Shock-Induced Payload Release

Antibubbles, liquid droplets encapsulated in gas, offer enhanced payload capacity and robustness compared to traditional microbubbles. We explore their response to laser-induced shock waves for biomedical payload delivery applications.

Contributors: Guillaume Bokman

Encapsulated Droplet Payload Release

Enlarged view: Image sequence of an example of shock-GED interaction within the drop impact regime. — Image sequence of an example of shock-GED interaction within the drop impact regime. The upper halves display the numerically computed volume fractions of air and drop water in blue and black, respectively. The lower halves show corresponding experimental radiographs. The dimensionless time of the bubble starting from the shock contact with the GED, is indicated in the bottom-left corner. The inset figure shows the normalised bubble pressure map.

Gas-encapsulated droplets are emerging as effective microfluidic transport systems. In our work, shock waves are proposed as a mechanism for instant payload release from such encapsulated structures. This process depends on the coupled dynamics of the encapsulating bubble and the inner droplet, which we investigate using a combination of theory, simulation, and x-ray imaging.

We characterize key phenomena such as complex shock wave patterns, pressure amplification, and the generation of sheet jet cascades. Analytical models are developed to predict water hammer pressure, sheet jet velocity, and droplet drift.

Experiments with millimetric gas-encapsulated droplets and laser-induced shock waves, complemented by numerical simulations, reveal three release regimes: drop impact, partial deposition, and jet impact. The prevailing regime depends on the shape of the impacting bubble interface and the associated Weber and Reynolds numbers. The drop impact and partial deposition regimes resemble canonical drop impact on flat surfaces, while the jet impact regime aligns with binary drop collisions. Using existing scaling laws, we model and interpret the dynamics, demonstrating that high Weber and Reynolds numbers promote mixing and effective droplet dissemination. More details can be found e.g. in our external page paper.

Micrometric Antibubble Payload Release

Enlarged view: Schematic describing the experimental setup employed for high-speed imaging. — (a) Top view schematic describing the experimental setup employed for high-speed imaging. The OPSL is turned on for high-speed fluorescence only and other light sources are switched off. The inset depicts the PEG hydrogel cultivated on a square glass capillary. Calcein (green) and Rhodamine-6G (red) antibubbles, displayed in 100 ×100 µm2 microscopy images, are hydrated and injected into the water tank below the hydrogel, allowing them to rise and settle on the hydrogel surface. A typical experimentally measured shock wave profile is shown, with the first and the second shock instants zoomed-in below.

Micrometric antibubbles resting on a soft, cell-mimicking substrate are subjected to single shock pulses. Using ultra-high-speed bright-field imaging (10 Mfps), we capture detailed dynamics including Pickering shell shedding, antibubble collapse, and oscillation. High-speed fluorescence imaging (200 kfps) reveals the release and dispersion of fluorescent payloads into the surrounding medium.

We identify three distinct release regimes, full, partial, and none, determined by shock intensity and antibubble size. In some cases, payload embedded within the substrate remains visible after activation, indicating successful localized delivery. These results demonstrate that shock waves can serve as an alternative acoustic mechanism for precisely timed and tunable payload release, with energy flux densities comparable to those in ultrasound-based therapeutic applications.

This work highlights the promise of shock-driven antibubble systems for targeted drug delivery, including cancer treatment and therapies for neurodegenerative disorders, offering a controllable and efficient release mechanism based on external acoustic triggering.

Enlarged view: Image sequence showing the interaction of an antibubble with a laser-induced shock wave. — Image sequence showing the interaction of an antibubble with a laser-induced shock wave having a peak pressure of 13.70 Mpa and the subsequent payload release within the full release regime. The shock wave comes from the lower left corner and makes contact at t = 0.0 µs. Time is given in microseconds and the scale bar shows 10 µm.