Implantable probe with integrated reference electrode for in situ neural signal and calcium ion monitoring

Monitoring the electrophysiology activity of neurons and blood calcium signals can enable a better understanding of disease-related neural system circuits.However,currently,in situ calcium ion monitoring tools are scarce and exhibit low integration and limited sensitivity.In this letter,we propose an implantable probe with an integrated in situ Ag/AgCl reference electrode(ISA/ARE)that can monitor action potential(AP)and Ca^(2+) concentrations.

Natural high-porous diatomaceous-earth based self-floating aerogel for efficient solar steam power generation

The application of solar steam generation in seawater desalination is an effective way to solve the shortage of fresh water resources.At present,many kinds of photothermal conversion materials have been developed and used as evaporators in seawater desalination.However,some evaporators need additional thermal insulation or water supply devices to achieve efficient photothermal conversion.In addition,their complex,time consuming and no scalable preparation process,high cost of raw materials and poor salt resistance hinder the practical application of these evaporator.Owing to its distinctive nanoporous structure,diatomite as fossilized single-cells algae diatoms is a promising natural silica-based material for seawater desalination.They are taken from sea and that makes true sense to use them in the sea.Herein,we report the first example of synthesis robust three-dimensional(3D)natural-diatomite composite by assembling polyaniline nanoparticles covered diatomite into the polyvinyl alcohol pre-treated melamine foam frameworks and demonstrate its application as new evaporator for seawater desalination.The porous framework does not only improve the sunlight scattering efficiency,but also offer large network of channels for water transportation.The inherent mechanism behind salt desalination process involves the absorption of water molecules on the surface of the internal silica micro-nano pores,and evaporation under the heat induced by the polyaniline absorbed sunlight.Meanwhile,the metal ions are segregated by many available pores and channels to achieve the self-desalting effect.The developed evaporator possesses the superiority of multi-stage pore structure,strong hydrophilicity,low thermal conductivity,excellent light absorption,fast water transportation and salt-resistant crystallization as well as good durability.The evaporation rate without an additional device is found to be 1.689 kg m^(-2)h^(-1)under 1-Sun irradiation,and the energy conversion efficiency is as high as 95%.This work creates a platform and develops the prospect of employing green and sustainable natural-diatomite composite evaporator for practical applications of seawater desalination.

Potassium alleviated high nitrogen-induced apple growth inhibition by regulating photosynthetic nitrogen allocation and enhancing nitrogen utilization capacity

There is a close relationship between potassium(K)and nitrogen(N).However,the roles of K under high N conditions remain unclear.Using a hydroponics approach,we monitored the morphological,physiological,and molecular changes in M9T337 apple(Malus domestica)rootstocks under different nitrate(10 and 30 mmol·L^(-1)NO_(3)^(-))and K supply(0.5,6,10,and 20 mmol·L_(-1)K^(+))conditions.Results revealed that high nitrate inhibited the root growth of M9T337 rootstocks,downregulated the expressions of K transporter genes(MdPT5,MdHKT1,and MdATK1),and reduced the net NO3-and K+influx at the surface of roots,thereby resulting in an N/K imbalance in rootstocks.Further investigation showed that 10 mmol·L^(-1)K increased the activity of N metabolic enzymes(NR,GS,NiR,and GOGAT),upregulated the expressions of genes related to nitrate uptake and transport(MdNRT1.1,MdNRT1.2,MdNRT1.5,and MdNRT2.4),promoted15N transport from the roots to the shoots,optimized leaf N distribution,and improved photosynthetic N utilization efficiency under high nitrate conditions.These results suggest that the negative effects of high nitrate may be related to the N/K imbalance and that reducing N/K in plants by increasing K supply level can effectively alleviate the inhibition of N assimilation by high nitrate stress.

