High‐Strength,Durable All‐Silk Fibroin Hydrogels with Versatile Processability toward Multifunctional Applications

Hydrogels are the focus of extensive research due to their potential use in fields including biomedical, pharmaceutical, biosensors, and cosmetics. However, the general weak mechanical properties of hydrogels limit their utility. Here, pristine silk fibroin (SF) hydrogels with excellent mechanical properties are generated via a binary‐solvent‐induced conformation transition (BSICT) strategy. In this method, the conformational transition of SF is regulated by moderate binary solvent diffusion and SF/solvent interactions. β‐sheet formation serves as the physical crosslinks that connect disparate protein chains to form continuous 3D hydrogel networks, avoiding complex chemical and/or physical treatments. The Young's modulus of these new BSICT–SF hydrogels can reach up to 6.5 ± 0.2 MPa, tens to hundreds of times higher than that of conventional hydrogels (0.01–0.1 MPa). These new materials fill the “empty soft materials' space” in the elastic modulus/strain Ashby plot. More remarkably, the BSICT–SF hydrogels can be processed into different constructions through different polymer and/or metal‐based processing techniques, such as molding, laser cutting, and machining. Thus, these new hydrogel systems exhibit potential utility in many biomedical and engineering fields.     

Self‐Healable Multifunctional Electronic Tattoos Based on Silk and Graphene

Electronic tattoos (E‐tattoos), which can be intimately mounted on human skin for noninvasive and high‐fidelity sensing, have attracted the attention of researchers in the field of wearable electronics. However, fabricating E‐tattoos that are capable of self‐healing and sensing multistimuli, similar to the inherent attributes of human skin, is still challenging. Herein, a healable and multifunctional E‐tattoo based on a graphene/silk fibroin/Ca²⁺ (Gr/SF/Ca²⁺) combination is reported. The highly flexible E‐tattoos are prepared through printing or writing using Gr/SF/Ca²⁺ suspension. The graphene flakes distributed in the matrix form an electrically conductive path that is responsive to environmental changes, such as strain, humidity, and temperature variations, endowing the E‐tattoo with high sensitivity to multistimuli. The performance of the E‐tattoo is investigated as a strain, humidity, and temperature sensor that shows high sensitivity, a fast response, and long‐term stability. The E‐tattoo is remarkably healed after damage by water because of the reformation of hydrogen and coordination bonds at the fractured interface. The healing efficiency is 100% in only 0.3 s. Finally, as proof of concept, its applications for monitoring of electrocardiograms, breathing, and temperature are shown. Based on its unique properties and superior performance, the Gr/SF/Ca²⁺ E‐tattoo may be a promising candidate material for epidermal electronics.     

Calcium‐Modified Silk as a Biocompatible and Strong Adhesive for Epidermal Electronics

With the increasing interest and demand for epidermal electronics, a strong interface between a sensor and a biological surface is essential, yet achieving such interface is still a challenge. Here, a calcium (Ca)‐modified biocompatible silk fibroin as a strong adhesive for epidermal electronics is proposed and the physical principles behind its interfacial and adhesive properties are reported. A strong adhesive characteristic (>800 N m^?1) is observed because of the increase in both viscoelastic property and mechanical interlocking through the incorporation of Ca ions. Furthermore, additional key characteristics of the Ca‐modified silk: reusability, stretchability, biocompatibility, and conductivity, are reported. These characteristics enable a wide range of applications as demonstrated in four epidermal electronic systems: capacitive touch sensor, resistive strain sensor, hydrogel‐based drug delivery, and electrocardiogram monitoring sensor. As a reusable, biocompatible, conductive, and strong adhesive with water‐degradability, the Ca‐modified silk adhesive is a promising candidate for the next‐generation adhesive for epidermal biomedical sensors.     

