High-performance green flexible electronics based on biodegradable cellulose nanofibril paper

Highly conductive carbon-based aqueous inks toward electroluminescent devices, printed capacitive sensors and flexible wearable electronics

Carbon-based conductive inks are one of the most important materials in the field of printing electronics. However, most carbon-based conductive inks with small electrical resistance are expensive, such as graphene. It limits the commercial use of carbon inks in the fields of flexible electronics and printed electronics. Here, we propose a low-cost and environmentally friendly formula based on dihydroxyphenyl-functionalized multi-walled carbon nanotubes (MWNT-f-OH)/carbon black/graphite as conductive fillers and waterborne acrylic resins as binders for preparing highly conductive carbon-based aqueous inks (HCCA-inks). Our study showed that when the mass fraction of carbon black, graphite and MWNT-f-OH was 3.0%, 10.2% and 4.1%, respectively, on a thickness of 40 μm, optimal conductivity (sheet resistance up to 29 Ω sq-1) was achieved, and the printed HCCA-inks on a paper could withstand extremely high folding cycles (>2000 cycles) while the resistance value of the flexible circuit only increased by 11%. The carbon-based aqueous inks showed high electrical conductivity and excellent mechanical stability, which makes it possible for them to be used as flexible wearable electronics, electroluminescent (EL) devices and printed capacitive sensors.

Paper-Based Disposable Molecular Sensor Constructed from Oxide Nanowires, Cellulose Nanofibers, and Pencil-Drawn Electrodes

Progress toward the concept of "a trillion sensor universe" requires sensor devices to become more abundant, ubiquitous, and be potentially disposable. Here, we report a paper-based disposable molecular sensor device constructed from a nanowire sensor based on common zinc oxide (ZnO), a wood-derived biodegradable cellulose nanofiber paper substrate, and a low-cost graphite electrode. The ZnO nanowire/cellulose nanofiber composite structure is embedded in the surface of the cellulose nanofiber paper substrate via a two-step papermaking process. This structure provides a mechanically robust and efficiently bridged network for the nanowire sensor, while ensuring efficient access to target molecules and allowing reliable electrical contact with electrodes. The as-fabricated paper sensor device with pencil-drawn graphite electrodes exhibits efficient resistance change-based molecular sensing of NO₂ as a model gas. The performance of our device is comparable to that of noble metal electrodes. Furthermore, we demonstrate cut-and-paste usability and easy disposal of the sensor device with its uniform in-plane sensing properties. Our strategy offers a disposable molecular sensing platform for use in future sensor network technologies.

Ultrahigh Tough, Super Clear, and Highly Anisotropic Nanofiber-Structured Regenerated Cellulose Films

While tremendous efforts have been dedicated to developing environmentally friendly films made from natural polymers and renewable resources, in particular, multifunctional films featuring extraordinary mechanical properties, optical performance, and ordered nanostructure, challenges still remain in achieving all these characteristics in a single material via a scalable process. Here, we designed a green route to fabricating strong, super tough, regenerated cellulose films featuring tightly stacked and long-range aligned cellulose nanofibers self-assembled from cellulose solution in alkali/urea aqueous systems. The well-aligned nanofibers were generated by directionally controlling the aggregation of cellulose chains in the hydrogel state using a preorientation-assisted dual cross-linking approach; i.e., a physical cross-linking was rapidly introduced to permanently reserve the temporarily aligned nanostructure generated by preorienting the covalent cross-linked gels. After a structural densification in air-drying of hydrogel, high strength was achieved, and more importantly, a record-high toughness (41.1 MJ m^-3) in anisotropic nanofibers-structured cellulose films (ACFs) was reached. Moreover, the densely packed and well-aligned cellulose nanofibers significantly decreased the interstices in the films to avoid light scattering, granting ACFs with high optical clarity (91%), low haze (<3%), and birefringence behaviors. This facile and high-efficiency strategy might be very scalable in fabricating high-strength, super tough, and clear cellulose films for emerging biodegradable next-generation packaging, flexible electronic, and optoelectronic applications.

Flexible and Highly Sensitive Humidity Sensor Based on Cellulose Nanofibers and Carbon Nanotube Composite Film

Flexible and highly sensitive humidity sensors are crucial for humidity detection. In this study, a flexible cellulose nanofiber/carbon nanotube (NFC/CNT) humidity sensor with high sensitivity performance was developed via fast vacuum filtration. CNTs were well dispersed in water by using 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-oxidized NFC as a dispersant. More importantly, NFC also acted as a humidity sensitive material, achieving superior performance of NFC/CNT humidity sensors. The obtained NFC/CNT humidity sensor with 5 wt % CNT loading exhibits outstanding sensitive performance, and its response value reaches a maximum of 69.9% (Δ I/ I₀) at 95% relative humidity (RH). It also displays good bending resistance and long-term stability. In addition, the NFC/CNT humidity sensor was employed to monitor human breath. Therefore, we believe that the flexible, highly sensitive, and simply designed NFC/CNT humidity sensor is a promising candidate for various applications in the field of humidity measurement.

