Living Synthelectronics: A New Era for Bioelectronics Powered by Synthetic Biology.

Bioelectronics, which converges biology and electronics, has attracted great attention due to their vital applications in human-machine interfaces. While traditional bioelectronic devices utilize nonliving organic and/or inorganic materials to achieve flexibility and stretchability, a biological mismatch is often encountered because human tissues are characterized not only by softness and stretchability but also by biodynamic and adaptive properties. Recently, a notable paradigm shift has emerged in bioelectronics, where living cells, and even viruses, modified via gene editing within synthetic biology, are used as core components in a new hybrid electronics paradigm. These devices are defined as "living synthelectronics," and they offer enhanced potential for interfacing with human tissues at informational and substance exchange levels. In this Perspective, the recent advances in living synthelectronics are summarized. First, opportunities brought to electronics by synthetic biology are briefly introduced. Then, strategic approaches to designing and making electronic devices using living cells/viruses as the building blocks, sensing components, or power sources are reviewed. Finally, the challenges faced by living synthelectronics are raised. It is believed that this paradigm shift will significantly contribute to the real integration of bioelectronics with human tissues.

Foodborne Carbon Dots Aggravate High-Fat-Diet-Induced Glucose Homeostasis Imbalance by Disrupting the Gut-Liver Axis.

Foodborne carbon dots (CDs) are generally produced during cooking and exist in food items. Generally, CDs are regarded as nontoxic materials, but several studies have gradually confirmed the cytotoxicity of CDs, such as oxidative stress, reduced cellular activity, apoptosis, etc. However, studies focusing on the health effects of long-term intake of food-borne CDs are scarce, especially in populations susceptible to metabolic disease. In this study, we reported that CDs in self-brewing beer had no effect on glucose metabolism in CHOW-fed mice but exacerbated high-fat-diet (HFD)-induced glucose metabolism disorders via the gut-liver axis. Chronic exposure to foodborne CDs increased fasting glucose levels and exacerbated liver and intestinal barrier damage in HFD-fed mice. The 16s rRNA sequencing analysis revealed that CDs significantly altered the gut microbiota composition and promoted lipopolysaccharide (LPS) synthesis-related KEGG pathways (superpathway of (Kdo)2-lipid A, Kdo transfer to lipid IVA Ill (Chlamydia), lipid IVA biosynthesis, and so on) in HFD-fed mice. Mechanically, CD exposure increased the abundance of Gram-negative bacteria (Proteobacteria and Desulfovibrionaceae), thus producing excessive endotoxin-LPS, and then LPS was transferred by the blood circulation to the liver due to the damaged intestinal barrier. In the liver, LPS promoted TLR4/NF-κB/P38 MAPK signaling, thus enhancing systemic inflammation and exacerbating HFD-induced insulin resistance. However, pretreating mice with antibiotics eliminated these effects, indicating a key role for gut microbiota in CDs exacerbating glucose metabolism disorders in HFD-fed mice. The finding herein provides new insight into the potential health risk of foodborne nanoparticles in susceptible populations by disturbing the gut-liver axis.

Liquid metal-hydrogel composites for flexible electronics.

As an emerging functional material, liquid metal-hydrogel composites exhibit excellent biosafety, high electrical conductivity, tunable mechanical properties and good adhesion, thus providing a unique platform for a wide range of flexible electronics applications such as wearable devices, medical devices, actuators, and energy conversion devices. Through different composite methods, liquid metals can be integrated into hydrogel matrices to form multifunctional composite material systems, which further expands the application range of hydrogels. In this paper, we provide a brief overview of the two materials: hydrogels and liquid metals, and discuss the synthesis method of liquid metal-hydrogel composites, focusing on the improvement of the performance of hydrogel materials by liquid metals. In addition, we summarize the research progress of liquid metal-hydrogel composites in the field of flexible electronics, pointing out the current challenges and future prospects of this material.

Using Flexible and Stretchable Surface Electromyography Electrode Array to Evaluate Congenital Muscular Torticollis in Children.

