spray rate significantly affected granule morphology but not granule size.
  
  
  CONCLUSIONS
  Unlike conventional fluidized bed granulation, ease of modulation of fluid dynamics and insensitivity of the bottom spray process to wetting allow flexible control of granule size, shape, and flow. Its good drying ability also indicated potential use in granulating moisture-sensitive materials.
authors.affiliation: Department of Pharmacy, Faculty of Science, National University of Singapore, Singapore.
authors.forename: Celine V
authors.initials: CV
authors.lastname: Liew
authors.forename: Dawn Z L
authors.initials: DZ
authors.lastname: Er
authors.forename: Paul W S
authors.initials: PW
authors.lastname: Heng
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods*; D010316:Particle Size; D004364:Pharmaceutical Preparations / Q000138:chemical synthesis* / Q000378:metabolism; D011897:Random Allocation; D012212:Rheology
chemical_list: D004364:Pharmaceutical Preparations