Photoacoustic drug delivery: The effect of laser parameters on spatial distribution of delivered drug

Photoacoustic drug delivery is a technique for delivering drugs to localized areas by timing laser-induced pressure transients to coincide with a bolus of drug. This study explores the effects of target material, laser energy, absorption coefficient, fiber size, repetition rate, and number of pulses on the spatial distribution of delivered drug. A microsecond flash-lamp pumped dye laser delivered 30-100 mJ pulses through optical fibers with diameters of 300-1000 m. Vapor bubbles were created 1-5 mm above clear gelatin targets submerged in mineral oil containing a hydrophobic dye (D&C Red#17). The absorption coefficient of the oil-dye solution was varied from 50-300 cm^-1. Spatially unconfined geometry was investigated. We have found that while the dye can be driven a few millimeters into the gels in both the axial and radial directions, the penetration was less than 500 ,tm when the gel surface remained macroscopically undamaged. Increasing the distance between the fiber tip and target, or decreasing the pulse energy reduced the extent of the delivery.