Arbitrary Three-dimensional Shape Research Articles

(Keynote) Macroscopic Materials Synthesized from Nanoparticle Superlattices

One of the promises of nanotechnology in its early developmental stages was the ability to make designer materials with precise control over individual building block composition and organization in 3D space. In recent years, material synthesis methods have advanced to be able to create a multitude of nanoparticles of varying sizes, shapes, and compositions, providing a vast array of building blocks to use as materials fabrication components. Additionally, processing methods have been developed to arrange these nanoparticles into ordered arrays, to dry them into thin films, and even to sinter them into more complex bulk solids. However, the fundamental promise of being able to build a material with controlled hierarchical structure across all length scales (atomic crystal structure, molecular composition; nanoscale feature size, shape, and organization; microstructure; macroscopic form) has been challenging to realize. A materials synthesis and processing route that could create free-standing, macroscopic materials or arbitrary three-dimensional shapes with precisely controlled nanoparticle positions across the entirety of the material composition would therefore be a major advancement. Here, we demonstrate a nanoparticle-based building block called a “Nanocomposite Tecton (NCT)” that enables a self-assembly route to fabricating free-standing 3D solids of arbitrary macroscopic shapes that can utilize a multitude of different nanoparticle compositions, and also possess specifically programmed nanoscale particle arrangements and controlled microstructure. This talk will outline the key synthesis and processing steps that enable this method of making materials with programmed material structure across ~7 orders of magnitude in length scale, thereby realizing a long-standing goal of nanomaterials fabrication.

Real-Time Simulation of Ground Vehicles on Deformable Terrain

Abstract Sophisticated modeling and simulation, based on rigid and flexible multibody dynamics, are nowadays a standard procedure in the design and analysis of vehicle systems and are widely adopted for on-road driving. Off-road driving for both terrestrial wheeled and tracked vehicles, as well as wheeled and legged robots and rovers for extra-terrestrial exploration pose additional modeling and simulation challenges, a primary one being that of the vehicle–terrain interaction, modeling of deformable terrain, and terramechanics in general. Techniques for modeling deformable terrain span an entire range varying in complexity, representation accuracy, and ensuing computational effort. While formulations such as fully resolved granular dynamics, continuum representation of granular material, or finite element can provide a high level of accuracy, they do so at a significant cost, even when the implementation leverages parallel computing and/or hardware accelerators. Real-time or faster than real-time terramechanics is a highly desired capability (in applications such as training of autonomous vehicles and robotic systems) or critical capability (in applications such as human-in-the-loop or hardware-in-the-loop). We present a real-time capable deformable soil implementation, extended from the soil contact model (SCM) developed at the German Aerospace Center which in turn can be viewed as a generalization of the Bekker-Wong and Janosi-Hanamoto semi-empirical models for soil interaction with arbitrary three-dimensional shapes and arbitrary contact patches. This SCM implementation is available, alongside more computationally intensive deformable soil representations, in the open-source multiphysics package Chrono. We describe the overall implementation and the features of the Chrono SCM model, the efficient underlying data structures, the current multicore parallelization aspects, and its scalability properties for concurrent simulation of multiple vehicles on deformable terrain.

Shape programming via discretizing the surface into cross-structured pixel units

Shape-morphing systems have a wide range of application scenarios. Its potential for controlling transformation into arbitrary three-dimensional (3D) shapes needs to be realized. This study aimed to develop a novel programming control strategy. A flat sheet obtained by discretizing the curved surface with cross-structure units without in-plane strain interference can be deformed into an arbitrary 3D space surface model. The division of the deformable and central fixed parts of the cross-structure prevents deformation interference. Fused filament fabrication pre-programmed four-dimensional printing technology was used to control the deformable part transformation. The self-developed software performed the flattening, discretization, and optimization of the target surface to generate a printed plane model composed of a cross-structure. A self-developed slicing tool completed the printing process. The finite element simulation results of the sample model were consistent with those of the target surface. The experimental results of the model deformation confirmed the effectiveness and accuracy of the approach. The novel programming control strategy for printing arbitrarily complex 3D deformation systems exhibited high theoretical precision. Its universality promotes development of the shape-morphing system manufacturing field.

High-Order Photonic Cavity Modes Enabled 3D Structural Colors.

