3. Conclusion

The ability to integrate and transport active components such as microelectronics in small-scale robots can impart functionality into an otherwise passive construct. However, conventionally manufactured components such as microelectronics are rigid and planar parts that are challenging to integrate into existing crawler designs without disrupting their intrinsic locomotion. In this study, we demonstrated the creation of a centralized internal compartment for functional integration by localizing the body flexibility of a flexible magnetic crawler. We then showed that the centralized compartment enables MR-LF to be readily integrated with a wide range of modular functional components and payloads, such as commercial off-the-shelf electronics and medication, while preserving its bidirectionality and ingestible form factor. We also showed a soft-bodied design with an internal lumen that can steer a continuum device such as a catheter in an endoluminal construct, for instance, to enable local delivery of drugs or diagnostic tools. Ultimately, we envision that MR-LF can address a broad range of unmet clinical needs by realizing a highly-functional ingestible system. 

4. Experimental Section

4.1. Locomotion experiments

In each locomotion experiment, the robot was placed in a clear polycarbonate circular channel (inner diameter [ID]: 19 mm) with the robot center at x = 0, y = 0. For locomotion and bending experiments, the cylindrical actuator magnet (DY0X0-N52, K&J Magnetics) was located at a fixed position (x = 0, y = ya) with the south pole initially pointing in the +x direction. Next, the actuator magnet was rotated by a geared DC motor at a fixed voltage, producing a frequency of 2.0 ± 0.1 Hz with rotation about the -z axis. Consistent with prior literature \cite{Steiner2021}, the direction of robot locomotion is oriented away from the fixed location of the actuator magnet (i.e., away from x = 0) to demonstrate the feasibility of moving against the attraction forces between the robot and actuator. Five trials were performed for each robot across ya offsets from 9 to 15 cm. Displacement was measured by tracking the center of the robot from a video recording of the test (Canon EOS 80D, frame rate: 29.97 fps). Displacement was calculated every 15 frames, or approximately one measurement per step. The initial speed was calculated by dividing the total displacement in the first ten steps by the number of steps. For variable-mass experiments, weight was added inside the rigid compartment of MR-LF. Variability in locomotion test results could be due to several factors, including slight variations in robot starting position and magnet rotation frequency, and minor fabrication defects. To reduce potential data bias from possible imperfections in the robot’s feet, the channel and robot were rotated about the x-axis between trials so different portions of the foot were in contact with the floor.