The four stages of a shock-induced high-speed liquid microjet

Two decades ago high-speed liquid jets resulting from the interaction of micro bubbles with low amplitude therapeutic shock waves had first been promoted as a mechanism for microinjection of cells, with great potential in applications such as targeted drug delivery. Here, experimental high-speed x-ray phase contrast images of laser-induced shock waves interacting with micro bubbles, complemented by numerical simulations, brings us within reach of controlling such jets. This work focuses on the limit at which jets form, presented in four distinct stages. The first phase suggests that the mean acceleration of the proximal point on the bubble interface plays a major role in defining wether a jet will form or not. The second phase indicates that, once developped, the jet travels through the bubble at an almost constant speed, and when lacking momentum, may succumb to hydrodynamic instabilities, resulting in gas-encapsulated droplets. If the jet reaches the distal side of the bubble, and the Weber number associated with the jet is greater than 100, the third phase shows the entrainment of gas by the jet on the distal side of the bubble. The final stage consists of a hollow cylindrical gas ejecta of a few nanoliters detaching from the bubble, suggesting a controlled way of injecting cells with small quantities of liquid and gas.