Femtosecond Laser 4D Printing of Light-Driven Intelligent Micromachines

Intelligent micromachines that respond to external light stimuli have a broad range of potential applications, such as microbots, biomedicine, and adaptive optics. However, artificial light-driven intelligent micromachines with a low actuation threshold, rapid responsiveness, and designable and precise 3D transformation capability remain unachievable to date. Here, a single-material and one-step 4D printing strategy are proposed to enable the nanomanufacturing of agile and low-threshold light-driven 3D micromachines with programmable shape-morphing characteristics. The as-developed carbon nanotube-doped composite hydrogel simultaneously enhanced the light absorption, thermal conductivity, and mechanical modulus of the crosslinked network, thus significantly increasing the light sensitivity and response speed of micromachines. Moreover, the structural design and assembly of asymmetric microscale mechanical metamaterial unit cells enable the highly efficient additive nanomanufacturing of 3D shape-morphable micromachines with large dynamic modulation and spatiotemporal controllability. Using this strategy, the world's smallest artificial beating heart with programmable light-stimulus responsiveness for the cardiac cycle is successfully printed. This 4D printing method paves the way for the construction of multifunctional intelligent micromachines for bionics, drug delivery, integrated microsystems, and other fields.     

Magnetic Control of Tubular Catalytic Microbots for the Transport,Assembly, and Delivery of Micro‐objects

Recently a significant amount of attention has been paid towards the development of man‐made synthetic catalytic micro‐ and nanomotors that can mimic biological counterparts in terms of propulsion power, motion control, and speed. However, only a few applications of such self‐propelled vehicles have been described. Here the magnetic control of self‐propelled catalytic Ti/Fe/Pt rolled‐up microtubes (microbots) that can be used to perform various tasks such as the selective loading, transportation, and delivery of microscale objects in a fluid is shown; for instance, it is demonstrated for polystyrene particles and thin metallic films (“nanoplates”). Microbots self‐propel by ejecting microbubbles via a platinum catalytic decomposition of hydrogen peroxide into oxygen and water. The fuel and surfactant concentrations are optimized obtaining a maximum speed of 275 µm s^?1 (5.5 body lengths per second) at 15% of peroxide fuel. The microbots exert a force of around 3.77 pN when transporting a single 5 µm diameter particle; evidencing a high propulsion power that allows for the transport of up to 60 microparticles. By the introduction of an Fe thin film into the rolled‐up microtubes, their motion can be fully controlled by an external magnetic field.     

Transparent Light-Driven Hydrogel Actuator Based on Photothermal Marangoni Effect and Buoyancy Flow for Three-Dimensional Motion

Marangoni-effect-driven actuators (MDAs) have the advantages of direct light-to-work conversion and convenient operation, which makes it widely researched in the cutting-edge fields including robots, micromachines, and intelligent systems. However, the MDA relies on the surface tension difference and it only works on the 2D liquid–air interface. Besides, the MDAs are normally pure black due to the light-absorption material limitation. Herein, a transparent light-driven 3D movable actuator (LTMA) and a 3D manipulation strategy are proposed. The LTMA is composed of photothermal nanoparticles-doped temperature-responsive hydrogel, whose surface energy changes as the nanoparticles absorb light energy. The 3D manipulation strategy combines Marangoni effect with photothermal buoyancy flow for realizing complex self-propellant and floating/sinking motions. The LTMA can perform more advanced tasks such as 3D obstacle avoidance and 3D sampling. Benefiting from the porous structure of hydrogel, LTMA can naturally absorb the chemical molecules for remote sampling and automated drug delivery. The light-driven, transparent, three-dimensionally movable, and programmable actuator has promising prospects in the field of micromachines and intelligent systems.     

Broad-Wavelength Light-Driven High-Speed Hybrid Crystal Actuators Actuated Inside Tissue-Like Phantoms

Research on molecular crystals exhibiting light-driven actuation has made remarkable progress through the development of various molecules and the identification of driving mechanisms. However, crystals developed to date have been driven mainly by ultraviolet (UV) or blue light irradiation, and driving by red or near-infrared (NIR) light has not been attempted yet. Herein, a broad-wavelength light-driven molecular crystals that exhibit high-speed bending by photothermal effect is developed. Titanium carbide (Ti₃C₂T_x) MXene nanosheets are integrated into salicylideneaniline crystals to extend the wavelength range that causes photothermally driven bending to UV, visible, and NIR light. In addition, unlike the thin pristine molecular crystals that show slow photoisomerization-induced bending only under UV light, the MXene layer enables the molecular crystals to be actuated rapidly regardless of their thickness over a wide range of wavelengths. The hybridization of molecular crystals with MXene, which exhibits strong biocompatibility as well as NIR light-driven photothermal effect, allows for the bending of the hybrid crystals inside agar phantoms mimicking biological tissue. Last, it is confirmed that MXene hybridization can be extended to common molecular crystals including various salicylideneaniline and anisole derivatives.     