It remains a challenge to directly print arbitrary three-dimensional shapes that exhibit structural colors at the micrometer scale. Woodpile photonic crystals (WPCs) fabricated via two-photon lithography (TPL) are elementary building blocks to produce 3D geometries that generate structural colors due to their ability to exhibit either omnidirectional or anisotropic photonic stop bands. However, existing approaches produce structural colors on WPCs when illuminating from the top, requiring print resolutions beyond the limit of commercial TPL, which necessitates postprocessing techniques. Here, we devised a strategy to support high-order photonic cavity modes upon side illumination on WPCs that surprisingly generate prominent reflectance peaks in the visible spectrum. Based on that, we demonstrate one-step printing of 3D photonic structural colors without requiring postprocessing or subwavelength features. Vivid colors with reflectance peaks exhibiting a full width at half-maximum of ∼25 nm, a maximum reflectance of 50%, a gamut of ∼85% of sRGB, and large viewing angles were achieved. In addition, we also demonstrated voxel-level manipulation and control of colors in arbitrary-shaped 3D objects constituted with WPCs as unit cells, which has potential for applications in dynamic color displays, colorimetric sensing, anti-counterfeiting, and light-matter interaction platforms.

Bubble-based propulsion of engineered particles for drug delivery and immunotherapy

Biological barriers, such as mucus and cellular endothelia, obstruct the transport of drugs to diseased tissues. In this talk, I will highlight our recent work to overcome these barriers using engineering particles that undergo bubble-based propulsion in response to ultrasound. I will focus on two innovations. First, I will share our collaborative effort to synthesize hydrophobically modified mesoporous silica nanoparticles (MSNs) stabilized with phospholipids that entrap hydrophobic drugs. When insonated with high-intensity focused ultrasound, the MSNs undergo cavitation to rapidly propel through dense media and release drugs. Second, I will share our effort to fabricate microparticles with arbitrary three-dimensional shapes using two-photon lithography. These microparticles are capable of entrapping air bubbles of a defined size, leading to their efficient, frequency-dependent propulsion when stimulated by ultrasound. By modifying the surfaces of these particles, they can robustly attach to epithelial cell layers and release small molecule drugs for extended durations. By way of outlook, I will discuss how these technologies have potential to stimulate immune cells against tumor progression and to abate inflammation in auto-immune diseases.

Three-Dimensional Printing of Liquid Crystal Elastomers and Their Applications

Liquid crystal elastomers (LCEs), which are composed of liquid crystal mesogens and polymer networks, exhibit excellent actuation performance and tailorable energy dissipation behavior. They have shown great potential in practical applications in artificial muscles, soft robotics, and wearable devices. However, it is challenging to fabricate LCE samples in arbitrary three-dimensional (3D) shapes and desired alignment patterns with traditional manufacturing methods. Recently, 3D printing techniques have been introduced in combination with alignment methods of LCEs to meet this challenge. In this Review, we highlight recent advances in the 3D printing techniques of LCEs. Two kinds of printing techniques, materials extrusion and vat photopolymerization, are discussed in detail. We compare the differences and key parameters in the printing techniques, such as director fields, resolutions, and printing speeds. The applications of the printed LCE structures in soft robots, reconfigurable surfaces, and haptic devices are also introduced.

Optical Phenomena in Mesoscale Dielectric Particles

During the last decade, new unusual physical phenomena have been discovered in studying the optics of dielectric mesoscale particles of an arbitrary three-dimensional shape with the Mie size parameter near 10 (q~10). The paper provides a brief overview of these phenomena from optics to terahertz, plasmonic and acoustic ranges. The different particle configurations (isolated, regular or Janus) are discussed, and the possible applications of such mesoscale structures are briefly reviewed herein in relation to the field enhancement, nanoparticle manipulation and super-resolution imaging. The number of interesting applications indicates the appearance of a new promising scientific direction in optics, terahertz and acoustic ranges, and plasmonics. This paper presents the authors’ approach to these problems.

Slender phoretic theory of chemically active filaments

Artificial microswimmers, or ‘microbots’, have the potential to revolutionise non-invasive medicine and microfluidics. Microbots that are powered by self-phoretic mechanisms, such as Janus particles, often harness a solute fuel in their environment. Traditionally, self-phoretic particles are point like, but slender phoretic rods have become an increasingly prevalent design. While there has been substantial interest in creating efficient asymptotic theories for slender phoretic rods, hitherto such theories have been restricted to straight rods with axisymmetric patterning. However, modern manufacturing methods will soon allow fabrication of slender phoretic filaments with complex three-dimensional shapes. In this paper, we develop a slender body theory for the solute of self-diffusiophoretic filaments of arbitrary three-dimensional shape and patterning. We demonstrate analytically that, unlike other slender body theories, first-order azimuthal variations arising from curvature and confinement can make a leading-order contribution to the swimming kinematics.

