Mechanism of the four-unit Kresling crawler based on the Kresling dipole. (A) Schematic of a Kresling unit, showing contraction coupled with a twist deformation. (B) Schematic of a Kresling dipole made of two standard Kresling units with reverse crease directions, showing no rotation at the two ends (green circles) but rotation at the center plane (blue circles) during contraction. (C) The experimentally measured torque contraction curve of the Kresling unit. Contraction is defined as ∆H/H, where H is the initial height of the unit and ∆H is the difference between the initial and contracted heights. Parameter Te is defined as the corresponding torque at 35% contraction of the unit for effective crawling motion. The solid line is the averaged responses of three Kresling unit samples, and the shaded region represents the range of responses. (D) Schematic of the Kresling crawler made of two Kresling dipoles, showing no rotation at the center plane and two ends. (E) The required torque distribution to actuate the Kresling crawler for simultaneous contraction of all units. (F) FEA verification of the derived torque distribution for simultaneous contraction of all units. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abm7834

Magnetic actuation mechanism of the Kresling crawler. (A) Image of a fingertip holding the fabricated Kresling crawler and designed magnetization directions of attached four magnetic plates for distributed torques. (B) Crawler configurations and magnetization directions at the initial state and the contracted state. By is the magnetic field applied to the crawler along its net magnetization direction. Angle θr is the total rotation angle of θ2 or θ3 during contraction. TmU1 , TmU2 , TmU3 , and TmU4 are torque magnitudes on units U1, U2, U3, and U4 under magnetic actuation, respectively. Green marks on the vertices of the magnetic plates indicate no rotation at the two ends of the Kresling crawler. (C) Torque ratio between units U1 and U2 (U4 and U3) during contraction. Contraction of the unit of 35% (rotation angle θr of 32°) is defined as an effective crawling motion under a reasonably small torque. Note that angles θ1 and θ4 stay unchanged during contraction. Angles θ2 and θ3 are designed to swing between 106° and 74° to minimize the dynamic fluctuation of magnetic torques during contraction. (D) The magnetically actuated contraction under a magnetic field of 40 mT. (E) Characterization of the Kresling crawler contraction at different magnetic field magnitudes. Contraction is defined as 1 − ℓ/L, where L and ℓ are lengths of the crawler at the initial state and after contraction, respectively. The solid line is the averaged responses of three Kresling crawler samples, and the shaded region represents the range of responses. Scale bars, 5 mm. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abm7834

Crawling mechanism of the Kresling robot. (A) Single stride of the Kresling crawler under a magnetic field of 40 mT. Scale bar, 5 mm. (B) Stride and (C) speed characterization of crawling motion at various magnetic field magnitudes and frequencies. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abm7834

Steering and navigation of the Kresling crawler. (A) The steering mechanism. (X and Y) and (x and y) refer to the global and local (deformed) configurations, respectively. The crawler always tends to align its net magnetization Mnet with the applied magnetic field direction. (B) The “Z” crawling path (three straight segments) at selected times. (C) The “O” crawling path (continuous angular changes) at selected times. Scale bars, 5 mm. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abm7834

. Conceptual scheme for drug storage and release using the Kresling crawler. (A) Exploded view and assembly of the modified Kresling crawler with a through hole. The internal cavity of the front Kresling unit is used for pill storage. (B) Pill positions at initial and contracted states of the Kresling crawler. The crawler contracts without interfering with the cylindrical pill. (C) Pill gradually dissolves in water as indicated by the intensity of the blue dye for 4 min. Scale bar, 5 mm. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abm7834

Contraction mechanism of the Kresling crawler. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abm7834