Forming electrical networks in three dimensions by self-assembly

A repertoire of nanoengineered short peptide-based hydrogels and their applications in biotechnology

Peptide nanotechnology has currently bridged the gap between materials and biological worlds. Bioinspired self-assembly of short-peptide building blocks helps take the leap from molecules to materials by taking inspiration from nature. Owing to their intrinsic biocompatibility, high water content, and extracellular matrix mimicking fibrous morphology, hydrogels engineered from the self-assembly of short peptides exemplify the actualization of peptide nanotechnology into biomedical products. However, the weak mechanical property of these hydrogels jeopardizes their practical applications. Moreover, their functional diversity is limited since they comprise only one building block. Nanoengineering the networks of these hydrogels by incorporating small molecules, polymers, and inorganic/carbon nanomaterials can augment the mechanical properties while retaining their dynamic supramolecular nature. These additives interact with the peptide building blocks supramolecularly and may enhance the branching of the networks via coassembly or crystallographic mismatch. This phenomenon expands the functional diversity of these hydrogels by synergistically combining the attributes of the individual building blocks. This review highlights such nanoengineered peptide hydrogels and their applications in biotechnology. We have included exemplary works on supramolecular modification of the peptide hydrogel networks by integrating other small molecules, synthetic/biopolymers, conductive polymers, and inorganic/carbon nanomaterials and shed light on their various utilities focusing on biotechnology. We finally envision some future prospects in this highly active field of research.

Microelectronic Morphogenesis: Smart Materials with Electronics Assembling into Artificial Organisms

Microelectronic morphogenesis is the creation and maintenance of complex functional structures by microelectronic information within shape-changing materials. Only recently has in-built information technology begun to be used to reshape materials and their functions in three dimensions to form smart microdevices and microrobots. Electronic information that controls morphology is inheritable like its biological counterpart, genetic information, and is set to open new vistas of technology leading to artificial organisms when coupled with modular design and self-assembly that can make reversible microscopic electrical connections. Three core capabilities of cells in organisms, self-maintenance (homeostatic metabolism utilizing free energy), self-containment (distinguishing self from nonself), and self-reproduction (cell division with inherited properties), once well out of reach for technology, are now within the grasp of information-directed materials. Construction-aware electronics can be used to proof-read and initiate game-changing error correction in microelectronic self-assembly. Furthermore, noncontact communication and electronically supported learning enable one to implement guided self-assembly and enhance functionality. Here, the fundamental breakthroughs that have opened the pathway to this prospective path are reviewed, the extent and way in which the core properties of life can be addressed are analyzed, and the potential and indeed necessity of such technology for sustainable high technology in society is discussed.

Control of charge transport in electronically active systems towards integrated biomolecular circuits (IbC)

The miniaturization of traditional silicon-based electronics will soon reach its limitation as quantum tunneling and heat become serious problems at the several-nanometer scale. Crafting integrated circuits via self-assembly of electronically active molecules using a "bottom-up" paradigm provides a potential solution to these technological challenges. In particular, integrated biomolecular circuits (IbC) offer promising advantages to achieve this goal, as nature offers countless examples of functionalities entailed by self-assembly and examples of controlling charge transport at the molecular level within the self-assembled structures. To this end, the review summarizes the progress in understanding how charge transport is regulated in biosystems and the key redox-active amino acids that enable the charge transport. In addition, charge transport mechanisms at different length scales are also reviewed, offering key insights for controlling charge transport in IbC in the future.

Colloidal robotics

Robots have components that work together to accomplish a task. Colloids are particles, usually less than 100 µm, that are small enough that they do not settle out of solution. Colloidal robots are particles capable of functions such as sensing, computation, communication, locomotion and energy management that are all controlled by the particle itself. Their design and synthesis is an emerging area of interdisciplinary research drawing from materials science, colloid science, self-assembly, robophysics and control theory. Many colloidal robot systems approach synthetic versions of biological cells in autonomy and may find ultimate utility in bringing these specialized functions to previously inaccessible locations. This Perspective examines the emerging literature and highlights certain design principles and strategies towards the realization of colloidal robots.

Heterogeneous Self-Assembly of a Single Type of Nanoparticle Modulated by Skin Formation

Self-assembly of colloidal nanoparticles has generated tremendous interest due to its widespread applications in structural colorations, sensors, and optoelectronics. Despite numerous strategies being developed to fabricate sophisticated structures, the heterogeneous self-assembly of a single type of nanoparticle in one step remains challenging. Here, facilitated by spatial confinement induced by a skin layer in a drying droplet, we achieve the heterogeneous self-assembly of a single type of nanoparticle by quickly evaporating a colloid-poly (ethylene glycol) (PEG) droplet. During the drying process, a skin layer forms at the droplet surface. The resultant spatial confinement assembles nanoparticles into face-centered-cubic (FCC) lattices with (111) and (100) plane orientations, generating binary bandgaps and two structural colors. The self-assembly of nanoparticles can be regulated by varying the PEG concentration so that FCC lattices with homo- or heterogeneous orientation planes can be prepared on demand. Besides, the approach is applicable for diverse droplet shapes, various substrates, and different nanoparticles. The one-pot general strategy breaks the requirements for multiple types of building blocks and predesigned substrates, extending the fundamental understanding underlying colloidal self-assembly.

