A review of particulate design for pharmaceutical powders and their production by spouted bed coating

This paper focuses on how fine particles are processed in a fluidized/spout ed bed coater without agglomeration and what kinds of functions are desired for particulate dosage forms, in order to preview the future contributions of fluidization technology in pharmaceutical dosage form development. Coat ing operation of particles smaller than 100 mum is very often troubled with particle agglomeration and adhesion due to the excessively high binding st rength of coating materials and to electrostatic charging. In order to avoi d these troubles, the binding strength has to be adjusted corresponding to the size of particles to be processed. The most efficient way to produce si ngle-core microcapsules is to separate the drying and film formation of spr ay droplets. This can be achieved by using latices whose softening temperat ure (T-s) is higher than the inlet air temperature. Particulate designs of the latex polymers based on this idea are also effective for solving some o ther troubles such as electrostatic charging and poor film formability in f ine particle coating. Meanwhile, multiple functions and high performance ar e required for particulate systems to exhibit desired characteristics in pr actical uses. The fluidized/spouted bed process, which can easily produce m ulti-layered and composite structures, is an excellent method for multi-fun ctional adaptation of particulate systems. This is demonstrated in this pap er in the preparation of microcapsules for cancer therapies, such as neutro n capture therapy (NCT) and chemoembolization therapy, and for stimuli-sens itive controlled-release therapy. In pharmaceutical technology, requirement s for producing functional particles of around 30 mum, which can be used, f or example, as injectable suspensions for cancer therapy, will increase in the future. This will require the processing of around 10-mum particles, th ough the smallest particle size that a fluidized/spouted bed can steadily p rocess seems to be 20 mum so far. Membrane and core formulations to process such fine particles seem available already, but we have no technique to st eadily fluidize or circulate 10-mum particles at high velocity in a dispers ed condition. Furthermore, nanoparticulate systems will be required for mor e efficient cancer treatments. Although the fluidized/spouted bed is unable to process nanoparticles directly, development of some smart devices as th eir generators will be made possible by its high potential to make multi-la yered and composite structures. (C) 2000 Elsevier Science S.A. All rights r eserved.