Visualization of penetration of a high-speed focused microjet into gel and animal skin

Realization of a needle-free drug delivery device can solve needle-caused problems. Recently, attention has been given to the use of a focused liquid jet instead of the use of the existing needle-free device that generates a turbulent liquid jet. This study experimentally visualized the penetration into a gel and animal skin of a focused liquid jet with a very high speed around 200 m/s. We first examined high-speed images to evaluate the dynamics of the jet penetration into a gel. We found that the penetration depth is determined within a short time $$t_p$$ (on the order of 0.01 ms). $$t_p$$ is similar to $$L/V_j$$ , where L and $$V_j$$ are, respectively, the penetration depth and the impact speed of the jet tip. We then investigated the overall shape of the penetration site represented by the length ratio $$\alpha =L/W$$ , where W is the width of the penetration site. Remarkably, the ratio $$\alpha$$ is greater than unity for a gel, as well as for the animal skin. This suggests that the focused liquid jet can create a narrow penetration site into the target.