A General Approach to Semimetallic,Ultra‐High‐Resolution,Electron‐Beam Resists

Commercial electron‐beam resists are modified into semimetallic resists by doping with 1–3 nm metal nanoparticles, which improve the resolution, contrast, strength, dry‐etching resistance, and other properties of the resist. With the modified resists, fine resist nanopatterns from electron‐beam lithography are readily converted into 5–50 nm, high‐quality multilayers for metallic nanosensors or nanopatterns via ion‐beam etching. This method solves the problem of the fabrication of fine (<50 nm) metallic nanodevices via pattern transferring.     

柔性神经微电极阵列设计及微加工工艺研究

采用聚对二甲苯(parylene)作为基底,通过对柔性神经微电极阵列结构、引线排布、电极材料等进行优化选择和设计,并采用微机电加工工艺(MEMS),设计并研制出了2×8柔性神经微电极阵列,旨在为视网膜神经接口电极的研究开发奠定基础.     

Nanopatterned Polymer Brushes for Triggered Detachment of Anchorage‐Dependent Cells

Surfaces modified with thermoresponsive poly(N‐isopropylacrylamide) (PNIPAAm) support mild and efficient harvesting of anchorage‐dependent cells. To enable cellular detachment, however, the surfaces must exhibit a narrow range of PNIPAAm thicknesses. In this work, this limitation is circumvented by introducing nanopatterns to grafted PNIPAAm brushes, eliminating the critical thickness requirement for cell‐culturing applications. Nanopatterned PNIPAAm surfaces are prepared using a combination of interferometric lithography (IL) and surface‐initiated polymerization. Above the lower critical solution temperature (LCST) of PNIPAAm (～32 °C), these surfaces support the attachment and proliferation of mammalian cells (e.g., fibroblasts and endothelial cells). Below the LCST of PNIPAAm, cells readily detach from the nanopatterned PNIPAAm surfaces without influence from the period of nanopatterns, which vary between 157 ± 9 nm to 1021 ± 17 nm. Cells selectively attach and proliferate on PNIPAAm nanopatterns as compared to thick unpatterned PNIPAAm, which is further exploited to spatially direct cellular growth to generate cellular micropatterns. Nanopatterned PNIPAAm surfaces provide a unique solution to the critical thickness issue for cell harvesting and facilitate spatial control of cellular growth on surfaces.     

3D Microstructured Carbon Nanotube Electrodes for Trapping and Recording Electrogenic Cells

Electrogenic cells such as cardiomyocytes and neurons rely mainly on electrical signals for intercellular communication. Microelectrode arrays (MEAs) have been developed for long‐term recording of cell signals and stimulation of electrogenic cells under low‐cell‐stress conditions, providing new insights in the behavior of electrogenic cells and the operation of the brain. To date, MEAs are relying on flat or needle‐shaped electrode surfaces, mainly due to limitations in the lithographic processes. This paper relies on a previously reported elasto‐capillary aggregation process to create 3D carbon nanotube (CNT) MEAs. This study shows that CNTs aggregate in well‐shaped structures of similar size as cardiomyocytes are particularly interesting for MEA applications. This is because i) CNT microwells of the right diameter preferentially trap individual cardiomyocytes, which facilitates single cell recording without the need for clamping cells or signal deconvolution, and ii) once the cells are trapped inside of the CNT wells, this 3D CNT structure is used as an electrode surrounding the cell, which increases the cell–electrode contact area. As a result, this study finds that the recorded output voltages increase significantly (more than 200%). This fabrication process paves the way for future study of complex interactions between electrogenic cells and 3D recording electrodes.     

