Design and Fabrication of Functional Electro-Thermal Micro-Origami

Origami inspired assemblages provide novel methods to convert 2D surfaces into 3D structures, which are beneficial for photolithography based micro-fabrication because the available fabrication processes tend to provide planar structures. These micro-origami have broad applications including bio-medical grippers, micro-containers, transducers, meta-materials, and more. Pragmatic solutions to create active origami at micro-scales include using novel materials and functional systems, such as active hydrogels, metallic morphs with differential strains, magnetic active materials, light active polymers, and others. Despite the advancement in building active micro-origami, these currently available systems tend to have one or more limitations. For example, the actuation of these active origami typically relies on applying environmental stimuli, and thus the origami tend to have just one active degrees-of-freedom that only provides a fold-unfold motion. Also, these systems tend to fold slowly because it takes time to change the environment (such as heat up the water), or because the mechanism of actuation is slow (swelling from water). Moreover, currently available systems can usually achieve large folding elastically (reversibly) or plastically (irreversibly) but not both. To address the above issues, this presentation will discuss an elastically and plastically foldable electro-thermal micro-origami designed and tested by our group recently[1]. We designed a novel electro-thermal bending actuator using a layer of SU-8 photoresist and a layer of gold. By applying a current through the patterned gold layer, we generate localized Joule heating, which causes the actuator creases to achieve large bending motion because the SU-8 expands more than the gold. We showed that these folding creases can achieve large folding rapidly and reversibly when the input heating power is low and the material response is elastic. The same actuator design can also achieve plastic folding by applying forces and extra current to heat the SU-8 to temperatures approaching its glass-transition temperature where it displays a visco-elasto-plastic material behavior. Thus, by controlling the input current, these micro-origami can fold both elastically and plastically, allowing greater programmability and functionality. These active origami can be designed to have multiple active degrees-of-freedom by creating separate heating circuits, which enables the system to achieve flexible and more complex folding motions and functions. Finally, we showed that by combing the elastic folding creases, plastic folding creases, and passive folding creases (like rotational springs) we can create complex origami systems that can self-assemble into intricate geometries and then achieve functions. For example, we created different types of gripper systems with multiple degrees-of-freedom, and an origami crane that can fold into a static three-dimensional shape and can then flap its wings. These proposed functional electro-thermal micro-origami systems provide superior programmability and can realize more complex functions than many existing micro-origami systems that tend to execute a single fold and unfold motion path. We envision that the proposed micro-origami can be used for creating micro-robots, biomedical devices, micro-packaging systems, and more, where rapid shape morphing, large folding, and highly flexible programmability is desired.

References

[1] Yi Zhu, Mayur Birla, Kenn R. Oldham, Evgueni T. Filipov (2020) “Elastically and Plastically Foldable Electro-Thermal Micro-Origami for Controllable and Rapid Shape Morphing.” Adv. Funct. Mater. (Accepted)