Ultrasound-guided system for light focusing using microbubbles generated from polytetrafluoroethylene nanoparticles

Intrinsic lipid and protein components in biological tissues hamper the translation of light-related techniques to in vivo applications and highlight the need for strategies to improve photon trafficking. To meet this demand, we propose a method for the production of transient micro-sized bubbles to improve the local light intensity in the scattering medium by combining ultrasound and super hydrophobic polytetrafluoroethylene nanoparticles (PTFE NPs) with a mean size of 350 nm. The underlying idea was to convert the initial Rayleigh scattering effect into a Mie scattering effect to reduce loss during light propagation. The Monte Carlo simulation confirmed our hypothesis that only a specific size of microbubbles would increase light propagation. By fine-tuning the acoustic parameters (1.5 MPa, 100 cycles, and 10 Hz of pulse repetition frequency) and PTFE NPs' concentration (0.05 mg/ml), shell-less microbubbles were transiently and locally generated, resulting in a reduction in the scattering coefficient of the medium and improving the delivered light fluence by 6.2%. The experimental results further confirmed that only microbubbles of the proper size could repeatedly increase the light propagation. This method may be suitable for in vivo deep-tissue optical applications such as the delivery of PTFE NPs to deep tumor regions to increase the efficiency of photothermal therapy.

Automated summary

This study proposes a method to improve the local light intensity in scattering media by generating transient microbubbles using ultrasound and super hydrophobic polytetrafluoroethylene nanoparticles (PTFE NPs). Results show that only microbubbles of the proper size can effectively increase light propagation.