Vacancy engineering of oxidized Nb_(2)CTx MXenes for a biased nitrogen fixation

The artificial nitrogen(N_(2)) reduction reaction(NRR) via electrocatalysis is a newly developed methodology to produce ammonia(NH3) at ambient conditions,but faces the challenges in N_(2)activation and poor reaction selectivity.Herein,Nb-based MXenes are developed to remarkably enhance the NRR activity through the engineering of the stretched 3D structure and oxygen vacancies(VO).The theoretical studies indicate that N_(2)could be initially adsorbed on VOwith an end-on configuration,and the potential determining step might be the first hydrogenation step.The catalysts achieve an NH3production rate of 29.1 μg h^(-1)mg_(cat)^(-1)and excellent Faradic efficiency of 11.5%,surpassing other Nbbased catalysts.The selectivity of NRR is assigned to the unique structure of the catalysts,including(1) the layered graphitic structure for fast electron transfer and active site distribution,(2) the reactive VOfor N_(2)adsorption and activation,and(3) the expanded interlayer space for mass transfer.

Quantitative features of myoelectric signals in the orbicularis oculi muscle during different motion states

Artificial facial nerve prostheses are thought to restore eye-closed function in peripheral facial paralysis patients.At present,however,there is no adequate quantitative or qualitative information regarding myoelectric signal（MES）features for healthy orbiculads oculi muscle（OOM）.The present study analyzed MES features of normal OOM in rabbits during the natural continuous eye-opening（N1）state,natural continuous eye-closing（N2）state,natural blink（N3）state,and evoked eye-closing（E）state according to time domain and frequency domain analysis.Results showed that OOM electrical activities in N1 and N2 states,as well as myoelectric amplitude,were low and stable.Nevertheless,during N3 and E states,OOM electrical activities were significantly increased and amplitude was much higher in the E state than in the N3 state.In the time domain,differences in MES peak absolute potential were not significant between N1 and N2 states,in the frequency domain,differences in power spectral density peak frequency of electromyogram signals were significant between two sets of four OOM movement states.These results suggest that OOM significantly contracts and induces eyelid-closing action.In addition,OOM is diastolic during the N1state.A N2 state does not require continuous intensive OOM contraction.Moreover,distinctions of quantitative information in time and frequency domain features of MES can be used as an OOM reference to identify muscle movement patterns.

Non-noble metal single-atom catalysts prepared by wet chemical method and their applications in electrochemical water splitting

Water splitting by electrolysis is an appealing pathway for sustainable hydrogen production. The practical performance of water splitting is highly dependent on the efficiency of electrocatalysts, which can promote the anodic oxygen evolution reaction(OER) or cathodic hydrogen evolution reaction(HER). Downsizing the metal nanostructures to atomic level to construct single-atom catalysts(SACs) has attracted enormous attention due to its distinct advantages in maximizing the efficiency of metal atom utilization and enhancing activity over corresponding metal nanoparticles. Research on SACs towards electrochemical water splitting application is an emerging field and intensive investigations have been focused on their rational syntheses and applications in HER/OER. In this review, we focus on the wet chemical method developed to prepare non-noble metal based SACs with an emphasis on the synthetic strategies and structure-activity relationship between single metal atoms and catalytic activity. Finally, the challenges and future opportunities for application of single-atom catalysts in water splitting are briefly addressed.

Artificial facial nerve reflex restores eyelid closure following orbicularis oculi muscle denervation

To date, treatment of peripheral facial paralysis has focused on preservation of facial nerve integrity. However, with seriously damaged facial nerve cases, it is difficult to recover anatomical and functional integrity using present therapies. Therefore, the present study utilized artificial facial nerve reflex to obtain orbicularis oculi muscle （OOM） electromyography signals on the uninjured side through the use of implanted recording electrodes. The implanted electrical chips analyzed facial muscle motion on the uninjured side and triggered an electrical stimulator to emit current pulses, which resulted in stimulation of injured OOM contraction and maintained bilateral symmetry and consistency. Following signal recognition, extraction, and computer analysis, electromyography signals in the uninjured OOM resulted in complete eyelid closure, which was consistent with the voltage threshold for eye closure. These findings suggested that artificial facial nerve reflex through the use of implanted microelectronics in unilateral peripheral facial paralysis could restore eyelid closure following orbicularis oculi muscle denervation.