Multiple configuration transitions of soft actuators under single external stimulus

Soft actuators have a wide range of applications in medical instruments, soft robotics, 3D electronics, and deployable structures, where configuration transitions are crucial for their function realization. However, most soft actuators can only morph from the initial configuration directly to the final configuration under a single external stimulus. Herein, we report a novel soft actuator by 3D printing parallel strips with crescent cross-sections onto a thin PDMS film. Multiple configuration transitions are observed when the soft actuator swells in ethyl acetate. Four factors, i.e., the geometric asymmetry of the strips, the fabrication-induced heterogeneity of the film, the differential swelling ratios of the strips and the film, and the geometric parameters of the actuator, are demonstrated to synergistically regulate the multiple configuration transitions of the actuator. Particularly, the underlying mechanisms for the configuration transitions are systematically investigated through experiments and theoretical analysis, and verified via finite element simulation. Benefitting from the multiple configuration transitions, the grasp-release-re-grab function of the actuator is demonstrated under a single stimulus. This work contributes to fundamental understanding of the morphing behaviors and the novel design of soft actuators.

Transparent and self-healing elastomers for reconfigurable 3D materials

Transparent soft materials have been widely used in applications ranging from packaging to flexible displays, wearable devices, and optical lenses. Nevertheless, soft materials are susceptible to mechanical damages, leading to functional failure and premature disposal. Herein, we introduce a transparent self-healing elastomer that is able to repair the polymer network via exchange reactions of dynamic disulfide bonds. Due to its self-healing ability, the mechanical properties of the elastomer can be recovered, as well as its transparency after multiple cycles of abrasion and healing. The self-healing polymer is fabricated into three-dimensional (3D) structures by folding or modular origami assembly of planar self-healing polymer sheets. The 3D polymer objects are employed as storage containers of solid and liquid substances, reactors for photopolymerization, and cuvettes for optical measurements (exhibiting superior properties to those of commercial cuvettes). These dynamic polymers show outstanding mechanical, optical, and recycling properties that could potentially be further adapted in adaptive smart packaging, reconfigurable materials, optical devices, and recycling of elastomers. This article is protected by copyright. All rights reserved.

Diversified applications of self-assembled nanocluster delivery systems- A state-of-the- art review

BACKGROUND

Self-assembled nanoclusters arrange the components into an organized structure for the nanoparticulate system and also in the transportation of cellular elements for the fabrication of microelectronic devices. Nanoclusters reduce transcytosis and increase endocytosis in intestinal mucin to strengthen the retrograde pathway that helped in the delivery of actives to the Golgi apparatus.

OBJECTIVES

This review article focuses on the self-assembled nanoclusters for cellular transportation, applications of self-assembled structures in the delivery of essential elements like the use of a peptide in targeted and stimuli-responsive drug delivery systems, self-assembly of tocopherol nanoclusters that promotes vitamin E delivery across the endothelial barrier. Methods Current innovation in the self-assembly of peptides includes the formation of nanostructures like vesicles, fibers, and rod-coil in the applications of wound healing, tissue engineering, treatment of atherosclerosis, in sensing heavy metals from biological and environmental samples and advanced drug delivery.

RESULTS

Self-assembled biodegradable nanoclusters are used as biomimetic structures for synergistic effect. Improvement in the methods of preparation like the addition of a copolymer is used for temperature-triggered drug release nanoclusters.

CONCLUSION

Green synthesis of nanoclusters, nanocluster-based biosensor and artificial intelligence are the future concept in the manufacturing and the prevention of toxicity in humans.

Plasmonic 3D Self-Folding Architectures via Vacuum Microforming

3D self-folding microarchitectures have been studied enormously since the past decade, because of the potential of utilizing the third dimension to reach a new level of device integration. However, incorporating various functionalities is a great challenge, due to the limited folding force and choice of materials. In particular, self-folding microarchitectures with advanced optical properties have yet to be demonstrated. Here, a unique folding technique is developed, namely vacuum microforming, successfully demonstrating the self-folding of microcubes that can be completed within 30 ms, a few orders of magnitudes faster as compared to various established strategies reported so far. Simultaneously, a metal-insulator-metal (MIM) plasmonic nanostructure is fabricated, invoking strong gap plasmon to obtain a wide and robust angle-independent optical behavior and high environmental sensitivity that is close to the theoretical limit. It is successfully proven that such superb plasmonic properties are well preserved in 3D architectures throughout the folding process. The nanofabrication method together with the self-folding strategy not only provide the fastest folding process so far, compatible for high-volume fabrication, but also create new opportunities in integrating various functionalities, more specifically, optical properties for untethered optical sensing and identification.