A Protein-Based, Water-Insoluble, and Bendable Polymer with Ionic Conductivity: A Roadmap for Flexible and Green Electronics

Proteins present an ecofriendly alternative to many of the synthetic components currently used in electronics. They can therefore in combination with flexibility and electroactivity uncover a range of new opportunities in the field of flexible and green electronics. In this study, silk-based ionic conductors are turned into stable thin films by embedding them with 2D nanoclay platelets. More specifically, this material is utilized to develop a flexible and ecofriendly motion-sensitive touchscreen device. The display-like sensor can readily transmit light, is easy to recycle and can monitor the motion of almost any part of the human body. It also displays a significantly lower sheet resistance during bending and stretching regimes than the values typically reported for conventional metallic-based conductors, and remains fully operational after mechanical endurance testing. Moreover, it can operate at high frequencies in the kilohertz (kHz) range under both normal and bending modes. Notably, our new technology is available through a simple one-step manufacturing technique and can therefore easily be extended to large-scale fabrication of electronic devices.

A Protein-Based, Water-Insoluble, and Bendable Polymer with Ionic Conductivity: A Roadmap for Flexible and Green Electronics

Proteins present an ecofriendly alternative to many of the synthetic components currently used in electronics. They can therefore in combination with flexibility and electroactivity uncover a range of new opportunities in the field of flexible and green electronics. In this study, silk-based ionic conductors are turned into stable thin films by embedding them with 2D nanoclay platelets. More specifically, this material is utilized to develop a flexible and ecofriendly motion-sensitive touchscreen device. The display-like sensor can readily transmit light, is easy to recycle and can monitor the motion of almost any part of the human body. It also displays a significantly lower sheet resistance during bending and stretching regimes than the values typically reported for conventional metallic-based conductors, and remains fully operational after mechanical endurance testing. Moreover, it can operate at high frequencies in the kilohertz (kHz) range under both normal and bending modes. Notably, our new technology is available through a simple one-step manufacturing technique and can therefore easily be extended to large-scale fabrication of electronic devices.

A nanofluidic ion regulation membrane with aligned cellulose nanofibers

The advancement of nanofluidic applications will require the identification of materials with high-conductivity nanoscale channels that can be readily obtained at massive scale. Inspired by the transpiration in mesostructured trees, we report a nanofluidic membrane consisting of densely packed cellulose nanofibers directly derived from wood. Numerous nanochannels are produced among an expansive array of one-dimensional cellulose nanofibers. The abundant functional groups of cellulose enable facile tuning of the surface charge density via chemical modification. The nanofiber-nanofiber spacing can also be tuned from ~2 to ~20 nm by structural engineering. The surface-charge-governed ionic transport region shows a high ionic conductivity plateau of ~2 mS cm^-1 (up to 10 mM). The nanofluidic membrane also exhibits excellent mechanical flexibility, demonstrating stable performance even when the membrane is folded 150°. Combining the inherent advantages of cellulose, this novel class of membrane offers an environmentally responsible strategy for flexible and printable nanofluidic applications.

The design, fabrication, and applications of flexible biosensing devices

Flexible biosensors form part of a rapidly growing research field that take advantage of a multidisciplinary approach involving materials, fabrication and design strategies to be able to function at biological interfaces that may be soft, intrinsically curvy, irregular, or elastic. Numerous exciting advancements are being proposed and developed each year towards applications in healthcare, fundamental biomedical research, food safety and environmental monitoring. In order to place these developments in perspective, this review is intended to present an overview on field of flexible biosensor development. We endeavor to show how this subset of the broader field of flexible and wearable devices presents unique characteristics inherent in their design. Initially, a discussion on the structure of flexible biosensors is presented to address the critical issues specific to their design. We then summarize the different materials as substrates that can resist mechanical deformation while retaining their function of the bioreceptors and active elements. Several examples of flexible biosensors are presented based on the different environments in which they may be deployed or on the basis of targeted biological analytes. Challenges and future perspectives pertinent to the current and future stages of development are presented. Through these summaries and discussion, this review is expected to provide insights towards a systematic and fundamental understanding for the fabrication and utilization of flexible biosensors, as well as inspire and improve designs for smart and effective devices in the future.

A highly conductive, pliable and foldable Cu/cellulose paper electrode enabled by controlled deposition of copper nanoparticles

There is great interest in extending cellulosic platforms to applications in flexible, lightweight, low-cost and sustainable electronics. The critical need is the development of methods to confer electronic properties to these materials platforms (i.e., paper and fabrics). Here we report a highly conductive, pliable and foldable Cu/cellulose paper electrode enabled by a simple low-cost and scalable wet-processing method to coat a Cu nanoparticle (NP) layer on common cellulose paper, where polydopamine adhesion and electroless deposition were used to yield highly conductive paper with a sheet resistance as low as 0.01 Ω sq-1. This Cu/cellulose paper has excellent stability because of the strong adhesion between Cu NPs and cellulose, and because the methods are sufficiently mild to prevent damage to the paper substrate. This fabrication method results in the controlled deposition of Cu NPs and yields Cu/cellulose paper with highly hydrophobic and self-cleaning properties, high photothermal conversion efficiency, and excellent electromagnetic interface (EMI) shielding effectiveness. This high-performance Cu/cellulose paper could have promising application potential for a range of emerging applications in flexible electronics and packaging.

