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This work described a bioinspired soft robotic finger with variable bending length to conform objects with different sizes by means of selectively varying the structural stiffness of its segments. The basic design is a shape memory alloy-based soft actuator with embedded stiffness-varying structures serving as modifiable endoskeletons. The stiffness-varying structure is composed of shape memory polymer (SMP) embedded with Nichrome (Ni-Cr) wires as heating elements. Joule heating of SMP through Ni-Cr wire inducing its phase change from the glassy state to the rubbery state enables the actuator structure change from the stiff state (

Recent advances in four-dimensional (4D) printing technology have developed various approaches for creating shape-morphing structures and devices. However, it is impractical as a universal method to fabricate directly available shape-morphing structures in any desired shapes. These 4D printed shape-morphing structures are either limited in structures with flat architectures or needed for the subsequent tedious thermo-mechanical programming process. To overcome these limitations, this work, as an example, demonstrates a versatile fabrication method for constructing soft grasping mechanisms with different architectures via mechanically assembling the basic self-bending units made of polymer-paper bilayer composite. The bilayer is fabricated in a single printing process by three-dimensional printing polymer fibers in parallel and layer-by-layer on the paper substrate. All the basic units are cut out in strip shape from the same piece of bilayer along the direction of the printed fiber being able to generate bending deformation in the direction transverse to the printed fibers upon heating. The obtained units are then mechanically assembled using pre-fabricated hard components for constructing three grasping mechanisms with different architectures. Upon heating, each unit generating the bending deformation endows the assembled structure with a desired integral shape-transition for the function of grasping. This method to the mechanical assembly of self-bending units provides new routes to the design of polymer-based shape-morphing structures.