Remote Modular Electronics for Wireless Magnetic Devices

Small-scale wireless magnetic robots and devices offer an effective solution to operations in hard-to-reach and high-risk enclosed places, such as inside the human body, nuclear plants, and vehicle infrastructure. In order to obtain functionalities beyond the capability of magnetic forces and torques exerted on magnetic materials used in these robotic devices, electronics need to be also integrated into them. However, their capabilities and power sources are still very limited compared to their larger-scale counterparts due to their much smaller sizes. Here, groups of milli/centimeter-scale wireless magnetic modules are shown to enable on-site electronic circuit construction and operation of highly demanding wireless electrical devices with no batteries, that is, with wireless power. Moreover, the mobility of the modular components brings remote modification and reconfiguration capabilities. When these small-scale robotic modules are remotely assembled into specific geometries, they can achieve, if not impossible, challenging electrical tasks for individual modules. Using such a method, several wireless and battery-free robotic devices are demonstrated using milli/centimeter-scale robotic modules, such as a wireless circuit to power light-emitting diodes with lower external fields, a device to actuate relatively high force-output shape memory alloy actuators, and a wireless force sensor, all of which can be modified on-site.

Precise macroscopic supramolecular assembly of photopatterned hydrogels

Here we demonstrate that a precise macroscopic supramolecular assembly (MSA) can be achieved using a surface photopatterning strategy. The electrostatic interaction of the photopatterned polyelectrolytes drives hydrogel cuboids to form a stable MSA on a millimeter scale and the spatial controllability of light enables the hydrogels to be assembled into complex supramolecular architectures.

Self-assembly of millimeter-scale magnetic particles in suspension

Self-assembly is ubiquitous at all scales in nature. Most studies have focused on the self-assembly of micron-scale and nano-scale components. In this study, we explore the self-assembly of millimeter-scale magnetic particles in a bubble-column reactor to form 9 different structures. Two component systems (N-N and S-S particles) assemble faster than one-component systems (all particles have N-S poles) because they have more numerous bonding pathways. In addition, two-components add control to process initiation and evolution, and enable the formation of complex structures such as squares, tetrahedra and cubes. Self-assembly is collision-limited, thus, the formation time increases with the total number of bonds required to form the structure and the injected power. The dimensionless Mason number captures the interplay between hydrodynamic forces and magnetic interactions: self-assembly is most efficient at intermediate Mason numbers (the system is quasi-static at low Mason numbers with limited chances for particle interaction; on the other hand, hydrodynamic forces prevail over dipole-dipole interactions and hinder bonding at high Mason numbers). Two strategies to improve yield involve (1) the inclusion of pre-assembled nucleation templates to prevent the formation of incorrect initial structures that lead to kinetic traps, and (2) the presence of boundaries to geometrically filter unwanted configurations and to overcome kinetic traps through particle-wall collisions. Yield maximization involves system operation at an optimal Mason number, the inclusion of nucleation templates and the use of engineered boundaries (size and shape).

Reconfigurable Magnetic Origami Actuators with On-Board Sensing for Guided Assembly

Origami utilizes orchestrated transformation of soft 2D structures into complex 3D architectures, mimicking shapes and functions found in nature. In contrast to origami in nature, synthetic origami lacks the ability to monitor the environment and correspondingly adjust its behavior. Here, magnetic origami actuators with capabilities to sense their orientation and displacement as well as detect their own magnetization state and readiness for supervised folding are designed, fabricated, and demonstrated. These origami actuators integrate photothermal heating and magnetic actuation by using composite thin films (≈60 µm thick) of shape-memory polymers with embedded magnetic NdFeB microparticles. Mechanically compliant magnetic field sensors, known as magnetosensitive electronic skins, are laminated on the surface of the soft actuators. These ultrathin actuators accomplish sequential folding and recovery, with hinge locations programmed on the fly. Endowing mechanically active smart materials with cognition is an important step toward realizing intelligent, stimuli-responsive structures.

Quick self-assembly of bio-inspired multi-dimensional well-ordered structures induced by ultrasonic wave energy

Bottom-up self-assembly of components, inspired by hierarchically self-regulating aggregation of small subunits observed in nature, provides a strategy for constructing two- or three-dimensional intriguing biomimetic materials via the spontaneous combination of discrete building blocks. Herein, we report the methods of ultrasonic wave energy-assisted, fast, two- and three-dimensional mesoscale well-ordered self-assembly of microfabricated building blocks (100 μm in size). Mechanical vibration energy-driven self-assembly of microplatelets at the water-air interface of inverted water droplets is demonstrated, and the real-time formation process of the patterned structure is dynamically explored. 40 kHz ultrasonic wave is transferred into microplatelets suspended in a water environment to drive the self-assembly of predesigned well-ordered structures. Two-dimensional self-assembly of microplatelets inside the water phase with a large patterned area is achieved. Stable three-dimensional multi-layered self-assembled structures are quickly formed at the air-water interface. These demonstrations aim to open distinctive and effective ways for new two-dimensional surface coating technology with autonomous organization strategy, and three-dimensional complex hierarchical architectures built by the bottom-up method and commonly found in nature (such as nacre, bone or enamel, etc.).

Rotary-actuated folding polyhedrons for midwater investigation of delicate marine organisms

Self-folding polyhedra have emerged as a viable design strategy for a wide range of applications, with advances largely made through modeling and experimentation at the micro- and millimeter scale. Translating these concepts to larger scales for practical purposes is an obvious next step; however, the size, weight, and method of actuation present a new set of problems to overcome. We have developed large-scale folding polyhedra to rapidly and noninvasively enclose marine organisms in the water column. The design is based on an axisymmetric dodecahedron net that is folded by an external assembly linkage. Requiring only a single rotary actuator to fold, the device is suited for remote operation onboard underwater vehicles and has been field-tested to encapsulate a variety of delicate deep-sea organisms. Our work validates the use of self-folding polyhedra for marine biological applications that require minimal actuation to achieve complex motion. The device was tested to 700 m, but the system was designed to withstand full ocean depth (11 km) pressures. We envision broader terrestrial applications of rotary-actuated folding polyhedra, ranging from large-scale deployable habitats and satellite solar arrays to small-scale functional origami microelectromechanical systems.

