M.E. Khosroshahi, Z.S. Mansoori, and Ardebili A. Jafari (Iran)
Superlong CO2 Laser, Drug Delivery, Fast Photography, Photothermal Deflection, Conical Cavitation.
To our knowledge most of the work in the field of drug delivery systems using lasers have been performed using short pulses with micron and submicron durations. We have carried out an experiment using a super long CO2 laser pulse (10ms) on simulated gelatin-ink model (GIM) .The mechanism of laser- GIM interaction was studied by photothermal deflection and time-resolved dynamics techniques. Energy balance consideration showed a complete non-adiabatic (ie diffusion limit) case with a threshold evaporation intensity of 3.1 kWCm-2 . The velocity of thermal waves and vaporized plume were measured at below and above ablation threshold as (0.5 2.5) ms-1 and (0.4-10) ms-1 respectively. The geometry of the modeled tissue at the onset of ablation was semi spherical but it gradually changed into a cone at later stages whose volume was linearly increased with fluence up to a maximum value of 55 mm3 at 15kWcm-2 with drilling velocity of 5.6 cms-1 after 20 pulses. We believe that the main mechanism at work with superlong pulses of CO2 laser is both photothermal due to vaporization and photomechanical due to photophorosis and also cavitation collapse. Thus, drug molecules can be transported into tissue bulk by thermal waves described by the Fick’s law in 3-D model for a given cavity geometry and the mechanical waves, unlike only by pure photomechanical waves (ie photoacoustically) as with short pulses.
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