In many drug dispensing devices, such as syringes and inhalers, a rubber ring is used as a seal. During device actuation the seal is subjected to friction which in turn causes it to deform. This can lead to suboptimal performance of the device and as a consequence variability in the delivered dose. Seal friction is complex, arising from adhesion of rubber in contact with a moving counterface, viscous action of a thin film of entrained fluid into the contact and ploughing of seal asperities. Therefore, the first step in the understanding of the conjunctional behaviour of rubber seals is the fundamental study of these friction mechanisms. A developed model can then be validated against measurements, prior to its use in a multi-body dynamic model of the inhaler valve to predict product performance, robustness and variability due to manufacturing tolerances. This paper undertakes two distinct studies. Firstly, a friction model for the rough elastomeric material, typically used for valve seals is developed. The model is then validated against measurements in nano-scale. Friction data is presented for nitrile rubber, using a silicon nitride AFM tip for nano-scale interactions. The validation is then extended to macro-scale motion of an instrumented trolley, incorporating an elastomeric surface sliding on a polymeric counterface. These tests are carried out for polybutylene terephthalate (PBT). Secondly, the validated friction model is used in an elastomeric seal model in-situ within the valve and in contact with a polymeric stem surface and subject to both global fittment deformation and canister pressure. Reasonable agreement is found between the measurements and model predictions for the nano-scale coefficient of friction of rubber against silicon nitride. Similarly, good agreement has been obtained for the mean coefficient of friction of rubber against PBT. In addition, the mechanism of adhesion between contacting surfaces of gasket and stem is taken into account.

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