Bio-Inspired Soft-Rigid Hybrid Smart Artificial Muscle Based on Liquid Crystal Elastomer and Helical Metal Wire.

Artificial muscles are of significant value in robotic applications. Rigid artificial muscles possess a strong load-bearing capacity, while their deformation is small; soft artificial muscles can be shifted to a large degree; however, their load-bearing capacity is weak. Furthermore, artificial muscles are generally controlled in an open loop due to a lack of deformation-related feedback. Human arms include muscles, bones, and nerves, which ingeniously coordinate the actuation, load-bearing, and sensory systems. Inspired by this, a soft-rigid hybrid smart artificial muscle (SRH-SAM) based on liquid crystal elastomer (LCE) and helical metal wire is proposed. The thermotropic responsiveness of the LCE is adopted for large reversible deformation, and the helical metal wire is used to fulfill high bearing capacity and electric heating function requirements. During actuation, the helical metal wire's resistance changes with the LCE's electrothermal deformation, thereby achieving deformation-sensing characteristics. Based on the proposed SRH-SAM, a reconfigurable blazed grating plane and the effective switch between attachment and detachment in bionic dry adhesion are accomplished. The SRH-SAM opens a new avenue for designing smart artificial muscles and can promote the development of artificial muscle-based devices.

Microcrack Arrays in Dense Graphene Films for Fast-Ion-Diffusion Supercapacitors.

Laminated graphene film has great potential in compact high-power capacitive energy storage owing to the high bulk density and opened architecture. However, the high-power capability is usually limited by tortuous cross-layer ion diffusion. Herein, microcrack arrays are fabricated in graphene films as fast ion diffusion channels, converting tortuous diffusion into straightforward diffusion while maintaining a high bulk density of 0.92 g cm-3 . Films with optimized microcrack arrays exhibit sixfold improved ion diffusion coefficient and high volumetric capacitance of 221 F cm-3 (240 F g-1 ), representing a critical breakthrough in optimizing ion diffusion toward compact energy storage. This microcrack design is also efficient for signal filtering. Microcracked graphene-based supercapacitor with 30 µg cm-2  mass loading exhibits characteristic frequency up to 200 Hz with voltage window up to 4 V, showing high promise for compact, high-capacitance alternating current (AC) filtering. Moreover, a renewable energy system is conducted using microcrack-arrayed graphene supercapacitors as filter-capacitor and energy buffer, filtering and storing the 50 Hz AC electricity from a wind generator into the constant direct current, stably powering 74 LEDs, demonstrating enormous potential in practical applications. More importantly, this microcracking approach is roll-to-roll producible, which is cost-effective and highly promising for large-scale manufacture.

Micropatterned Fluororubber-Based Dry Adhesive for Pan-Semiconductor Production Line with Complicated Operating Conditions.

The efficient and safe manipulation of precision materials (such as thin and fragile wafers and glass substrates for flat panel displays) under complicated operating conditions with vacuum, high temperature, and low preload stress is an essential task for pan-semiconductor production lines. However, current manipulation approaches such as suction-based gripping (invalid under vacuum conditions) and mechanical clamping (stress concentration at the contact interfaces) are challenged to satisfy such complex requirements. Herein, fluororubber (FKM) is employed as an adhesive material to overcome such challenges due to its outstanding thermostability, availability under vacuum environments, and high adhesion at low contacting preloads. However, the adhesion of the FKM film decreases significantly with increasing temperature (decrease by 84.83% at 245 °C). Consequently, a micropatterned FKM-based dry adhesive (MFA) fabricated by laser etching is developed. The experimental results reveal that MFAs are efficient in restraining adhesion attenuation at high temperatures (minimum 15% decrease at 245 °C). The numerical analysis and in situ observations reveal the mechanism of the MFAs in restraining adhesion attenuation. The contamination-free and high adhesion at low contacting preload of MFAs can be of great interest in pan-semiconductor production lines that require complicated operating conditions on temperature, vacuum, and interface stress.

Nanoimprinting Metal-Containing Nanoparticles-Doping-Grating for High Polarization Performance Light Emitting Chips by Scattering-Induced Enhancement.