Artificial Optoelectronic Synapses Based on TiNxO2–x/MoS2 Heterojunction for Neuromorphic Computing and Visual System

Being capable of dealing with both electrical signals and light, artificial optoelectronic synapses are of great importance for neuromorphic computing and are receiving a burgeoning amount of interest in visual information processing. In this work, an artificial optoelectronic synapse composed of Al/TiN_xO_2–x/MoS₂/ITO (H-OSD) is proposed and experimentally realized. The H-OSD can enable basic electrical voltage-induced synaptic functions such as the long/short-term plasticity and moreover the synaptic plasticity can be electrically adjusted. In response to the light stimuli, versatile advanced synaptic functions including long/short-term memory, and learning-forgetting-relearning are successfully demonstrated, which could enhance the information processing capability for neuromorphic computing. Most importantly, based on these light-induced salient features, a 4 × 4 synapse array is developed to show the potential application of the proposed H-OSD in constructing artificial visual system. It is shown that the perceiving and memorizing of the light information that are respectively relevant to the visual perception and visual memory functions, can be readily attained through tuning of the light intensity and the number of illuminations. As such, the proposed optoelectronic synapse shows great potentials in both neuromorphic computing and visual information processing and will facilitate the applications such as electronic eyes and light-driven neurorobotics.     

Laser-Induced Graphene Tapes as Origami and Stick-On Labels for Photothermal Manipulation via Marangoni Effect

Direct light-to-work conversion enables remote actuation through a non-contact manner, among which the photothermal Marangoni effect is significant for developing light-driven robots because of the diversity of applicable photothermal materials and light sources, as well as the high energy conversion efficiency. However, the lack of nanotechnologies that enable flexible integration of advanced photothermal materials with actuators of complex configurations significantly restricts their practical applications. In this paper, laser-induced graphene (LIG) tape is reported as stick-on photothermal labels for developing light-driven actuators based on the Marangoni effect. With the help of direct laser writing technology, graphene patterns with superior photothermal properties are prepared on the PI tape. The patterned LIG tape can be stuck on any desired objects and generates an asymmetric photothermal field under light irradiation, forming a photothermal Marangoni actuator. Additionally, the PI tape with LIG patterns can be folded into 3D origami actuators that permit photothermal Marangoni actuation including both translation and rotation. The graphene-based photothermal Marangoni actuators feature biocompatibility, which is confirmed by MDA-MB-231 cells proliferation experiments. Owing to the excellent photothermal property of LIG patterns, the as-produced photothermal actuators can be manipulated by a variety of light sources, holding great promise for developing light-driven soft robots.     

Laser-Empowered Random Metasurfaces for White Light Printed Image Multiplexing

Printed image multiplexing based on the design of metasurfaces has attracted much interest in the past decade. Optical switching between different images displayed directly on the metasurface is performed by altering the parameters of the incident light such as polarization, wavelength, or incidence angle. When using white light, only two-image multiplexing is implemented with polarization switching. Such metasurfaces are made of nanostructures perfectly controlled individually, which provide high-resolution pixels but small images and involve long fabrication processes. Here, it is demonstrated that laser processing of nanocomposites offers a versatile low-cost, high-speed method with large area processing capabilities for controlling the statistical properties of random metasurfaces, allowing up to three-image multiplexing under white light illumination. By independently controlling absorption and interference effects, colors in reflection and transmission can be varied independently yielding two-image multiplexing under white light. Using anisotropy of plasmonic nanoparticles, a third image can be multiplexed and revealed through polarization changes. The design strategy, the fundamental properties, and the versatility of implementation of these laser-empowered random metasurfaces are discussed. The technique, applied on flexible substrate, can find applications in information encryption or functional switchable optical devices, and offers many advantages for visual security and anticounterfeiting.     

