Developing a magnetic system for endoscopic retrieval of kidney stones

PROJECT SUMMARY Kidney stones are an increasingly prevalent disease in which the urinary tract becomes obstructed by mineral deposits (stones); it can cause debilitating pain and life-threatening infection or kidney failure. To avoid these negative consequences, the kidney stones must be removed surgically. This is most commonly performed through a minimally invasive procedure (ureteroscopy) in which a laser is used to fragment the stones into small pieces. These fragments, often numbering in the hundreds, are then either removed during surgery or left to be removed by passively washing down the urinary tract to the bladder as urine drains. However, residual fragments remain in approximately 40% of surgeries and can re-obstruct or grow into larger stones, leading to downstream clinical complications that range from unplanned medical visits for pain to requiring repeat surgery. The current standard of care for removing kidney stone fragments is a wire basket that generally removes only one fragment at a time, and it cannot effectively remove smaller stone fragments, leading to high rates of residual fragments. In contrast, the novel MagStone System uses a magnet to remove fragments: First, stone fragments are magnetized by coating them with a magnetic iron oxide-based hydrogel, then they are retrieved using a magnetic wire. This is especially effective on small fragments that the current standard of care cannot retrieve, and because fragments of any size can be coated en masse, the MagStone System enables the re- trieval of more stone fragments in a single pass. By more effectively removing residual fragments of all sizes, the MagStone System should reduce postoperative complications, hospitalizations, and interventions. The current prototype of the MagStone System has demonstrated more effective stone removal compared to baskets in benchtop models and a good safety profile in preliminary in vivo porcine models. Nevertheless, MagStone’s efficacy relies upon proper injection of the hydrogel precursors through an injection catheter to mag- netize the stone fragments. The current injector has several shortcomings, including a high user-dependent variability, premature gel formation and inappropriate mixing. The lack of appropriate dosage and unreliable injection has prevented us from studying the potential effects of residual hydrogel in the kidney. In the proposed Phase I SBIR, we will first develop robust candidate prototypes of the hydrogel delivery catheter that facilitates reliable injection and sufficient magnetization of stone fragments. Thereafter, we will evaluate and rank the performance of these candidate prototypes on a ureteroscopy simulation model with ex- perienced endourologists. The final design will then be used to conduct in vivo experiments demonstrating the removal and clearance of the magnetic hydrogel from the kidney. The successful completion of the proposed studies will give the MagStone System a solid foundation from which to launch downstream preclinical tests needed to secure regulatory approval, bringing the device one step closer to patients who continue to suffer from recurrent kidney stone disease and incomplete stone evacuation.