Polarized radiative semiconductor luminous chips have huge application potentials in lots of high value-added fields. Integrating a subwavelength grating is recognized as the most promising method for development of polarized chips, but still faces the challenge of lower polarized radiation performance. The paper proposed and developed a scattering-induced polarization enhancement light emitting diodes chips by directly nanoimprinting metal-containing nanoparticles-doping-grating on the top surface of a common flip-chips. The utilization rate of quantum well light emission on the developed polarized chips was improved more than 30%. More attractively, the doped scattering nanoparticles play as a scattering-induced polarization state converter that sandwiched in the top aluminum grating and bottom silver reflector on the chips. The originally non-radiative light with an electric field vector parallel to the grating lines is reflected back and forth among the sandwich until it changes to the perpendicular vibration mode to radiate outside the chips. Therefore, the polarization extinction ratio was greatly improved compared with the samples without doping.

Nanoimprinting metal-containing nanoparticle-doped gratings to enhance the polarization of light-emitting chips by induced scattering.

Polarized radiative luminous semiconductor chips have huge application potential in many highly value-added fields. The integration of a subwavelength grating is recognized to be the most promising method for the development of polarized chips, but still faces the challenge of low polarized radiative performance. This paper describes a proposal for, and the development of, a scattering-induced enhanced-polarization light-emitting diode chip by directly nanoimprinting a metal-containing nanoparticle-doped grating onto the top surface of a common flip chip. The rate at which quantum-well light emission is used by the developed polarized chip is improved by more than 30%. More attractively, the doped scattering nanoparticles function as a scattering-induced polarization state converter that is sandwiched in between the top aluminum grating and the bottom silver reflector of the chips. The originally non-radiated light, with an electric-field vector parallel to the grating lines, is reflected back and forth inside the sandwich until it changes to the perpendicular vibration mode and is radiated outside the chip. Therefore, the polarization extinction ratio is greatly improved, compared to undoped samples.

High-Speed Handling Robot with Bionic End-Effector for Large Glass Substrate in Clean Environment.

The development of "large display, high performance and low cost" in the FPD industry demands glass substrates to be "larger and thinner". Therefore, the requirements of handling robots are developing in the direction of large scale, high speed, and high precision. This paper presents a novel construction of a glass substrate handling robot, which has a 2.5 m/s travelling speed. It innovatively adopts bionic end-suction technology to grasp the glass substrate more firmly. The structure design is divided into the following three parts: a travel track, a robot body, and an end-effector. The manipulator can be smoothly and rapidly extended by adjusting the transmission ratio of the reducer to 1:2:1, using only one motor to drive two sections of the arm. This robot can transfer two pieces of glass substrate at one time, and improves the working efficiency. The kinematic and dynamic models of the robot are built based on the DH coordinate. Through the positioning accuracy experiment and vibration experiment of the end-effector, it is found that the robot has high precision during handling. The robots developed in this study can be used in large-scale glass substrate handling.

An electrically active gecko-effect soft gripper under a low voltage by mimicking gecko's adhesive structures and toe muscles.

With the combination of the passive adhesion generated by micro/nano-structures at their feet and the active mechanical stimulus of their toe muscles, geckos can stably walk on vertical walls and horizontal ceilings. Inspired by such stimuli-responsive systems in nature, an active adhesive soft gripper stimulated by low voltage (usually ≤6 V), consisting of a passive mushroom-like adhesive structure and an electrically active liquid crystal elastomer working as toe muscles, is proposed in this study. Through voltage on/off switching, reversible deformation can be generated for switchable adhesion, where high adhesion can be achieved under the action of a preload force accompanied by a 0 V voltage and low adhesion can be obtained under an exerted voltage. This gecko-inspired soft gripper was tested and found to be successful as a transport device for gripping/releasing objects with different features, such as a glass ball, a sample bottle, and a steel weight. To the best of our knowledge, the present study is the first to propose an electrically active gecko-inspired soft gripper for transferring objects with different surfaces by the control of low voltage, processing great application potential in industrial lines and daily life and providing a novel perspective on soft gripper design.

Protective integrated transparent conductive film with high mechanical stability and uniform electric-field distribution.

