AUA 2023: Efficacy and Safety of a Magnetic Hydrogel for Stone Fragment Removal: An In Vitro and In Vivo Study

(UroToday.com) The 2023 American Urological Association Annual Meeting included a stone disease and surgical therapy session featuring work from Dr. Daniel Massana Roquero and colleagues presenting results of their study investigating the use of a novel integrated stone fragment removal system to decrease stone disease recurrence. While flexible ureteroscopy and laser lithotripsy are the gold standard for treatment of small to medium size stones, there is no management regimen that leads to complete stone clearance on a consistent basis. Flexible stone baskets are used to remove stone fragments after laser lithotripsy; however, these devices are ineffective in removing fragments smaller than 2 mm in diameter. Residual fragments increase the likelihood of stone recurrence. As a potential answer to this issue, Dr. Roquero and colleagues have developed MagSToNE, a system that utilizes a magnetic hydrogel to coat and magnetize stone fragments, as well as a magnetic wire for extraction. Their comparison of MagSToNE to a standard nitinol basket extraction in both an in vitro model and in vivo in a porcine model both evaluates the effectiveness of this system as well as its safety.

Stone fragments were both loaded into an ex vivo kidney model and introduced endoscopically to the kidneys of female pigs under general anesthesia. In the in vivo porcine model. The magnetic hydrogel components were injected through flexible ureteroscopy. A magnetic wire was inserted through the working channel of the ureteroscope and was used to capture stone fragments. Pigs were either immediately euthanized or monitored for up to 72 hours post-procedure. Blood was collected at regular intervals to monitor the complete blood count and metabolic panels. Kidneys were bivalved for gross examination and processed for histology after nephrectomy was completed.

Figure 1. Above: images captured during ureteroscopy in the in vivo model. Below: histology slides that demonstrate residual hydrogel particles and their penetration into cells.


In the in vitro model, Dr. Roquero and colleagues found that MagSToNE removed stone fragments at a rate that was 57% higher than that of conventional basketing. They also demonstrated that in in vivo porcine models, the injection catheter and magnetic wire of 1 mm diameter were highly compatible with a disposable clinical ureteroscope, which provides support for the system’s feasibility. Magnetized fragments were removed through the ureteral access sheath. Based on initial results, MagSToNE application within in vivo models indicate that the hydrogel and extraction method are safe: there was no observance of significant changes in vitals, blood count, or metabolic serum chemistries. Through visual inspection of the bivalved kidneys post procedure confirmed the absence of visible hydrogel. It is interesting to note, however, that hydrogel particles were clearly visible in collected urine. Dr. Roquero stated that survival studies within the porcine model are currently ongoing to further assess the safety of the MagSToNE stone fragment removal system.

Figure 2. Demonstration of hydrogel particles collected in urine.

To conclude the presentation, Dr. Roquero emphasized that MagSToNE is a promising approach to leave patients stone free after ureteroscopy and to avoid recurrence. It not only is superior to basketing from an efficiency standpoint, but is also safe to use within an in vivo model. Magnetic extraction of kidney stone fragments may someday be the gold standard as further studies continue to demonstrate its feasibility and utility.

This study generated considerable buzz from the audience and moderators alike. The first question raised was from an audience member, who mentioned that they performed a similar study in the past. They found it difficult to create a sufficient magnetic attraction to remove the majority of fragments and inquired on specific practices that led to this study’s success. Dr. Roquero first mentioned that the aforementioned “failed” study was the basis for his work. He then went on to explain that success was dependent on the properties of the gel, which consisted of more than one magnetic nanoparticle layer. This has led to the successful movement and retraction of stones up to 7 mm in diameter, an impressive feat that only creates further excitement for this technology. A similar question was then raised by another audience member, who also shared his failures in a magnetic-based experiment and wished to know if there were any other factors at play. Dr. Roquero stated that the properties of the guidewire setup also greatly contributed. The “secret” lies in how the magnet is designed, which creates magnetization along the length of the entire wire, rather than just the tip. This is critical in maximizing the magnetic field and the ability to attract and remove fragments. One last question was regarding safety, to which Dr. Roquero responded that the nanoparticles used in their MagSToNE gel have already been FDA approved to treat anemia. While cells easily uptake the nanoparticles, they are also easily broken down – any gel left behind will dissolve in 10 days. As an exciting new method that may one day eliminate residual stone fragments, becoming the new gold standard and reducing suffering for patients worldwide, MagSToNE is a system that Dr. Roquero and colleagues should be extremely proud of to have developed and to be tested further in the fight against stone disease.

1. Daniel Massana Roquero, T. Jessie Ge, Grace H. Holton, Kathleen E. Mach, Zachary Kornberg, Ryan Sun, Simon Conti, Shan X. Wang, Joseph C. Liao. Efficacy and Safety of a Magnetic Hydrogel for Stone Fragment Removal: An In Vitro and In Vivo Study [abstract]. In: American Urological Association Annual Meeting, April 28-May 1, 2023, Chicago, Illinois