Investigating Kidney-Stone Erosion Induced by Dual-Bubble Dynamics: Experiments and Simulations
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Extracorporeal shock wave lithotripsy (ESWL) employs focused shock waves to fragment kidney stones, with cavitation-induced erosion playing a significant role alongside direct mechanical loading in the fragmentation process [1]. However, the mechanisms governing multi-bubble interactions remain poorly understood. This study investigates dual-bubble dynamics through combined ultra-high-speed X-ray phase-contrast imaging (100 kfps), conducted at ESRF-ID19, and diffuse-interface numerical simulations using ECOGEN [2]. We examine interactions between stone-attached and distant cavitation bubbles with BEGO stone (kidney-stone phantom) which is subjected to medical-grade shock waves (peak pressure 92 MPa, incident compression phase of the shock is approximately 1 µs) generated by the MODULITH® SLK ≫intellect≪ lithotripter (Storz Medical AG). The numerical simulations accurately reproduce experimentally observed bubble dynamics, demonstrating good qualitative and temporal agreement in jet formation, penetration, and collapse sequences. Our simulations reveal that dual-bubble configurations generate peak pressures of 87.1 MPa, with sustained and localised high pressures for approximately 25 µs, at the jet-impact location, compared to 10.4 MPa for single stone-attached bubble cases, representing an order-of-magnitude amplification that substantially exceeds typical kidney stone compressive strengths (3.2 MPa to 6.2 MPa). This amplification results from constructive interference when the distant bubble jet penetrates the stone-attached bubble and impacts the stone surface coincident with the larger bubble’s collapse. Systematic parametric studies (distant bubble standoff distance, size and aspect ratio) establish that the standoff distance is the dominant parameter governing pressure amplification. Simulations correctly predict erosive loading locations consistent with observed surface erosion patterns, providing a foundation for future investigations incorporating fluid-structure interaction and damage mechanics, with implications not only for optimising ESWL treatment protocols through controlled bubble dynamics but also for advancing the broader understanding of cavitation erosion in biomedical and engineering systems such as burst wave lithotripsy (BWL) and hydraulic machinery.
