Barrier properties and hydrothermal ageing of amorphous alumina coatings applied on pharmaceutical vials
Résumé
Actual requirements of the pharmaceutics industry for reliable, safe, long term storage of biopharmaceuticals imply the use of chemically inert glass vials. This can be achieved by applying a barrier coating on their internal surface. In the present work we investigate the hydrolytic resistance of amorphous alumina coatings applied by chemical vapor deposition at the interior of soda lime glass containers. Autoclaving for 60 min at 121 • C and 2 bar absolute pressure of water filled such containers according to normed tests defined by the European Pharmacopeia, reveal that the concentrations of extractables obtained from the glass and released into the solution in contact, are low. The acidification of the water inside the bottle leads to the partial delamination of a 300 nm thick alumina coating and results in a significant release of aluminum ions. This is due to the previously identified alteration of the external part of the film. In contrast, alumina layers thinner than 20 nm, show concentrations of extractables, both glass and aluminum ions, that are significantly lower than those of an uncoated bottle. This preliminary result is particularly promising. It is attributed to the transformation of the nanometric alumina coating into an aluminosilicate interdiffusion layer during the deposition process, which acts as an efficient barrier, while remaining unaffected from the interaction with the content during the shelf life of the drug.
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