Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy


Chemical and Biochemical Engineering


Jesse Zhu


This project applied electrostatic dry powder coating technology on hard gelatin and HPMC capsules using Eudragit® RS/RL and Eudragit® L 100-55 to achieve sustained release and enteric release respectively. Dry powder coating eliminated the difficulties associated with conventional liquid coating processes such as poor adhesion and stickiness for capsules. Additionally, through optimizing sprayed plasticizer volume, the coating powders deposited on the capsules could be efficiently maximized. The weight gain of coating and the formulation of coating materials were important parameters which controlled the release profiles of coated capsules. The release mechanism of coated capsules was quite different from tablets owing to the existence of capsule shells.

Enteric release aspirin capsules were developed and compared with aspirin tablets. The investigation showed that enteric release capsules could be an alternative form to deliver aspirin. The capsules eliminated the migration of the drug from cores to the coating films, a problem observed with aspirin tablets. It was also found that enteric coating film would not protect aspirin from hydrolysis for both tablets and capsules. And an important factor that caused hydrolysis of aspirin could be the moisture in the environment that penetrated the film.

Finally, the dry powder coating process was scaled up and optimized successfully with tablets. Compared to the conventional aqueous coating process, the dry powder coating process had shorter processing time, lower energy consumption and comparable coating efficiency. And the coated aspirin tablets had similar release profiles as aqueous coated. Additionally, due to the absence of water, less hydrolysis occurred for aspirin coated by the dry powder coating process.

Summary for Lay Audience

In pharmaceutical manufacturing process, drugs and excipients are mixed first. And then, the mixture is compressed into tablets or filled into capsules, two of the most common oral solid dosage forms. After tablets and capsules are manufactured, thin polymer films can be applied on their surface to achieve different functions like enhancing stability, modifying drug release profiles, etc. which process is called coating process.

Currently, the coating process is based on organic solvent or water. The polymers are dissolved or dispersed into organic solvent or water and sprayed onto tablets or capsules. After evaporation, the polymers are left on the surface and form films. However, this process is not suitable for capsules owing to their smooth surface and moisture sensitivity. Additionally, the organic solvent coating process would cause pollution and safety issues while the aqueous coating process would require high energy consumption and long processing time.

The electrostatic dry powder coating process was developed to coat pharmaceutical oral solid dosage forms. This process avoids the use of organic solvent and water. Thus, organic solvent and water related issues mentioned above were eliminated. The dry powder coating process was successfully applied on capsule coating and showed its benefits. Capsules were coated directly to achieve modified release profiles like enteric release and sustained release. The coating process and the parameters that would influence the release profiles like weight gain after coating, formulation of the coating materials, etc. were investigated to have a better understanding of this process.

Aspirin is normally made into tablets and coated to achieve enteric release. However, there are some problems for aspirin tablets such as drug migration. Thus, enteric release aspirin capsule was first developed to prevent aspirin migration. It provided a new dosage form for aspirin. The differences of these two dosage forms were investigated which indicated that the capsule would be a better form to deliver aspirin.

In addition, electrostatic dry powder coating process was scaled up and optimized for commercialization. This process proved to be more energy saving and less time consuming than aqueous coating process. And it caused less degradation for moisture sensitive drugs like aspirin.

Available for download on Sunday, April 28, 2024