Exploiting Colloidal Metamaterials for Achieving Unnatural Optical Refractions

The scaling down of meta-atoms or metamolecules (collectively denoted as metaunits) is a long-lasting issue from the time when the concept of metamaterials was first suggested. According to the effective medium theory, which is the foundational concept of metamaterials, the structural sizes of meta-units should be much smaller than the working wavelengths (e.g., << 1/5 wavelength). At relatively low frequency regimes (e.g., microwave and terahertz), the conventional monolithic lithography can readily address the materialization of metamaterials. However, it is still challenging to fabricate optical metamaterials (metamaterials working at optical frequencies such as the visible and near-infrared regimes) through the lithographic approaches. This serves as the rationale for using colloidal self-assembly as a strategy for the realization of optical metamaterials. Colloidal self-assembly can address various critical issues associated with the materialization of optical metamaterials, such as achieving nanogaps over a large area, increasing true 3D structural complexities, and cost-effective processing, which all are difficult to attain through monolithic lithography. Nevertheless, colloidal self-assembly is still a toolset underutilized by optical engineers. Here, the design principle of the colloidally self-assembled optical metamaterials exhibiting unnatural refractions, the practical challenge of relevant experiments, and the future opportunities are critically reviewed.

Electron Irradiation Driven Nanohands for Sequential Origami

Sequence plays an important role in self-assembly of 3D complex structures, particularly for those with overlap, intersection, and asymmetry. However, it remains challenging to program the sequence of self-assembly, resulting in geometric and topological constrains. In this work, a nanoscale, programmable, self-assembly technique is reported, which uses electron irradiation as "hands" to manipulate the motion of nanostructures with the desired order. By assigning each single assembly step in a particular order, localized motion can be selectively triggered with perfect timing, making a component accurately integrate into the complex 3D structure without disturbing other parts of the assembly process. The features of localized motion, real-time monitoring, and surface patterning open the possibility for the further innovation of nanomachines, nanoscale test platforms, and advanced optical devices.

Magnetic levitational bioassembly of 3D tissue construct in space

Magnetic levitational bioassembly of three-dimensional (3D) tissue constructs represents a rapidly emerging scaffold- and label-free approach and alternative conceptual advance in tissue engineering. The magnetic bioassembler has been designed, developed, and certified for life space research. To the best of our knowledge, 3D tissue constructs have been biofabricated for the first time in space under microgravity from tissue spheroids consisting of human chondrocytes. Bioassembly and sequential tissue spheroid fusion presented a good agreement with developed predictive mathematical models and computer simulations. Tissue constructs demonstrated good viability and advanced stages of tissue spheroid fusion process. Thus, our data strongly suggest that scaffold-free formative biofabrication using magnetic fields is a feasible alternative to traditional scaffold-based approaches, hinting a new perspective avenue of research that could significantly advance tissue engineering. Magnetic levitational bioassembly in space can also advance space life science and space regenerative medicine.

Three-dimensional self-assembly using dipolar interaction

Interaction between dipolar forces, such as permanent magnets, generally leads to the formation of one-dimensional chains and rings. We investigated whether it was possible to let dipoles self-assemble into three-dimensional structures by encapsulating them in a shell with a specific shape. We found that the condition for self-assembly of a three-dimensional crystal is satisfied when the energies of dipoles in the parallel and antiparallel states are equal. Our experiments show that the most regular structures are formed using cylinders and cuboids and not by spheroids. This simple design rule will help the self-assembly community to realize three-dimensional crystals from objects in the micrometer range, which opens up the way toward previously unknown metamaterials.

3D Self-Assembled Microelectronic Devices: Concepts, Materials, Applications

Modern microelectronic systems and their components are essentially 3D devices that have become smaller and lighter in order to improve performance and reduce costs. To maintain this trend, novel materials and technologies are required that provide more structural freedom in 3D over conventional microelectronics, as well as easier parallel fabrication routes while maintaining compatability with existing manufacturing methods. Self-assembly of initially planar membranes into complex 3D architectures offers a wealth of opportunities to accommodate thin-film microelectronic functionalities in devices and systems possessing improved performance and higher integration density. Existing work in this field, with a focus on components constructed from 3D self-assembly, is reviewed, and an outlook on their application potential in tomorrow's microelectronics world is provided.

Coordinated behaviors of artificial micro/nanomachines: from mutual interactions to interactions with the environment

The interactions leading to coordinated behaviors of artificial micro/nanomachines are reviewed.

