Urinary stone crystals glittering like galaxies: Reading the human body's internal environment using meteorite research methods

Urinary tract stones are stones formed in the kidneys that block the ureters, the pathways through which urine passes. They cause intense pain in the back and other areas. When applying meteorite research methods to polish the surface of stones thinned to about 20-30 micrometers and observing them under a polarizing microscope, images that glitter like cosmic galaxies appear.

"The colorful pink and blue parts are calcium oxalate dihydrate crystals, and the brownish areas are likely monohydrate," said Professor Mihoko Maruyama of the Graduate School of Engineering at the University of Osaka, who leads research on elucidating the formation mechanisms and predicting the onset of urinary tract stones.

The history of urinary tract stone research is long. In 1937, plaques (masses) were reported where calcium oxalate crystallized around a calcium phosphate nucleus on the kidney wall surface. In 2003, calcium phosphate plaques adhering to renal papillae were confirmed by endoscopy.

How does calcium oxalate gather around a calcium phosphate nucleus and grow to the size of a stone? When reading medical journals and other sources to unravel the formation process of urinary tract stones, researchers had been pulverizing stones to examine their molecular composition or observing cut stone pieces. However, "when you grind it into powder, even though you can numerically understand the material composition in the stone, you lose sight of the distribution of materials," Maruyama said.

Maruyama, who comes from an engineering background, specializing in crystal engineering, focused on thin section preparation that she learned about from an acquaintance who researches meteorites. By polishing the surface of thinly sliced stones containing hard crystals, it becomes possible to observe stones in a state close to that inside a living body. She thought, "Just as we can read the history of the universe from meteorites, perhaps we can read the internal environment of the human body from stones."

In 2024, she demonstrated that not only calcium phosphate on the walls of human tissue, but also calcium phosphate in urine aggregates into various forms and becomes the nucleus of the stones. In 2025, she is advancing research to use this calcium phosphate as a biomarker, aiming to develop the world's first testing device for urinary tract stone onset risk.