Neuronal network morphology and electrophysiologyof hippocampal neurons cultured on surface-treated multielectrode arrays

Toward the development of biocompatible surfaces for implantable electrode arrays and the creation of patterned neuronal networks, the impact of select biochemical substrates [poly-D-lysine (PDL), polyornithine (PO), polyethylenimine (PEI), and a basement membrane extract (BM)] on network morphology and spontaneous electrophysiological activity of dissociated hippocampal neurons was investigated. Cultured in serum-free Neurobasal medium at 100 000 cells/cm(2), neurons attached to each substrate. PDL, PO, and PEI induced little or no neuronal clustering and process fasciculation, whereas the addition of BM promoted these features. The ratios of somas to processes, and axons to dendrites, as determined by immunohistochemical staining and image analysis were comparable across all substrates. Spontaneous firing was recorded using planar multielectrode arrays (MEAs) at the third week in vitro for the two most divergent morphologies according to Euclidian cluster analysis, namely those induced by PO + BM and PEI. Mean spike amplitude, mean firing rate, median interspike interval (ISI), mean burst rate, and correlation index were analyzed and compared to morphological features. Synchronized bursting was highly correlated with neuronal clustering and process fasciculation. Spike amplitude was negatively correlated with thin branching which was most evident in neurons grown on PEI. These data indicate that factors, which influence adherence of neurons to surfaces, can profoundly impact both neuronal network morphology and electrophysiological activity in vitro.     

Ultracompliant Hydrogel‐Based Neural Interfaces Fabricated by Aqueous‐Phase Microtransfer Printing

Hydrogel‐based electronics are ideally suited for neural interfaces because they exhibit ultracompliant mechanical properties that match that of excitable tissue in the brain and peripheral nerve. Hydrogel‐based multielectrode arrays (MEAs) can conformably interface with tissues to minimize inflammation and improve the reliability to enhance signal transduction. However, MEA substrates composed of swollen hydrogels exhibit low toughness and poor adhesion when laminated on the tissue surface and also present incompatibilities with processes commonly used in MEA fabrication. Here, a strategy to fabricate an ultracompliant MEA is described based on aqueous‐phase transfer printing. This technique employs redox active adhesive motifs in hygroscopic polymer precursors that simultaneously form hydrogels through sol–gel phase transitions and bond to materials in the underlying microelectronic structures. Specifically, in situ gelation of four‐arm‐polyethylene glycol‐grafted catechol [PEG‐Dopa]₄ hydrogels induced by oxidation using Fe³⁺ produces conformal adhesive contact with the underlying MEA, robust adhesion to electronic sub‐structures, and rapid dissolution of water‐soluble sacrificial release layers. MEAs are integrated on hydrogel‐based substrates to produce free‐standing ultracompliant neural probes, which are then laminated to the surface of the dorsal root ganglia in feline subjects to record single‐unit neural activity.     

Selective Immobilization of Protein Clusters on Polymeric Nanocraters

A method for fabricating chemically nanopatterned surfaces based on a combination of colloidal lithography and plasma‐ enhanced chemical vapor deposition (PECVD) is presented. This method can be applied for the creation of different nanopatterns, and it is in principle not limited in patterning resolution. Nanocraters of poly(acrylic acid) (carboxylic moieties) surrounded by a matrix of poly(ethylene glycol) are fabricated. Chemical force microscopy demonstrates that the process is able to produce the expected surface chemical contrast. Finally, the carboxylic groups of the craters are activated in order to induce the covalent binding of fluorescent‐labeled proteins. Fluorescence investigation using scanning confocal microscopy shows that the proteins are preferentially attached inside the functional craters.     

A Fully Transparent and Flexible Ultraviolet–Visible Photodetector Based on Controlled Electrospun ZnO‐CdO Heterojunction Nanofiber Arrays

It is essential for novel photodetectors to show good photoresponses, high stability, and have facile fabrication methods. Herein, an optimized electrospinning method to fabricate a photodetector based on nanowire arrays that has a wide spectral response range is demonstrated. Arrays of ZnO‐CdO hybrid nanowires are carefully fabricated fusing ZnO and CdO portions into the same nanowires and subsequently assembling those nanowires into a regular structure. Compared to pure ZnO or CdO nanowire arrays, the hybrid arrays show comparable photocurrent/dark current ratios and response speeds, but they possess a much wider spectral response range from ultraviolet to visible light. The optoelectronic and electronic properties of the ZnO‐CdO hybrid nanowire arrays are systematically explored. Based on this, a transparent and flexible photodetector made of ZnO‐CdO hybrid nanowire arrays is fabricated. It shows a high transparency of around 95% in the spectral range of 400–800 nm and maintains its properties even after 200 bending cycles. Importantly, the developed, simple method can be directly applied to many types of substrates and a transfer of the nanowires becomes unnecessary, which guarantees a high quality of the devices.     

