Abstract
Vapor-phase deposited polymer coatings are applied on thin indomethacin films to modify the drug release. Hydrogel-forming co-polymers of 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate were prepared directly on top of solution cast indomethacin thin films by initiated Chemical Vapor Deposition (iCVD). This technique allows for solvent-free processing under mild conditions, thus minimizing a potential impact on the pharmaceutical. The drug release behavior, among other properties, was evaluated for polymers of different compositions and at different temperatures. The data show that the release kinetics can be tuned by several orders of magnitude as the cross-linker fraction is varied in the polymer coating. While uncoated indomethacin films were fully released within an hour, polymer coatings showed gradual liberation over several hours to days. Additional insight is gained from evaluating the experimental dissolution data in the framework of diffusive transport. The results of this study show that the iCVD technique has some promises for pharmaceutical technology, potentially allowing for tailored release behavior also for other drug systems.
Highlights
Matrix-type systems where intermixing is desired, such an approach is not well suited for reservoir systems
A solvent-free approach lies in polymer synthesis by initiated Chemical Vapor Deposition[19]
The initiated Chemical Vapor Deposition (iCVD) process is based on the mechanism of radical polymerization in solution, with the difference being that all reagents are supplied in their vapor phase form at low reactor pressure
Summary
The coating of crystalline indomethacin with iCVD polymers leaves the underlying drug layer mostly unaffected and changes in morphology or solid state are not observed. A more detailed look at the data in Fig. 3 reveals that surface features appear smoothed when covered by the polymers, indicating that such structures become slowly buried as the polymer thickness increases during deposition While this behavior is noted both for the pEGDMA homopolymer and the hydrogel-forming p(HEMA-co-EGDMA) coating, detailed inspection reveals another difference. It should be noted that with no or little cross-linking, pHEMA exhibits strong water uptake, detaching from the surface While such a behavior is undesirable for controlled release, it is potentially useful for targeted drug delivery, especially when combined with stimuli-responsive functionalities. The mesh size ξ is given by ξ lφ−1/3Cn1
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