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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.

Controlling the printing parameters of four-dimensional (4D) printed actuators can be used to set the internal strain of the actuators. This approach can be utilised when using the fused deposition modelling method to develop 4D-printed actuators, allowing non-manual shape programming. However, there is a lack of comprehensive studies that investigate the effects of printing parameters on the actuation performance of 4D-printed actuators. In this study, the effects of four printing parameters on the bending angle of 4D-printed polylactic acid (PLA) actuators are reported. These printing parameters include the printing speed, printing temperature, ratio of passive-to-active layers, and layer height. In addition, these printing parameters are investigated while changing the height of the actuators. The results show that increasing the printing speed increases the internal strain while increasing the printing temperature, layer height, or actuator height has the opposite effect. Moreover, it is found that a ratio of passive-to-active layers of 50% maximises the strain while selecting a higher or lower ratio causes the opposite effect. Based on the results, four mathematical predictive models are developed to determine the bending angle induced in the actuators when printed based on each printing parameter. Then, a predictive model that relates all the printing parameters and actuator height to the bending angle is developed. The predictive model is based on the characterization results of 534 PLA actuators, providing an R-squared value of 0.98. Then, a finite element analysis (FEA) model is developed to replicate the shape memory effect in actuators. To prove the accuracy of the proposed concept, two grippers with four and eight fingers are developed. The results show that the printing parameters can be used to control the bending angle of each finger based on the design specifications.

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This paper presents two novel large-stroke XY micropositioning stages that are fabricated completely using four-dimensional (4D) printed polylactic acid (PLA). The proposed designs do not require manual training to perform actuation. Instead, printing speed is used to achieve shape programming and manipulate the deformation and shrinking levels of the PLA microactuators that control the microstage. A relationship between the printing speed, number of layers, and deformation value is formulated to model the performance of the microactuators based on these variables. The same approach is then used to develop the two proposed designs in this work. Actuations in the x- and y-axes are achieved using PLA actuators that are printed at speeds in the range of 40 – 80 mm/s, while the rest of the structure (passive part) is printed at a speed of 10 mm/s to minimize unwanted deformations. The microactuators are activated by immersing the designs in hot water at 85 °C. The maximum values of the x- and y-actuations are achieved when using the highest printing speed for the microactuators. Design 1 offers actuation values of 1.99 and 1.40 mm along the x- and y-axes, respectively, while these values are 1.76 and 2.30 mm when using Design 2. The proposed designs offer a cost-effective batch fabrication solution for micropositioning applications, where the weight of the PLA required for Design 1 and Design 2 is 48.37 g and 12.61 g, respectively, which respectively costs $0.65 and $0.17. In addition, the designs offer a promising performance compared to the currently available large-stroke micropositioning stages in terms of the simplicity of the fabrication process and the area ratio.

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