Magnetorheological Fluid–Driven Rolling Soft Robot for Tissue-Sparing Minimally Invasive Therapy

EdwinetoFiuld

Diseases affecting tubular organs, such as blood vessels and the gastrointestinal tract, create a major global health burden. For example, Cardiovascular and cerebrovascular diseases remain leading causes of death and long-term disability worldwide. Problems in these structures often require minimally invasive procedures to remove blockages or foreign objects.

Current surgical treatments often use mechanical tools such as guidewires, catheters, and endoscopes. Although these tools can be flexible, they still rely on sliding contact, pushing, pulling, or scraping, which may damage delicate tissue and increase the risk of complications such as bleeding or tissue injury.

This creates an important clinical need for a device that can move through tubular organs with precise control while reducing unnecessary tissue interaction.

Rolling motion addresses this issue. It reduces relative motion at the contact point, and its lower frictional impulse may reduce tissue trauma.

To make rolling controllable, magnetorheological fluid (MRF) was used, which is mainly composed of micron-sized magnetic particles suspended in oil.

It flows like a liquid without a magnetic field but increases stiffness under one because the particles rapidly align into chains.

This allows MRF to be soft and deformable, while still being controlled by external magnetic fields, allowing untethered control of motion.

The goal of my project was to design and experimentally validate a magnetically controlled, MRF-based rolling soft robot for minimally invasive therapy, with potential applications in foreign body retrieval within tubular structures in the human body.

Background Research

This project began by studying electromagnetism and fluid behavior using textbooks and research articles on soft robotics and magnetorheological fluid (MRF).

Physical Formulas & COMSOL Simulation

Before building the hardware, two key steps were completed. First, physical formulas were derived to show that this actuation concept was theoretically feasible. Second, COMSOL simulation was used to test this idea. An MRF droplet was modeled under alternating magnetic fields from electromagnets. The simulation showed that switching the fields in sequence could create controlled motion, supporting the rolling concept.

System Design and Development

Next, the project moved into the experimental stage by designing a soft robot system controlled by magnetic fields. A small capsule filled with MRF was created, and an electromagnetic control system using programmable coils was built to control its motion.

Testing and Data Collection

Using this system, five experiments were carried out to test functions relevant to medical use.

Rolling feasibility was tested on a flat surface.

Targeted positioning was tested using a tilting platform with a 3D-printed ED-shaped pathway simulating part of the gastrointestinal tract.

Stopping ability was tested in medical silicone tubing using a blood-like fluid at different flow rates.

Object grasping and transport were tested by shaping the MRF into a claw-like form and measuring the heaviest load it could move.

Rolling and sliding were compared to estimate which motion would likely cause less tissue damage.

Fair Testing and Reliability

To ensure fair results, key factors were kept the same in each experiment, such as capsule size, materials, and electromagnet strength. Only one variable was changed at a time, such as flow rate or load, and experiments were repeated to ensure reliability.

To validate my design, I used simulation and performed a series of physical experiments.

COMSOL Simulation

The key takeaway here was that sequentially switching electromagnets can reliably create alternating magnet fields that produce controllable MRF motion. This provided support that the rolling concept was physically sound before I moved to hardware.

Experiment 1: Rolling Feasibility

The MRF ball successfully rolled for 20 cm with a 92% success rate (n=50). All failures were caused by a manufacturing defect at a shell seal protrusion, not a problem with the actuation concept itself, supporting that this rolling mechanism is reliable.

Experiment 2: Gastrointestinal Targeted Positioning

The MRF ball’s targeting precision was tested in the ED maze. The robot achieved an

average positioning error of 0.51 mm (n=20), demonstrating submillimeter precision and an

repeatable ability the stop at intended locations.

Experiment 3: Vascular Retention Against Blood Flow

To test performance under flow, vascular retention experiments were conducted. The MRF remained anchored at all tested flow rates from 6.25 L/min to 25 L/min, covering conditions from rest to exercise physiological flow, with no detachment observed.

Experiment 4: Foreign Body Grasping and Removal

For functionality, object manipulation was tested. The robot successfully grasped and transported loads up to 4.5 N, exceeding the force range of typical targets (0.05–3.0 N), indicating sufficient strength for retrieval tasks.

Experiment 5: Rolling vs. Sliding Tissue Damage

Rolling produced significantly lower instantaneous friction than sliding. At 0.15 kg, sliding friction was 0.559 N, while rolling friction was 0.022 N, about 25x less than the amount of friction generated by sliding. It also reduced the overall cumulative friction impulse applied to surfaces to about 96% of that produced by sliding.

Overall Findings

Together, these results show that the system can be precisely controlled, remain stable in flow, interact with objects, and significantly reduce total frictional force through rolling motion in delicate biological environments.

The results show that a rolling MRF-based system is not only theoretically possible, but also experimentally functional.

The 92% rolling success rate, with all failures caused by a fixable manufacturing defect, confirms that the actuation concept itself is reliable.

The ability to control the robot with sub-millimeter precision shows that it can be positioned accurately in narrow, curved environments.

The robot remained stable even under high flow conditions, demonstrating that it can function in environments like inside the body.

Its ability to remove foreign bodies with a sufficient load capacity allows for multifunctional foreign body removal in future medical applications.

The comparison between rolling and sliding is also crucial. Rolling reduced the total frictional force applied to surfaces to about 96% of that produced by sliding. This suggests that changing the motion strategy can significantly reduce potential damage.

This is important because the project shows that designing how a device moves can be just as important as its function. A rolling soft robotic system could offer a safer and gentler way to perform tasks in delicate environments, such as foreign body retrieval and clot removal.

This project remains an early-stage proof of concept with limitations before clinical application.

Magnetic Actuation: Magnetic field strength decreases with distance, so effective in vivo control would require stronger electromagnets, higher current, or optimized coil design.

Biocompatibility: PVC worked under experimental conditions, but its long-term stability and safety in the body require further testing.

1.Improve magnetic actuation:

Develop stronger and more efficient electromagnet designs, such as optimized coil geometry or higher-current systems, for deeper and more precise in vivo control.

2.Enhance biocompatibility:

Replace PVC with clinically relevant materials and conduct long-term stability and safety testing in biological environments. This is essential for future medical use and will be the main focus of my next science fair project.

3.Test in more realistic environments:

Move from models to more realistic biological conditions, such as compliant tubes, variable flow, and tissue-mimicking materials, to better evaluate real-world performance.

I would like to thank my parents for their constant support throughout this project, especially during the early experimental design and iterative testing stages. Their encouragement helped me continue improving the project through challenges.

I would also like to thank Ms. Murray-Hoenig for her support and encouragement as I began my science fair journey.

Finally, I would like to thank the GVRSF judges for their constructive feedback. Their questions and suggestions helped me refine my project, and identify meaningful directions for future improvement.

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