Jamming-induced stiffness modulation using 3D-printed hexagonal microfibers in cylindrical structures

초록

Active stiffness modulation is essential for soft robotics, wearable devices, and minimally invasive instruments, in which adaptability and mechanical stability are required. However, most existing fiber jamming systems use circular fibers, which provide a limited contact area and reduce inter-fiber friction, thereby limiting their ability to modulate stiffness. This study investigated how the cross-sectional geometry of fibers affects the jamming performance, specifically in terms of contact behavior and resulting mechanical resistance. We fabricated microscale fibers with circular, square, and hexagonal cross sections using a 3D printer and integrated them into polydimethylsiloxane hollow cylinders produced via water-soluble mold casting. Their mechanical responses were evaluated under both unjammed and vacuum-jammed conditions. Hexagonal fibers showed superior performance, achieving a jammed-state stiffness of 342.1 N/mm-56% and 22% higher than those of circular and square fibers, respectively-due to their face-to-face contact and high packing density. The hexagonal structure also sustained a stable stiffness over 10,000 cycles and enabled accurate force sensing in the range of 320-910 mN. This work demonstrates that the cross-sectional geometry serves as an effective design parameter for tuning the stiffness in jamming systems, providing a scalable and accessible route toward programmable stiffness devices for compact robotic and biomedical applications.

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