A stable and uniform electric field is to be generated even though a large mechanical deformation is the primary criterion for a transparent conductive film. This study proposes a protective integrated transparent conductive film (PITCF) including indium tin oxide (ITO), a silver nanowire (Ag NW) network, and a protective polydimethylsiloxane (PDMS) layer. A firmly bonding process of ITO/Ag NW/PDMS is established to avoid the failure of Ag NW to be oxidized by interlayer residual air or wrapped by liquid PDMS. Besides the good optical transparency, haze, and electrical conductivity as the only ITO film, the developed PITCF exhibits excellent bending resistance and mechanical stability. The ITO rupture fragments after bending deformation are firmly interconnected by the constrained Ag NWs. Even though the PITCF is bended more than 1000 cycles at a 6.5 mm bending distance, the changes in electrical resistance of PITCF are below 9.7%. Finally, an electroluminescent device with high bending resistance and uniform and high luminance is developed based on the designed PITCF.

High-Performance Piezoelectric Nanogenerators with Imprinted P(VDF-TrFE)/BaTiO3 Nanocomposite Micropillars for Self-Powered Flexible Sensors.

Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high-performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE))/barium titanate (BaTiO3 ) for energy harvesting and highly sensitive self-powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF-TrFE)/BaTiO3 nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm-2 , which an enhancement by a factor of 7.3 relatives to the pristine P(VDF-TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF-TrFE)/BaTiO3 nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self-powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.

Investigation of the role of template features on the electrically induced structure formation (EISF) for a faithful duplication.

Electrically induced structure formation, as a physical approach to fabricate micro/nanostructures, has attracted much attention because of the simple process, low-cost, high-efficiency, and wide applications on electronics, microfluidics, and so forth. Hitherto, the influence of some process parameters, such as voltage, air gap, film thickness, polymer properties, on the polymeric behavior, and the structure formation has been explored, neglecting the effects of the template features, which affect the polymer deformation. Especially for the conductive protrusions directly contacting the polymer, the phenomenon of electric breakdown may occur, leading to a failure of structure formation. The limitation of the research on the template features triggers the necessity to study its influence for a faithful deformation. In this paper, three types of patterned template are studied based on the electric field at the air-polymer interface, consisting of completely conductive template, partially conductive template, and dielectric template. Comprehensive consideration of the electric intensity for a sufficient driving pressure and the leaky current for preventing damaging the polymer, some guiding opinions on the template material and geometry can be provided to design the patterned template for the electrically induced structure formation process with a purpose for a faithful structure.

A photocurable leaky dielectric for highly electrical insulating electrohydrodynamic micro-/nanopatterns.

This communication describes an innovative photocurable leaky dielectric for electrohydrodynamic patterning (EHDP). Based on the well-designed molecular structure, the material in its liquid state exhibits low viscosity, high homogeneity, and more importantly a leaky dielectric characteristic; meanwhile, UV light irradiation transforms it from a liquid leaky dielectric into a solid perfect dielectric instantaneously via an interfacial reaction. Two typical EHDP processes have confirmed that the beneficial properties of this material help to rapidly fulfill a higher aspect ratio and/or smaller feature size patterning compared to its perfect dielectric counterpart. Therefore, this material provides the potential in accessing high-performance EHDP towards fabricating electrically insulating micro-/nanostructures.

Electrohydrodynamic pressure enhanced by free space charge for electrically induced structure formation with high aspect ratio.

Electrically induced structure formation (EISF) is an interesting and unique approach for generating a microstructured duplicate from a rheological polymer by a spatially modulated electric field induced by a patterned template. Most of the research on EISF have so far used various dielectric polymers (with an electrical conductivity smaller than 10(-10) S/m that can be considered a perfect dielectric), on which the electric field induces a Maxwell stress only due to the dipoles (or bounded charges) in the polymer molecules, leading to a structure with a small aspect ratio. This paper presents a different approach for improving the aspect ratio allowed in EISF by doping organic salt into the perfect dielectric polymer, i.e., turning the perfect dielectric into a leaky dielectric, considering the fact that the free space charges enriched in the leaky dielectric polymer can make an additional contribution to the Maxwell stress, i.e., electrohydrodynamic pressure, which is desirable for high aspect ratio structuring. Our numerical simulations and experimental tests have shown that a leaky dielectric polymer, with a small conductivity comparable to that of deionized water, can be much more effective at being electrohydrodynamically deformed into a high aspect ratio in comparison with a perfect dielectric polymer when both of them have roughly the same dielectric constant.