Congenital Muscular Torticollis (CMT) is a neuromuscular disease in children, which leads to exacerbation of postural deformity and neck muscle dysfunction with age. Towards facilitating functional assessment of neuromuscular disease in children, topographic electromyography (EMG) maps enabled by flexible and stretchable surface EMG (sEMG) electrode arrays are used to evaluate the neck myoelectric activities in this study. Customed flexible and stretchable sEMG electrode arrays with 84 electrodes were utilized to record sEMG in all subjects during neck motion tasks. Clinical parameter assessments including the cervical range of motion (ROM), sonograms of the sternocleidomastoid (SCM), and corresponding histological analysis were also performed to evaluate the CMT. The muscle activation patterns of neck myoelectric activities between the CMT patients and the healthy subjects were asymmetric during different neck motion tasks. The CMT patients presented significantly lower values in spatial features of two-dimensional (2D) correlation coefficient, left/right energy ratio, and left/right energy difference (p < 0.001). The 2D correlation coefficient of activation patterns of neck rotation and extension in CMT patients significantly correlated with clinical parameter assessments (p < 0.05). The findings suggest that the spatial features of muscle activation patterns based on the sEMG electrode arrays can be utilized to evaluate the CMT. The flexible and stretchable sEMG electrode array is promising to facilitate the functional evaluation and treatment strategies for children with neuromuscular disease.

Wide Range Strain Distributions on the Electrode for Highly Sensitive Flexible Tactile Sensor with Low Hysteresis.

Flexible piezoresistive tactile sensors are widely used in wearable electronic devices because of their ability to detect mechanical stimuli. However, achieving high sensitivity and low hysteresis over a broad detection range remains a challenge with current piezoresistive tactile sensors. To address these obstacles, we designed elastomeric micropyramid arrays with different heights to redistribute the strain on the electrode. Furthermore, we mixed single-walled carbon nanotubes in the elastomeric micropyramids to compensate for the conductivity loss caused by random cracks in the gold film and increase the adhesion strength between the gold film (deposited on the pyramid surface) and the elastomer. Thus, the energy loss of the sensor during deformation and hysteresis (∼2.52%) was effectively reduced. Therefore, under the synactic effects of the percolation effect, tunnel effect, and multistage strain distribution, the as-prepared sensor exhibited a high sensitivity (1.28 × 106 kPa-1) and a broad detection range (4.51-54837.06 Pa). The sensitivity was considerably higher than those of most flexible pressure sensors with a microstructure design. As a proof of concept, the sensors were successfully applied in the fields of health monitoring and human-machine interaction.

Highly Sensitive and Omnidirectionally Stretchable Bioelectrode Arrays for In Vivo Neural Interfacing.

Flexible electrode array, a new-generation neural microelectrode, is a crucial tool for information exchange between living tissues and external electronics. Till date, advances in flexible neural microelectrodes are limited because of their high impedance and poor mechanical consistency at tissue interfaces. Herein, a highly sensitive and omnidirectionally stretchable polymeric electrode array (PEA) is introduced. Micropyramid-nanowire composite structures are constructed to increase the effective surface area of PEA, achieving an exponential reduction in impedance compared with gold (Au) and flat polypyrrole electrodes. Moreover, for the first time, a suspended umbrella structure to enable PEA with omnidirectional stretchability of up to ≈20% is designed. The PEA can withstand 1000 cycles of mechanical loads without decrease in performance. As a proof of concept, PEA is conformally attached to a rat heart and tibialis anterior muscle, and electrophysiological signals (electrocardiogram and electromyogram) of the rat are successfully recorded. This strategy provides a new perspective toward highly sensitive and omnidirectionally stretchable PEA that can facilitate the practical application of neural electrodes.

Salt-Triggered Adaptive Dissociation Coating with Dual Effect of Antibacteria and Anti-Multiple Encrustations in Urological Devices.

