Capsule coatings have a wide range of applications as they afford protection to active pharmaceutical ingredients. However, few studies have focused on capsule coating owing to the sensitivity of hard gelatin shells to solvents and high temperature. In the present study, we aimed to coat capsules using two thermoforming coating techniques: vacuum forming coating (VFC) and centrifugal forming coating (CFC). Rheological and mechanical properties were investigated to comprehensively elucidate the processes and mechanisms underlying the two coating techniques. The corresponding coating integrity and drug release behavior were characterized and compared. Herein, we observed that a lower temperature was more suitable for the VFC process than the CFC process. The drug release rate decreased with the film thickness increased. Both optimal VFC and CFC capsules revealed a 24 h sustained-release property following Fick's diffusion law. The coating thickness distribution was more homogeneous for the VFC capsule than the CFC capsule. With the advantage solvent-free of functional capsule coatings, thermoforming coating techniques are convenient and efficient solutions for small-scale personalized coating of oral solid preparations.
Keywords: Capsule coating; Centrifugal forming coating; Sustained-release; Thickness distribution; Vacuum forming coating.
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