Stone removal may be simplified with magnetic technology

Dallas-A novel experimental technology for removing kidney stone fragments using magnetic energy has passed a pair of early tests.

Researchers at the University of Texas Southwestern Medical Center, Dallas, and the Erik Jonsson School of Engineering and Computer Science, Richardson, TX, envision a system that incorporates an iron-rich surgical irrigation solution that deposits iron-containing microparticles onto the surface of stone fragments. Magnetized tools can then be used to manipulate and extract fragments.

"Coating stone fragments with iron renders them paramagnetic," explained co-author Sara Best, MD, during a podium presentation at the AUA annual meeting in San Francisco. "You can essentially vacuum up the coated fragments using a magnetic tool. But before we can incorporate iron-based particles into surgical fluids, we have to evaluate for potential toxicity and the effects of urine on microparticle binding and paramagnetism."

The new fragment collection system, dubbed StoneMag, works well in an inanimate model. Iron-based microparticles are coated with a protein that binds to calcium oxalate monohydrate in human stone fragments. Dr. Best described a series of in vitro toxicology tests and functionality evaluation in the presence of biologic urine concentrations. The salts and proteins found in urine have the potential to interfere with microparticle binding to stone fragments.

No toxicities observed after exposure

Toxicology testing used three different cell lines, murine fibroblasts, human transitional cell carcinoma, and human urothelium. Researchers used an agarose overlay technique to expose cells to 1-mg/mL concentrations of particles. Assays were run in triplicate. No toxicities were observed in any of the cell lines after 48 hours of exposure to the microparticles, Dr. Best reported.

Biologic functionality was evaluated by incubating human stone fragments in a 1-mg/mL solution of microparticles with different concentrations of urine from 10% to 50%. Researchers attempted to collect fragments of two different size ranges, 3 mm to 4 mm and 6 mm to 8 mg, after 10 minutes of urine exposure using an 8F magnetic tool. Assays were run in triplicate for each fragment size and urine concentration and in a saline control solution.

"We found that urine did not interfere with magnetic collection of any of the fragments," Dr. Best said. "These particles perform well in the biologic conditions of urine."

The potential effect of residual iron particles in the kidney during postsurgical magnetic resonance imaging is a potential concern, Dr. Best noted in response to a question from the audience.

"These particles are tiny, 1 micron in size, but it definitely needs study," she said. "We have not used this system clinically at all-there are a lot of engineering steps that have to be taken before then, but further testing in animal models is appropriate."