Dynamic Assembly of Small Parts in Vortex-Vortex Traps Established within a Rotating Fluid

Stable, purely fluidic particle traps established by vortex flows induced within a rotating fluid are described. The traps can manipulate various types of small parts, dynamically assembling them into high-symmetry clusters, cages, interlocked architectures, jammed colloidal monoliths, or colloidal formations on gas bubbles. The strength and the shape of the trapping region can be controlled by the strengths of one or both vortices and/or by the system's global angular velocity. The system exhibits a range of interesting dynamical behaviors including a Hopf-bifurcation transition between equilibrium-point trapping and the so-called limit cycle in which the particles are confined to circular orbits. Theoretical considerations indicate that these vortex-vortex traps can be further miniaturized to manipulate objects with sizes down to ≈10 µm.

Catalytic self-folding of 2D structures through cascading magnet reactions

While thousands of proteins involved in development of the human body are capable of self-assembling in a distributed manner from merely 20 types of amino acid, macroscopic products that can be assembled spontaneously from 'alive' components remains an aspiration in engineering. To attain such a mechanism, a major challenge lies in understanding which attributes from the bio-molecular realm must be leveraged at the macro-scale. Inspired by protein folding, we present a centimetre-size 1D tile chain whose self-folding processes are directed by structure-embedded magnetic interactions, which can theoretically self-assemble into convex 2D structures of any size or shape without the aid of a global 'controller'. Each tile holds two magnets contained in paths designed to control their interactions. Once initiated by a magnetic unit (termed Catalyst), the chain self-reconfigures by consuming magnetic potential energy stored between magnet pairs, until the final 2D structure is reached at an energetic minimum. Both simulation and experimental results are presented to illustrate the method's efficacy on chains of arbitrary length. Results demonstrate the promise of a physically implemented, bottom-up, and scalable self-assembly method for novel 2D structure manufacturing, bridging the bio-molecular and mechanical realms.

Mimicking the Structure and Function of Ant Bridges in a Reconfigurable Microswarm for Electronic Applications

In nature, social insects are capable of self-organizing into various sophisticated and functional structures through local communications, which facilitate their cooperative accomplishment of complex tasks that are beyond the capabilities of individuals. Emulating this collective behavior in artificial robotic systems promises benefits in various engineering fields and has been partially realized through elaborate algorithm and physical designs. However, developing a swarm robotic system with group-level functionality at small scales remains a challenge. Herein, a microswarm system that mimics the structure and function of an ant bridge is realized by employing functionalized magnetite nanoparticles, which are paramagnetic and electrically conductive, as the building blocks. Through the application of a programmed oscillating magnetic field, the building blocks are reconfigured into a ribbon-like microswarm, which can perform reversible elongation with a high aspect ratio and, thus, is capable of constructing a conductive pathway for electrons between two disconnected electrodes with the bodies of functionalized nanoparticles. Furthermore, the microswarm is demonstrated to serve as a microswitch, repair broken microcircuits, and constitute flexible circuits, exhibiting a promising future for the practical applications in the electronics field.

Quick liquid packaging: Encasing water silhouettes by three-dimensional polymer membranes

One of the most important substances on Earth is water. It is an essential medium for living microorganisms and for many technological and industrial processes. Confining water in an enclosed compartment without manipulating it or by using rigid containers can be very attractive, even more if the container is biocompatible and biodegradable. Here, we propose a water-based bottom-up approach for facile encasing of short-lived water silhouettes by a custom-made adaptive suit. A biocompatible polymer self-assembling with unprecedented degree of freedom over the water surface directly produces a thin membrane. The polymer film could be the external container of a liquid core or a free-standing layer with personalized design. The membranes produced have been characterized in terms of physical properties, morphology and proposed for various applications from nano- to macroscale. The process appears not to harm cells and microorganisms, opening the way to a breakthrough approach for organ-on-chip and lab-in-a-drop experiments.

Biogenic synthesis and characterization of silver nanoparticles using aqueous leaf extract of Scoparia dulcis L. and assessment of their antimicrobial property

Naturally occurring phytochemicals serve as an excellent substitute in synthesizing nanomaterials. A process for the synthesis of silver nanoparticles (AgNPs) from the aqueous leaf extract of naturally occurring Scoparia dulcis is described here. The extracellular formation of AgNPs occurred within few minutes upon incubation of S. dulcis aqueous leaf extract (0.1 mL) (100% extract) with silver nitrate (2 mM AgNO₃) at 90 °C for 30 min, is first of its kind work. The appearance of bright yellow color with λ_max 420 nm confirm the formation of AgNPs. Zeta potential and X-ray diffraction (XRD) studies reveal stable AgNPs (-22.7 mV) and characteristic spectra for silver. Fourier transform infrared (FTIR) spectroscopy indicate the involvement of carboxyl, amine and hydroxyl groups in the synthetic process. Transmission electron microscopy (TEM) show the spherical nature of AgNPs measuring 3-18 nm in size. Additional characterization using Dynamic light scattering (DLS) revealed the average particle size distribution of AgNPs as around 8.2 nm. Further antimicrobial testing through agar disc diffusion plate method indicated that silver nanoparticles are potentially active against pathogenic bacteria such as Pseudomonas aeruginosa, Escherichia coli, Bacillus subtilis and Staphylococcus aureus and are only optimally active against fungi such as Aspergillus niger and Candida albicans and measurement of minimal inhibition concentration by standard microdilution method. In conclusion, the study suggests that successful synthesis of green nanoparticles (AgNPs) using aqueous S. dulcis leaf extract is simple, rapid, environmentally benign and economical. Moreover, these synthesized silver nanoparticles showed antimicrobial activity.

