Reinforcement learning control methods can impart robots with the ability to discover effective behavior, reducing their modeling and sensing requirements, and enabling their ability to adapt to environmental changes. However, it remains challenging for a robot to achieve navigation in confined and dynamic environments, which are characteristic of a broad range of biomedical applications, such as endoscopy with ingestible electronics. Herein, a compact, 3D‐printed three‐linked‐sphere robot synergistically integrated with a reinforcement learning algorithm that can perform adaptable, autonomous crawling in a confined channel is demonstrated. The scalable robot consists of three equally sized spheres that are linearly coupled, in which the extension and contraction in specific sequences dictate its navigation. The ability to achieve bidirectional locomotion across frictional surfaces in open and confined spaces without prior knowledge of the environment is also demonstrated. The synergistic integration of a highly scalable robotic apparatus and the model‐free reinforcement learning control strategy can enable autonomous navigation in a broad range of dynamic and confined environments. This capability can enable sensing, imaging, and surgical processes in previously inaccessible confined environments in the human body.
The gastrointestinal (GI) tract plays a crucial role in the human body as a naturally evolved interface between the body and its environment. Ingestible electronics perform surgical-free screenings and diagnoses within the GI tract and have been proposed since 1957. [1][2][3][4] Recent advancements have demonstrated the ability to integrate ingestible electronics with sensing, actuation, and drug delivery capabilities, with several examples that have been FDA approved and are in clinical use. [5][6][7][8] For example, the pill-shaped PillCam provides access to areas of the GI tract that are challenging or infeasible via endoscopic procedures. [8] However, the size of an ingestible device is fundamentally constrained to enable swallowing (e.g., PillCam SB 3 has a diameter of 11.4 mm and a length of 26.2 mm) [9] and to mitigate the risks of unexpected retention (1.4% for conventional capsule endoscopes) [10] or intestinal obstruction that requires surgical interventions. The limitation in size constrains the possible functionalities that can be integrated into an ingestible system, especially since active components such as microelectronics are rigid and planar parts that have to be assembled into the system. For example, most ingestible electronics do not have the ability to be actively transported toward target regions of interest. [8] Indeed, integrating functionalities into ingestible, untethered robots with active locomotion capabilities can enable a broader range of surgical-free diagnostic and treatment strategies. [11][12][13][14][15] Earlier research has demonstrated a wide range of locomotion strategies for small-scale robots, including legged, [16,17] rolling, [18][19][20][21] peristaltic (i.e., earthworm-like), [22][23][24][25][26][27][28] undulatory, [29][30][31] crawling, [32][33][34][35][36][37][38][39][40][41][42][43] and other motions. [6,[44][45][46][47][48][49][50][51][52] Among the demonstrated mechanisms, magnetically controlled actuation is particularly promising because it does not require onboard power or control systems, [45] freeing critically needed space for additional functional integration.Recent advances have demonstrated the ability of miniature magnetic crawlers to actively transport cargo in complex and confined systems, such as the GI tract, by leveraging magnetic fields to induce locomotion. For instance, Zhao et al. demonstrated a magnetic origami robot that crawled by in-plane contraction [22] where the anisotropic friction on the robot's feet enabled forward locomotion that can be steered. Nevertheless, the need for anisotropic friction on the feet also precluded bidirectional locomotion in a confined space, such as in a lumen, where reversing direction by turning in place is challenging. Other recent works demonstrated entirely-soft crawlers with impressive multi-gait bending locomotion that could transport objects by gripping and direct attachment, [53][54][55] including cargos 20 times their mass
This Supporting Information includes information regarding the magnetic field of the actuator magnet, MR-LF-S (which has the same geometry as MR-LF and a soft compartment), and a table comparing MR-LF to other small-scale, flexible magnetic crawler robots. Corresponding author email: yong.kong@utah.edu
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