Simulating a Spring with the ElectroPuls

As the number of patients seeking “in-home” medical care grows larger, medical device companies find themselves catering to an increasing demand for safer, more user-friendly biomedical solutions. 

In an attempt to mitigate the injection process, medical device companies have developed the auto-injector, a spring loaded syringe that delivers a prescribed amount of drug subcutaneously into the bloodstream, forgoing the need for physician oversight and allowing patients to self-administer medication from the comfort of their own home. To design the ideal auto-injector, the delivery time of the syringe must be optimized so that drug release is neither too long nor too short, thus reducing the level of discomfort experienced by the patient. The delivery time can be optimized by choosing the appropriate spring and preload for a given syringe/drug system, which is currently achieved by subjecting springs with varying degrees of stiffness to different loads. However, medical device companies need to be able to get through this iterative auto-injector design process more quickly, and testing a large number of springs is time consuming and less than economical. Simulating the spring eradicates the supply chain issues of multiple springs testing, thereby significantly reducing the required design time. Instron solves this control challenge using Modal Control, an advanced feature of the 8800 controller that creates a composite channel to allow the applied load to vary with actuator position. The user simply needs to specify the initial preload and spring stiffness in order for the system to adjust itself based on the actual load seen by the syringe. A force vs. time graph is produced, from which the Calculations Module feature in WaveMatrix, determines the dispensing time and stall force of the syringe. The user can then determine if the chosen parameters for spring stiffness and preload have yielded an ideal auto-injector dispensing time for a given drug.