Two-Dimensional Antifouling Fluidic Channels on Nanopapers for Biosensing

Two-dimensional (hydrophilic) channels were patterned on films prepared from cellulose nanofibrils (CNF) using photolithography and inkjet printing. Such processes included UV-activated thiol-yne click coupling and inkjet-printed designs with polystyrene. The microfluidic channels were characterized (SEM, wetting, and fluid flow) and applied as platforms for biosensing. Compared to results from the click method, a better feature fidelity and flow properties were achieved with the simpler inkjet-printed channels. Human immunoglobulin G (hIgG) was used as target protein after surface modification with either bovine serum albumin (BSA), fibrinogen, or block copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) (PDMAEMA- block-POEGMA copolymers). Surface plasmon resonance (SPR) and AFM imaging were used to determine their antifouling effect to prevent nonspecific hIgG binding. Confocal laser scanning microscopy revealed diffusion and adsorption traces in the channels. The results confirm an effective surface passivation of the microfluidic channels (95% reduction of hIgG adsorption and binding). The inexpensive and disposable systems proposed here allow designs with space-resolved blocking efficiency that offer a great potential in biosensing.

Fungi-Enabled Synthesis of Ultrahigh-Surface-Area Porous Carbon

The growth of white-rot fungi is related to the superior infiltrability and biodegradability of hyphae on a lignocellulosic substrate. The superior biodegradability of fungi toward plant substrates affords tailored microstructures, which benefits subsequently high efficient carbonization and chemical activation. Here, the mechanism underlying the direct growth of mushrooms toward the lignocellulosic substrate is elucidated and a fungi-enabled method for the preparation of porous carbons with ultrahigh specific surface area (3439 m² g^-1 ) is developed. Such porous carbons could have potential applications in energy storage, environment treatment, and electrocatalysis. The present study reveals a novel pore formation mechanism in root-colonizing fungi and anticipates a valuable function for fungi in developing the useful porous carbons with a high specific surface area.

Macroscale Biomolecular Electronics and Ionics

The conduction of ions and electrons over multiple length scales is central to the processes that drive the biological world. The multidisciplinary attempts to elucidate the physics and chemistry of electron, proton, and ion transfer in biological charge transfer have focused primarily on the nano- and microscales. However, recently significant progress has been made on biomolecular materials that can support ion and electron currents over millimeters if not centimeters. Likewise, similar transport phenomena in organic semiconductors and ionics have led to new innovations in a wide variety of applications from energy generation and storage to displays and bioelectronics. Here, the underlying principles of conduction on the macroscale in biomolecular materials are discussed, highlighting recent examples, and particularly the establishment of accurate structure-property relationships to guide rationale material and device design. The technological viability of biomolecular electronics and ionics is also discussed.

Anisotropic nanocomposite films of hydroxypropylcellulose and graphene oxide with multi-responsiveness

Anisotropic nanocomposite films of hydroxypropylcellulose (HPC) and graphene oxide (GO) were fabricated by blade-coating of the aqueous mixture to align the substance and subsequent solvent evaporation to freeze the oriented structure. Owing to the anisotropic structure, the composite films showed anisotropic mechanical properties and response to external stimuli. The influences of GO content, stretch rate, and relative humidity on the anisotropic structure and mechanical properties of the films were investigated. The incorporation of GO did not destroy the anisotropic structure of the HPC film, but improved the mechanical properties to some extent and favoured the bending deformation and locomotion of the composite film under the humidity gradient. These behaviours were associated with the large aspect ratio and excellent gas barrier property of GO nanosheets that favoured suppressing the slippage of HPC chains and enhanced the differential volume change at the top and bottom surfaces of the film. The composite HPC film with GO or reduced GO also responded to near-infrared light due to the photothermal effect and the variation of HPC matrix at a high temperature. This facile strategy should be applicable to other natural or synthetic polymers to fabricate anisotropic composite films with potential applications as optical devices, sensors, and actuators.

Nanocomposite films fabricated by blade-coating possess anisotropic mechanical properties and multi-responsiveness to external stimuli, affording potential applications as sensors and actuators.

Flexible Electronics Based on Micro/Nanostructured Paper

Over the past several years, a new surge of interest in paper electronics has arisen due to the numerous merits of simple micro/nanostructured substrates. Herein, the latest advances and principal issues in the design and fabrication of paper-based flexible electronics are highlighted. Following an introduction of the fascinating properties of paper matrixes, the construction of paper substrates from diverse functional materials for flexible electronics and their underlying principles are described. Then, notable progress related to the development of versatile electronic devices is discussed. Finally, future opportunities and the remaining challenges are examined. It is envisioned that more design concepts, working principles, and advanced papermaking techniques will be developed in the near future for the advanced functionalization of paper, paving the way for the mass production and commercial applications of flexible paper-based electronic devices.