Evolutionary optimization for pattern synthesis and reduction of mutual coupling of linear antenna arrays

Optimal design of antenna arrays to minimize the mutual coupling effects in the geometrical arrangements of the linear antenna array (LAA) and circular antenna array (CAA) is dealt with in this work. Two different cases are considered to reduce the effect of LAA and CAA: Case‐1 in which the current excitations of the antenna array are considered to get the optimal radiation pattern of two geometry called LAA and CAA and Case‐2 in which inter‐element spacing and current excitations are both optimized for LAA geometry. A cost function that involves the mutual coupling factor as an optimization factor is developed to reduce the side lobe level (SLL), which takes mutual coupling effects into consideration. Excitation values and inter‐elemental spacing are optimized using particle swarm optimization (PSO). In LAA, for 8‐, 12‐, 16‐element arrays, SLLs are reduced by ?15.52, ?16.71, and ?17.78 dB in Case‐1. For the same sets of element arrays, SLLs were reduced by ?17.35, ?19.71, and ?20.26 dB in Case‐2. In CAA, the current excitations of the antenna array are optimized. For 8‐, 12‐, and 16‐ element arrays, SLLs are reduced to ?7.405, ?10.52, and ?9.43 dB, respectively. The arrays coded with the help of MATLAB based computation and the results obtained by MATLAB are validated by using CST.     

Field-Effect Transistor Based on the Proton Conductivity of Graphene Oxide and Nafion Films

Proton conductivity in graphene oxide and Nafion films depending on humidity and voltages across electrodes is studied in the model of a field-effect transistor. The electrical characteristics of the films are similar to one another, but the mobility of positive charges in Nafion and the current gain are higher by 2–3 orders of magnitude compared with graphene oxide. The negative ion current in graphene-oxide films at positive bias voltage is significant compared with the proton current (up to ~10%), while it is almost lacking in Nafion films (<1%).     

Surface Nanometer‐Scale Patterning in Realizing Large‐Scale Ordered Arrays of Metallic Nanoshells with Well‐Defined Structures and Controllable Properties

Surface patterns of nanoshell arrays play an important role in diverse applications including surface‐enhanced Raman scattering (SERS) sensors, lithium‐ion batteries, solar cells, and optical devices. This paper describes an innovative surface nanopatterning technique for realizing large‐scale ordered arrays of metallic spherical nanoshells with well‐defined structures. Ag nanoshell arrays are prepared using polystyrene sphere templates by an electrophoretic process in Ag colloidal solutions. The fabricated Ag nanoshell arrays have a high controllability of the structural parameters, including the diameter, the surface roughness, and the intershell spacing, giving rise to the tunable properties of nanoshell arrays. As an example, tunable SERS and localized surface plasmon resonance of the nanoshell arrays are demonstrated by controlling the structural parameters. The surface nanopatterning technique shown in this paper is a general fabrication process in achieving not only metallic nanoshell arrays, but also nanoshell arrays of semiconductors and metallic oxides.     

Engineering of Mature Human Induced Pluripotent Stem Cell‐Derived Cardiomyocytes Using Substrates with Multiscale Topography

