A pinboard by
Haiwen Luan

PhD Candidate in Mechanical Engineering, Northwestern University


Transforming planar precursor films into diverse, targeted 3D structures by compressive buckling

3D microstructures are of increasing attention due to their extensive applications in micro-systems technologies, such as energy storage devices, photonic and plasmonic systems, micro-electronic circuits, biomedical tools, and optical/mechanical metamaterials. Previous methods for forming interesting 3D micro-architectures include those utilizing self-actuating materials, bending/folding of thin films induced by residual stresses or capillary forces, and 3D printing and/or writing. These existing approaches are compatible, however, only with a narrow range of materials and/or 3D geometries.

My PhD research projects aim to develop a series of mechanically-guided, deterministic approaches, using compressive buckling, of assembling complex 3D microstructures from 2D micro-films. Such approaches are of interest due to their intrinsic compatibility with a broad range of advanced materials (e.g., monocrystalline silicon), their high-speed, parallel operation, and their applicability over characteristic length scales from nanometers to centimeters.

I have been working hard to conceive diverse concepts to expand the accessible topologies and to pursue various application opportunities enabled by the compressive buckling-based approaches. My finished work has expanded the applicability of these approaches by addressing two limitations, a) the 3D structures yielded were only in open-network mesh type layouts and b) the compression driving the 2D to 3D transformation lacked the ability to vary spatially. I, together with my collaborators, introduce a) concepts for a form of Kirigami for the precise, mechanically driven assembly of 3D microstructures from 2D micro-membranes with strategically designed geometries and patterns of cuts and b) ideas for elastomeric substrates with engineered distributions of thickness & modulus to yield desired strain distributions for targeted control over resultant 3D microstructures geometries. Theoretical and experimental studies demonstrate the applicability across diverse length scales, in various materials, with topographical complexity significantly exceeding that possible with other approaches. A broad set of examples includes 3D silicon microstructures and hybrid membrane-ribbon systems, including heterogeneous combinations with polymers and metals, with critical dimensions ranging from 100 nm to 30 mm. The resulting functional 3D microstructures have important implications for tunable optics and stretchable electronics, etc.


Controlled Mechanical Buckling for Origami‐Inspired Construction of 3D Microstructures in Advanced Materials

Abstract: Origami is a topic of rapidly growing interest in both the scientific and engineering research communities due to its promising potential in a broad range of applications. Previous assembly approaches for origami structures at the micro/nanoscale are constrained by the applicable classes of materials, topologies, and/or capability for reversible control over the transformation process. Here, a strategy is introduced that exploits mechanical buckling for autonomic origami assembly of 3D structures across material classes from soft polymers to brittle inorganic semiconductors, and length scales from nanometers to centimeters. This approach relies on a spatial variation of thickness in the initial 2D structures as a means to produce engineered folding creases during the compressive buckling process. The elastic nature of the assembly scheme enables active, deterministic control over intermediate states in the 2D to 3D transformation in a continuous and reversible manner. Demonstrations include a broad set of 3D structures formed through unidirectional, bidirectional, and even hierarchical folding, with examples ranging from half cylindrical columns and fish scales, to cubic boxes, pyramids, starfish, paper fans, skew tooth structures, and to amusing system‐level examples of soccer balls, model houses, cars, and multifloor textured buildings.

Pub.: 25 Feb '16, Pinned: 31 Aug '17

Plasticity-induced origami for assembly of three dimensional metallic structures guided by compressive buckling

