Innovative Magnetic Retrieval System
Stanford University researchers have developed a ureteroscopy-compatible magnetic device that efficiently magnetizes and retrieves kidney stone fragments using a wire. In preclinical testing on pigs, this approach outperformed traditional stone removal techniques.
Addressing a Persistent Problem
Kidney stone disease affects nearly 11% of the U.S. population and frequently requires ureteroscopic laser lithotripsy. However, after the procedure, fragment removal often remains incomplete, leaving residual pieces in up to 40% of patients. These remnants can lead to pain, infection, repeat procedures, and rising healthcare costs.
Stones form when crystallized salts obstruct the urinary tract, leading to severe pain and potential kidney injury. While laser lithotripsy effectively breaks stones into smaller pieces, achieving complete clearance remains a clinical challenge. Over time, 30% of patients with residual fragments require another operation, compared to only 4% among those completely stone-free.
The Economic Burden of Incomplete Clearance
The consequences are both medical and financial. Kidney stones account for 1.3 million emergency visits and over $4 billion in healthcare costs annually in the U.S. With obesity and diabetes—key risk factors—on the rise, related expenses may increase by an additional $1.2 billion per year by 2030.
Breakthrough Study in Device Journal
In the study, “Magnetic retrieval of kidney stones via ureteroscopy in a porcine model,” published in Device, the Stanford team engineered a magnetize-and-retrieve system. The approach uses a hydrogel to magnetize stone fragments, enabling their retrieval via a magnetic wire under direct endoscopic visualization.
Experimental Design and Setup
Researchers created a 3D-printed kidney model immersed in saline, positioning human-derived stone fragments within it. Two hydrogel precursors—ferumoxytol and chitosan—were co-delivered through a dual-lumen injector, forming a magnetic hydrogel coating on the fragments. The magnetic wire then successfully retrieved the magnetized stones.
In pig models, researchers retrogradely placed human-derived calcium oxalate fragments smaller than 3 mm in the kidneys. After hydrogel application, the magnetic wire removed the fragments. Control kidneys underwent standard basket retrieval for comparison.
Optimization and Results
Initial tests revealed a density mismatch between the hydrogel components, which researchers corrected by adding glycerol. This adjustment quadrupled magnetic labeling efficiency for 1–2 mm fragments. Using this optimized formulation, 28 fragments were retrieved in just six passes after a single hydrogel application.
Safe and Effective in Animal Models
During one-week survival experiments, treated pigs recovered normally with no urinary complications. Urinalysis and blood tests stayed within normal limits. Magnetic particle imaging confirmed that the hydrogel cleared completely within a week, with no detectable magnetic residue in organs or fluids.
Combining magnetic retrieval with irrigation cleared 99.8% of the gel in just 10 minutes, compared to 70% with irrigation alone.
Next Steps and Future Potential
As reported by medicalxpress, the research demonstrates that a magnetize-and-retrieve technique is both feasible and safe in animal models. The team plans further studies focusing on optimized hydrogel formulations, improved catheter design, and alternative magnetic geometries to enhance clinical compatibility.
If successfully translated to human use, this technology could significantly increase stone-free rates, reduce repeat interventions, and lower healthcare costs associated with kidney stone disease.