Formation of arbitrary patterns in ultraviolet cured polymer film via electrohydrodynamic patterning.

Electrohydrodynamic patterning of arbitrary patterns is achieved by optimizing the critical parameters (applied voltage and spacer height). The applied voltage has a great influence on the fidelity of L-shaped line structures with different sizes. The L-shaped line structures with high fidelity are obtained by using the moderate applied voltage. The spacer height has a great influence on the fidelity of square structures with different sizes. The square structures with high fidelity are obtained by using the low height spacer. The multi-field coupling transient finite element simulation demonstrates that the lack of polymer owing to the high height spacer leads to the formation of defects.

Bioinspired Suspended Sensing Membrane Array with Modulable Wedged-Conductive Channels for Crosstalk-Free and High-Resolution Detection.

High spatial-resolution detection is essential for biomedical applications and human-machine interaction. However, as the sensor array density increases, the miniaturization will lead to interference between adjacent units and deterioration in sensing performance. Here, inspired by the cochlea's sensing structure, a high-density flexible pressure sensor array featuring with suspended sensing membrane with sensitivity-enhanced customized channels is presented for crosstalk-free and high-resolution detection. By imitating the basilar membrane attached to spiral ligaments, a sensing membrane is fixed onto a high-stiffness substrate with cavities, forming a stable braced isolation to provide an excellent crosstalk-free capability (crosstalk coefficient: 47.24 dB) with high-density integration (100 units within 1 cm2). Similar to the opening of ion channels in hair cells, the wedge-type expansion of the embedded cracks introduced by stress concentration structures enables a high sensitivity (0.19 kPa-1) and a large measuring range (400 kPa). Finally, it demonstrates promising applications in distributed displays and the condition monitoring of medical-surgical intubation.

Modulation of wetting state switching of droplets on superhydrophobic microstructured surfaces by external electric field.

HYPOTHESIS: Electrowetting on conventional dielectrics requires direct fluid-electrode contact to generate strong electric fields at the three-phase contact line to modulate the wetting. Since the electric field alters wetting, the modulation of wetting can be achieved by applying an external electric field through insulated electrodes, preventing the liquid from contacting the electrodes. EXPERIMENT: A simple and efficient method for non-contact between the fluid and the electrode external electric field modulation of fluid wetting was proposed. The switching ability of droplets on microgroove surfaces from Cassie-Baxter to Wenzel wetting state under an external electric field was used to drive and quantify the relationship between wetting, contact angle, and the applied voltage. FINDINGS: Applying an external electric field modulates the wetting of deionized water, ionic liquids, and high-viscosity liquids on microgrooves. The wetting degree of liquid can be controlled by adjusting the external voltage parameters. The finite element simulations revealed that the Maxwell force drove this process. The effects of substrate size and liquid properties on wetting behavior were also examined. Post-application cross-sectional imaging showed the formation of a conformal interface, highlighting the relevance of the proposed method in advanced adaptive shape fabrication and microfluidic control, among other applications.

Treefrog-Inspired Flexible Electrode with High Permeability, Stable Adhesion, and Robust Durability.

Long-term continuous monitoring (LTCM) of physiological electrical signals is an effective means for detecting several cardiovascular diseases. However, the integrated challenges of stable adhesion, low impedance, and robust durability under different skin conditions significantly hinder the application of flexible electrodes in LTCM. This paper proposes a structured electrode inspired by the treefrog web, comprising dispersed pillars at the bottom and asymmetric cone holes at the top. Attachment structures with a dispersed pillar improve the contact stability (adhesion increases 2.79/13.16 times in dry/wet conditions compared to an electrode without structure). Improved permeable duct structure provides high permeability (12 times compared to cotton). Due to high adhesion and permeability, the electrode's durability is 40 times larger than commercial Ag/AgCl electrodes. The treefrog web-like electrode has great advantages in permeability, adhesion, and durability, resulting in prospects for application in physiological electrical signal detection and a new design idea for LTCM wearable dry electrodes.

