Newsletter 2018.1 Index
Theme : "Mechanical Engineering Congress, 2017 Japan (MECJ-17)"
Recently, a laser-induced microjet is expected to be applied to the needle-free injection devices due to its unique highly-focused jet shape. The highly-focused microjet is generated by irradiating a liquid filled in a capillary tube with a pulsed laser. Considering practical use of the needle-free injection, we should control the injection depth. Although the microjet injection phenomena into a model material of the skin have been studied, the effect of the distance L where a microjet travels before impacting at a soft material on injection depth Di have not been researched. The distance L is not a parameter which controls the jet generation, but it is necessary to know appropriate value of the distance L in order to determine the condition of use of the injection system. We investigate experimentally the effect of the distance L where a microjet travels before impacting at a soft material on injection depth Di. As a soft material, we used 5wt% gelatin. We clarify the trend that, with increase of the distance L, the injection depth Di increases, obtains a peak value, and then decreases. Furthermore, experimental results suggest that the focused jet shape is important for jet injection. Additionally, we consider what determines the distance Lpeak at which the injection depth Di obtains a peak value. Based on scaling argument using the focusing time scaleﾎ杯f estimated by the initial velocity U0 of free surface and the curvature radius r, we find that r has a great influence on the distance Lpeak. In order to verify this, we normalize the result of the injection experiments with the capillary tubes of various inner diameter d. The normalized result indicate that the distance Lpeak depend on the curvature radius r.
Laser-induced microjet, Needle-free injection, Injection depth, Jet shape, Travering distance
Fig. (a) Side view of a capillary tube and a container filled with gelatin. The sketch shows definition of experimental parameters. (b) One example of a series of snapshots taken by high-speed camera. The microjet travels from bottom to up and injects into gelatin.