Producing mature and functional cardiomyocytes (CMs) by in vitro differentiation of induced pluripotent stem cells (iPSCs) using only biochemical cues is challenging. To mimic the biophysical and biomechanical complexity of the native in vivo environment during the differentiation and maturation process, polydimethylsiloxane substrates with 3D topography at the micrometer and sub‐micrometer levels are developed and used as cell‐culture substrates. The results show that while cylindrical patterns on the substrates resembling mature CMs enhance the maturation of iPSC‐derived CMs, sub‐micrometer‐level topographical features derived by imprinting primary human CMs further accelerate both the differentiation and maturation processes. The resulting CMs exhibit a more‐mature phenotype than control groups—as confirmed by quantitative polymerase chain reaction, flow cytometry, and the magnitude of beating signals—and possess the shape and orientation of mature CMs in human myocardium—as revealed by fluorescence microscopy, Ca²⁺ flow direction, and mitochondrial distribution. The experiments, combined with a virtual cell model, show that the physico‐mechanical cues generated by these 3D‐patterned substrates improve the phenotype of the CMs via the reorganization of the cytoskeletal network and the regulation of chromatin conformation.     

Ion‐Current Rectification in Nanopores and Nanotubes with Broken Symmetry

This article focuses on ion transport through nanoporous systems with special emphasis on rectification phenomena. The effect of ion‐current rectification is observed as asymmetric current–voltage (I–V) curves, with the current recorded for one voltage polarity higher than the current recorded for the same absolute value of voltage of opposite polarity. This diode‐like I–V curve indicates that there is a preferential direction for ion flow. Experimental evidence that ion‐current rectification is inherent to asymmetric, e.g., tapered, nanoporous systems with excess surface charge is provided and discussed. The fabrication and operation of asymmetric polymer nanopores, gold nanotubes, glass nanocapillaries, and silicon nanopores are presented. The possibility of tuning the direction and extent of rectification is discussed in detail. Theoretical models that have been developed to explain the ion‐current rectification effect are also presented.     

Uncovering the Structure of Nafion–SiO2 Hybrid Ionomer Membranes for Prospective Large‐Scale Energy Storage Devices

Nafion nanocomposite membranes are attractive candidates for the ion conducting phase in energy storage devices such as vanadium redox flow batteries. Herein, vanadium crossover and Nafion–SiO₂ nanostructure are quantified in a series of hybrid membranes created via solution‐casting Nafion films with discrete SiO₂ nanoparticles, as well as membranes created using an in situ silica sol–gel condensation process. The crossover of vanadium ions is suppressed in all Nafion membranes with the SiO₂ inorganic phase when compared to unannealed, neat Nafion membranes. However, it is also observed that annealing the neat Nafion membranes is equally as effective at suppressing vanadium crossover. Small‐angle neutron scattering measurements show that no significant changes to the Nafion structure occurred in membranes with discrete nanoparticles. In contrast, drastic changes in the scattering profiles of the Nafion–SiO₂ membranes created via sol–gel chemistry are observed, where the SiO₂ nanoclusters are determined to be on the order of 10 nm in diameter. These scattering length scales are verified through real space images using transmission electron microscopy. Insights from this investigation help elucidate the structure of the Nafion–SiO₂ membranes and suggest that the current hypothesis by how vanadium crossover is reduced may not be fully accurate.     

DNA‐Assisted Monolayer Immobilization of 2D Opaline Arrays

DNA supramolecular recognition is employed for the immobilization of 2D photonic crystals of monodisperse colloidal microspheres. Amine‐terminated DNA oligomers are covalently attached to carboxy‐decorated microspheres and substrates while preserving their colloidal stability and organization properties. Following a capillary‐force‐assisted organization of DNA‐decorated microspheres into close‐packed 2D opaline arrays, the first monolayer is immobilized by DNA hybridization. Various parameters affecting the long‐range order of such opaline arrays are investigated, including surface hydrophobicity and the relative strengths of the specific versus nonspecific interactions. The type and concentration of salt and the process temperature are also optimized for the hybridization between microspheres and substrate. The selective removal of non‐specifically bound multilayers is accomplished by carefully passing an air/liquid interface over these arrays. DNA hybridization was found to play an important role in immobilizing the first monolayer of 2D opaline arrays while preserving its long‐range order, with an approximate binding strength three times higher than that of non‐specific interactions.     

