Magnetic wire for retrieval and elimination of calculus from the urinary tract
Inventors
Ge, Tianjia Jessie • Conti, Simon • Liao, Joseph C. • Sheth, Kunj Raju • Wang, Shan X.
Assignees
US Department of Veterans Affairs • Leland Stanford Junior University
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Publication Number
US-11903666-B2
Publication Date
2024-02-20
Expiration Date
2041-11-11
Abstract
A medical device for retrieval of kidney stone fragments from a urinary tract is provided. The medical device has a plurality of magnets arranged within a flexible sheath forming a flexible wire. The magnets are magnetically attached end-to-end and arranged with their magnetic polarities alternating in direction. The magnetization direction of each of the magnets is orthogonal to the length axis of the flexible wire. A removable inner stylet is situated within the flexible sheath allowing for modifiable flexibility of the wire. The medical device is dimensioned to be introduced into the urinary tract and standard endoscopic devices. The medical device is further dimensioned to allow for the wire with magnetically attached stone fragments to be retrieved from the urinary tract. The magnetic field along the length axis is sufficient to attract to the surface of the flexible wire superparamagnetic nanoparticles which have bound themselves to kidney stone fragments.
Core Innovation
The present invention provides a medical device and method for retrieval of kidney stone fragments from the urinary tract. The device comprises a plurality of magnets arranged within a flexible sheath to form a flexible wire. The magnets are magnetically attached end-to-end and arranged with their magnetic polarities alternating in direction, with the magnetization direction of each magnet orthogonal to the length axis of the flexible wire. An inner stylet is situated within the sheath and can be removed to allow modifiable flexibility of the wire. The device is dimensioned to be introduced into the urinary tract and standard endoscopic devices and to allow retrieval of the wire with magnetically attached stone fragments.
The problem being solved addresses limitations in current kidney stone retrieval techniques, including the inefficiency of conventional wire baskets which capture only one fragment per pass and have difficulty capturing small fragments. Conventional active retrieval methods are time-consuming and often leaves clinically significant residual fragments, leading to complications and additional surgeries. Existing magnetic stone retrieval prototypes suffer from poor visualization due to large magnet size and insufficient magnetic forces, limiting their efficacy.
This invention solves these problems by using a flexible magnetic wire composed of multiple alternating polarity magnets providing strong magnetic field gradients (100 to 10,000 T/m) along the entire length, enabling multiple stone fragments to be captured simultaneously along the wire rather than only at the tip. The device incorporates features such as a removable inner stylet for optimizing wire stiffness and flexibility, magnetic forces sufficient to attract superparamagnetic nanoparticles bound to stone fragments, and surface modifications like bristles or shields to promote retention of fragments during retrieval. The method includes administration of superparamagnetic particles that bind to calculi, improving the magnetic capture of stone fragments with enhanced specificity and efficiency.
Claims Coverage
The patent discloses one independent claim covering a medical device with multiple inventive features focused on configuration, magnetic arrangement, and functional adaptability for kidney stone fragment retrieval.
Flexible wire with alternating polarity magnets
A medical device comprising a plurality of magnets arranged within a flexible sheath forming a flexible wire. The magnets are magnetically attached end-to-end with their polarities alternating in direction, and the magnetization direction of each magnet is orthogonal to the length axis of the wire.
Removable inner stylet for modifiable flexibility
The device includes a removable inner stylet within the flexible sheath allowing adjustment of the wire's flexibility to facilitate insertion and navigation within the urinary tract and endoscopic devices.
Dimensioning for urinary tract compatibility and retrieval
The device is dimensioned to be introduced into the urinary tract and standard endoscopic devices, and further dimensioned to allow retrieval of the wire along with magnetically attached stone fragments from the urinary tract.
Magnetic field sufficient for attracting superparamagnetic nanoparticles
The flexible wire generates a magnetic field along its length axis sufficient to attract superparamagnetic nanoparticles that have bound themselves to kidney stone fragments comprising calcium, uric acid, struvite, cystine, or combinations thereof.
The independent claim encompasses a flexible magnetic wire with alternating polarity magnets and removable stylet that is dimensioned for urinary tract use, capable of attracting superparamagnetic nanoparticles bound to kidney stones to facilitate fragment retrieval effectively.
Stated Advantages
The device can retrieve multiple stone fragments on a single pass, increasing retrieval yield compared to conventional baskets limited to one fragment per pass.
Strong magnetic field across the entire wire length allows fragments to be captured without precise guidance, improving ease of operability and potentially allowing single-person operation.
The device can capture smaller fragments that conventional baskets cannot grasp, potentially reducing residual fragments and improving stone-free rates and patient outcomes.
The flexibility and dimensions resemble commonly used guidewires, allowing safe introduction into the urinary tract without trauma and compatibility with existing equipment.
If resistance is encountered during withdrawal, the magnetic force allows fragments to detach safely rather than causing damage to the urinary system, mitigating risks such as ureteral avulsion.
Documented Applications
Retrieval of kidney stone fragments composed of calcium, uric acid, struvite, cystine, or their combinations from the urinary tract after their binding to superparamagnetic nanoparticles.
Use within the working channel of standard endoscopic devices such as cystoscopes, ureteroscopes, and nephroscopes for introduction into the urinary tract.
Combination with delivery of superparamagnetic particles, optionally mixed with a hydrogel polymer that binds to calculi and forms a magnetic coating to enhance fragment capture.
Construction of multiple flexible magnetic wires combined into a wire basket configuration to facilitate capturing magnetically-labeled stone fragments.
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