Abstract
Encapsulation of pharmaceutical powders within thin functional polymer films is a powerful and versatile method to modify drug release properties. Conformal coating over the complete surface of the particle via chemical vapor deposition techniques is a challenging task due to the compromised gas–solid contact. In this study, an initiated chemical vapor deposition reactor was adapted with speakers and vibration of particles was achieved by playing AC/DC’s song “Thunderstruck” to overcome the above-mentioned problem. To show the possibilities of this method, two types of powder of very different particle sizes were chosen, magnesium citrate (3–10 µm, cohesive powder) and aspirin (100–500 µm, good flowability), and coated with poly-ethylene-glycol-di-methacrylate. The release curve of coated magnesium citrate powder was retarded compared to uncoated powder. However, neither changing the thickness coating nor vibrating the powder during the deposition had influence on the release parameters, indicating, that cohesive powders cannot be coated conformally. The release of coated aspirin was as well retarded as compared to uncoated aspirin, especially in the case of the powder that vibrated during deposition. We attribute the enhancement of the retarded release to the formation of a conformal coating on the aspirin powder.
Highlights
Current coating techniques for encapsulating pharmaceutical powders within polymer films are typically wet spray-based methods
A thin polymer film with well-defined properties is covering the particles [1]. Even though this technique provides a large variety of coated forms, it is not applicable to all polymers and pharmaceutical powders as toxic solvents may remain in the structure or the pharmaceutics may degenerate under the harsh process conditions
Among the possible chemical vapor deposition methods, initiated chemical vapor deposition suits the requirements to coat pharmaceutics as it operates without plasma, works under mild pressure (>100 mTorr) and low substrate temperature (20–60 ◦C) and is, suitable for delicate substrates such as tissue paper, pharmaceutics or even ionic liquids [4,5,6]. iCVD was invented in 2005 by the group of Karen Gleason at the Massachusetts Institute of Technologies and is a vacuum-based free radical polymerization technique [7,8,9]
Summary
Current coating techniques for encapsulating pharmaceutical powders within polymer films are typically wet spray-based methods. The deposition process needs to be interrupted several times to open the reactor to manually shake the powder The drawbacks of this technique are that it does not provide a continuous polymerization throughout the thickness, has statistical non-conformal coating thicknesses and takes a lot of time. Proper model powders for this preliminary study were chosen following the theory of Geldart In this theory powders can be classified in terms of particle size and density which can be linked to how easy they can be fluidized via gases [26]. Group C contains powders which are cohesive mainly due to their small particle size (
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