A new technique has been developed that uses ultrasound to vapourise encased nano-droplets, at the tumour site. This technology could be used to image the tumour, damage it or even deliver chemotherapy drugs with precision.
Existing applications of ultrasound therapy include thermal excitation of tissues, for example to dilate blood vessels, and creating cavitation to break up kidney stones. Ultrasonic toothbrushes have also been shown to remove dental plaque with better efficiency than conventional toothbrushes, and about the same as that of mechanical electrical toothbrushes. Micrometre-sized droplets, encased in a stabilising shell, can already be visualised with ultrasound, but these are too large to enter tumours. Nanometre-sized droplets can do so, however.
Vapourisation is tricky to control in reality, since the process requires a point of nucleation. The researchers demonstrated an efficient way to achieve vapourisation: by applying a frequency at the exact resonant frequency of the droplet, the pressure inside suddenly drops and the liquid vapourises. This is much the same principle as shattering a crystal glass by bombarding it with sound at its resonant frequency.
The researchers used hydrofluorocarbons, which have a very low boiling point, for the droplets. The resonance of the droplet being six times higher makes vapourisation much easier. The speed of sound of the droplet fluid being lower than the speed of sound in the bodily fluids surrounding it.
This resonant droplet vapourisation technology has a number of possible medical applications. The bubbles from the bursting droplets could be used to physically damage the tumour. Or, the droplets could contain chemotherapy drugs and made to break open precisely inside the tumour and reducing exposure of the rest of the body.
Source: News-Medical.Net
Journal information: Lajoinie, G. et al. (2021) High-Frequency Acoustic Droplet Vaporization is Initiated by Resonance’ by Guillaume Lajoinie, Tim Segers, and Michel Versluis. Physical Review Letters. doi.org/10.1103/PhysRevLett.126.034501.