A Preliminary Study on Ultrasonic Cutting Process for Carbon Fibre Prepreg

In ultrasonic cutting process, the cutting pressure is still essential for achieving good quality cut edge compared with traditional mechanical cutting process. With the increase of the cutting power, the cutting pressure demand decreases. The cutting velocity range is extended broadly. The experiment results show that ultrasonic cutting technique is an effective, clean and controllable method for machining of carbon fibre prepreg.

Brainmask:an ultrasoft and moist microelectrocorticography electrode for accurate positioning and long-lasting recordings

Bacterial cellulose(BC),a natural biomaterial synthesized by bacteria,has a unique structure of a cellulose nanofiberweaved three-dimensional reticulated network.BC films can be ultrasoft with sufficient mechanical strength,strong water absorption and moisture retention and have been widely used in facial masks.These films have the potential to be applied to implantable neural interfaces due to their conformality and moisture,which are two critical issues for traditional polymer or silicone electrodes.In this work,we propose a micro-electrocorticography(micro-ECoG)electrode named“Brainmask”,which comprises a BC film as the substrate and separated multichannel parylene-C microelectrodes bonded on the top surface.Brainmask can not only guarantee the precise position of microelectrode sites attached to any nonplanar epidural surface but also improve the long-lasting signal quality during acute implantation with an exposed cranial window for at least one hour,as well as the in vivo recording validated for one week.This novel ultrasoft and moist device stands as a next-generation neural interface regardless of complex surface or time of duration.

Flexible inorganic piezoelectric functional films and their applications

Piezoelectric materials play an increasingly important role in energy harvesters,sensors,and actuators.Flexible and thin piezoelectric films have been demonstrated to provide advanced functionalities and improved performances.However,the research on flexible inorganic piezoelectric thin films has rarely been systematically summarized.Here,we summarize the recent advances in the flexible inorganic piezoelectric thin films,focusing on their structural designs,fabrication techniques,and applications in various practical scenarios.Specifically,different fabrication techniques suitable for diverse inorganic piezoelectric nanostructures are reviewed,including sol-gel,hydrothermal,electrospinning,and other techniques,and the integration process with flexible substrates is further discussed.Biomedical and industrial applications of the flexible piezoelectric thin films are emphasized.Finally,some existing challenges and future perspectives are discussed.

VO2·0.2H2O nanocuboids anchored onto graphene sheets as the cathode material for ultrahigh capacity aqueous zinc ion batteries

Aqueous Zinc-ion batteries(ZIBs),using zinc negative electrode and aqueous electrolyte,have attracted great attention in energy storage field due to the reliable safety and low-cost.A composite material comprised of VO2·0.2H2O nanocuboids anchored on graphene sheets(VOG)is synthesized through a facile and efficient microwave-assisted solvothermal strategy and is used as aqueous ZIBs cathode material.Owing to the synergistic effects between the high conductivity of graphene sheets and the desirable structural features of VO2·0.2H2O nanocuboids,the VOG electrode has excellent electronic and ionic transport ability,resulting in superior Zn ions storage performance.The Zn/VOG system delivers ultrahigh specific capacity of 423 mAh·g^−1 at 0.25 A·g^−1 and exhibits good cycling stability of up to 1,000 cycles at 8 A·g^−1 with 87%capacity retention.Systematical structural and elemental characterizations confirm that the interlayer space of VO2·0.2H2O nanocuboids can adapt to the reversible Zn ions insertion/extraction.The as-prepared VOG composite is a promising cathode material with remarkable electrochemical performance for low-cost and safe aqueous rechargeable ZIBs.

