Shock Dynamic Study of Laser Ablation Induced Drug Delivery

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In the Interdisciplinary Shock Wave Research Center, Tohoku University, we have aimed to apply the shock wave phenomena to medicine. We have already finished the extracorporeal shock wave lithotripsy and now are working for the development of system for revascularization of cerebral thrombosis, which is expected to be completed in very near future. In these topics a shock wave plays always an important role*. When a Q-switched laser beam focused a spot on a metal foil surface, instantaneously a plasma cloud ejected from the spot and as its reaction a shock wave is generated inside the metal foil which propagate and reflected from the other surface. The plasma formation is called laser ablation. The reflected wave an expansion one and as a result of it the foil is instantaneously bulged at 2 to 5 km/s. When small* particles are attached on the metal surface these would be ejected at such a high speed at the moment laser beam irradiation. This principle has been applied to accelerate dry … More drug particles or metal particles* of the order of magnitude of one micron or so into human tissue. We have used Q-switched Nd:YAG laser focused on the surface of a 5 mm thick glass plate backed up with 0.1 mm this aluminum foil on which tungsten or gold particles were attached. We measured the particle ejection speed to be in the order of magnitude of 1 to 2 km/s. Injecting these particles against agarose cell, mouse liver, and mouse skin, we measured penetration depths against these and found the maximum penetration depth was about 6 mm for individual materials. The free flight of such small particles belongs to hypersonic Stokes flow which has never be discussed seriously in the field gas dynamics. We have developed numerical scheme to estimate particle free flight as well as penetration into soft tissues. We have examined with this method the penetration into cell lines in liquid solution and observed a beautiful penetration of a one micron tungsten particle into a cell. Based on these basic studies we concluded that this method is superior to the existing mechanical gene delivery systems and so robust and compact that it can be redesigned as a therapeutic device. We believe we have accomplished our main goal which we proposed at first. Less