Tribology of rough ultra-film contacts in drug delivery devices

Elastomeric seals are extensively used in an assortment of drug delivery devices, such as syringes and pressurized metered dose inhalers. Although tribology of rubber seals and o-rings is reasonably well understood in engineering applications, the drug mixtures and formulations do not enjoy the required rheology to ensure coherent hydrodynamic action. In fact formation of uninterrupted hydrodynamic films is not actually sought in drug delivery devices, which often contain mixtures that are volatile when exposed to the environment. Furthermore, while engineering devices are often driven to overcome friction, many drug delivery systems are actuated manually and frequently by frail individuals. Therefore, the tribological problem is quite complex with many biological and environmental constraints. This paper highlights a parametric friction model for combined adhesive friction due to asperity interactions and non-Newtonian viscous action of the formulation. The model predicts the hysteretic behaviour of elastomeric seal contacts and conforms reasonably well to the experimental measurements of the same through actuation and release of inhaler valves.