Abstract
Natural kidney stones are heterogeneous in structure, composition, material properties and fragility, and as such are problematic for use in determining the mechanisms of SW-action in SWL. A variety of model stones have been developed. We have adopted Ultracal-30 gypsum [Dahake and Gracewski, J. Acoust. Soc. Am. 102, 2138 (1997)] for in-vitro and in-vivo studies. U-30 stones (7.5×6.5 mm) cast in polystyrene molds were liberated with chloroform and stored in water. Drop-impact testing of dry stones showed a linear relationship between increase in surface area of fragments and energy applied. Breakage of hydrated stones in a research-electrohydraulic lithotripter, likewise showed a linear increase in fragment area with increased SW-number and SW-voltage. The density (1800 kg/m3) and transverse (1520 m/s) and longitudinal (3100 m/s) wave speeds of U-30 stones place them in the range determined for natural stones. U-30 stones implanted in pig kidneys exhibited cavitation erosion and spall fracture similar to stones in-vitro, and U-30 stones in-vitro and in-vivo showed equivalent response to SW-rate (200% higher fragmentation at 0.5 Hz compared to 2 Hz). U-30 stones softened with prolonged exposure to water and degraded during long-term implantation in-vivo. With these cavaets U-30 stones provide a useful model for SWL research. [Work supported by NIH P01-DK43881.]
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