Design and preparation of nanocomposite acrylate coating agents for binder-free dry coating of 100 µm-sized drug-containing particles and their coating performance.

For binder-free dry particulate coating to prepare controlled-release micron-sized particles, we designed nanocomposite coating agents with the intention to form a core-shell structure composed of two types of acrylic polymers with different glass transition temperatures (Tg) and evaluated their coating performance. A series of nanocomposite acrylic latexes synthesized by emulsion polymerization was freeze-dried after salting-out to create the powder form. An ion-exchange resin loaded with diclofenac sodium (DS, a model drug) (IER-DS) with a median diameter of approximately 100 µm was used as the core particle. Dry coating of the IER-DS with nanocomposite coating agents was carried out using a laboratory-made coating apparatus assisted with mild-intensity vibration and zirconia bead impaction. The coated particles were cured by heating at a temperature 20 °C higher than the Tg for 12 h to complete the film-forming process. It was found that the highest coating efficiency (more than 70%) and a remarkably prolonged release period of the drug (the time required for 50% release reached approximately 12 h) could be achieved when nanocomposite coating agents with a soft polymeric core (Tg = 30 °C) and a hard polymeric shell (Tg = 80 °C) were applied. In contrast, nanocomposite coating agents with a combination of a hard polymeric core and a soft polymeric shell resulted in lower coating efficiency. These results demonstrate that nanocomposite polymeric coating agents composed of a soft core and a hard shell are effective for the production of drug-loaded microparticles with a prolonged release function by a binder-free dry-coating process.