Versatile Hydrogel Ensembles with Macroscopic Multidimensions

Methods allowing construction of macroscopic programmed materials in a flexible and efficient fashion are highly desirable. However, the existing approaches are far removed from such materials. A new self-healing-driven assembly (SHDA) strategy to fabricate various programmed materials by using uniform gel beads (microsize of 212 µm or millimeter size of 4 mm) as building blocks is described here. In virtue of hydrogen bonds and host-guest interactions between gel beads, a series of linear, planar, and 3D beaded assemblies are fabricated via SHDA in microfluidic channels in a continuous and controlled manner. From the perspective of practical applications, the use of gel assemblies is exploited for tissue engineering with controlled cells coculture, as well as light conversion materials toward white-light-emitting diodes (WLEDs). The SHDA strategy developed in this study gives a new insight into the facile and rapid fabrication of various programmed materials toward biological tissue and optoelectronic device.

Shell buckling: from morphogenesis of soft matter to prospective applications

Being one of the commonest deformation modes for soft matter, shell buckling is the primary reason for the growth and nastic movement of many plants, as well as the formation of complex natural morphology. On-demand regulation of buckling-induced deformation associated with wrinkling, ruffling, folding, creasing and delaminating has profound implications for diverse scopes, which can be seen in its broad applications in microfabrication, 4D printing, actuator and drug delivery. This paper reviews the recent remarkable developments in the shell buckling of soft matter to explain the most representative natural morphogenesis from the perspectives of theoretical analysis in continuum mechanics, finite element analysis, and experimental validations. Imitation of buckling-induced shape transformation and its applications are also discussed for the innovations of sophisticated materials and devices in future.

Constructing a Multiplexed DNA Pattern by Combining Precise Magnetic Manipulation and DNA-Driven Assembly

There is an urgent demand to construct multiplexed biomolecular patterns to obtain more biological information from a single experiment. However, with only limited reports focusing on defective top-down approaches, challenges remain to develop a bottom-up strategy for multiplexed patterning. To this end, a novel strategy has been proposed to fabricate multiplexed DNA patterns via macroscopic assembly through combined precise magnetic manipulation and DNA hybridization-driven self-assembly. Therefore, a multiplexed DNA pattern composed of glass fibers loaded with multiple specific strands of DNA was constructed, and its potential application in simultaneous detection of multiplex target DNA was demonstrated. Moreover, the fabricated multiplexed DNA pattern shows an erasable behavior because the hybridized DNA can be disassembled by strand displacement.

Magnetically Guided Self-Assembly and Coding of 3D Living Architectures

In nature, cells self-assemble at the microscale into complex functional configurations. This mechanism is increasingly exploited to assemble biofidelic biological systems in vitro. However, precise coding of 3D multicellular living materials is challenging due to their architectural complexity and spatiotemporal heterogeneity. Therefore, there is an unmet need for an effective assembly method with deterministic control on the biomanufacturing of functional living systems, which can be used to model physiological and pathological behavior. Here, a universal system is presented for 3D assembly and coding of cells into complex living architectures. In this system, a gadolinium-based nonionic paramagnetic agent is used in conjunction with magnetic fields to levitate and assemble cells. Thus, living materials are fabricated with controlled geometry and organization and imaged in situ in real time, preserving viability and functional properties. The developed method provides an innovative direction to monitor and guide the reconfigurability of living materials temporally and spatially in 3D, which can enable the study of transient biological mechanisms. This platform offers broad applications in numerous fields, such as 3D bioprinting and bottom-up tissue engineering, as well as drug discovery, developmental biology, neuroscience, and cancer research.

Laser-Assisted Mist Capillary Self-Alignment

This paper reports a method combining laser die transfer and mist capillary self-alignment. The laser die transfer technique is employed to feed selected microchips from a thermal release tape onto a receiving substrate and mist capillary self-alignment is applied to align the microchips to the predefined receptor sites on the substrate in high-accuracy. The parameters for a low-power laser die transfer process have been investigated and experimentally optimized. The acting forces during the mist-induced capillary self-alignment process have been analyzed and the critical volume enabling capillary self-alignment has been estimated theoretically and experimentally. We have demonstrated that microchips can be transferred onto receptor sites in 300⁻400 ms using a low-power laser (100 mW), and chips can self-align to the corresponding receptor sites in parallel with alignment accuracy of 1.4 ± 0.8 μm. The proposed technique has great potential in high-throughput and high-accuracy assembly of micro devices. This paper is extended from an early conference paper (MARSS 2017).

