Rendering stone fragments paramagnetic with iron-oxide microparticles improves the efficiency and effectiveness of endoscopic stone fragment retrieval.

Objectives: To develop peptide-coated iron oxide-based microparticles that selectively adhere to calcium stone fragments, thereby enabling magnetic manipulation of human stone fragments.

Methods: In phase 1, human stone fragments were coated overnight with iron oxide-based microparticles. Groups of 10 coated stones (1.5-3 mm) were placed into a bladder simulator and removed cystoscopically with either an 8 Fr magnetic extraction device or a 2.4 Fr nitinol basket. In phase 2, the peptide coating was optimized and 2 stone fragment sizes (1-2 mm and 2-3 mm) were exposed to 3 separate concentrations of microparticles for 3 different incubation times. In each trial, 10 fragments were placed into a glass vial and removed using the 8 Fr magnetic device.

Results: In phase 1, mean total time for removal of all fragments was 53% shorter using the magnetic instrument compared with basket extraction. An average of 3.7 extractions was required to magnetically remove all fragments versus 9.4 for basket extraction. In phase 2, 18 different combinations of particle concentrations, fragment sizes, and incubation times were tested; 91% of small fragment trials and 43% of large fragment trials yielded successful fragment extraction. Of the small fragments, 100% were successfully extracted at both the middle and high particle concentrations after 2 minutes, and of the large fragments 70% and 100% were successfully extracted after 10 minutes of incubation at the lowest and highest concentrations, respectively.

Conclusions: Rendering stone fragments paramagnetic with novel microparticles allows manipulation and removal using a novel magnetic device in vitro, potentially improving surgical efficacy and efficiency.