Origami-Inspired 3D Assembly of Egg-Crate Shaped Metamaterials Using Stress and Surface Tension Forces
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Origami-Inspired 3D Assembly of Egg-Crate Shaped Metamaterials Using Stress and Surface Tension Forces Joyce Breger1, Dongyeon Helen Shin1, Kate Malachowski1, Shivendra Pandey1, and David H. Gracias1,2 1
Department of Chemical and Biomolecular Engineering
2
Department of Materials Science and Engineering, Johns Hopkins University, 3400 N Charles Street, Baltimore, MD 21218, USA. ABSTRACT We discuss the self-folding of patterned metallic sheets using both differential stress and surface forces. The advantageous characteristics of the technique include, (a) The creation of 3D patterned corrugated metamaterials with pattern resolution limited only by that of planar lithography. Since planar lithography is highly versatile, a variety of patterns with different sizes and shapes can be formed. (b) The hands-free and wire-free self-folding of these materials use two orthogonal forces derived from the release of residual stress and the minimization of surface tension. Hence, this process is highly parallel and scalable allowing such materials to be mass produced. (c) Finally, the edges of the materials self-align and seal due to capillary forces of the liquid hinges—this self-sealing enhances overall rigidity and strength of the materials. Consequently, the self-folding of patterned and sealed “egg-crate” shaped metamaterials was realized. Patterns were incorporated in the form of “smart” patches on the walls of the eggcrates which can be selectively functionalized with biomolecules. Apart from the intellectual appeal of these hands-free, self-sealing materials, we envision applicability of these egg-crate like microstructures in lab-on-a-chip assays as functionalized microwells and as light weight mechanical metamaterials. INTRODUCTION In nature, plants, insects and animals incorporate intricate folding patterns into their anatomical structures to increase surface area and perform complex functions in varied environments. These complex 3D structures, ranging from skin folds to insect wings to elaborate leaf arrangements, often self-organize via a planar to a 3D structure transition. Drawing inspiration from this mode of self-assembly, researchers have been trying to design synthetic thin films that fold into functional materials. Self-folding is a type of self-assembly process wherein patterned planar thin films spontaneously fold into an equilibrium 3D state driven by a balance between bending rigidity and differential strain. As reviewed previously, [1-8] self-folding has been used to create a wide range of micro and nanostructured materials and designs utilizing metals, semiconductors, polymers and hydrogels. In this work, we describe a method that combines two previously utilized forces for selffolding. The first force is generated due to the release of strain in pre-stressed bilayers composed of chromium (Cr) and gold (Au). [9-10] The second force is a capillary force generated by the
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