High-speed video investigation of jet dynamics from narrow orifices for needle-free injection

An experimental study to examine the hydrodynamic performance and start-up phase of liquid jets for needle-free injection was performed. With the use of high-speed videography at frame rates up to 311,111 fps, the initial stages of jets exiting from narrow orifices were captured. In addition to the very early-time (t < 50 μs) dynamics, we assessed the fully-developed jet form and the penetration dynamics into various gel substrates. The viscosity of the jet fluid was varied along with the nozzle diameter, and the gel stiffness (by varying the solids fraction, %w/w). For the penetration into gels, we observe that the speed of the tip of the hole did not exhibit any quantifiable dependence of jet fluid properties. Moreover, we observe the formation of fluid reservoirs which led to a step-wise penetration regime for depths z ≳ 12 mm.