Recombinant Spider Silk as Mediator for One‐Step,Chemical‐Free Surface Biofunctionalization

A unique strategy for effective, versatile, and facile surface biofunctionalization employing a recombinant spider silk protein genetically functionalized with the antibody‐binding Z domain (Z‐4RepCT) is reported. It is demonstrated that Z‐silk can be applied to a variety of materials and platform designs as a truly one‐step and chemical‐free surface modification that site specifically captures antibodies while simultaneously reducing nonspecific adsorption. As a model surface, SiO₂ is used to optimize and characterize Z‐silk performance compared to the Z domain immobilized by a standard silanization method. First, Z‐silk adsorption is investigated and verified its biofunctionality in a long‐term stability experiment. To assess the binding capacity and protein–protein interaction stability of Z‐silk, the coating is used to capture human antibodies in various assay formats. An eightfold higher binding capacity and 40‐fold lower detection limit are obtained in the immunofluorescence assay, and the complex stability of captured antibodies is shown to be improved by a factor of 20. Applicability of Z‐silk to functionalize microfluidic devices is demonstrated by antibody detection in an electrokinetic microcapillary biosensor. To test Z‐silk for biomarker applications, real‐time detection and quantification of human immunoglobulin G are performed in a plasma sample and C1q capture from human serum using an anti‐C1q antibody.     

Ultra‐High Capacity Lithium‐Ion Batteries with Hierarchical CoO Nanowire Clusters as Binder Free Electrodes

Although transition metal oxide electrodes have large lithium storage capacity, they often suffer from low rate capability, poor cycling stability, and unclear additional capacity. In this paper, CoO nanowire clusters (NWCs) composed of ultra‐small nanoparticles (≈10 nm) directly grown on copper current collector are fabricated and evaluated as an anode of binder‐free lithium‐ion batteries, which exhibits an ultra‐high capacity and good rate capability. At a rate of 1 C (716 mA g^?1), a reversible capacity as high as 1516.2 mA h g^?1 is obtained, and even when the current density is increased to 5 C, a capacity of 1330.5 mA h g^?1 could still be maintained. Importantly, the origins of the additional capacity are investigated in detail, with the results suggesting that pseudocapacitive charge and the higher‐oxidation‐state products are jointly responsible for the large additional capacity. In addition, nanoreactors for the CoO nanowires are fabricated by coating the CoO nanowires with amorphous silica shells. This hierarchical core–shell CoO@SiO₂ NWC electrode achieves an improved cycling stability without degrading the high capacity and good rate capability compared to the uncoated CoO NWCs electrode.     

Silicon Inverse‐Opal‐Based Macroporous Materials as Negative Electrodes for Lithium Ion Batteries

Several types of silicon‐based inverse‐opal films are synthesized, characterized by a range of experimental techniques, and studied in terms of electrochemical performance. Amorphous silicon inverse opals are fabricated via chemical vapor deposition. Galvanostatic cycling demonstrates that these materials possess high capacities and reasonable capacity retentions. Amorphous silicon inverse opals perform unsatisfactorily at high rates due to the low conductivity of silicon. The conductivity of silicon inverse opals can be improved by their crystallization. Nanocrystalline silicon inverse opals demonstrate much better rate capabilities but the capacities fade to zero after several cycles. Silicon–carbon composite inverse‐opal materials are synthesized by depositing a thin layer of carbon via pyrolysis of a sucrose‐based precursor onto the silicon inverse opals. The amount of carbon deposited proves to be insufficient to stabilize the structures and silicon–carbon composites demonstrate unsatisfactory electrochemical behavior. Carbon inverse opals are coated with amorphous silicon producing another type of macroporous composite. These electrodes demonstrate significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increases the material conductivity but also results in lower silicon pulverization during cycling.     

Self‐Adhesive Macroporous Carbon Electrodes for Efficient and Stable Perovskite Solar Cells

Carbon electrode are a low‐cost and great potential strategy for stable perovskite solar cells (PSCs). However, the efficiency of carbon‐based PSCs lags far behind compared with that of state‐of‐the‐art PSCs. The poor interface contact between the carbon electrode and the underlying layer dominates the performance loss of the reported carbon‐based PSCs. In this respect, a sort of self‐adhesive macroporous carbon film is developed as counter electrode by a room‐temperature solvent‐exchange method. Via a simple press transfer technique, the carbon film can form excellent interface contact with the underlying hole transporting layer, remarkably beneficial to interface charge transfer. A power conversion efficiency of up to 19.2% is obtained for mesoporous‐structure PSCs, which is the best achieved for carbon‐based PSCs. Moreover, the device exhibits greatly improved long‐term stability. It retains over 95% of the initial efficiency after 1000 h storage under ambient atmosphere. Furthermore, after aging for 80 h under illumination and maximum power point in nitrogen atmosphere, the carbon‐based PSC retains over 94% of its initial performance.     