Dendrite Integration Mimicked on Starch-Based Electrolyte-Gated Oxide Dendrite Transistors

Emulation of dendrite integration on brain-inspired hardware devices is of great significance for neuromorphic engineering. Here, solution-processed starch-based electrolyte films are fabricated, demonstrating strong proton gating activities. Starch gated oxide dendrite transistors with multigates are fabricated, exhibiting good electrical performances. Most importantly, dendrite modulation, spatiotemporal dendrite integration, and linear/superlinear dendrite algorithm are demonstrated on the proposed dendrite transistor. Furthermore, a low energy consumption of ∼1.2 pJ is obtained for triggering a synaptic response on the dendrite transistor. Accordingly, the signal-to-noise ratio is still as high as ∼2.9, indicating a high sensitivity of ∼4.6 dB. Such artificial dendrite transistors have potential applications in brain-inspired neuromorphic platforms.

Flexible Transient Phototransistors by Use of Wafer-Compatible Transferred Silicon Nanomembranes

Flexible transient photodetectors, a form of optoelectronic sensors that can be physically self-destroyed in a controllable manner, could be one of the important components for future transient electronic systems. In this work, a scalable, device-first, and bottom-up thinning process enables the fabrication of a flexible transient phototransistor on a wafer-compatible transferred silicon nanomembrane. A gate modulation significantly restrains the dark current to 10^-12 A. With full exposure of the light-sensitive channel, such a device yields an ultrahigh photo-to-dark current ratio of 10⁷ with a responsivity of 1.34 A W^-1 (λ = 405 nm). The use of a high-temperature degradable polymer transient interlayer realizes on-demand self-destruction of the fabricated phototransistors, which offers a solution to the technical security issue of advanced flexible electronics. Such demonstration paves a new way for designing transient optoelectronic devices with a wafer-compatible process.

Fully Water-Soluble, High-Performance Transient Sensors on a Versatile Galactomannan Substrate Derived from the Endosperm

Green electronics on biodegradable substrates from natural sources have gained broad interest because of the advantages of being biodegradable, recyclable, sustainable, and cost-efficient. This study presents a low-cost, yet simple extraction and purification method that explores aqueous extraction and precipitation with ethanol for the synthesis of galactomannan films. In salient contrast to the other materials of natural origin, the process to obtain galactomannan films is energy efficient and environmentally friendly. As an alternative biodegradable material, galactomannan has direct relevance to the recent emerging biodegradable or transient electronics. The galactomannan substrate with temperature sensors and electrodes fabricated from zinc, a biodegradable material noted for its essential biological function, demonstrates a high-precision measurement of temperature and high-fidelity monitoring of electrophysiological signals (electromyogram or electrocardiogram). The resulting disposable sensors disappear without a trace in water and produce environmentally benign end products that could even be used for alkaline soil amendments. The set of materials explored in this study is also stable in organic solutions, enabling solvent-based fabrication that may be combined with recent advances in additive manufacturing techniques for a novel manufacturing method.

Materials and Devices for Biodegradable and Soft Biomedical Electronics

Biodegradable and soft biomedical electronics that eliminate secondary surgery and ensure intimate contact with soft biological tissues of the human body are of growing interest, due to their emerging applications in high-quality healthcare monitoring and effective disease treatments. Recent systematic studies have significantly expanded the biodegradable electronic materials database, and various novel transient systems have been proposed. Biodegradable materials with soft properties and integration schemes of flexible or/and stretchable platforms will further advance electronic systems that match the properties of biological systems, providing an important step along the path towards clinical trials. This review focuses on recent progress and achievements in biodegradable and soft electronics for biomedical applications. The available biodegradable materials in their soft formats, the associated novel fabrication schemes, the device layouts, and the functionality of a variety of fully bioresorbable and soft devices, are reviewed. Finally, the key challenges and possible future directions of biodegradable and soft electronics are provided.

Solventless Conducting Paste Based on Graphene Nanoplatelets for Printing of Flexible, Standalone Routes in Room Temperature

Novel printable composites based on high aspect ratio graphene nanoplatelets (GNPs), fabricated without using solvents, and at room temperature, that can be employed for flexible, standalone conducting lines for wearable electronics are presented. The percolation threshold of examined composites was determined to be as low as 0.147 vol% content of GNPs. Obtained sheet resistance values were as low as 6.1 Ω/sq. Stretching and bending tests are presented, proving suitability of the composite for flexible applications as the composite retains its conductivity even after 180° folding and 13.5% elongation.

