Binder-free dry particulate coating process using a mild vibration field: Effects of glass-transition temperature and powdering method of polymeric coating agents on coating performance.

We employed a new dry coating process with mild-intensity vibration to prepare a 100-µm-sized microparticle capable of prolonged release of a drug. To accomplish this without using a binder, a series of laboratory-made acrylic latexes with different glass transition temperatures (Tg) ranging from 30 °C to 80 °C were employed as coating agents, and the effects of Tg and powdering method of the coating agents on coating performance were investigated. The laboratory-made acrylic latexes were powdered by spray-drying (SD) or freeze-drying (FD). Diclofenac sodium (DS)-loaded ion-exchange-resin with particle size ∼100 µm was used as a core particle. The process utilized vibrations with amplitude of 0.5 mm and frequency of 90 Hz to form an ordered mixture composed of the core particles with the loosely-layered coating agents. Subsequently, the coating agents were fixed mechanically on the core particle by impaction of zirconia beads. The coating agents powdered by FD showed higher coating efficiencies than those powdered by SD, irrespective of the differences in Tg values. Among the coating agents powdered by FD, the particles coated at Tg = 60 °C exhibited the most prolonged drug-release, although the coating efficiency was not the highest. In our proposed process utilizing mild vibration, we demonstrated that adjusting the Tg of the coating agents is crucial to the formation of binder-free multiple coating layers for prolonged drug release.