Highly Interconnected Porous Electrodes for Dye‐Sensitized Solar Cells Using Viruses as a Sacrificial Template

A novel means of generating highly interconnected and nano‐channeled photoelectrodes by employing one‐dimensionally shaped M13 viruses as a sacrificial template is proposed for highly efficient dye‐sensitized solar cells (DSSCs). The electrostatic binding between oppositely charged TiO₂ nanoparticles and M13 viruses provides a uniform complexation and suppresses random aggregation of TiO₂ nanoparticles. After the calcination process, the traces of viruses leave porously interconnected channel structures inside TiO₂ nanoparticles, providing efficient paths for electrolyte contact as well as increased surface sites for dye adsorption. As a result, DSSCs generated using a sacrificial virus template exhibit an enhanced current density (J_SC) of 12.35 mA cm‐² and a high photoconversion efficiency (η) of 6.32%, greater than those of conventional photoelectrodes made of TiO₂ nanoparticles (J_SC of 8.91 mA cm‐² and η of 4.67%). In addition, the stiffness and shape of the M13 virus can be varied, emphasizing the usefulness of the one‐dimensional structural characteristics of M13 viruses for the highly interconnected porous structure of DSSC photoelectrodes.     

Novel Film‐Casting Method for High‐Performance Flexible Polymer Electrodes

A new film‐casting method for polymer electrodes is reported, in which thickness‐controlled drop‐casting (TCDC), using polyaniline doped with camphorsulfonic acid (PANI:CSA) is used. By combining the advantages of conventional spin‐casting and drop‐casting methods, and by rigorously controlling the film formation parameters, flexible polymer electrodes with high conductivity and excellent transmittance can be produced. The PANI:CSA electrodes cast by the TCDC method exhibited constant thickness‐independent conductivities of ～600 S cm^?1 down to a film thickness of 0.2 μm, and a high optical transmittance of about 85% at 550 nm. Furthermore, the new casting method significantly reduced the sheet resistance (～90 Ω/square) of the PANI:CSA electrodes compared with the conventional spin‐cast films, enhancing the performance of the devices deposited on plastic substrates. The flexible polymer light‐emitting diode produced a brightness of 6000 cd m^?2, and the flexible polymer solar cell exhibited a power conversion efficiency of 2%, both of which were much higher than those of the devices fabricated by the conventional spin‐casting method.     

A Thermal‐Reflow‐Based Low‐Temperature,High‐Pressure Sintering of Lyophilized Silk Fibroin for the Fast Fabrication of Biosubstrates

Solid fibroin is a bulk nonporous material that can be prepared with two methods: a liquid–gel–solid transition from a fibroin solution or a sintering procedure starting from silk powder. Both methods have their own disadvantages: the first requires several weeks and the process is size dependent; the second requires high temperatures. To overcome these limitations, a low‐temperature sintering procedure based on a thermal‐reflow is proposed in this work to produce in fast‐fashion monoliths of solid fibroin. Thermal‐reflow is a well‐known mechanism that takes place when the glass transition temperature of the material is lower than the temperature used to process it. Water plays an important role decreasing the glass transition temperature down to 40 °C. For the first time, a thermal reflow is conducted on lyophilized silk fibroin at 40 °C, associating to the water addition a high‐pressure compression. To optimize the process, a full factorial design of experiment is used. The material is then studied in the crucial phases by digital scanning calorimetry, Fourier‐transform infrared spectroscopy, and scanning electron microscopy. Finally, a mechanical characterization and a preliminary in vitro test are conducted.     