Bacterial infections and multiple encrustations are life-threatening complications in patients implanted with urological devices. Limited by time-consuming procedures and substrate dependence, it is difficult to simultaneously prevent the aforementioned complications. Herein, is reported the design of a salt-triggered chondroitin sulfate complex (CS/Si-N+ ) coating with adaptive dissociation, which realizes the dual functions of antibacterial and anti-multiple encrustations in urological devices with arbitrary shapes. The existence of covalent interactions between the complex and the interface ensures the formation of a robust coating, especially in harsh environments. Benefiting from the adaptive dissociation of the ion pairs in the CS/Si-N+ coating in urine electrolytes, the exposed ion groups and enhanced hydrophilicity are more conducive to the inhibition of bacterial infection and multiple encrustations simultaneously. The coating exhibits broad-spectrum bactericidal effects. As a proof of concept, in a simulated metabolic encrustation model, the coating exhibits significant advantages in resisting calcium oxalate encrustation, with a reduction in the calcium content by over 90%. In addition, this non-leachable all-in-one coating shows good biocompatibility in a pig in vivo model. Such a coating strategy is expected to be a practical approach for preventing urological medical device-related complications.

A Nonswelling Hydrogel with Regenerable High Wet Tissue Adhesion for Bioelectronics.

Reducing the swelling of tissue-adhesive hydrogels is crucial for maintaining stable tissue adhesion and inhibiting tissue inflammation. However, reported strategies for reducing swelling always result in a simultaneous decrease in the tissue adhesive strength of the hydrogel. Furthermore, once the covalent bonds break in the currently reported hydrogels, they cannot be rebuilt, and the hydrogel loses its tissue adhesive ability. In this work, a nonswelling hydrogel (named as "PAACP") possessing regenerable high tissue adhesion is synthesized by copolymerizing and crosslinking poly(vinyl butyral) with acrylic acid, gelatin, and chitosan-grafted N-acetyl-l-cysteine. The tissue adhesive strength of the obtained PAACP reaches 211.4 kPa, which is approximately ten times higher than that of the reported nonswelling hydrogels, and the hydrogel can be reused for multiple cycles. The as-prepared hydrogel shows great potential in soft bioelectronics, as muscle fatigue is successfully monitored via the electrode array and strain sensor integrated on PAACP substrates. The success of these bioelectronics offers potential applicability in the long-term diagnosis of muscle-related health conditions and prosthetic manipulations.

On-demand biomanufacturing through synthetic biology approach.

Biopharmaceuticals including protein therapeutics, engineered protein-based vaccines and monoclonal antibodies, are currently the mainstay products of the biotechnology industry. However, the need for specialized equipment and refrigeration during production and distribution poses challenges for the delivery of these technologies to the field and low-resource area. With the development of synthetic biology, multiple studies rewire the cell-free system or living cells to impact the portable, on-site and on-demand manufacturing of biomolecules. Here, we review these efforts and suggest future directions.

Thermal-Sinterable EGaIn Nanoparticle Inks for Highly Deformable Bioelectrode Arrays.

Liquid metal (especially eutectic gallium indium, EGaIn) nanoparticle inks overcome the poor wettability of high surface tension EGaIn to elastomer substrates and show great potential in soft electronics. Normally, a sintering strategy is required to break the oxide shells of the EGaIn nanoparticles (EGaIn NPs) to achieve conductive paths. Herein, for the first time, thermal-sinterable EGaIn NP inks are prepared by introducing thermal expansion microspheres (TEMs) into EGaIn NP solution. Through the mechanical pressure induced by the expansion of the heated TEMs, the printed EGaIn NPs can be sintered into electrically conductive paths to achieve highly stretchable bioelectrode arrays, which exhibit giant electromechanical performance (up to 680% strain), good cyclic stability (over 2 × 104  cycles), and stable conductivity after high-speed rotation (6000 rpm). Simultaneously, the recording sites are hermetically sealed by ionic elastomer layers, ensuring the complete leakage-free property of EGaIn and reducing the electrochemical impedance of the electrodes (891.16 Ω at 1 kHz). The bioelectrode is successfully applied to monitor dynamic electromyographic signals. The sintering strategy overcomes the disadvantages of the traditional sintering strategies, such as leakage of EGaIn, reformation of large EGaIn droplets, and low throughput, which promotes the application of EGaIn in soft electronics.

A Light-Permeable Solar Evaporator with Three-Dimensional Photocatalytic Sites to Boost Volatile-Organic-Compound Rejection for Water Purification.

