Further studies on the Drug Deposition Mechanisms of Surface-treated pMDI Canisters 

Skemperi¹, D. Worrall¹, G. Critchlow², P. Jinks³

¹Chemistry Department, Loughborough University, Loughborough, Leicestershire, UK

²Materials Department, Loughborough University, Loughborough, Leicestershire, UK

³3M Drug Delivery Systems, Loughborough, Leicestershire, UK

Summary

Building on previously published work [1], further studies were conducted on the drug deposition mechanisms occurring with the aluminium canisters employed with pressurised Metered Dose Inhalers (pMDIs). The current studies explored an expanded range of surface treatments, applied to the canisters, with canister drug deposition quantification providing a final benchmark of performance. Interactions between the coating applied and the humidity present during drug deposition testing were also explored. Physicochemical characterisation of the surface treated canisters was performed to explore potential links between surface topography, surface chemical composition, total surface free energy, and canister drug deposition. The data from these analyses were correlated with those from a drug deposition test, using a model dispersion of salbutamol sulphate in decafluoropentane to enable deposition quantification. The commercial coating treatments explored were; Fluorinated Ethylene Propylene (FEP) lacquer, a 3M proprietary fluorosilane applied to both plain canisters and to Polyethersulphone (PES) lacquered canisters, vapour deposited Parylene, and anodised canisters both with and without the 3M proprietary fluorosilane coating as a final treatment. The results obtained indicated a close correlation between canister total surface free energy, along with Relative Humidity (RH), and drug deposition on canister walls. 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 to canisters pre-treated with a PES lacquer.  In this case a surface free energy value of 13.75 mN/m was obtained with essentially zero measured drug deposition across a wide humidity range. 

Keywords: pMDI canisters, Drug deposition, Surface treatments, Physicochemical characterisation, UV spectrophotometry, Relative humidity, Surface free energy