Switchable DNA-origami nanostructures that respond to their environment and their applications.

Structural DNA nanotechnology, in which Watson-Crick base pairing drives the formation of self-assembling nanostructures, has rapidly expanded in complexity and functionality since its inception in 1981. DNA nanostructures can now be made in arbitrary three-dimensional shapes and used to scaffold many other functional molecules such as proteins, metallic nanoparticles, polymers, fluorescent dyes and small molecules. In parallel, the field of dynamic DNA nanotechnology has built DNA circuits, motors and switches. More recently, these two areas have begun to merge-to produce switchable DNA nanostructures, which change state in response to their environment. In this review, we summarise switchable DNA nanostructures into two major classes based on response type: molecular actuation triggered by local chemical changes such as pH or concentration and external actuation driven by light, electric or magnetic fields. While molecular actuation has been well explored, external actuation of DNA nanostructures is a relatively new area that allows for the remote control of nanoscale devices. We discuss recent applications for DNA nanostructures where switching is used to perform specific functions-such as opening a capsule to deliver a molecular payload to a target cell. We then discuss challenges and future directions towards achieving synthetic nanomachines with complexity on the level of the protein machinery in living cells.

A numerical method for axisymmetric adhesive contact based on kalker’s variational principle

A numerical method for axisymmetric adhesive contact of elastic bodies is proposed. It allows computing the size of the contact spot, the force of interaction as well as the contact pressure distribution unrestricted to any particular form of the initial gap between the bodies. Therefore, compared to the existing analytical theories, it is a more versatile research tool that can be used to study such phenomena as adhesive strength of conjugate bodies and stability loss induced energy dissipation in oscillating contact. A variational principle that can be used to construct an approximate solution is proposed. The derived nonlinear equations of the discretized mini-max problem determine the unknown radius of the circular contact spot and the nodal values of the thought-for contact pressure. Unlike other numerical methods where contact domain is updated by subtracting or adding separate boundary elements of finite size, the proposed approach enables gradual continuous variation of the contact area. The arc-length method was implemented in the numerical routine in order to solve for the unstable sections of the adhesive interaction process. Besides the distance and force variables, the increment of the contact area is included in the control for the sake of convergence. The numerical error of the approximate method with respect to the known analytical solutions is evaluated. Linear convergence with mesh refinement in computed force and contact area is observed. Extension of the proposed approach for arbitrary three-dimensional shape of the contacting bodies is planned for the future. This is required to study the impact of the random surface roughness on their adhesive properties.

Evaluation Method for Ship Hull Plates’ Process Molding

The evaluation procedure is an important step for the ship hull plates automatic processing, which serves as a basis for secondary processing. In this paper, an evaluation method was proposed, based on the experienced workers' knowledge. The design surface and the measured surface were registered by transforming to the new coordinate system. Then the profile errors were evaluated and decomposed into three directions: transverse, longitudinal, and torsional. Finally, the experiment results shown that the evaluation indexes, which were based on the errors decomposed result, can be served as the basis for secondary processing of the ship hull plates. 1. Introduction Ship hull plates are thick large steel plates with arbitrary threedimensional (3D) shapes. Usually, the steel plates are plastically deformed to the design shape by line heating process. And the shapes of the machining plates are evaluated by the wooden bending templates, which are generated by ship's design data. Experienced workers can evaluate the transverse bending, longitudinal bending, as well as torsional angle of the plates by this process, and get the essential factual basis for the secondary processing. However, this process has no clear-cut methodology, the evaluation results and the secondary processing plan are heavy, depending on the tacit knowledge, skill, and experience of the craftsmen during the line heating processing (Woo-Jae et al. 2010; Hiekata et al. 2011; Seong et al. 2013; Sun et al. 2013). For ship hull plates profile error evaluation, Hiekata et al. (2011) had put forward an accuracy evaluation system, using 3D laser scanner to measure the ship hull plates, and then evaluated the displacement errors by comparing the measured surface with the design surface. This system had achieved digital evaluation, but the evaluation indexes were difficult to guide the secondary processing. Sun et al. (2013) evaluated the ship hull plates by the virtual templates, and generated the processing plan, according to the evaluation results. Nevertheless, this method only evaluates the longitudinal bending and torsional condition. it still needs to be improved. Also, other researchers (Wen et al. 2013; Liu 2014; He et al. 2015; Nasri et al. 2015) had put forward various evaluation methods, but the purposed methods were aimed to improve the evaluation accuracy, seldom consider the line heating process. Thus, these methods have failed to provide the factual basis for the secondary processing.

