Laser-based drug delivery is attractive for the targeting capability due to high spatial controllability of laser energy.
Recently, we found that photomechanical waves (PMWs) can transiently increase the permeability of blood vessels in
skin, muscle and brain of rats. In this study, we examined the use of annular-shaped PMWs to increase pressure at target
depths due to superposition effect of pressure waves. This can increase the permeability of blood vessels located in the
specific depth regions, enabling depth-targeted transvascular drug delivery. Annular PMWs were produced by irradiating
a laser-absorbing material with annular-shaped pulsed laser beams that were produced by using an axicon lens. We first
examined propagation and pressure characteristics of annular PMWs in tissue phantoms and confirmed an increased
pressure at a target depth, which can be controlled by changing laser parameters. We injected Evans blue (EB) into a rat
tail vein, and annular PMWs (inner diameter, 3 mm; outer diameter, 5 mm) were applied from the myofascial surface of
the anterior tibialis muscle. After perfusion fixation, we observed fluorescence originating from EB in the tissue. We
observed intense fluorescence at a target depth region of around 5 mm. These results demonstrate the capability of
annular PMWs for depth-targeted transvascular drug delivery.