Reversible Self-Assembly of 3D Architectures Actuated by Responsive Polymers

An assembly of three-dimensional (3D) architectures with defined configurations has important applications in broad areas. Among various approaches of constructing 3D structures, a stress-driven assembly provides the capabilities of creating 3D architectures in a broad range of functional materials with unique merits. However, 3D architectures built via previous methods are simple, irreversible, or not free-standing. Furthermore, the substrates employed for the assembly remain flat, thus not involved as parts of the final 3D architectures. Herein, we report a reversible self-assembly of various free-standing 3D architectures actuated by the self-folding of smart polymer substrates with programmed geometries. The strategically designed polymer substrates can respond to external stimuli, such as organic solvents, to initiate the 3D assembly process and subsequently become the parts of the final 3D architectures. The self-assembly process is highly controllable via origami and kirigami designs patterned by direct laser writing. Self-assembled geometries include 3D architectures such as "flower", "rainbow", "sunglasses", "box", "pyramid", "grating", and "armchair". The reported self-assembly also shows wide applicability to various materials including epoxy, polyimide, laser-induced graphene, and metal films. The device examples include 3D architectures integrated with a micro light-emitting diode and a flex sensor, indicting the potential applications in soft robotics, bioelectronics, microelectromechanical systems, and others.

Planning and Control for Microassembly of Structures Composed of Stress-Engineered MEMS Microrobots

We present control strategies that implement planar microassembly using groups of stress-engineered MEMS microrobots (MicroStressBots) controlled through a single global control signal. The global control signal couples the motion of the devices, causing the system to be highly underactuated. In order for the robots to assemble into arbitrary planar shapes despite the high degree of underactuation, it is desirable that each robot be independently maneuverable (independently controllable). To achieve independent control, we fabricated robots that behave (move) differently from one another in response to the same global control signal. We harnessed this differentiation to develop assembly control strategies, where the assembly goal is a desired geometric shape that can be obtained by connecting the chassis of individual robots. We derived and experimentally tested assembly plans that command some of the robots to make progress toward the goal, while other robots are constrained to remain in small circular trajectories (closed-loop orbits) until it is their turn to move into the goal shape. Our control strategies were tested on systems of fabricated MicroStressBots. The robots are 240-280 μm × 60 μm × 7-20 μm in size and move simultaneously within a single operating environment. We demonstrated the feasibility of our control scheme by accurately assembling five different types of planar microstructures.

Programming 2D/3D shape-shifting with hobbyist 3D printers

Materials and devices with advanced functionalities often need to combine complex 3D shapes with functionality-inducing surface features. Precisely controlled bio-nanopatterns, printed electronic components, and sensors/actuators are all examples of such surface features. However, the vast majority of the refined technologies that are currently available for creating functional surface features work only on flat surfaces. Here we present initially flat constructs that upon triggering by high temperatures change their shape to a pre-programmed 3D shape, thereby enabling the combination of surface-related functionalities with complex 3D shapes. A number of shape-shifting materials have been proposed during the last few years based on various types of advanced technologies. The proposed techniques often require multiple fabrication steps and special materials, while being limited in terms of the 3D shapes they could achieve. The approach presented here is a single-step printing process that requires only a hobbyist 3D printer and inexpensive off-the-shelf materials. It also lends itself to a host of design strategies based on self-folding origami, instability-driven pop-up, and 'sequential' shape-shifting to unprecedentedly expand the space of achievable 3D shapes. This combination of simplicity and versatility is a key to widespread applications.

Yield prediction in parallel homogeneous assembly

We investigate the parallel assembly of two-dimensional, geometrically-closed modular target structures out of homogeneous sets of macroscopic components of varying anisotropy. The yield predicted by a chemical reaction network (CRN)-based model is quantitatively shown to reproduce experimental results over a large set of conditions. Scaling laws for parallel assembling systems are then derived from the model. By extending the validity of the CRN-based modelling, this work prompts analysis and solutions to the incompatible substructure problem.

Shape and size dependent nonlinear refraction and absorption in citrate-stabilized, near-IR plasmonic silver nanopyramids

Using a combination of a mild stabilizer and a mild reductant, sodium citrate and hydrazine hydrate, anisotropic silver nanocrystals (NCs) were synthesized with tunable plasmon peaks at 550 nm, 700 nm, 800 nm, 900 nm and 1010 nm (the samples are named Ag-550, Ag-700, Ag-800, Ag-900 and Ag-1010, respectively). TEM investigations revealed that Ag-550 NCs were pentagonal nanoplates while the other four samples were nanopyramids with a pentagonal base with the edge length varying between 15 and 30 nm. The non-linear optical (NLO) properties of these NCs were studied by the Z-scan technique using the CW He-Ne laser (632.8 nm, 15 mW). The shape change from 2D nanoplates (Ag-550) to 3D nanopyramids (Ag-700) resulted in sign reversal of the non-linear refractive index, n₂, from a negative (-3.164 × 10^-8 cm² W^-1) to a positive one (1.195 × 10^-8 cm² W^-1). This corresponds to a change from a self-defocussing effect to a self-focussing one. Besides shape, the size effect is also prominently observed. Amongst nanopyramids, as the edge length increases, n₂ increases linearly and reaches a maximum of 3.124 × 10^-8 cm² W^-1. Doubling the edge length from 15 nm to 30 nm resulted in 162% increase in n₂. On moving from Ag-550 to Ag-900 NCs, with the increasing plasmon wavelength, the non-linear absorption (NLA) coefficient increased exponentially to a high value of 8.52 × 10^-4 cm W^-1. However, Ag-1010 showed 29% decrease in NLA which is attributed to twinning present in the crystal structure as seen in the HR-TEM images. Due to the tunable NLO properties, these anisotropic Ag NCs hold great potential for applications in optical limiting, switching and data storage.