Blending Electronics with the Human Body: A Pathway toward a Cybernetic Future

At the crossroads of chemistry, electronics, mechanical engineering, polymer science, biology, tissue engineering, computer science, and materials science, electrical devices are currently being engineered that blend directly within organs and tissues. These sophisticated devices are mediators, recorders, and stimulators of electricity with the capacity to monitor important electrophysiological events, replace disabled body parts, or even stimulate tissues to overcome their current limitations. They are therefore capable of leading humanity forward into the age of cyborgs, a time in which human biology can be hacked at will to yield beings with abilities beyond their natural capabilities. The resulting advances have been made possible by the emergence of conformal and soft electronic materials that can readily integrate with the curvilinear, dynamic, delicate, and flexible human body. This article discusses the recent rapid pace of development in the field of cybernetics with special emphasis on the important role that flexible and electrically active materials have played therein.

Recent progress on biodegradable materials and transient electronics

Transient electronics (or biodegradable electronics) is an emerging technology whose key characteristic is an ability to dissolve, resorb, or physically disappear in physiological environments in a controlled manner. Potential applications include eco-friendly sensors, temporary biomedical implants, and data-secure hardware. Biodegradable electronics built with water-soluble, biocompatible active and passive materials can provide multifunctional operations for diagnostic and therapeutic purposes, such as monitoring intracranial pressure, identifying neural networks, assisting wound healing process, etc. This review summarizes the up-to-date materials strategies, manufacturing schemes, and device layouts for biodegradable electronics, and the outlook is discussed at the end. It is expected that the translation of these materials and technologies into clinical settings could potentially provide vital tools that are beneficial for human healthcare.

Universal Nature-Inspired and Amine-Promoted Metallization for Flexible Electronics and Supercapacitors

Economical and abundant natural biological materials provide a low-cost and scalable approach to develop next-generation flexible and wearable electronics. Herein, a universal strategy of nature-inspired and amine-promoted metallization, namely, NIAPM, is presented to make high-quality metals for electronics fabrication. The introduction of poly(ethyleneimine) (PEI) significantly shortens the time of metallization from >48 h to ≈6 h, and the phenol compounds (TP) from green tea make metals bond tightly on all demonstrated surfaces. The as-made thin metal films of Cu and Ni feature high conductivity (∼1.0 Ω/□), excellent mechanical stability and flexibility even at the bending radius of ∼1 mm. Moreover, NIAPM is compatible with typical lithography techniques for fabricating metallic patterns, showing considerable potential applications in flexible electronics. As a proof-of-concept, two devices based on melamine-templated Cu sponges are first prepared for detecting the change of external pressure with a resistance sensitivity of 18.1 kPa^-1 and collecting high-viscosity crude oil, respectively. Then, a high-performance bendable solid supercapacitor is demonstrated using as-prepared Ni metallized fabrics and the activated porous carbon from the recycled waste in NIPAM as flexible electrodes, which possesses comparable areal capacitance of 45.5 F·g^-1, and energy density of 7.88 Wh·g^-1 at the power density of 35 W·g^-1. Therefore, it is anticipated that such a time-saving, cost-effective and whole solution-processed NIAPM strategy can inspire further practical applications in the fields of surface chemistry, material science, flexible and wearable electronics, etc.

Isotropic Paper Directly from Anisotropic Wood: Top-Down Green Transparent Substrate Toward Biodegradable Electronics

Flexible electronics have found useful applications in both the scientific and industrial communities. However, substrates traditionally used for flexible electronics, such as plastic, cause many environmental issues. Therefore, a transparent substrate made from natural materials provides a promising alternative because it can be degraded in nature. The traditional bottom-up fabrication method for transparent paper is expensive, environmentally unfriendly, and time-consuming. In this work, for the first time, we developed a top-down method to fabricate isotropic, transparent paper directly from anisotropic wood. The top-down method includes two steps: a delignification process to bleach the wood by lignin removal and a pressing process for removing light-reflecting and -scattering sources. The resulting isotropic, transparent paper has high transmittance of about 90% and high haze over 80% and is demonstrated as a nature-disposable substrate for electronic/optical devices. Adjusting the pressing ratio used changes the density of the resulting paper, which tunes the microstructure-related properties of the isotropic, transparent paper. This top-down method is simple, fast, environmentally friendly, and cost-effective, which can greatly promote the development of paper-based green optical and electronic devices.

Transient security transistors self-supported on biodegradable natural-polymer membranes for brain-inspired neuromorphic applications

Transient electronics, a new generation of electronics that can physically or functionally vanish on demand, are very promising for future "green" security biocompatible electronics. At the same time, hardware implementation of biological synapses is highly desirable for emerging brain-like neuromorphic computational systems that could look beyond the conventional von Neumann architecture. Here, a hardware-security physically-transient bidirectional artificial synapse network based on a dual in-plane-gate Al-Zn-O neuromorphic transistor was fabricated on free-standing laterally-coupled biopolymer electrolyte membranes (sodium alginate). The excitatory postsynaptic current, paired-pulse-facilitation, and temporal filtering characteristics from high-pass to low-pass transition were successfully mimicked. More importantly, bidirectional dynamic spatiotemporal learning rules and neuronal arithmetic were also experimentally demonstrated using two lateral in-plane gates as the presynaptic inputs. Most interestingly, excellent physically-transient behavior could be achieved with a superfast water-soluble speed of only ∼120 seconds. This work represents a significant step towards future hardware-security transient biocompatible intelligent electronic systems.

