Intra-Crater Bubble Expansion Drives the Fracture of Impacted Ureteral Artificial and Human Calcium Phosphate Stones in Laser Lithotripsy.

To investigate the fracture mechanism of impacted ureteral stones during laser lithotripsy (LL).Impacted 6 × 6 mm cylindrical BegoStone samples embedded in a hydrogel ureter model and a 100% calcium phosphate (CaP) stone (58 × 60 mm) were treated in saline using holmium:YAG (Ho:YAG) laser or thulium fiber laser (TFL) via three clinical strategies: "drill and core," contact, and near-contact modes. Laser pulses were delivered at 0.8 J/12 Hz, 1.0 J/10 Hz, and 1.2 J/8 Hz with a 3 s on/3 s off protocol under continuous irrigation (40 mL/min). Crater formation, surface crack development, and bubble dynamics were assessed via optical coherence tomography, ureteroscope video, high-speed photography, and hydrophone measurements. To delineate the contributions of different plausible damage mechanisms, bubble collapse was suppressed using the ureteroscope's proximity effect, and photothermal ablation was minimized by treating donut-shaped BegoStones with central tunnels. The role of bubble expansion in stone fracture was evaluated by varying either tunnel size or pulse energy.Surface cracks and stone fractures occurred only in Ho:YAG-treated BegoStone and CaP stone samples under the "drill and core" strategy. TFL produced deeper craters yet failed to induce significant cracks under any test conditions. Although Ho:YAG-induced bubble collapses generated stronger acoustic emissions than TFL, suppression of bubble collapse or photothermal ablation had minimal impact on crack growth beyond localized surface damage. Instead, the number and length of surface cracks correlated strongly with the maximum bubble lateral diameter and expansion rate - both substantially greater for Ho:YAG laser than TFL. Crack formation also correlated inversely with the initial crater or tunnel size. These observations have significant clinical implications for optimizing stone fragmenting in LL procedures.Intra-crater bubble expansion, rather than photothermal ablation or bubble collapse, is the primary mechanism driving the fracture of impacted ureteral stones in LL.

Duke Scholars

Author Pei Zhong Thomas Lord Department of Mechanical Engineering and Materia ...