Magnetically Actuated Soft Miniature Robots for Applications in the Urinary Tract

Abstract

Kidney stones, affecting approximately 10\% of the global population, pose significant health concerns due to their prevalence and recurrence. The formation of these stones, known medically as nephrolithiasis, involves the aggregation of various types of crystals such as calcium oxalate, uric acid, struvite, and cystine. Traditional treatments range from pain management for mild cases to invasive procedures for severe obstructions. However, the high recurrence rates of the disease and the complications of current treatments necessitate innovative and minimally invasive solutions.

This thesis explores the development of a small-scale soft magnetic robot designed to facilitate the dissolution of kidney stones and prevent their recurrence. The robot uses magnetic actuation, a preferred method due to its minimal interaction with human tissues and reliable control.

The magnets used for actuation are modeled in MATLAB and COMSOL Multiphysics to observe and compare the fields in different sizes and distances, furthermore, the forces and torques are calculated for different cases. After modeling the actuation, filamentous magnetic robots made of gelatin-methacrylate were designed and experimented with in 3D-printed urinary tract organ models which showed their maneuverability in their target environment, with analysis done on the best location and orientation of the magnet inside the filament. Furthermore, the filaments were loaded with different drug choices to determine an efficient chemical for the dissolution of uric acid kidney stones.

We highlight the integration of miniature robots in medical applications, emphasizing their potential for targeted drug delivery, minimally invasive procedures, and real-time diagnostics.

This research shows that the robot configuration which has the actuation magnet perpendicular to the robot magnet has the capacity for movements up to 3 times faster than parallel-placed magnets, their movement reaching about 18 mm/s. However, this is only true in confined spaces and in non-confined environments, parallel-placed magnets in the robot and actuator show stability and reliability with speeds of 8 mm/s. Experiments showed no significance in the location of the robot magnet placement along the filament and the addition of the active chemical to the filaments showed a mass reduction of about 30\% in uric acid stones, which is double the amount of control samples.