Development of repetitive mechanical oscillation needle-free injection through electrically induced microbubbles

A research paper by scientists at Kyushu University presented a novel needle-free reagent injection method that improves the depth of reagent injection by reflecting shock waves through microbubble dynamics.

The research paper, published on Mar. 19, 2025 in the journal Cyborg and Bionic Systems.

Currently, drug administration for disease treatment and prophylaxis generally adopts an injector with a metal needle. However, because the needle is in direct contact with the patient’s mucus and blood, the spread of infectious diseases through the use of different syringes has long been a worldwide problem. To solve this problem, needle-free drug injection systems have been developed worldwide. Most needlefree drug injection systems perforate the skin and introduce a drug through a high-pressure water jet. “We have developed the electrically induced microbubble generator for needle-free injection through repetitive mechanical oscillation due to microbubble dynamics. Comparing to the existing needle-free injectors, it can be easily integrated into existing medical devices with low cost and easy operation.” said the author Yibo Ma, a researcher at Kyushu University, “In this research, we improved the reagent introduction ability of an electrically induced microbubble needle-free injection system by reflecting the shock wave from the microbubble dynamics.”

The principle of needle-free injection based on the reflection of shock waves through microbubble dynamics is as follows: When a voltage pulse is applied to an electrode, there is a concentrated high-voltage electric field at the electrode tip. A microbubble forms at the electrode tip. The microbubble expands and collapses. As the microbubble collapses, a shock wave is generated and a microjet forms. At the first voltage pulse, the shock wave is transmitted to the tissue and the tissue vibrates without perforation. The microjet then forms and perforates the tissue. At the second voltage pulse, the shock wave is transmitted to the tissue and the perforation wound expands through the vibration of the tissue. The microjet then perforates and deepens the wound. This process was repeated for 3,000 cycles to achieve tissue injection. The authors propose a semi-ellipsoid reflector to reflect the shock wave from a microbubble. The shock wave is transmitted in all directions after the microbubble collapses. Only the part of the shock wave transmitted toward the target expands the wound, and most of the mechanical energy of the shock wave is thus lost. However, part of the shock wave transmitted away from the target is reflected by the reflector and thus transmitted to the target. The reflected shock wave expands the wound again. This process occurs at each microbubble generation and improves the perforation ability.

In this study, the reagent introduction ability of the needle free injection system induced by electric microbubbles was improved by reflecting the shock wave of microbubble dynamics. Authors compared the injection depth with and without the shock wave reflection and imaged the shock wave through schlieren photography. Our results show that the use of a shock-wave reflection device could achieve the reflection of shock wave and improved the reagent depth by approximately 200 μm. This demonstrated the potential of this method for needle-free injection. “In the future, we will optimize the shock wave reflection method and focus the shock wave to improve the performance of our needle-free injection method.” said Yibo Ma.

Authors of the paper include Yibo Ma, Wenjing Huang, Naotomo Tottori, and Yoko Yamanishi.

This work was supported by JSPS KAKENHI Grant Number JP22K18783, JP22H00198, JST, CREST (JPMJCR19S6), JST Moonshot R&D (JPMJMS2217-3-1), and JST SPRING (JPMJSP2136).

The paper, “Development of Repetitive Mechanical Oscillation Needle-Free Injection through Electrically Induced Microbubbles” was published in the journal Cyborg and Bionic Systems on Mar. 19, 2025, at DOI: 10.34133/cbsystems.0225.

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