Self-consistent evolution of tissue damage under stress wave propagation

摘要

Laser-initiated stress waves are reflected from tissue boundaries, thereby inducing tensile stresses, which are responsible for tissue damage. A self-consistent model of tissue failure evolution induced by stress wave propagation is considered. The failed tissue is represented by an ensemble of spherical voids and includes the effect of nucleation, growth and coalescence of voids under stress wave tension. Voids nucleate around impurities and grow according to an extended Rayleigh model that includes the effects of surface tension, viscosity and acoustic emission at void collapse. The damage model is coupled self-consistently to a one-dimensional planar hydrodynamic model of stress waves generated by a short pulse laser. We considered the problem of a bipolar wave generated by a short pulse laser absorbed on a free boundary of an aqueous system. The propagating wave includes a tensile component, which interacts with the impurities of exponential distribution in dimension, and an ensemble of voids is generated. For moderate impurity density (approximately 10$+8$/ cm$+$MIN@3$/) void growth reduces the tensile wave component and causes the pressure to oscillate between tension and compression. For low impurity density (approximately 10$+6$/ cm$+$MIN@3$/) the bubbles grown on a long time scale (5 - 10 microseconds) relative to the wave interaction time (approximately 100 nsec). At later times the growing bubbles interact with each other causing pressure oscillations between tension and compression, with an average compression pressure below 1 bar. This effect increases considerably the bubble lifetime consistent with experiments. At the collapse stage small bubbles collapse earlier and induce pressures, which reduce the collapse time of the larger bubbles.