Genomic instability in adult men involved in processing electronic waste in Northern China

BACKGROUND

Managing and recycling electronic waste (e-waste), while useful and necessary, has resulted in significant contamination of several environments in China. The area around Tianjin, China has become one of the world's largest e-waste disposal centers, where electronics are processed by manually disassembly or burning, which can result in serious exposure of workers to a multitude of toxicants.

OBJECTIVE

The present study assessed potential genomic damage in workers involved in recycling e-waste.

METHODS

To detect cytogenetic and DNA damage, chromosomal aberrations (CA), cytokinesis blocking micronucleus (CBMN) and the comet assay were performed. Concentrations of some trace elements, markers of oxidative stress and polychlorinated biphenyls (PCBs) in whole blood or serum were measured, and relationships among the markers described above, age, and duration of exposure were analyzed. The profiles of expression of genes in lymphocytes in peripheral blood were assessed to determine the status of the regulation of genes involved in genome stability.

RESULTS

Concentrations of 28 PCB congeners in the whole blood of the exposed group were significantly (P<0.001) greater than those in the control individuals. Frequency of CA (8.01%) and CBMN (26.3‰) in lymphocytes and the level of DNA damage in the lymphocytes and spermatozoa of the exposed men were also significantly (P<0.0001) greater than those of the controls. There were significant relationships between CA, CBMN, DNA damage and duration of exposure. Concentrations of malondialdehyde (MDA) and lead (Pb) in the blood serum were significantly greater, but activities of superoxide dismutase (SOD), glutathione (GSH) and concentrations of calcium (Ca) and magnesium (Mg) were lower in the serum of the exposed men. MDA, Pb, Ca and Mg were associated with the duration of exposure to handling e-waste. In males involved in handling of e-waste, there were 13 genes - ATM, ATR, ABL1, CHEK1, CHEK2, GADD45A, CDK7, GTSE1, OGG1, DDB1, PRKDC, XRCC1 and CCNH - for which expression of mRNA was up-regulated and 7 genes - BRCA1, GTF2H1, SEMA4A, MRE11A, MUTYH, PNKP and RAD50 - for which the expression of mRNA was down-regulated.

CONCLUSIONS

A strong correlation between indicators of damage of DNA, which could result in instability of the genome, and duration of processing e-waste was observed. If proper procedures are not followed, there are significant risks to the health of the individuals involved in such activities.

Biosafe, Eco-Friendly Levan Polysaccharide toward Transient Electronics

New options in the material context of transient electronics are essential to create or expand potential applications and to progress in the face of technological challenges. A soft, transparent, and cost-effective polymer of levan polysaccharide that is capable of complete, programmable dissolution is described when immersed in water and implanted in an animal model. The results include chemical analysis, the kinetics of hydrolysis, and adjustable dissolution rates of levan, and a simple theoretical model of reactive diffusion governed by temperature. In vivo experiments of the levan represent nontoxicity and biocompatibility without any adverse reactions. On-demand, selective control of dissolution behaviors with an animal model demonstrates an effective triggering strategy to program the system's lifetime, providing the possibility of potential applications in envisioned areas such as bioresorbable electronic implants and drug release systems.

A Water Dissolvable Electrolyte with an Ionic Liquid for Eco-Friendly Electronics

A water-dissolvable electrolyte is developed by combining an ionic liquid (IL) with poly(vinyl alcohol) (PVA), which decays over time by contact with water. An IL generally consists of two species of ions (anion and cation), and forms an electrical double layer (EDL) of a large electrostatic capacitance due to the ions accumulated in the vicinity of a conductive electrode when voltage is applied. In a similar manner, the ionic gel developed in this work forms an EDL due to the ions suspended in the conjugated polymer network while maintaining the gel form. Test measurements show a large capacitance of 13 µF cm^-2 within the potential window of the IL. The ionic gel shows an electrical conductance of 20 µS cm^-1 due to the ionic conduction, which depends on the weight ratio of the IL with respect to the polymer. The developed ionic gel dissolves into water in 16 h. Potential application includes the electrolyte in disposable electronics such as distributed sensors and energy harvesters that are supposed to be harmless to environment.

Facilitated Transport of CO2 Through the Transparent and Flexible Cellulose Membrane Promoted by Fixed-Site Carrier

Facilitated transport cellulose membranes with different zinc ion loadings are fabricated via a facile and green solvent system (zinc chloride/calcium chloride solution). Zn²⁺ ions lower the pristine hydrogen bonds that normally reinforce the cellulose chains, and Ca²⁺ ions facilitate interactions among the Zn-cellulose chains to form nanofibrils. The strategy provides an effective route to immobilize zinc species into membrane matrix and constructs facilitated transport pathway for CO₂ molecules. The self-standing membranes are transparent, flexible and demonstrate ultraselective CO₂ permeation. The optimum separation performance is achieved over CM-0 with the highest zinc content (22.2%), and it exhibits a CO₂ permeability of 155.0 Barrer, with selectivity ratios of 27.2 (CO₂/N₂) and 100.6 (CO₂/O₂). The excellent separation performance is assigned to the π complexation mechanism between Zn²⁺ and CO₂.

