Design of microcapsules with hydrogel as a membrane component and their preparation by a spouted bed

This paper describes particulate design and preparation to control drug release thermosensitively or in a delayed mode from microcapsules (MCs) that were prepared by coating with a membrane incorporating hydrogel as a particulate or chemical component. The particulate preparation was carried out by a spouted bed coating process. The microcapsules releasing drug with a positive thermosensitivity were prepared by dispersing the newly developed latex particles in the ethylcellulose matrix membrane. The latex particles were synthesized so as to have a thermoinsensitive core and a thermosensitive poly(N-isopropylacrylamide) hydrogel shell. Poly(N-isopropylacrylamide) with a lower critical solution temperature (LCST) at 32 °C in water shrank at higher temperatures and highly swelled at lower temperatures than LCST, leading to so-called positively thermosensitive release. On the other hand, when the acrylic ter-polymer of latex particles has a hydrophilic component, 2-hydroxyethyl methacrylate, the water uptake rate of microcapsules could be controlled by its content in the ter-polymer and membrane thickness. The release was characterized by a delayed mode; then the lag time was controlled by the 2-hydroxyethyl methacrylate content and the membrane thickness. This content was also related to the mechanical flexibility of membrane that was critical in the release rate control after the release of drug starts.