High‐Performance Polypyrrole/Graphene/SnCl2 Modified Polyester Textile Electrodes and Yarn Electrodes for Wearable Energy Storage

Flexible supercapacitors have potential for wearable energy storage due to their high energy/power densities and long operating lifetimes. High electrochemical performance with robust mechanical properties is highly desired for flexible supercapacitor electrodes. Usually, the mechanical properties are improved by choosing high flexible textile substrates but at the much expense of electrochemical performance due to the nonideal contact between conductive materials and textile substrates. Herein, the authors present an efficient, scalable, and general strategy for the simultaneous fabrication of high‐performance textile electrodes and yarn electrodes. It is interesting to find that the conformal reduced graphene oxide (RGO) layer is uniformly and successively painted on the surface of SnCl₂ modified polyester fibers (M‐PEF) via a repeated “dyeing and drying” strategy. The large‐area textile electrodes and ultralong yarn electrodes are fabricated by using RGO/M‐PEF as substrate with subsequent deposition of polypyrrole. This work provides new opportunities for developing high flexible textile electrodes and yarn electrodes with further increased electrochemical performance and scalable production.     

Solution‐Processed Metallic Nanowire Electrodes as Indium Tin Oxide Replacement for Thin‐Film Solar Cells

Solution processed silver nanowire (Ag NW) films are introduced as transparent electrodes for thin‐film solar cells. Ag NW electrodes were processed by doctor blade‐coating on glass substrates at moderate temperatures (less than 100 °C). The morphological, optical, and electrical characteristics of these electrodes were investigated as a function of processing parameters. For solar‐cell application, Ag NW electrodes with an average transparency of 90% between 450 and 800 nm and a sheet resistivity of ≈10 Ω per square were chosen. The performance of poly(3‐hexylthiophen‐2,5‐diyl):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PCBM) solar cells on Ag NW electrodes was found to match the performance of otherwise identical cells on indium tin oxide. Overall, P3HT:PCBM solar cells with an efficiency of 2.5% on transparent Ag NW electrodes have been realized.     

Development of Vanadium‐Coated Carbon Microspheres: Electrochemical Behavior as Electrodes for Supercapacitors

Vanadium‐coated carbon‐xerogel microspheres are successfully prepared by a specific designed sol–gel method, and their supercapacitor behavior is tested in a two‐electrode system. Nitrogen adsorption shows that these composite materials present a well‐developed micro‐ and mesoporous texture, which depends on the vanadium content in the final composite. A high dispersion of vanadium oxide on the carbon microsphere surface is reached, being the vanadium particle size around 4.5 nm. Moreover, low vanadium oxidation states are stabilized by the carbon matrix in the composites. The complete electrochemical characterization of the composites is carried out using cyclic voltammetry, chronopotentiometry, cycling charge–discharge, and impedance spectroscopy. The results show that these composites present high capacitance as 224 F g^?1, with a high capacitance retention which is explained on the basis of the presence of vanadium oxide, texture, and chemistry surface.     

All‐Solution‐Processed Indium‐Free Transparent Composite Electrodes based on Ag Nanowire and Metal Oxide for Thin‐Film Solar Cells

Fully solution‐processed Al‐doped ZnO/silver nanowire (AgNW)/Al‐doped ZnO/ZnO multi‐stacked composite electrodes are introduced as a transparent, conductive window layer for thin‐film solar cells. Unlike conventional sol–gel synthetic pathways, a newly developed combustion reaction‐based sol–gel chemical approach allows dense and uniform composite electrodes at temperatures as low as 200 °C. The resulting composite layer exhibits high transmittance (93.4% at 550 nm) and low sheet resistance (11.3 Ω sq^‐1), which are far superior to those of other solution‐processed transparent electrodes and are comparable to their sputtered counterparts. Conductive atomic force microscopy reveals that the multi‐stacked metal‐oxide layers embedded with the AgNWs enhance the photocarrier collection efficiency by broadening the lateral conduction range. This as‐developed composite electrode is successfully applied in Cu(In_1‐x,Ga_x)S₂ (CIGS) thin‐film solar cells and exhibits a power conversion efficiency of 11.03%. The fully solution‐processed indium‐free composite films demonstrate not only good performance as transparent electrodes but also the potential for applications in various optoelectronic and photovoltaic devices as a cost‐effective and sustainable alternative electrode.     

