From All‐Printed 2D Patterns to Free‐Standing 3D Structures: Controlled Buckling and Selective Bonding

Abstract

3D structure into thin cross-sections and fabricate the structure layer-by-layer. [29] This 3D fabrication route relies mainly on metal powders or polymeric materials that are deposited then cooled, crosslinked, or sintered to create the desired 3D structure. [24,29] While these approaches are very successful for expedited prototyping, the resulting printed 3D structures are typically constrained to nonfunctional materials and have limited functionalities that, based primarily on their geometrical shape. [24] Recent efforts have led to kirigami-inspired fabrication process that uses existing semiconductor fabrication to design 2D patterns of electronic materials that can morph into complex 3D structures by stress-induced buckling. [24,27,28,30] This approach uses lithography to fabricate silicon planar designs with selective sites for bonding. [24,27,28] Once this planar design is transferred onto a strained elastomer substrate, with selective bonding, the relaxation of the substrate will induce strain in unbounded locations of the design, thus converting a 2D planar design into a 3D mesostructure. [24,27,28,[31][32][33] The planar device will bend from its 2D precursor into a diverse library of complex 3D constructs (e.g., baskets, cuboid cages, starbursts, cars, or flowers). [24] While such photolithographic fabrication of 3D structures is scalable for microstructures and suitable for a high-performance electronic materials, this approach is relatively expensive, requires rigorous operating environment and usually involves complex procedures. [34] Other methods, such as laser cutting or mechanical dicing, can be useful for prototyping, but are relatively lowthroughput for large-scale manufacturing. Many disciplines rely on a variety of materials or composites, such as nano materials, smart polymers, alloys, carbonaceous, biomaterials, composites, or temperature-sensitive dyes. [13,14,[35][36][37][38][39][40][41][42][43][44][45][46][47][48] The assimilation of these diverse materials and composites is essential to the widespread use and progression of 3D mesostructures.Here, we introduce a thick-film screen-printing fabrication technique that is high-throughput, low-cost that can produce diverse highly tunable buckled 3D structures (with freestanding segments) composed of different materials, shapes, and sizes. The novelty of the new approach hinges on the formulation and dimensions of the sacrificial layer that can be tailored to control which specific segments of the 2D precursor Current methods to create 3D structures are limited to few materials and designs, are costly, and have low processing throughput. Planar designs (of printed sacrificial, flexible, and guiding layers) fabricated by thick film technique that can reversibly fold between their 2D and 3D forms through compressive buckling and selective bonding is reported in this work. Versatile ink compositions based on a wide variety of materials (e.g., carbonaceous, polymers, and nanomaterials) are used along with screen printing technique for creating ...

Elastic Energy Storage Enables Rapid and Programmable Actuation in Soft Machines

“…Here, we present a design strategy to significantly increase the elastic strain energy stored by completely soft robots upon actuation, enabling their rapid and programmable actuation and recovery. Our work finds its foundations in previous approaches to create 3D structures using controlled buckling and selective bonding as a design principle and the work of Cafferty et al, who demonstrated the fabrication of soft grippers using a combination of direct‐ink printing and relaxation of strain. Complimentary to these works, we propose a strategy to exploit elastic energy storage to fabricate a variety of prestressed soft actuators (PSAs) by attaching a flexible but inextensible sheet (paper, textile, or plastic) to a prestressed elastomeric layer.…”

Fabricating 3D Structures by Combining 2D Printing and Relaxation of Strain

“…(iv) It produces structures that can be deformed reversibly by reapplying strain, which can be used to fabricate more complex structures and actuators. This approach differs from prior work, in which strain relaxation formed buckled “pop‐up” structures on flat elastomeric substrates, in that the approach described here allows the entire composite structure, including the substrate, to be fabricated with positive or negative curvature.…”

“…Buckling instabilities and bending due to compressive in‐plane stresses in 2D sheets may be used to generate 3D shapes . These compressive stresses can result, for example, from swelling of an inhomogeneous hydrogel, or from selective swelling of a homogeneous hydrogel using a mask .…”

“…Bilayers may also form 3D structures when materials with “mismatching” strain or internal stress are bonded to one another. For example, bonding a stretched elastomeric material to an unstretched elastomeric material will cause bending in the resulting bilayer due to residual stresses . This concept has also been applied at the nanoscale: when two thin layers of materials with different lattice constants are deposited on a substrate, the bilayer “rolls” into a nanotube upon release from the substrate …”

Highly Stable Battery Pack via Insulated, Reinforced, Buckling‐Enabled Interconnect Array

“…Due to the extreme out‐of‐plane buckling that may take place during stretching, the conductive layer should have commensurate flexibility and conductivity to minimize change in resistance (≈1 Ω) and avoid the formation of permanent damage. Here, an ink formulation, coupling silver flakes and an elastomer binder (Ag‐SIS), described in our previous work, is chosen owing to its superior flexibility and conductivity. Then, the water‐soluble ink is printed to define the free‐standing region of the interconnect.…”