Figure from Sci. Rep. 2, 989 (2012)
A major treatment mechanism of LGFU is based on cavitation-induced mechanical disturbance. In this sense, LGFU shares a similar mechanism with other focused ultrasound therapy known as "histotripsy", but we seek more with LGFU: (1) histotripsy with micro-precision that can even compete with laser surgery (note that a deep region can be reached by ultrasound, but not by light) and (2) ultimate investigation of underlying physical mechanisms by a "single micro-bubble" with complete single-pulsed control (exclusively with LGFU).
Laser generation of ultrasound takes advantages of obtaining high-frequency (tens of MHz) and high-amplitude ultrasound output. Especially, the high-pressure output can be realized by an unique nanostructural design of ultrasound transmitters (e.g. CNT-PDMS nanocomposite) allowing excellent energy conversion efficiency and mechanical robustness. The CNT-PDMS transmitter has been fabricated on a spherically curved substrate to form an "optoacoustic lens" that converts an incident laser pulse into a powerful focused ultrasonic beam (peak pressure of tens of MPa).
Optical ultrasound transmitters have been developed earlier in Univ. of Michigan, pioneered by Matthew O'donnell's group (even before 2000). Later, performance of such optical transmitters has culminated with CNT-PDMS nanocomposites [Baac et al., Appl. Phys. Lett. 97, 234104 (2010)], finally inspiring us with the idea of optoacoustic lens and LGFU.
As a non-thermal ultrasonic micro-scalpel, optoacoustic lens and LGFU are extending their territory over tissue surgery in eyes and precision treatment in small animal brain. Furthermore, new structures are actively being developed, including a hybrid platform with piezoelectric transducers and a miniaturized platform integrated with an endoscopic probe.
What is Laser-Generated Focused Ultrasound (LGFU)?
LGFU is an innovative modality capable of producing high-amplitude focused ultrasound onto a tight spot of <100 μm, developed by Hyoung Won Baac and L. Jay Guo (University of Michigan) [Sci. Rep. 2, 989 (2012)]. This enables unprecedented micro-ultrasonic treatment in a non-thermal high-precision manner, opening numerous new applications such as single-cell surgery (removing a single target cell and cutting cell-cell junction), single-cell drug delivery (transmembrane drug delivery), micro-fragmentation of kidney stone and cell cluster, liquid micro jetting, and many more.