Stimuli‐Responsive Liquid Marbles: Controlling Structure,Shape, Stability,and Motion

“Liquid marbles” are liquid‐in‐gas dispersed systems stabilized by hydrophobic solid particles adsorbed at the gas‐liquid interface. The structure, stability and movement of these liquid marbles can be controlled by external stimuli such as pH, temperature, light, magnetic and electric fields, ultrasonic, mechanical stress and organic solvents. Stimuli‐responsive modes can be categorized into five classes: (i) liquid marbles whose stability can be controlled by adsorption/desorption of solid particles to/from liquid surfaces, (ii) liquid marbles that can open and close their particle‐coated surface by moving particles to and from the gas‐liquid surface, (iii) liquid marbles that can move, (iv) liquid marbles that can change their shape and (v) liquid marbles that can be split. As a result of these stimuli‐responsive characteristics, liquid marbles offer potential in the areas of controlled encapsulation, delivery and release.     

Working prototype of an optoelectronic XOR/OR/YES reconfigurable logic device based on nanocrystalline semiconductors

Photoelectrodes made of nanocrystalline titanium dioxide modified with hexacyanoferrate anions exhibit unique photoelectrochemical properties: photocurrent direction can be switched from anodic to cathodic and vice versa upon changes in photoelectrode potential and incident light wavelength. This effect, called photoelectrochemical photocurrent switching (PEPS effect), can serve as a basis for construction of chemical logic gates with optical inputs and electric output. At certain potentials anodic photocurrent generated upon UV irradiation has the same intensity as the cathodic photocurrent generated upon visible irradiation. Under these conditions simultaneous irradiation with UV and visible light results in compensation of anodic and cathodic photocurrents and zero net photocurrent is observed. This process can be used for construction of unique light-driven chemical logic gates. Due to reversible electrochemical process leading to oxidation or reduction of the surface species the device can be programmed to perform XOR, OR or YES logic operations.     

Vertical 3D Printed Forest-Inspired Hierarchical Plasmonic Superstructure for Photocatalysis

Efficient light-harvesting is of significant importance to achieve high solar energy utilization efficiency for various solar-driven technologies. Compared with a 2D planar structure, a 3D plasmonic structure can largely increase the light adsorption/interaction areas and also utilizes the plasmonic effect to achieve much higher light utilization efficiency. However, this remains challenging in terms of structural design, reliable manufacturing, and ability to scale up. Herein, inspired by the light absorption strategy of natural forests, a hierarchical plasmonic superstructure is demonstrated composed of vertical TiO₂ pillar arrays (as tree trunks), dense nanorod arrays (as branches), and a large number of plasmonic Au nanoparticles (as leaves). Such a forest-like plasmonic superstructure can effectively absorb light from the surface plasmonic resonance effects of Au nanoparticles and the multiple scattering of light in the hierarchical branched structure. The strong light absorption and abundant photocatalytic active sites help yield a 15-fold higher nitrogen photo-fixation activity than that of the flat TiO₂ films decorated with Au nanoparticles. The study provides an effective strategy to construct 3D plasmonic superstructures with excellent light-harvesting efficiency and high stability and can be readily applied to a range of light-driven applications     

Structural Orientation and Anisotropy in Biological Materials: Functional Designs and Mechanics

Biological materials exhibit anisotropic characteristics because of the anisometric nature of their constituents and their preferred alignment within interfacial matrices. The regulation of structural orientations is the basis for material designs in nature and may offer inspiration for man‐made materials. Here, how structural orientation and anisotropy are designed into biological materials to achieve diverse functionalities is revisited. The orientation dependencies of differing mechanical properties are introduced based on a 2D composite model with wood and bone as examples; as such, anisotropic architectures and their roles in property optimization in biological systems are elucidated. Biological structural orientations are designed to achieve extrinsic toughening via complicated cracking paths, robust and releasable adhesion from anisotropic contact, programmable dynamic response by controlled expansion, enhanced contact damage resistance from varying orientations, and simultaneous optimization of multiple properties by adaptive structural reorientation. The underlying mechanics and material‐design principles that could be reproduced in man‐made systems are highlighted. Finally, the potential and challenges in developing a better understanding to implement such natural designs of structural orientation and anisotropy are discussed in light of current advances. The translation of these biological design principles can promote the creation of new synthetic materials with unprecedented properties and functionalities.     