Intrinsically ionic conductive cellulose nanopapers applied as all solid dielectrics for low voltage organic transistors

Biodegradability, low-voltage operation, and flexibility are important trends for the future organic electronics. High-capacitance dielectrics are essential for low-voltage organic field-effect transistors. Here we report the application of environmental-friendly cellulose nanopapers as high-capacitance dielectrics with intrinsic ionic conductivity. Different with the previously reported liquid/electrolyte-gated dielectrics, cellulose nanopapers can be applied as all-solid dielectrics without any liquid or gel. Organic field-effect transistors fabricated with cellulose nanopaper dielectrics exhibit good transistor performances under operation voltage below 2 V, and no discernible drain current change is observed when the device is under bending with radius down to 1 mm. Interesting properties of the cellulose nanopapers, such as ionic conductivity, ultra-smooth surface (~0.59 nm), high transparency (above 80%) and flexibility make them excellent candidates as high-capacitance dielectrics for flexible, transparent and low-voltage electronics.

Next-generation organic electronics require flexible organic field effect transistors that show low-voltage operation and are biodegradable. Here, Huang and co-workers demonstrate high-performance transistors that utilize solid-state ionic conductive cellulose nanopaper as the dielectric.

Transparent and flexible fingerprint sensor array with multiplexed detection of tactile pressure and skin temperature

We developed a transparent and flexible, capacitive fingerprint sensor array with multiplexed, simultaneous detection of tactile pressure and finger skin temperature for mobile smart devices. In our approach, networks of hybrid nanostructures using ultra-long metal nanofibers and finer nanowires were formed as transparent, flexible electrodes of a multifunctional sensor array. These sensors exhibited excellent optoelectronic properties and outstanding reliability against mechanical bending. This fingerprint sensor array has a high resolution with good transparency. This sensor offers a capacitance variation ~17 times better than the variation for the same sensor pattern using conventional ITO electrodes. This sensor with the hybrid electrode also operates at high frequencies with negligible degradation in its performance against various noise signals from mobile devices. Furthermore, this fingerprint sensor array can be integrated with all transparent forms of tactile pressure sensors and skin temperature sensors, to enable the detection of a finger pressing on the display.

Next-generation mobile security devices require fingerprint sensors that can be incorporated directly into the display. Here, Park et al. demonstrate a highly transparent, multifunctional capacitive fingerprint sensor array that simultaneously detects tactile pressure and finger skin temperature.

From Wood to Textiles: Top-Down Assembly of Aligned Cellulose Nanofibers

Advanced textiles made of macroscopic fibers are usually prepared from synthetic fibers, which have changed lives over the past century. The shortage of petrochemical resources, however, greatly limits the development of the textile industry. Here, a facile top-down approach for fabricating macroscopic wood fibers for textile applications (wood-textile fibers) comprising aligned cellulose nanofibers directly from natural wood via delignification and subsequent twisting is demonstrated. Inherently aligned cellulose nanofibers are well retained, while the microchannels in the delignified wood are squeezed and totally removed by twisting, resulting in a dense structure with approximately two times higher mechanical strength (106.5 vs 54.9 MPa) and ≈20 times higher toughness (7.70 vs 0.36 MJ m^-3 ) than natural wood. Dramatically different from natural wood, which is brittle in nature, the resultant wood-textile fibers are highly flexible and bendable, likely due to the twisted structures. The wood-textile fibers also exhibit excellent knitting properties and dyeability, which are critical for textile applications. Furthermore, functional wood-textile fibers can be achieved by preinfiltrating functional materials in the delignified wood film before twisting. This top-down approach of fabricating aligned macrofibers is simple, scalable, and cost-effective, representing a promising direction for the development of smart textiles and wearable electronics.

Materials, Processes, and Facile Manufacturing for Bioresorbable Electronics: A Review

Bioresorbable electronics refer to a new class of advanced electronics that can completely dissolve or disintegrate with environmentally and biologically benign byproducts in water and biofluids. They have provided a solution to the growing electronic waste problem with applications in temporary usage of electronics such as implantable devices and environmental sensors. Bioresorbable materials such as biodegradable polymers, dissolvable conductors, semiconductors, and dielectrics are extensively studied, enabling massive progress of bioresorbable electronic devices. Processing and patterning of these materials are predominantly relying on vacuum-based fabrication methods so far. However, for the purpose of commercialization, nonvacuum, low-cost, and facile manufacturing/printing approaches are the need of the hour. Bioresorbable electronic materials are generally more chemically reactive than conventional electronic materials, which require particular attention in developing the low-cost manufacturing processes in ambient environment. This review focuses on material reactivity, ink availability, printability, and process compatibility for facile manufacturing of bioresorbable electronics.