Abstract: Development of origami-inspired routes to assembly of three dimensional structures is an area of growing activity in scientific and engineering research communities due to fundamental interest in mathematical topics in topology and to the potential for practical applications in areas ranging from advanced surgical tools to systems for space exploration. Recently reported approaches that exploit the controlled, compressive buckling of 2D precursors induced by dimensional change in an underlying elastomer support offer broad versatility in material selection (from polymers to device grade semiconductors), feature sizes (from centimeters to nanometers), topological forms (open frameworks to closed form polyhedra) and shape controllability (dynamic tuning of shape), thereby establishing a promising avenue to autonomic assembly of complex 3D systems. Localization of origami-like folding deformations at targeted regions can be achieved through the use of engineered, spatial variations in the thicknesses of the 2D precursors. While this approach offers high levels of control in the targeted formation of creases, creating the necessary thickness variations requires a set of additional processing steps in the fabrication This paper presents an alternative, and complementary, approach that exploits controlled plastic deformation in the precursors, as validated in a comprehensive set of experimental and theoretical studies. Specifically, plasticity and strain localization can be used to dramatically reduce the bending stiffness at targeted regions, to form well-defined creases as mountain or valley folds during the 2D to 3D geometrical transformation process. The content begins with studies of a model system that consists of a 2D precursor in the form of a straight ribbon with reduced widths at certain sections. The results illustrate the important role of plasticity in the course of folding, in such a manner that dictates the final 3D layouts. A broad range of complex 3D shapes, achieved in both the millimeter-scale and the mesoscale structures (i.e. micron to sub-millimeter), demonstrate the power of these ideas.

Pub.: 23 Nov '16, Pinned: 31 Aug '17

Deterministic assembly of 3D mesostructures in advanced materials via compressive buckling: A short review of recent progress

Abstract: Publication date: Available online 27 December 2016 Source:Extreme Mechanics Letters Author(s): Zheng Yan, Mengdi Han, Yiyuan Yang, Kewang Nan, Haiwen Luan, Yiyue Luo, Yihui Zhang, Yonggang Huang, John A. Rogers Nearly all micro/nanosystems found in biology have function that is intrinsically enabled by hierarchical, three-dimensional (3D) designs. Compelling opportunities exist in exploiting similar 3D architectures in man-made devices for applications in biomedicine, sensing, energy storage and conversion, electronics and many other areas of advanced technology. Although a lack of practical routes to the required 3D layouts has hindered progress to date, recent advances in mechanically-guided 3D assembly have the potential to provide the required access to wide-ranging structural geometries, across a broad span of length scales, in a way that leverages the most sophisticated materials and design concepts that exist in state-of-the-art 2D microsystems. This review summaries the key concepts and illustrates their use in four major categories of 3D mesostructures: open filamentary frameworks, mixed structures of membranes/filaments (Kirigami-inspired structures), folded constructs (Origami-inspired structures) and overlapping, nested and entangled networks. The content includes not only previously published examples, but also several additional illustrative cases. A collection of 3D starfish-like and jellyfish-like structures with critical dimensions that span nearly a factor of ten million, from one hundred nanometers to nearly one meter, demonstrates the scalability of the process.

Pub.: 06 Jan '17, Pinned: 31 Aug '17

3D Tunable, Multiscale, and Multistable Vibrational Micro-Platforms Assembled by Compressive Buckling

Abstract: Microelectromechanical systems remain an area of significant interest in fundamental and applied research due to their wide ranging applications. Most device designs, however, are largely 2D and constrained to only a few simple geometries. Achieving tunable resonant frequencies or broad operational bandwidths requires complex components and/or fabrication processes. The work presented here reports unusual classes of 3D micromechanical systems in the form of vibratory platforms assembled by controlled compressive buckling. Such 3D structures can be fabricated across a broad range of length scales and from various materials, including soft polymers, monocrystalline silicon, and their composites, resulting in a wide scope of achievable resonant frequencies and mechanical behaviors. Platforms designed with multistable mechanical responses and vibrationally decoupled constituent elements offer improved bandwidth and frequency tunability. Furthermore, the resonant frequencies can be controlled through deformations of an underlying elastomeric substrate. Systematic experimental and computational studies include structures with diverse geometries, ranging from tables, cages, rings, ring-crosses, ring-disks, two-floor ribbons, flowers, umbrellas, triple-cantilever platforms, and asymmetric circular helices, to multilayer constructions. These ideas form the foundations for engineering designs that complement those supported by conventional, micro-electromechanical systems, with capabilities that could be useful in systems for biosensing, energy harvesting, and others.

Pub.: 03 Mar '17, Pinned: 31 Aug '17