Solar-driven interfacial evaporation (SIE) is emerging as an energy-efficient technology to alleviate the global water shortages. However, there is a fatal disadvantage in using SIE, that is, the volatile organic compounds (VOCs) widely present in feedwater would concurrently evaporate and transport in distilled water, which threatens the water safety. Photocatalysis is a sustainable technology for pollution control, and after years of development, it has become a mature method. Considering the restriction by the insufficient reaction of the permeating VOCs on the two-dimensional (2D) light-available interface of conventional materials, a 3D photocatalytic approach can be established to boost VOC rejection for photothermal evaporation. In the present work, a light-permeable solar evaporator with 3D photocatalytic sites is constructed by a porous sponge decorated with BiOBrI nanosheets with oxygen-rich vacancies. The 3D microchannels in the evaporator provide a light-permeable path with the deepest irradiation depth of about 580 µm, and the reactive interface is increased by tens of times compared with the traditional 2D membrane, resulting in suppression of VOC remnants in distilled water by around four orders of magnitude. When evaporating river water containing 5 mg L-1 extra added phenol, no phenol residues (below 0.001 mg/L) were detected in the produced freshwater. This development is believed to provide a powerful strategy to resolve the VOC bottleneck of SIE.

Strategies for interface issues and challenges of neural electrodes.

Neural electrodes, as a bridge for bidirectional communication between the body and external devices, are crucial means for detecting and controlling nerve activity. The electrodes play a vital role in monitoring the state of neural systems or influencing it to treat disease or restore functions. To achieve high-resolution, safe and long-term stable nerve recording and stimulation, a neural electrode with excellent electrochemical performance (e.g., impedance, charge storage capacity, charge injection limit), and good biocompatibility and stability is required. Here, the charge transfer process in the tissues, the electrode-tissue interfaces and the electrode materials are discussed respectively. Subsequently, the latest research methods and strategies for improving the electrochemical performance and biocompatibility of neural electrodes are reviewed. Finally, the challenges in the development of neural electrodes are proposed. It is expected that the development of neural electrodes will offer new opportunities for the evolution of neural prosthesis, bioelectronic medicine, brain science, and so on.

Electrostatic Interaction-Based High Tissue Adhesive, Stretchable Microelectrode Arrays for the Electrophysiological Interface.

The drift or fall of stretchable neural microelectrodes from the surface of wet and dynamic tissues severely hampers the adoption of microelectrodes for electrophysiological signal monitoring. Endowing the stretchable electrodes with adhesive ability is an effective way to overcome these problems. Current adhesives form tough adhesion to tissues by covalent interaction, which decreases the biocompatibility of the adhesives. Here, we fabricate a strong electrostatic adhesive (noncovalent interaction), highly conformal, stretchable microelectrode arrays (MEAs) for the electrophysiological interface. This MEA was composed of polypyrrole (PPy) as the electrode material and hydrogel as the stretchable substrate [the cross-linked and copolymerized hydrogel of 2-acrylamido-2-methylpropane sulfonic acid (AMPS), gelatin, chitosan, 2-methoxyethyl acrylate, and acrylic acid is named PAGMA]. Strong and stable electrostatic adhesion (85 kPa) and high stretchability (100%) allow for the integration of PPy MEAs based on the PAGMA hydrogel substrate (PPy-PAGMA MEAs) on diverse wet dynamic tissues. Additionally, by adjusting the concentration of AMPS in PAGMA, the hydrogel (PAGMA-1) can produce tough adhesion to many inorganic and elastomer materials. Finally, the PPy-PAGMA MEAs were toughly and conformally adhered on the rat's subcutaneous muscle and beating heart, and the rat's electrophysiological signals were successfully recorded. The development of these adhesive MEAs offers a promising strategy to establish stable and compliant electrode-tissue interfaces.

Interface Chelation Induced by Pyridine-Based Polymer for Efficient and Durable Air-Processed Perovskite Solar Cells.

