Magnetized approach to kidney stone retrieval outperforms standard methods in preclinical study

Stanford University has unveiled a ureteroscopy-compatible device that magnetizes and retrieves kidney stone fragments with a wire, with performance in a pig model beating traditional removal techniques.

Kidney stone disease affects around 11% of the US population and often requires ureteroscopic laser lithotripsy. Fragment removal after lithotripsy remains inefficient, leaving many patients with residual pieces that can trigger pain, infection, repeat procedures, and added costs.

Stones form from crystallized salts that can then obstruct the thin tubes that carry urine from the kidneys to the bladder, causing pain, infection, and kidney injury.

Ureteroscopic laser lithotripsy remains the most common procedure. An endoscope enters through the urethra to the upper urinary tract, a laser fiber breaks stones into fragments under saline irrigation, and surgeons then aim for removal or spontaneous passage of small pieces.

Residual fragments persist in up to 40% of patients after ureteroscopy, driving complications that range from emergency visits to repeat interventions. Risk accumulates with time, as 30% of patients with any residual fragments required another operation within five years, compared with 4% among those with no residual pieces.

Care demands are substantial, with more than 1.3 million emergency visits and more than $4 billion in annual expenditures in the US. Coupled with rising obesity and diabetes, major risk factors for formation, kidney stones are estimated to add another $1.2 billion per year in health care costs by 2030.

In the study, “Magnetic retrieval of kidney stones via ureteroscopy in a porcine model,” published in Device, researchers engineered a ureteroscopy-compatible system to magnetize stone fragments with a hydrogel and retrieve them using a magnetic wire under direct endoscopic visualization in pigs.

Experimental setups

Instruments mirrored those used in clinical ureteroscopy with some controlled optimization. A 3D-printed kidney model was positioned in a 0.9% saline bath. Human-derived kidney stone fragments were positioned in the model kidney.

Two hydrogel precursors, ferumoxytol and chitosan, were co-delivered through the dual-lumen injector so they contacted on the fragment surface and formed the magnetic hydrogel in situ, after which the magnetic wire attempted retrieval.

Pig kidneys received retrograde placement of human-derived calcium oxalate fragments under 3 mm, magnetic hydrogel was delivered onto the fragments, and the magnetic wire attempted retrieval. Control kidneys underwent fragment placement and basket retrieval only.

Survival experiments used three pigs. One kidney per animal received magnetic hydrogel with endoscopic confirmation of gel formation, and the contralateral kidney remained untreated as a control.

3D-printed kidney results

Benchtop optimization identified an initial density mismatch between ferumoxytol and chitosan in saline. Addition of glycerol to the chitosan precursor matched densities and increased magnetic labeling of 1–2 mm calcium oxalate fragments by four-fold.

Ureteroscopy runs demonstrated multi-fragment removal after a single hydrogel application. A total of 28 fragments sized 1–2 mm were removed in six passes following approximately 100 μL ferumoxytol and 200 μL chitosan delivered through the injector.

Performance in pigs

One-week survival experiments recorded uneventful stone-free recovery with normal urination. Urinalysis and bloodwork remained within normal ranges.

Irrigation alone cleared about 70% of the instilled gel. Combined magnetic retrieval and irrigation cleared 99.8% of the gel within 10 minutes. Magnetic particle imaging of urine, blood, kidneys, ureters, bladder, and selected organs at one week showed signals below the detection limit, supporting complete elimination of the hydrogel by that time point.

Future research plans

The authors conclude that a magnetize-and-retrieve strategy is feasible and compatible with clinical ureteroscopes in a porcine model, with a favorable short-term safety profile and demonstrable pathways for intraoperative removal and physiologic clearance.

Future plans include head-to-head testing in a ureteroscopy model, hydrogel formulation refinement toward simplified dosing ratios, catheter improvements, and exploration of alternate magnetic geometries.

Successful translation to a clinical method could raise stone-free elimination rates, reduce patient adverse outcomes and lower health care burdens.

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