Novel Needle-Free Reagent Injection Method to Reduce Spread of Infectious Diseases

Currently, drug administration for disease treatment and prevention commonly uses injectors with metal needles. However, as the needle directly contacts the patient’s mucus and blood, the use of different syringes has long been a significant global problem in terms of spreading infectious diseases. To address this issue, needle-free drug injection systems have been developed worldwide. Most of these systems work by perforating the skin and administering the drug through a high-pressure water jet. Now, researchers have developed an electrically induced microbubble generator that uses repetitive mechanical oscillation driven by microbubble dynamics for needle-free injection. Compared to existing needle-free injectors, this method is more cost-effective, easily operable, and can be seamlessly integrated into existing medical devices.

The innovative needle-free injection technique developed by scientists at Kyushu University (Fukuoka, Japan) enhances the depth of drug injection through shock wave reflection facilitated by microbubble dynamics. The basic principle of this needle-free injection technique involves the reflection of shock waves generated by microbubble dynamics. When a voltage pulse is applied to an electrode, a high-voltage electric field forms at the tip of the electrode, causing a microbubble to form. The microbubble expands and contracts, and when it collapses, it generates a shock wave that creates a microjet. Upon the first voltage pulse, the shock wave is transmitted to the tissue, causing it to vibrate without perforating it. The microjet is then formed, perforating the tissue.

During the second voltage pulse, the shock wave transmits to the tissue and causes the perforation to expand as the tissue vibrates. The microjet further deepens the perforation. This process is repeated for 3,000 cycles, leading to effective tissue injection. The researchers introduced a semi-ellipsoid reflector to reflect the shock wave from the microbubble. After the microbubble collapses, the shock wave is transmitted in all directions. Only the part of the shock wave directed toward the target expands the wound, and most of the mechanical energy of the shock wave is lost. However, the shock wave that is directed away from the target is reflected by the semi-ellipsoid reflector and redirected toward the target. The reflected shock wave then expands the wound again, improving the perforation ability with each microbubble generation.

The findings of this research, published in the journal Cyborg and Bionic Systems, show that the use of a shock-wave reflection device enhances the reagent introduction ability of the needle-free injection system induced by electric microbubbles. The researchers compared the injection depth with and without the shock wave reflection and visualized the shock wave using schlieren photography. The results demonstrated that the shock-wave reflection device improved the injection depth by approximately 200 μm, indicating the method's potential for effective needle-free drug injection.

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Kyushu University