Polymer doping is a significant approach to precisely control nucleation and crystal growth of perovskites and enhance electronic quality in perovskite solar cells (PSC) prepared in air. Here, a brand-new self-healing polysiloxane (SHP) with dynamic 2,6-pyridinedicarboxamide (PDCA) coordination units and plenty of hydrogen bonds was designed and incorporated into perovskite films. PDCA units, showing strong intermolecular Pb2+ -Namido , I- -Npyridyl , and Pb2+ -Oamido coordination interactions, were expected to enhance crystallinity and passivate the grain boundary. In addition, abundant hydrogen bonds in SHP afforded the self-healing of cracks at grain boundaries for fatigue PSCs. Significantly, the doped device demonstrated a champion efficiency of 19.50 % with inconspicuous hysteresis, almost rivaling those achieved in control atmosphere. This strategy of heterocyclic-based macromolecular doping in PSCs will pave a way for realizing efficient and durable crystalline semiconductors.

Stretchable Electronics Based on PDMS Substrates.

Stretchable electronics, which can retain their functions under stretching, have attracted great interest in recent decades. Elastic substrates, which bear the applied strain and regulate the strain distribution in circuits, are indispensable components in stretchable electronics. Moreover, the self-healing property of the substrate is a premise to endow stretchable electronics with the same characteristics, so the device may recover from failure resulting from large and frequent deformations. Therefore, the properties of the elastic substrate are crucial to the overall performance of stretchable devices. Poly(dimethylsiloxane) (PDMS) is widely used as the substrate material for stretchable electronics, not only because of its advantages, which include stable chemical properties, good thermal stability, transparency, and biological compatibility, but also because of its capability of attaining designer functionalities via surface modification and bulk property tailoring. Herein, the strategies for fabricating stretchable electronics on PDMS substrates are summarized, and the influence of the physical and chemical properties of PDMS, including surface chemical status, physical modulus, geometric structures, and self-healing properties, on the performance of stretchable electronics is discussed. Finally, the challenges and future opportunities of stretchable electronics based on PDMS substrates are considered.

Polymeric Membranes with Selective Solution-Diffusion for Intercepting Volatile Organic Compounds during Solar-Driven Water Remediation.

Solar evaporation through a photothermal porous material provides a feasible and sustainable method for water remediation. Several photothermal materials have been developed to enhance solar evaporation efficiency. However, a critical limitation of current photothermal materials is their inability to separate water from the volatile organic compounds (VOCs) present in wastewater. Here, a microstructured ultrathin polymeric membrane that enables freshwater separation from VOC pollutants by solar evaporation with a VOC removal rate of 90%, is reported. The different solution-diffusion behaviors of water and VOCs with polymeric membranes facilitate their separation. Moreover, owing to increased light absorption, enlarged liquid-air interface, and shortened mass transfer distance, the microstructured and ultrathin configuration of the membrane helps to balance the tradeoff between permeation selectivity and water production capacity. The membrane is not only effective for evaporation of simulated volatile pollutants in a prototype, but can also intercept complex volatile organic contaminants in natural water sources and produce water that meets drinking-water standards. With practical demonstration and satisfactory purification performance, this work paves the way for practical application of solar evaporation for effective water remediation.

Volatile-Organic-Compound-Intercepting Solar Distillation Enabled by a Photothermal/Photocatalytic Nanofibrous Membrane with Dual-Scale Pores.

Solar distillation is emerging as a robust and energy-effective tool for water purification and freshwater production. However, many water sources contain harmful volatile organic compounds (VOCs), which can evaporate through the photothermal evaporators and be collected together with distilled water, or even be enriched in the distilled water. In view of the penetration of volatile organic compounds, herein, we rationally demonstrate a dual-scale porous, photothermal/photocatalytic, flexible membrane for intercepting volatile organic compounds during solar distillation, which is based on a mesoporous oxygen-vacancy-rich TiO2-x nanofibrous membrane (m-TiO2-x NFM). The dual-scale porous structure was constructed by micrometer-sized interconnected tortuous pores formed by the accumulation of m-TiO2-x nanofibers and nanometer-sized pores in the m-TiO2-x individual nanofibers. Consequently, the membrane can sustainably in situ intercept VOCs by providing more photocatalytic reactive sites for collision (mainly by mesopores) and longer tortuous channels for prolonging VOC retention (mainly by micrometer-sized pores); thus, it results in less than 5% of phenol residual in distilled water. As a proof of concept, when the m-TiO2-x NFM is employed to purify practical river water in an evaporation prototype under real solar irradiation, complex volatile natural organic contaminants can be effectively intercepted and the produced distilled water meets the drinking water standards of China. This development will promote the application prospects of solar distillation.

