A study on the drug deposition mechanisms of surface-treated pMDI canisters

The aim of this project was to explore drug deposition mechanisms on the aluminium canisters employed with Pressurised Metered Dose Inhalers (pMDIs). The investigation explored the influence of various surface treatments, applied to the canisters, to drug deposition phenomena. Physicochemical characterisation of the canisters was performed after the application of different surface treatments to explore potential links between: surface topography, surface chemical composition, total surface energy, and drug caking appearing on the canister walls. The coating treatments which were tested were; Fluorinated Ethylene Propylene (FEP) lacquer, vapour deposited Parylene and a 3M-proprietary, fluid-applied fluorosilane. Anodisation was also explored both with and without additional fluorosilane treatment. A number of surface physicochemical characterisation techniques were employed, namely; Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS) and Contact Angle (CA) analysis. The data from these analyses were correlated with those from a Drug Deposition test employing drug quantification by UV spectrophotometry. The results obtained indicated a direct correlation of drug deposition on canister walls to the total surface free energy. The lowest total surface free energy values and lowest deposition values were seen when the 3M-proprietary fluorosilane coating was applied as the final treatment. In this case a surface free energy value of 15.73 mN/m and a percentage drug deposition of 7% compared to the calibration can, were achieved.