Bubbles and droplets for nanotechnology and nanomedicine

Abstract: The acoustic excitation of bubbles and droplets has widespread use in medical technology and nanotechnology applications. These applications include bulk and surface acoustic waves for bubble and droplet production, as well as bubble and droplet actuation to perform local drug delivery or local and well-controlled surface cleaning. For example, the controlled jet breakup of droplets can be accelerated through the resonant acoustic excitation of instable modes on the jet to form monodisperse droplets at a uniform production rate. Beat frequencies can be exploited to form larger droplet constructs through well-controlled coalescence in flight to be used to efficiently generate extreme ultraviolet wavelengths for the next-generation nanolithography technology. Acoustically driven bubbles can promote efficient mixing on the microscale through acoustic streaming and stable cavitation. Microbubbles and low-boiling point nanodroplets can also be decorated with a payload which carries great potential for their use as drug delivery agents in the context of personalized medical therapy. Key to all these emerging applications is a precise acoustic control of the interaction of ultrasound with the bubbles and droplets. The challenge here is the combined microscopic length scales and ultrashort time scales associated with the mechanisms controlling bubble and droplet formation and its activation processes, which we solve by high-resolution ultrafast microscopy, even down to the nanosecond. Together with theoretical modeling and numerical simulations these experiments assist in our in-depth fundamental understanding of bubble and droplet behavior, which then provides intriguing new prospects for innovative solutions in nanotechnology industry and in nanomedicine.