DNA origami: The bridge from bottom to top

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Selective laser melting of aluminum alloys

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Recent Strategies in Osteochondral Substitutes Design: Towards the Mimicking of a Multifaceted Anatomical Unit from the Nano to the Macro Level

Nowadays regenerative medicine takes advantages not only of traditional implants, but also of engineered biocompatible parts, including degradable porous scaffolds integrated with cells or molecules. These approaches, positioned at the interdisciplinary area between biomedical materials science and medicine, will become more achievable when combined with biomimicry, which not only optimizes biomaterial interaction with biological tissues but also mimics biogenic materials in their structure and functionalities. Such methodologies are particularly attractive for bone and osteochondral related materials: in other words, cartilage and mineralized tissues are ideal example to learn-from in setting up biomaterial science researches. These tissues are highly integrated systems, having found a compromise between different properties and functions, above all thanks to their hierarchical structure. Hard tissues display order on multiple lengths scale, from the nano to the macro level, whereas osteochondral tissue in particular exhibits an inherent gradient structure. Bearing this in mind, bone and osteochondral scaffold design must enable hierarchical composites porous structures to attain desired mechanical function and mass transport, for example, permeability and diffusion, and to produce these structures within arbitrary and complex three-dimensional (3D) anatomical shapes. In this context, this review will supply a hint of the strategies for biomimetic orthopaedic substitutes, actualizing the role of biomimicry, materials chemistry and process engineering in projecting and fabricating custom-made scaffolds.

Free-form Light Actuators — Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers' attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge. In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Free-form Light Actuators - Fabrication and Control of Actuation in Microscopic Scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers' attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Mutual inductance between piecewise-linear loops

We consider a current-carrying wire loop made out of linear segments of arbitrary sizes and directions in three-dimensional space. We develop expressions to calculate its vector potential and magnetic field at all points in space. We then calculate the mutual inductance between two such (non-intersecting) piecewise-linear loops. As simple applications, we consider in detail the mutual inductance between two square wires of equal length that either lie in the same plane or lie in parallel horizontal planes with their centers on the same vertical axis. Our expressions can also be used to obtain approximations to the mutual inductance between wires of arbitrary three-dimensional shapes.

Robust Superhydrophilic/Hydrophobic Surface Based on Self-Aggregated Al2O3 Nanowires by Single-Step Anodization and Self-Assembly Method

Superhydrophilic and superhydrophobic surfaces were studied with an eye to industrial applications and use as research tools. Conventional methods involve complex and time-consuming processes and cannot feasibly produce large-area three-dimensional surfaces. Here, we report robust and large-area alumina nanowire structures with superhydrophobic or superhydrophilic properties, generated by an inexpensive single-step anodization process that can routinely create arbitrary three-dimensional shapes. This process is expected to open up diverse applications.

Planar and non-planar solidification of optically organised smectic films

This letter describes an original freezing process that yields homogeneous solid films at ambient temperature with preservation of the layered structure of the chiral smectic phase. One of the most remarkable features of the process is its ability to provide complexly bent films with arbitrary three-dimensional shapes. Their optical homogeneity is observed in the planar as well as in the bent films. The method is very simple. After forming the films by spreading the liquid crystal above a hole in a glass slice placed over a hot stage, the film is heated from below. The hot film is exposed to ambient temperature. Then, a solid object at room temperature with a specifically adapted shape is immersed in the liquid film. The mechanical constraints imposed by the object curves the film and stabilises various solid two- and three-dimensional structures. Their homogeneous optical properties are due to long-range organisation of the molecular orientation (tilt), which combines with a complex helical arrangement of the frozen smectic layers.

A Robust Method to Accurately Treat Arbitrarily Curved 3-D Thin Conductive Sheets in FDTD

In this paper, we propose a novel method to treat thin conductive (TC) sheets of arbitrary three-dimensional (3-D) shape and curvature with the electromagnetic (EM) finite-difference time-domain (FDTD) algorithm without the need to resolve the sheet thickness spatially. We show that the physical properties of TC sheets enable us to do so without introducing additional field components to the conventional Yee scheme. Due to this noninvasive approach, in addition to the preserved stability of the FDTD algorithm, the method can be directly applied to any existing FDTD kernel, such as parallelized or hardware accelerated versions. The method has been developed within the framework of a professional EM FDTD software package and tested on real-world problems.