Surface Plasmons and Visible Light Iniferter Initiated Polymerization for Nanolocal Functionalization of Mesoporous Separation Layers

Although the technological relevance of mesoporous ceramic polymer hybrid materials is well accepted, missing functionalization concepts enabling 3D nanoscale local control of polymer placement into mesoporous materials, including thin films, and ideally using controlled polymerization techniques limit the application potential. Here, nanolocal functionalization of mesoporous separation layers using controlled, visible light iniferter initiated polymerization allowing responsive polymer functionalization locally limited to the irradiated spot is introduced. Thereby, two visible light sensitive iniferters, s-p-trimethoxysilylbenzyl-S´-dodecyltrithiocarbonate and 4-cyano-4-((dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid, are developed for polymer functionalization of mesoporous films in a grafting from and a grafting through approach. 3D nanolocal polymer placement close to the proximity of the plasmonic field source is demonstrated by combining these visible light iniferter initiated polymerizations with optical near field modes, such as localized surface plasmon resonance (LSPR). As the location of the LSPR in mesoporous films can be controlled by placing metal alloy nanoparticles into these films and film thicknesses can be adjusted, this strategy is applied for precise positioning of polymers into mesoporous films with nanolocal control in three dimensions and thus reduces the gap in precision of functional group positioning between technological and biological nanopores.     

Hierarchical Design of Metal Micro/Nanohole Array Films Optimizes Transparency and Haze Factor

Thin films containing metal nanohole arrays can be fabricated with high precision, and regular, tunable features via colloidal lithography. They are ideal model structures to study the relation between structural design and optoelectronic properties, for example as transparent, conducting electrodes, where the percolation threshold sets an upper limit on the achievable transparency. An important, but less systematically studied property of transparent conductive electrodes is the amount of scattered light, as described by the haze factor. Here, the influence of structural parameters on the resulting haze factor of metal nanohole array films is investigated. It is found that transmission, transparency, and haze factor cannot be independently controlled, and propose a new fabrication paradigm to optimize the optoelectronic properties of such films. Hierarchical metal micro/nanohole array films are designed, which combine precisely controlled and highly regular structural features at two length scales. These hierarchical structures maximize transparency while simultaneously providing low haze factors. Computer simulations based on finite elements and ray optics are in close agreement with the experimental results and reveal that the reduced haze factor results from a drastic decrease of grating diffraction efficiency in the hierarchical films.     

Phototuning Selectively Hole and Electron Transport in Optically Switchable Ambipolar Transistors

One of the grand challenges in organic electronics is to develop multicomponent materials wherein each component imparts a different and independently addressable property to the hybrid system. In this way, the combination of the pristine properties of each component is not only preserved but also combined with unprecedented properties emerging from the mutual interaction between the components. Here for the first time, that tri‐component materials comprised of an ambipolar diketopyrrolopyrrole‐based semiconducting polymer combined with two different photochromic diarylethene molecules possessing ad hoc energy levels can be used to develop organic field‐effect transistors, in which the transport of both, holes and electrons, can be photo‐modulated. A fully reversible light‐switching process is demonstrated, with a light‐controlled 100‐fold modulation of p‐type charge transport and a tenfold modulation of n‐type charge transport. These findings pave the way for photo‐tunable inverters and ultimately for completely re‐addressable high‐performance circuits comprising optical storage units and ambipolar field‐effect transistors.     

Multifunctional Visible‐Light Powered Micromotors Based on Semiconducting Sulfur‐ and Nitrogen‐Containing Donor–Acceptor Polymer

Photosensitive micromotors that can be remotely controlled by visible light irradiation demonstrate great potential in biomedical and environmental applications. To date, a vast number of light‐driven micromotors are mainly composed from costly heavy and precious metal‐containing multicomponent systems, that limit the modularity of chemical and physical properties of these materials. Herein, a highly efficient photocatalytic micromotors based exclusively on a purely organic polymer framework—semiconducting sulfur‐ and nitrogen‐containing donor–acceptor polymer, is presented. Thanks to precisely tuned molecular architecture, this material has the ability to absorb visible light due to a conveniently situated energy gap. In addition, the donor‐acceptor dyads within the polymer backbone ensure efficient photoexcited charge separation. Hence, these polymer‐based micromotors can move in aqueous solutions under visible light illumination via a self‐diffusiophoresis mechanism. Moreover, these micromachines can degrade toxic organic pollutants and respond to an increase in acidity of aqueous environments by instantaneous colour change. The combination of autonomous motility and intrinsic fluorescence enables these organic micromotors to be used as colorimetric and optical sensors for monitoring of the environmental aqueous acidity. The current findings open new pathways toward the design of organic polymer‐based micromotors with tuneable band gap architecture for fabrication of self‐propelled microsensors for environmental control and remediation applications.     