Fabrication of large curvature microlens array using confined laser swelling method.

This Letter proposes a confined laser swelling method to fabricate large curvature microlens arrays. Unlike the polymers in conventional free laser swelling, the swelling polymer, which is methyl red-doped polymethyl methacrylate here, is confined between walls formed by a substrate and a flexible cover layer. Because swelling occurs in an enclosed space, decomposed segments remain in the matrix, resulting in a large hump at the side of the flexible cover layer. The results show that these humps are tens of times higher than those acquired by conventional methods and this method has potential for high efficiency large curvature microlens fabrication.

Numerical characterization of electrohydrodynamic micro- or nanopatterning processes based on a phase-field formulation of liquid dielectrophoresis.

The electrohydrodynamic patterning of polymer is a unique technique for micro- and nanostructuring where an electric voltage is applied to an electrode pair consisting of a patterned template and a polymer-coated substrate either in contact or separated by an air gap to actuate the deformation of the rheological polymer. Depending on the template composition, three processes were proposed for implementing the EHDP technique and have received a great amount of attention (i.e., electrostatic force-assisted nanoimprint, dielectrophoresis-electrocapillary force-driven imprint, and electrically induced structure formation). A numerical approach, which is versatile for visualizing the full evolution of micro- or nanostructures in these patterning processes or their variants, is a desirable critical tool for optimizing the process variables in industrial applications of this structuring technique. Considering the fact that all of these processes use a dielectric and viscous polymer (behaving mechanically as a liquid) and are carried out in ambient air, this Article presents a generalized formulation for the numerical characterization of the EHDP processes by coupling liquid dielectrophoresis (L-DEP) and the phase field of the air-liquid dual phase. More importantly, some major scale effects, such as the surface tension, contact angle, liquid-solid interface slip, and non-Newtonian viscosity law are introduced, which can impact the accuracy of the numerical results, as shown experimentally by our electrical actuation of a dielectric microdroplet as a test problem. The numerical results are in good agreement with or are well explained by experimental observations published for the three EHDP processes.

Electrically modulated microtransfer molding for fabrication of micropillar arrays with spatially varying heights.

The ability to generate a large area micropillar array with spatially varying heights allows for exploring numerous new interesting applications in biotechnology, surface engineering, microfluidics, and so forth. This Letter presents a clever and straightforward method, called electrically modulated microtransfer molding (EM3), for generating such unique microstructures from a silicon mold arrayed with microholes. The key to the process is an application of electrically tunable wettability caused by a spatially modulated voltage, which electrohydrodynamically drives a photocurable and dielectric prepolymer to fill the microholes to a depth depending on the voltage amplitude. Using EM3, micropillar arrays with stepwise or continuously varying heights are successfully fabricated, with the diameter scalable to 1.5 µm and with the maximum height being equal to the depth of the high-aspect-ratio (more than 10:1) microholes.

Smart Manipulation of Complex Optical Elements via Contact-adaptive Dry Adhesives.

The implementation of complex, high-precision optical devices or systems, which have vital applications in the aerospace, medical, and military fields, requires the ability to reliably manipulate and assemble optical elements. However, this is a challenging task as these optical elements require contamination-free and damage-free manipulation and come in a variety of sizes and shapes. Here, a smart, contact-adaptive adhesive based on magnetic actuation is developed to address this challenge. Specifically, the surface bio-inspired adhesives made of fluororubber facilitate contamination-free and damage-free adhesion. The stiffness modulation of packaged magnetorheological grease based on the magnetorheological effect endows the smart adhesive with a high conformability to the optical elements in the soft state, a high grip force in the stiff state, and the ability to quickly release the optical elements in the recovered soft state. The smart adhesive provides a versatile solution for reliably and quickly manipulating and assembling multiscale optical elements with planar or complex 3D shapes without causing surface contamination or damage. These extraordinary capabilities are demonstrated by the manipulation and assembly of various optical elements, such as convex/concave/ball lenses and extremely complex-shaped light guide plates. The proposed smart adhesive is a promising candidate for conventional optical element manipulation technologies.