Influence of focused shock waves upon a sonosensitive material

Interaction of two successive shock waves (tandem shocks) in water focused to a common focal point has been investigated. Amplitude of the compression part of the wave s as high as 100 MPa, while amplitude of the dilution part of the wave reaches down to -25 MPa in the focus. At that underpressure numerous cavitations are produced. It was demonstrated that the acoustical inhomogeneity created in water by the first wave strongly modifies propagation of the second one. Measurements of waveforms by PVDF shock gauges at the focus indicate that the second wave is strongly attenuated at some time delays between shocks. At time delays in the interval 50-500 mus the second wave is totally damped at the focus. Schlieren photography of the focal region demonstrates that the interaction of two successive shocks results in creation of a very complex pressure field at the focus to which contribute many secondary spherical short wavelength shocks that originate in collapsing cavitations. The tandem shock waves can be potentially applied to sonodynamic treatment of cancer tumors. Effect of the tandem shock waves on melanoma cells B16 has been investigated. Micro photographs of cells demonstrate that even a small number of shocks (100) result in perforation of cell membranes. At present an enhancement of treatment efficiency by the activation of sonosensitizers combined with the perforation of cell membranes is studied.