Characterization of jets for impulsively-started needle-free jet injectors: Influence of fluid properties

An experimental study was performed to assess the hydrodynamics of liquid jets used for needle-free injection, where the typical orifice diameter is ~155 μm and velocity is in range of ~ 60–140 m/s. The jet is impulsively started by a spring-piston that forces a plunger through a cartridge filled with the liquid. Liquid exiting the orifice then forms a jet. However, despite a fixed spring force, the jet speed can vary significantly depending on the fluid physical properties - in particular - the effective viscosity. Since in practice a wide range of fluids may be used for injection, we seek herein to study the jet formation and speed for a broad range of fluids, characterized by viscosity or rheological profile. In addition, we also characterize the jet performance with a peak impact force, measured by a dynamic load cell, and ex-vivo injection experiments on porcine tissue. We find that jet speeds and impact forces decrease in a non-linear fashion with increasing viscosity, but that shear-thinning effects are significant and can render high jet speeds (>100 m/s) even for low-shear viscosities μ0~100 Pa.s.