Concentration Effect of Reducing Agents on Green Synthesis of Gold Nanoparticles: Size, Morphology, and Growth Mechanism

Under various concentration conditions of reducing agents during the green synthesis of gold nanoparticles (AuNPs), we obtain the various geometry (morphology and size) of AuNPs that play a crucial role in their catalytic properties. Through both theoretical and experimental approaches, we studied the relationship between the concentration of reducing agent (caffeic acid) and the geometry of AuNPs. As the concentration of caffeic acid increases, the sizes of AuNPs were decreased due to the adsorption and stabilizing effect of oxidized caffeic acids (OXCAs). Thus, it turns out that optimal concentration exists for the desired geometry of AuNPs. Furthermore, we investigated the growth mechanism for the green synthesis of AuNPs. As the caffeic acid is added and adsorbed on the surface of AuNPs, the aggregation mechanism and surface free energy are changed and consequently resulted in the AuNPs of various geometry.

Programmable Potentials: Approximate N-body potentials from coarse-level logic

This paper gives a systematic method for constructing an N-body potential, approximating the true potential, that accurately captures meso-scale behavior of the chemical or biological system using pairwise potentials coming from experimental data or ab initio methods. The meso-scale behavior is translated into logic rules for the dynamics. Each pairwise potential has an associated logic function that is constructed using the logic rules, a class of elementary logic functions, and AND, OR, and NOT gates. The effect of each logic function is to turn its associated potential on and off. The N-body potential is constructed as linear combination of the pairwise potentials, where the “coefficients” of the potentials are smoothed versions of the associated logic functions. These potentials allow a potentially low-dimensional description of complex processes while still accurately capturing the relevant physics at the meso-scale. We present the proposed formalism to construct coarse-grained potential models for three examples: an inhibitor molecular system, bond breaking in chemical reactions, and DNA transcription from biology. The method can potentially be used in reverse for design of molecular processes by specifying properties of molecules that can carry them out.

Constructing 3D heterogeneous hydrogels from electrically manipulated prepolymer droplets and crosslinked microgels

Formation of multifunctional, heterogeneous, and encoded hydrogel building blocks, or microgels, by crosslinking and assembly of microgels are two essential steps in establishing hierarchical, complicated, and three-dimensional (3D) hydrogel architectures that recapitulate natural and biological structures or originate new materials by design. However, for the variety of the hydrogel materials crosslinked differently and for the varied scales of microgels and architectures, the formation and assembly processes are usually performed separately, which increases the manufacturing complexity of designed hydrogel materials. We show the construction of hydrogel architectures through programmable formation and assembly on an electromicrofluidic platform, adopting two reciprocal electric manipulations (electrowetting and dielectrophoresis) to manipulate varied objects (i) in multiple phases, including prepolymer liquid droplets and crosslinked microgels, (ii) on a wide range of scales from micrometer functional particles or cells to millimeter-assembled hydrogel architectures, and (iii) with diverse properties, such as conductive and dielectric droplets that are photocrosslinkable, chemically crosslinkable, or thermally crosslinkable. Prepolymer droplets, particles, and dissolved molecules are electrically addressable to adjust the properties of the microgel building blocks in liquid phase that subsequently undergo crosslinking and assembly in a flexible sequence to accomplish heterogeneous and seamless hydrogel architectures. We expect the electromicrofluidic platform to become a general technique to obtain 3D complex architectures.

Fluid-Mediated Stochastic Self-Assembly at Centimetric and Sub-Millimetric Scales: Design, Modeling, and Control

Stochastic self-assembly provides promising means for building micro-/nano-structures with a variety of properties and functionalities. Numerous studies have been conducted on the control and modeling of the process in engineered self-assembling systems constituted of modules with varied capabilities ranging from completely reactive nano-/micro-particles to intelligent miniaturized robots. Depending on the capabilities of the constituting modules, different approaches have been utilized for controlling and modeling these systems. In the quest of a unifying control and modeling framework and within the broader perspective of investigating how stochastic control strategies can be adapted from the centimeter-scale down to the (sub-)millimeter-scale, as well as from mechatronic to MEMS-based technology, this work presents the outcomes of our research on self-assembly during the past few years. As the first step, we leverage an experimental platform to study self-assembly of water-floating passive modules at the centimeter scale. A dedicated computational framework is developed for real-time tracking, modeling and control of the formation of specific structures. Using a similar approach, we then demonstrate controlled self-assembly of microparticles into clusters of a preset dimension in a microfluidic chamber, where the control loop is closed again through real-time tracking customized for a much faster system dynamics. Finally, with the aim of distributing the intelligence and realizing programmable self-assembly, we present a novel experimental system for fluid-mediated programmable stochastic self-assembly of active modules at the centimeter scale. The system is built around the water-floating 3-cm-sized Lily robots specifically designed to be operative in large swarms and allows for exploring the whole range of fully-centralized to fully-distributed control strategies. The outcomes of our research efforts extend the state-of-the-art methodologies for designing, modeling and controlling massively-distributed, stochastic self-assembling systems at different length scales, constituted of modules from centimetric down to sub-millimetric size. As a result, our work provides a solid milestone in structure formation through controlled self-assembly.