An Electrochemical Bottom‐Up Approach to Producing Nanostructured Electrodes Based on Nanocolumnar ZnO Acting as a Self‐Assembled Template

An Fe₃O₄/Cu nanostructured prototype electrode was developed from a 100% bottom‐up approach thanks to an original three‐step electrodeposition procedure that enlists 1) the growth of a ZnO nanocolumnar template, 2) the filling of the template voids by copper prior to the dissolution of the zincite nanopillars, and 3) the plating on the remaining copper nanodots of the Fe₃O₄ phase. The key technological point is that ZnO readily forms nanorod arrays by self‐assembly when an aqueous solution of Zn^II, saturated by dioxygen, is cathodically polarized. The as‐obtained inorganic solid template is sufficiently stable for further deposition steps of any kind (metals, oxides, polymers, and so on) but is easy to remove in both acidic and alkaline media. The self‐supported Fe₃O₄/Cu nanostructured electrode shows, besides sustained capacity retention, outstanding rate capability when electrochemically tested versus Li. This original and soft process, derived from template‐assisted synthesis, avoids fixing (mechanically) a nanoporous membrane on the substrate, thus, enabling nanostructural design on shapeless surfaces.     

Constitutional Isomerization Enables Bright NIR‐II AIEgen for Brain‐Inflammation Imaging

The shortage of high quantum yield (QY) organic fluorophores in the second near‐infrared window (NIR‐II) has become a bottleneck in bioimaging field. Now, a simple strategy is proposed to address this: constitutional isomerization on the basis of the molecular design philosophy of aggregation‐induced emission. With the combination of backbone distortion and rotor twisting, the resultant NIR‐II fluorophore 2TT‐oC6B displays an emission peak at 1030 nm and a QY of 11% in nanoparticles, one of the highest reported so far. Control molecules confirm that the distorted backbone and twisted rotors play equally important roles in determining the fluorescence properties of the NIR‐II fluorophores. To allow for the targeting ability to reach deeply located diseases, neutrophils (NEs) are used to penetrate the brain tissues and accumulate in the inflammation site. Herein, it is shown that NEs carrying 2TT‐oC6B nanoparticles can penetrate the blood‐brain‐barrier and visualize the deeply located inflammation through an intact scalp and skull. Notably, the bright 2TT‐oC6B contributes to a significantly enhanced signal‐to‐background ratio of 30.6 in the brain inflammation site.     

Fabrication of Silk Microneedles for Controlled‐Release Drug Delivery

Microneedles are emerging as a minimally invasive drug delivery alternative to hypodermic needles. Current material systems utilized in microneedles impose constraints hindering the further development of this technology. In particular, it is difficult to preserve sensitive biochemical compounds (such as pharmaceuticals) during processing in a single microneedle system and subsequently achieve their controlled release. A possible solution involves fabricating microneedles systems from the biomaterial silk fibroin. Silk fibroin combines excellent mechanical properties, biocompatibility, biodegradability, benign processing conditions, and the ability to preserve and maintain the activity of biological compounds entrained in its material matrix. The degradation rate of silk fibroin and the diffusion rate of the entrained molecules can be controlled simply by adjusting post‐processing conditions. This combination of properties makes silk an ideal choice to improve on existing issues associated with other microneedle‐based drug delivery system. In this study, a fabrication method to produce silk biopolymer microstructures with the high aspect ratios and mechanical properties required to manufacture microneedle systems is reported. Room temperature and aqueous‐based micromolding allows for the bulk loading of these microneedles with labile drugs. The drug release rate is decreased 5.6‐fold by adjusting the post‐processing conditions of the microneedles, mainly by controlling the silk protein secondary structure. The release kinetics are quantified in an in vitro collagen hydrogel model, which allows tracking of the model drug. Antibiotic loaded silk microneedles are manufactured and used to demonstrate a 10‐fold reduction of bacterial density after their application. The processing strategies developed in this study can be expanded to other silk‐based structural formats for drug delivery and biologicals storage applications.     

