A study found that kidney stones can be neatly removed using magnets. Kidney stones are stones that form in the kidneys or ureters and cause pain. Typically, an endoscope is inserted to break up the stones, but in 40% of patients, the stone remnants are not completely removed. This is where magnets come in.
A research team led by Joseph Liao of Stanford University School of Medicine in the United States said on Jan. 29 (local time) that kidney stone fragments can be completely removed by harnessing magnetic properties, in the international journal Device.
Kidney stones are usually removed by inserting an endoscope into the ureter under anesthesia and directly fragmenting them with a laser. The ureter is the duct that carries urine excreted from the kidneys to the bladder. If the stone is large, it is difficult to remove at once and is broken up over several sessions.
During repeated insertions of the endoscope, body tissues can be damaged, and bacterial infections can lead to fatal sepsis. Moreover, stones broken up by laser are also difficult to remove completely. Even after laser surgery, 40% of patients have residual stone fragments.
To find out whether magnets could pick up residual stone fragments, the researchers implanted dozens of human kidney stone fragments into four pigs. They then injected the pigs with a magnetic iron oxide (酸化鐵) hydrogel. Hydrogel is a soft polymer material, like muk or jelly, that contains a lot of water.
The iron oxide hydrogel enveloped the stone fragments. The researchers inserted a wire acting as a magnet into the pigs' ureters. The wire drew in the hydrogel containing iron oxide and removed 28 residual stone fragments in seven minutes. The remaining hydrogel is expelled in the urine.
The researchers said that using a magnetic hydrogel and a magnetic wire also reduces the risk that residual fragments remain, form new stones, or lead to additional surgery. In this experiment, the pigs had their kidney stones removed and recovered their health. No toxic reactions or internal damage were observed in the pigs.
As of 2018, 11% of Americans have kidney stones. In the United States, 1.3 million people visit emergency rooms each year for kidney stones, and medical expenditure reaches $400,000 (5.7 trillion won). The researchers said that even when stones are removed, remnants are bound to remain, adding that 30% of patients with residual fragments need reoperation within five years, but when there are no remnants, the rate is only 4%.
References
Device (2025): https://www.cell.com/device/fulltext/S2666-9986(25)00284-4