基于Parylene的柔性微电极阵列微加工工艺研究

基底集成的柔性微电极阵列(MEAs)从一个全新的角度演绎了植入式神经系统,对神经进行电刺激并记录神经电信号.以一种新型聚合物材料聚对二甲苯(parylene)为基底,制备出了用于神经接口的柔性神经微电极阵列.采用MEMS加工技术,设计了一种基于parylene柔性神经微电极阵列的加工工艺方法,并讨论了在流片过程中的关键问题,如掩膜层的选择、电极的剥离及焊接与封装等.该柔性微电极阵列在用于视觉假体的神经接口方面具有独特的应用优势.     

Nanoholes by soft UV nanoimprint lithography applied to study of membrane proteins

In this paper, we present an alternative technique to the well-known electron beam lithography in order to realize nanoholes in the silicon substrates for biological applications. The used technique is soft UV nanoimprint lithography (UV-NIL). We optimized the fabrication of silicon based supports obtained by soft UV-NIL and reactive ion etching to carry out very large arrays of nanoholes. The resolution limits are investigated when using poly(dimethylsiloxane) as flexible mold material. RIE conditions are initiated to limit the lateral mask resist etch.     

Surface Textured Polymer Fibers for Microfluidics

This article introduces surface textured polymer fibers as a new platform for the fabrication of affordable microfluidic devices. Fibers are produced tens of meters‐long at a time and comprise 20 continuous and ordered channels (equilateral triangle grooves with side lengths as small as 30 micrometers) on their surfaces. Extreme anisotropic spreading behavior due to capillary action along the grooves of fibers is observed after surface modification with polydopamine (PDA). These flexible fibers can be fixed on any surface—independent of its material and shape—to form three‐dimensional arrays, which spontaneously spread liquid on predefined paths without the need for external pumps or actuators. Surface textured fibers offer high‐throughput fabrication of complex open microfluidic channel geometries, which is challenging to achieve using current photolithography‐based techniques. Several microfluidic systems are designed and prepared on either planar or 3D surfaces to demonstrate outstanding capability of the fiber arrays in control of fluid flow in both vertical and lateral directions. Surface textured fibers are well suited to the fabrication of flexible, robust, lightweight, and affordable microfluidic devices, which expand the role of microfluidics in a scope of fields including drug discovery, medical diagnostics, and monitoring food and water quality.     

High‐Performance Ionic‐Polymer–Metal Composite: Toward Large‐Deformation Fast‐Response Artificial Muscles

As promising candidates in the field of artificial muscles, ionic‐polymer–metal composites (IPMCs) still cannot simultaneously provide large deformations and fast responses, which has limited their practical applications. In this study, to overcome this issue, a Nafion‐based IPMC with high‐quality metal electrodes is fabricated via novel isopropanol‐assisted electroless plating. The IPMC exhibits a large tip displacement (35.3 mm, 102.3°) under a low direct‐current driving voltage and ultrafast response (>10 Hz) under an alternating‐current (AC) voltage. Furthermore, the simultaneous integration of a large deformation and fast response can be achieved by the IPMC under a high‐frequency (19 Hz) AC voltage, where the largest bending amplitude is 5.9 mm and the highest bending speed reaches 224.2 mm s^?1 (596.2° s^?1). Additionally, the lightweight IPMC exhibits a decent load capacity and can lift objects 20 times heavier. The outstanding performances of the Nafion IPMC are demonstrated by mimicking biological motions such as petal opening/closing, tendril coiling/uncoiling, and high‐frequency wing flapping. This study paves the way for the fabrication of lightweight actuators with simultaneous large displacements and fast responses for promising applications in biomedical devices and bioinspired robotics.     

LED阵列型紫外光固化光源系统

提出了一种适用于紫外光固化的新型光源系统.该系统以大功率紫外光LED和光学系统组成阵列结构来实现固化光源的高辐照度,大功率LED阵列由多路可控恒流源系统控制,根据固化材料的特点外部设定驱动电流,控制光源发光强度.与常用的高压汞灯相比,该系统无需高压驱动和冷却设备,具有操作简单、固化效率高和绿色无污染等优点.实验结果表明,该系统能够发出均匀稳定的高强度紫外光.