Nickel Silicide Nanowire Arrays for Anti‐Reflective Electrodes in Photovoltaics

Conductive nanowires (NWs) provide several advantages as a template and electrode material for solar cells due to their favorable light scattering properties. While the majority of NW solar cell architectures studied are based on semiconductor materials, metallic NWs could provide equivalent anti‐reflection properties, while acting as a low‐resistance back contact for charge transport, and facilitate light scattering in thin layers of semiconductors coated on the surface. However, fabrication of single‐crystalline highly anti‐reflective NWs on low‐cost, flexible substrates remains a challenge to drive down the cost of NW solar cells. In this study, metallic Ni_xSi NW arrays are fabricated by a simple, bottom‐up, and low‐cost method based on the thermal decomposition of silane on the surface of flexible Ni foil substrates without the need for lithography, etching or catalysts. The optical properties of these NW arrays demonstrate broadband suppression of reflection to levels below 1% from 350 nm to 1100 nm, which is among the highest values reported for NWs. A simple route to control the diameter and density of the NWs is introduced based on variations in a carrier gas flow rate. A high‐resolution TEM, XRD and TEM‐EDS study of the NWs reveals that they are single crystalline, with the phase and composition varying between Ni₂Si and NiSi. The nanowire resistivity is measured to be 10^?4 Ω‐cm, suggesting their use as an efficient back electrode material for nanostructured solar cells with favorable light scattering properties.     

Rugged Textile Electrodes for Wearable Devices Obtained by Vapor Coating Off‐the‐Shelf,Plain‐Woven Fabrics

Fabrics are pliable, breathable, lightweight, ambient stable, and have unmatched haptic perception. Here, a vapor deposition method is used to transform off‐the‐shelf plain‐woven fabrics, such as linen, silk, and bast fiber fabrics, into metal‐free conducting electrodes. These fabric electrodes are resistant to wear, stable after laundering and ironing, and can be body‐mounted with little detriment to their performance. A unique by‐product of conformally vapor coating plain‐woven fabrics is that textile parameters, such as thread material and fabric porosity, significantly affect the conductivity of the resulting fabric electrodes. The resistivities of the electrodes reported herein are linearly, not exponentially, dependent on length, meaning that they can be feasibly incorporated into garments and other large‐area body‐mounted devices. Further, these fabric electrodes possess the feel, weight, breathability, and pliability of standard fabrics, which are important to enable adoption of wearable devices.     

Transparent Ultrathin Oxygen‐Doped Silver Electrodes for Flexible Organic Solar Cells

An effective method for depositing highly transparent and conductive ultrathin silver (Ag) electrodes using minimal oxidation is reported. The minimal oxidation of Ag layers significantly improves the intrinsic optical and structural properties of Ag without any degradation of its electrical conductivity. Oxygen‐doped Ag (AgO_x) layers of thicknesses as low as 6 nm exhibit completely 2D and continuous morphologies on ZnO films, smaller optical reflections and absorbances, and smaller sheet resistances compared with those of discontinuous and granular‐type Ag layers of the same thickness. A ZnO/AgO_x/ZnO (ZAOZ) electrode using an AgO_x (O/Ag = 3.4 at%) layer deposited on polyethylene terephthalate substrates at room temperature shows an average transmittance of 91%, with a maximum transmittance of 95%, over spectral range 400?1000 nm and a sheet resistance of 20 Ω sq^?1. The average transmittance value is increased by about 18% on replacing a conventional ZnO/Ag/ZnO (ZAZ) electrode with the ZAOZ electrode. The ZAOZ electrode is a promising bottom transparent conducting electrode for highly flexible inverted organic solar cells (IOSCs), and it achieves a power conversion efficiency (PCE) of 6.34%, whereas an IOSC using the ZAZ electrode exhibits a much lower PCE of 5.65%.