Bioinspired Pattern-Driven Single-Material 4D Printing for Self-Morphing Actuators

Abstract

Four-dimensional (4D) printing of shape memory polymers is a leading research field due to the possibilities allowed by using these materials. The strain difference in the structures that is caused by the different stiffness profiles can be used to influence the shape-memory effect in the actuators. In this study, the influence of patterns on the strain is tested in polylactic acid (PLA) actuators using patterns made of different shapes. Five bioinspired geometrical shapes, namely, circles, squares, hexagons, rhombuses, and triangles, are used in the three-dimensional (3D) printing of the actuators. The use of shapes of different sizes along with combinations of different patterns in the PLA actuators is carried out to develop 40 actuators with different designs. The effects of the patterns and their characteristics are analysed and compared. The self-bending angles of the actuators range from 6.19° to 30.86°, depending on the patterns and arrangement used. To demonstrate the feasibility of utilizing the proposed designs in practical applications, a hand-like shaped gripper is developed. The results show that the gripper can grip objects with uniform and non-uniform cross-sections. The developed gripper demonstrates that the proposed concept can be implemented in various applications, including self-morphing structures and soft robotics.

Octopus‐Inspired Adaptable Soft Grippers Based on 4D Printing: Numerical Modeling, Inverse Design, and Experimental Validation

“…Most proposed stimuli‐responsive soft grippers only used actuators with a single deformation pattern, usually pure bending, to grasp objects. [ 20–22,24,26–29,31,35,36 ] Figure 3b shows the comparison of the reachable workspace between an octopus‐inspired gripper and a pure‐bending soft gripper. The octopus‐inspired gripper and the pure‐bending soft gripper have the same length for comparability, where the length of an octopus‐inspired gripper refers to R + L .…”

“…technology, as a combination of additive manufacturing and smart materials which was first proposed by Tibbits in 2014, [19] has enabled the creation of soft grippers with sophisticated capabilities by programming structures to deform under external stimuli. A broad range of smart materials including hydrogels, [20][21][22][23][24] shape memory polymers (SMPs), [25][26][27][28][29] liquid crystal elastomers (LCE), [30,31] UV-curable elastomers, [32,33] and magnetic composites [34][35][36] has been applied in soft grippers using 4D printing. However, since the functional materials for soft grippers are too soft, one of the main problems of this kind of soft grippers is that the actuation cannot provide enough grasping force, which usually lifts objects with a weight of 50.0 g or less.…”

“…However, since the functional materials for soft grippers are too soft, one of the main problems of this kind of soft grippers is that the actuation cannot provide enough grasping force, which usually lifts objects with a weight of 50.0 g or less. [20][21][22][23][24]26,27,[29][30][31][32][33]35,36] . The grasping objects in these studies are mostly regular objects, such as spheres, [21,27,[30][31][32]35,36] cubes, [22][23][24] or shaft-like objects.…”

“…Most proposed stimuli-responsive soft grippers only used actuators with a single deformation pattern, usually pure bending, to grasp objects. [20][21][22]24,[26][27][28][29]31,35,36] Figure 3b shows the comparison of the reachable workspace between an octopus-inspired gripper and a pure-bending soft gripper. The octopus-inspired gripper and the pure-bending soft gripper have the same length for comparability, where the length of an octopus-inspired gripper refers to R þ L. Defining the limit state as the state where the interference of the gripper occurs at the center line, the reachable workspace of the pure-bending gripper is calculated as the swept area from the initial state to the limit state, as denoted by the faint yellow area in Figure 3b.…”

Recent Advances in the Additive Manufacturing of Stimuli‐Responsive Soft Polymers

“…[530][531][532][533] Recent studies showed the development of smart grippers, actuators, and robots for different applications. [534][535][536][537][538][539][540] For instance, Cecchini et al [381] exploited the reshaping ability of humidityresponsive materials to develop a seed-like soft robot by using FDM printing, as illustrated in Figure 17A. In this approach, PCL-based filament were used to print a passive layer and electrospun cellulose nanocrystals (CNCs)/polyethylene oxide (PEO)based was used as an active layer to develop bilayer hygroscopic structures.…”