Low-Tortuosity Water Microchannels Boosting Energy Utilization for High Water Flux Solar Distillation.

Solar distillation through photothermal evaporators has approached solar light energy (E1) limit under no solar concentration but still suffers from modest vapor and clean water production. Herein, a nature-inspired low-tortuosity three-dimensional (3D) evaporator is demonstrated to significantly improve water production. The solar evaporator, prepared from polypyrrole-modified maize straw (PMS), had upright vascular structures enabling high water lifting and horizontal microgaps facilitating broad water distribution to the out-surface. Consequently, this novel PMS evaporator dramatically enhanced the utilization of the solar heat energy stored in the environment (E2) for promoting evaporation. The maximum vapor generation rate of a single PMS respectively increases 2.5 and 6 times compared with the conventional 3D evaporators and the planar evaporators of an identical occupied area. Consequently, a scaled-up PMS array achieved a state-of-the-art vapor generation rate of 3.0 L m-2 h-1 (LMH) under a simulated condition and a record-high clean water production of 2.2 LMH for actual seawater desalination under natural conditions (1 sun intensity). This breakthrough reveals great potentials for cost-effective freshwater production as well as the rational design of high-performance photothermal evaporators for solar distillation.

An Artificial Somatic Reflex Arc.

The emulation of human sensation, perception, and action processes has become a major challenge for bioinspired intelligent robotics, interactive human-machine interfacing, and advanced prosthetics. Reflex actions, enabled through reflex arcs, are important for human and higher animals to respond to stimuli from environment without the brain processing and survive the risks of nature. An artificial reflex arc system that emulates the functions of the reflex arc simplifies the complex circuit design needed for "central-control-only" processes and becomes a basic electronic component in an intelligent soft robotics system. An artificial somatic reflex arc that enables the actuation of electrochemical actuators in response to the stimulation of tactile pressures is reported. Only if the detected pressure by the pressure sensor is above the stimulus threshold, the metal-organic-framework-based threshold controlling unit (TCU) can be activated and triggers the electrochemical actuators to complete the motion. Such responding mechanism mimics the all-or-none law in the human nervous system. As a proof of concept, the artificial somatic reflex arc is successfully integrated into a robot to mimic the infant grasp reflex. This work provides a unique and simplifying strategy for developing intelligent soft robotics, next-generation human-machine interfaces, and neuroprosthetics.

Highly Stable and Stretchable Conductive Films through Thermal-Radiation-Assisted Metal Encapsulation.

Stretchable conductors are the basic units of advanced flexible electronic devices, such as skin-like sensors, stretchable batteries and soft actuators. Current fabrication strategies are mainly focused on the stretchability of the conductor with less emphasis on the huge mismatch of the conductive material and polymeric substrate, which results in stability issues during long-term use. Thermal-radiation-assisted metal encapsulation is reported to construct an interlocking layer between polydimethylsiloxane (PDMS) and gold by employing a semipolymerized PDMS substrate to encapsulate the gold clusters/atoms during thermal deposition. The stability of the stretchable conductor is significantly enhanced based on the interlocking effect of metal and polymer, with high interfacial adhesion (>2 MPa) and cyclic stability (>10 000 cycles). Also, the conductor exhibits superior properties such as high stretchability (>130%) and large active surface area (>5:1 effective surface area/geometrical area). It is noted that this method can be easily used to fabricate such a stretchable conductor in a wafer-scale format through a one-step process. As a proof of concept, both long-term implantation in an animal model to monitor intramuscular electric signals and on human skin for detection of biosignals are demonstrated. This design approach brings about a new perspective on the exploration of stretchable conductors for biomedical applications.