Penetration of impact-induced jets into skin-simulating materials

TL;DR

A shear deformation model is proposed, in which the jet kinetic energy is dissipated through deformation of the gelatin, which shows good agreement with experimental results and provides a unified physical basis for liquid jet penetration.

Abstract

This study compares the penetration characteristics of impact-induced jets with those of laser-induced jets, focusing on the underlying penetration mechanism rather than device performance for needle-free injection. Using an impact-induced jet system capable of ejecting a highly focused liquid jet at high speed without the use of lasers, we examine jet penetration into skin-simulating materials. Unlike conventional needle-free injectors that produce diffused liquid jets, the impact-induced method generates a highly focused jet that limits the injected area, thereby reducing invasiveness. Comparative experiments with laser-induced jets show that, even at similar jet tip velocities, impact-induced jets achieve greater penetration depth. The penetration depth remains constant regardless of the offset distance D from the target, owing to the high and nearly uniform velocity of the cylindrical jet root region, indicating that penetration is governed by the cylindrical jet structure. Furthermore, we systematically vary the liquid viscosity, jet inertia, and elastic modulus of the skin-simulating material. To account for cylindrical liquid jet penetration, a shear deformation model is proposed, in which the jet kinetic energy is dissipated through deformation of the gelatin. The model shows good agreement with experimental results and provides a unified physical basis for liquid jet penetration.

Figures (13)

• Figure 1: A positioning map comparing the cost, safety risk, invasiveness, and injection volume of a conventional needle-free injector, a laser-induced jet, and an impact-induced jet. The vertical axis represents cost and safety risk, and the horizontal axis represents invasiveness and injection volume.
• Figure 2: (a) A sketch of an impact-induced jet. The ejector is dropped downward to collide with a metal block, generating a high-speed jet upon impact. (b) A high-speed image sequence of a focused impact-induced jet ejected with silicone oil (kinematic viscosity: $10~\mathrm{mm^2/s}$).
• Figure 3: (a) A three-dimensional schematic of the experimental setup for the impact-induced jet. (b) A two-dimensional side-view schematic of the experimental setup. The upper high-speed camera (160,000-200,000 fps) captures the jet ejection process, while the lower high-speed camera (100,000 fps) captures the penetration behavior into the gelatin. (c) The gas–liquid interface before jet ejection (yellow dotted line) and a jet ejection image; $a_1$ and $a_2$ denote the two reference points located $150~\mu$m away from the nozzle-orifice center. (d) $D$ is defined as the distance from the top of the meniscus to the gelatin surface, and the penetration depth is $P$.
• Figure 4: (a) A three-dimensional schematic of the experimental setup for the laser-induced jet. (b) A schematic of the experimental setup. The upper high-speed camera (200,000 fps) captures the jet ejection process, while the lower high-speed camera (28,000 fps) captures the penetration into the gelatin. (c) The gas–liquid interface before jet ejection (yellow dotted line) and a jet ejection image. (d) The distance $D$ is defined from the top of the meniscus to the gelatin surface and the penetration depth is $P$.
• Figure 5: An image sequence of the injection of (a) an impact-induced jet (jet tip velocity $V_{\mathrm{jet\,tip}} = 88.8~\mathrm{m/s}$) and (b) a laser-induced jet (jet tip velocity $V_{\mathrm{jet\,tip}} = 86.8~\mathrm{m/s}$), using a gelatin target with a shear modulus of $5542~\mathrm{Pa}$.