Hybrid Paper-Plastic Microchip for Flexible and High-Performance Point-of-Care Diagnostics

A low-cost and easy-to-fabricate microchip remains a key challenge for the development of true point-of-care (POC) diagnostics. Cellulose paper and plastic are thin, light, flexible, and abundant raw materials, which make them excellent substrates for mass production of POC devices. Herein, a hybrid paper-plastic microchip (PPMC) is developed, which can be used for both single and multiplexed detection of different targets, providing flexibility in the design and fabrication of the microchip. The developed PPMC with printed electronics is evaluated for sensitive and reliable detection of a broad range of targets, such as liver and colon cancer protein biomarkers, intact Zika virus, and human papillomavirus nucleic acid amplicons. The presented approach allows a highly specific detection of the tested targets with detection limits as low as 10² ng mL^-1 for protein biomarkers, 10³ particle per milliliter for virus particles, and 10² copies per microliter for a target nucleic acid. This approach can potentially be considered for the development of inexpensive and stable POC microchip diagnostics and is suitable for the detection of a wide range of microbial infections and cancer biomarkers.

Cellulose and nanocellulose-based flexible-hybrid printed electronics and conductive composites - A review

Flexible-hybrid printed electronics (FHPE) is a rapidly growing discipline that may be described as the precise imprinting of electrically functional traces and components onto a substrate such as paper to create functional electronic devices. The mass production of low-cost devices and components such as environmental sensors, bio-sensors, actuators, lab on chip (LOCs), radio frequency identification (RFID) smart tags, light emitting diodes (LEDs), smart fabrics and labels, wallpaper, solar cells, fuel cells, and batteries are major driving factors for the industry. Using renewable and bio-friendly materials would be advantageous for both manufacturers and consumers with the increased use of (FHPE) electronics in our daily lives. This review article describes recent developments in cellulose and nanocellulose-based materials for FHPE, and the necessary developments required to propagate their use in commercial applications. The aim of these developments is to enable the creation of FHPE devices and components made almost entirely of cellulose materials.

Laser-Induced Molybdenum Carbide-Graphene Composites for 3D Foldable Paper Electronics

Versatile and low-cost manufacturing processes/materials are essential for the development of paper electronics. Here, a direct-write laser patterning process is developed to make conductive molybdenum carbide-graphene (MCG) composites directly on paper substrates. The hierarchically porous MCG structures are converted from fibrous paper soaked with the gelatin-mediated inks containing molybdenum ions. The resulting Mo₃ C₂ and graphene composites are mechanically stable and electrochemically active for various potential applications, such as electrochemical ion detectors and gas sensors, energy harvesters, and supercapacitors. Experimentally, the electrical conductivity of the composite is resilient to mechanical deformation with less than 5% degradation after 750 cycles of 180° repeated folding tests. As such, the direct laser conversion of MCGs on papers can be applicable for paper-based electronics, including the 3D origami folding structures.

Dictating anisotropic electric conductivity of a transparent copper nanowire coating by the surface structure of wood

In this article, a robust, air-stable, flexible and transparent copper (Cu) nanowire (NW) network coating on the surface of the wood is presented, based on a fusion welding of the Cu NWs by photonic curing. Thereby, an anisotropic conductivity can be achieved, which is originating from the structural organization of the wood body and its surface. Furthermore, the Cu NWs are protected from oxidation or wear by a commercially available paraffin wax-polyolefin, which also results in surface water repellency. The developed processing steps present a facile and flexible routine for applying Cu NW transparent conductors to abundant biomaterials and solve current manufacturing obstacles for corrosion-resistant circuits while keeping the natural appearance of the substrate. It may open a venue for more extensive utilization of materials from renewable resources such as wood for electronic devices in smart buildings or mobility applications.

Plasticizing Silk Protein for On-Skin Stretchable Electrodes

Soft and stretchable electronic devices are important in wearable and implantable applications because of the high skin conformability. Due to the natural biocompatibility and biodegradability, silk protein is one of the ideal platforms for wearable electronic devices. However, the realization of skin-conformable electronic devices based on silk has been limited by the mechanical mismatch with skin, and the difficulty in integrating stretchable electronics. Here, silk protein is used as the substrate for soft and stretchable on-skin electronics. The original high Young's modulus (5-12 GPa) and low stretchability (<20%) are tuned into 0.1-2 MPa and > 400%, respectively. This plasticization is realized by the addition of CaCl₂ and ambient hydration, whose mechanism is further investigated by molecular dynamics simulations. Moreover, highly stretchable (>100%) electrodes are obtained by the thin-film metallization and the formation of wrinkled structures after ambient hydration. Finally, the plasticized silk electrodes, with the high electrical performance and skin conformability, achieve on-skin electrophysiological recording comparable to that by commercial gel electrodes. The proposed skin-conformable electronics based on biomaterials will pave the way for the harmonized integration of electronics into human.