An experimentally validated dynamic model for spring-driven autoinjectors.

This study focuses on developing a predictive dynamic model for spring-driven autoinjectors. The values of unknown physical parameters, such as the heat convection coefficient and the friction force between the plunger and the syringe barrel, are obtained by fitting the experimentally measured displacements of the plunger and the syringe barrel. The predicted kinematics of the components, such as the displacement and velocity of the syringe barrel, agree well with the experiments with a l-norm error smaller than 10%. The predictions of the needle displacement at the start of drug delivery agree with the experimental measurements with a l-norm error of 20%. The maximum air gap pressure and temperature decrease with the initial air gap height but increase with the elasticity and viscosity of the plunger and the mechanical stop. The proposed experimentally validated dynamic model can be effectively used for device design optimization as it is not computationally demanding.