Reactive species created in the collapse of laser-induced cavitation bubbles: Generation mechanism and sensitivity analysis

Abstract

Reactive species (RS) play a critical role in postoperative complications in the medical application of lasers. From the mechanistic point, the RS arising from laser irradiation are produced from two channels: ionization and dissociation of water in the breakdown plasma, and the violent collapse of the laser-induced cavitation bubble. The latter channel is especially important for nanosecond pulses but poorly understood. In this paper, we conducted a simulation of the chemical reactions coupled with bubble dynamic calculation to quantitatively identify the RS produced in the collapsing bubble. The generation mechanism is explored by the analysis of the reaction pathway. Our calculation shows that while the absolute quantity of the produced RS is small, very high concentrations can be achieved inside the strongly compressed bubble. The initial composition of the bubble recovered from plasma recombination and expansion is found to influence the chemical reactions significantly. Unlike the direct splitting of water molecules in radiolysis and photolysis, the RS productions mainly involve the decomposition of hydrogen peroxide and the reactions between hydrogen, oxygen, and various free radicals. Furthermore, the produced RS is observed to increase with pulse energy as a result of the larger-sized bubbles and more violent collapses. These findings complement our current knowledge of RS in laser surgery and can be used to develop strategies to mitigate the adverse effects or exploit the associated benefits.

Production and dispersion of free radicals from transient cavitation Bubbles: An integrated numerical scheme and applications

“…Very large values of c i- max are also observed for O • and H • atoms. Similar results have been reported in the case of laser-induced bubbles [25] .…”

“…It has been optimized through a systematic procedure and extensively validated [29] . Its reliability in simulating cavitation-related chemistry has also been verified before [25] using test data from Kalus et al [30] , [31] . Owing to the huge number of reactions involved in this mechanism, the complete reaction data is not listed here but can be accessed from the database [23] .…”

“…The methods for simulating the bubble dynamics and the chemical reactions have been introduced in our previous studies [25] , [39] , [40] , [41] . Therefore, only the method for the dispersion simulation is illustrated in this section.…”

“…The coupled simulation yields the category and quantity of radicals at each moment in the bubble collapse. The implementation details of these models are presented in our recent publication [25] and therefore will not be elaborated here. We only listed the corresponding equations in Table.1 with the parameters explained in the Nomenclature.…”

Penetration of hydroxyl radicals in the aqueous phase surrounding a cavitation bubble

“…For brevity, the reaction data is not listed here but can be accessed through the reference [15] . The simulation of intracavity chemistry is integrated into the calculation of bubble dynamics by the open-source platform Cantera [33] , [34] .…”