Dynamics of laser-induced cavitation bubbles near an elastic boundary used as a tissue phantom

The behavior of a laser-produced cavitation bubble near an elastic boundary as well as the deformation of the boundary induced by bubble motion are investigated by means of high-speed photography and acoustic measurements. The elastic boundary, used as a tissue phantom, consists of a polyacrylamide (PAA) gel whose elastic properties can be controlled, by modifying the water content of the sample, to mimic various biological tissues. The bubble dynamics is strongly dependent on the dimensionless distance $γ=s/Rmax$ between bubble and boundary and on the elastic properties of the boundary. For example, in the case of a PAA gel with 80% water concentration, the general features of the bubble dynamics are, for $γ>0.8,$ bubble migration and jet formation directed away from the boundary, for $0.8>γ>0.2,$ formation of a mushroom-like shape of the bubble during collapse, bubble splitting and penetration of a re-entrant liquid jet into the boundary while, for $γ<0.52,$ jet formation of PAA-material directed away from the elastic boundary occurs. The latter phenomenon can be used to enhance the efficiency of laser-induced tissue ablation.