Alternating pressure control system for hydraulic robots

Hydraulics is a promising technology for robots. However, traditional hydraulic infrastructures are often large and power-inefficient, with large power sources that hinder mobility. In contrast, electro-hydrostatic actuators are relatively power efficient, but their cost and weight can be excessive in systems with a higher number of degrees of freedom. In this paper, we propose a new alternating pressure control system for hydraulic systems with a higher number of degrees of freedom based on an alternating pressure source system. In this system, the valves open and close in synchronization with a pump with sensor feedback, allowing either pressure or position in each actuator to be controlled independently. With the proposed system, a centralized pump can be used with simplified tubing and simple on–off valves. Moreover, we developed a dynamic duty ratio system that improves performance and reduces pump utilization time. The experimental results confirmed that both the position and pressure of each actuator can be controlled in parallel on a multi-degree-of-freedom system.     

A Multidirectional Locomotion Light-Driven Soft Crawling Robot

Soft robots based on bionics with multi-freedom and communication abilities have attracted extensive attention in recent years. However, the solutions for soft robots with multidirectional locomotion currently concentrate on complex drive modes and exhibit application unfriendliness. In this work, an untethered multidirectional locomotion light-driven soft crawling robot is proposed with the integration of communication module, which can traverse in four directions with a fixed near-infrared (NIR) light source and is also capable of positioning and perception. Owing to the photothermal response of graphene oxide and ingenious structural design, the critical states of robot deformation can be determined simply by controlling the duration of NIR light, ultimately resulting in different crawling directions. Furthermore, a communication module is integrated into the robot enabling the robot to locate and sense humidity by magnetic coupling. The proposed robot provides an innovative strategy for the design and integration of multidirectional locomotion soft crawling robots, showing great potential in intelligent robots.     

Organic Solid Solutions: Formation and Applications in Organic Light‐Emitting Diodes

To enhance the performance of organic devices, doping and graded mixed‐layer structures, formed by co‐evaporation methods, have been extensively adopted in the formation of organic thin films. Among the criteria for selecting materials systems, much attention has been paid to the materials' energy‐band structure and carrier‐transport behavior. As a result, some other important characteristics may have been overlooked, such as material compatibility or solubility. In this paper, we propose a new doping method utilizing fused organic solid solutions (FOSSs) which are prepared via high‐pressure and high‐temperature processing. By preparing fused solid solutions of organic compounds, the stable materials systems can be selected for device fabrication. Furthermore, by using these FOSSs, doping concentration and uniformity can be precisely controlled using only one thermal source. As an example of application in organic thin films, high‐performance organic light‐emitting diodes with both single‐color and white‐light emission have been prepared using this new method. Compared to the traditional co‐evaporation method, a FOSS provides us with a more convenient way to optimize the doping system and fabricate relatively complicated organic devices.     

Wide Bandgap Phase Change Material Tuned Visible Photonics

Light strongly interacts with structures that are of a similar scale to its wavelength, typically nanoscale features for light in the visible spectrum. However, the optical response of these nanostructures is usually fixed during the fabrication. Phase change materials offer a way to tune the properties of these structures in nanoseconds. Until now, phase change active photonics has used materials that strongly absorb visible light, which limits their application in the visible spectrum. In contrast, Sb₂S₃ is an underexplored phase change material with a bandgap that can be tuned in the visible spectrum from 2.0 to 1.7 eV. This tuneable bandgap is deliberately coupled to an optical resonator such that it responds dramatically in the visible spectrum to Sb₂S₃ reversible structural phase transitions. It is shown that this optical response can be triggered both optically and electrically. High‐speed reprogrammable Sb₂S₃ based photonic devices, such as those reported here, are likely to have wide applications in future intelligent photonic systems, holographic displays, and microspectrometers.     

Implementation of adaptive modulation as A fade countermeasure

Three key problem areas associated with implementation of the concept of adaptive modulation as a fade countermeasure in a practical VSAT system are addressed in this paper. First, the heart of such a system, an adaptive modem, is described; such a device should be able to support a number of different modulation schemes, independently for modulation and demodulation. It is shown how an adaptive modulator can be built around a VLSI numerically controlled oscillator and that an adaptive demodulator is feasible once the universal carrier tracking loop is implemented with use of digital signal processing. As regards system operation, a data transfer scenario is described which highlights that it is important to expand the set of commands and responses of the data link control protocol in order to cater for the new abilities of the system. Finally, the article describes a computer simulation of system performance evaluation under dynamic rain fading propagation conditions and applied to a K_a band link. The results confirm earlier theoretical work and show great advantage over systems using fixed modulation schemes and fixed link propagation budget margins.