Stagnation Pressure in Liquid Needle-Free Injection: Modeling and Experimental Validation

Liquid needle-free injectors employ high-velocity liquid jets to deliver drugs and vaccines. Several parameters are critical to the injection quality: nozzle diameter, volume of drug delivered, ampoule diameter, pressure that drives liquid volume, and impact gap (distance between piston and trigger). A physical model is presented to calculate the stagnation pressure of the injection jet. Two types of the injection systems were tested: a spring-powered system and a voice-coil powered system. The calculation results show that the variation of stagnation pressure with time matches the experimental measurement under the same system conditions. The maximum stagnation pressure determines whether the jet can erode and penetrate into the skin. The maximum stagnation pressure was calculated under three conditions: different volumes, different spring rates and different ampoule diameters, and the results were compared with the experimental measurements. The experiments validated the physical model.