A flexible three-dimensional electrode mesh:An enabling technology for wireless brain-computer interface prostheses

The neural interface is a key component in wireless brain–computer prostheses.In this study,we demonstrate that a unique three-dimensional(3D)microneedle electrode on a flexible mesh substrate,which can be fabricated without complicated micromachining techniques,is conformal to the tissues with minimal invasiveness.Furthermore,we demonstrate that it can be applied to different functional layers in the nervous system without length limitation.The microneedle electrode is fabricated using drawing lithography technology from biocompatible materials.In this approach,the profile of a 3D microneedle electrode array is determined by the design of a two-dimensional(2D)pattern on the mask,which can be used to access different functional layers in different locations of the brain.Due to the sufficient stiffness of the electrode and the excellent flexibility of the mesh substrate,the electrode can penetrate into the tissue with its bottom layer fully conformal to the curved brain surface.Then,the exposed contact at the end of the microneedle electrode can successfully acquire neural signals from the brain.

Flexible polyimide-based hybrid optoelectric neural interface with 16 channels of micro-LEDs and electrodes

In this paper,a polyimide-based flexible device that integrates 16 micro-LEDs and 16 IrO_(x)-modified microelectrodes for synchronous photostimulation and neural signal recording is presented.The 4×4 micro-LEDs(dimensions of 220×270×50μm^(3),700μm pitch)are fixed in the SU-8 fence structure on a polyimide substrate and connected to the leads via a wire-bonding method.The recording electrodes share a similar fabrication process on the polyimide with 16 microelectrode sites(200μm in diameter and 700μm in pitch)modified by iridium oxide(IrO_(x)).These two subparts can be aligned with alignment holes and glued back-to-back by epoxy,which ensures that the light from the LEDs passes through the corresponding holes that are evenly distributed around the recording sites.The long-term electrical and optical stabilities of the device are verified using a soaking test for 3 months,and the thermal property is specifically studied with different duty cycles,voltages,and frequencies.Additionally,the electrochemical results prove the reliability of the IrO_(x)-modified microelectrodes after repeated pressing or friction.To evaluate the tradeoff between flexibility and strength,two microelectrode arrays with thicknesses of 5 and 10μm are evaluated through simulation and experiment.The proposed device can be a useful mapping optogenetics tool for neuroscience studies in small(rats and mice)and large animal subjects and ultimately in nonhuman primates.

Monolithically integrated CoP nanowire array： An on/off switch for effective on-demand hydrogen generation via hydrolysis of NaBH4 and NH3BH3

The issues of hydrogen generation and storage have hindered the widespread use and commercialization of hydrogen fuel cell vehicles. It is thus highly attractive, but the design and development of highly active non-noble-metal catalysts for on-demand hydrogen release from alkaline NaBH4 solution under mild conditions remains a key challenge. Herein, we describe the use of CoP nanowire array integrated on a Ti mesh （CoP NA/Ti） as a three-dimensional （3D） monolithic catalyst for efficient hydrolytic dehydrogenation of NaBH4 in basic solutions. The CoP NAFFi works as an on/off switch for on-demand hydrogen generation at a rate of 6,500 mL/（min.g） and a low activation energy of 41 kJ/mol. It is highly robust for repeated usage after recycling, without sacrificing catalytic performance. Remarkably, this catalyst also performs efficiently for the hydrolysis of NH3BH3.

PDMS/MWCNT-based tactile sensor array with coplanar electrodes for crosstalk suppression

The severe crosstalk effect is widely present in tactile sensor arrays with a sandwich structure.Here we present a novel design for a resistive tactile sensor array with a coplanar electrode layer and isolated sensing elements,which were made from polydimethylsiloxane(PDMS)doped with multiwalled carbon nanotubes(MWCNTs)for crosstalk suppression.To optimize its properties,both mechanical and electrical properties of PDMS/MWCNT-sensing materials with different PDMS/MWCNT ratios were investigated.The experimental results demonstrate that a 4 wt% of MWCNTs to PDMS is optimal for the sensing materials.In addition,the pressure-sensitive layer consists of three microstructured layers(two aspectant PDMS/MWCNT-based films and one top PDMS-based film)that are bonded together.Because of this three-layer microstructure design,our proposed tactile sensor array shows sensitivity up to−1.10 kPa^(−1),a response time of 29 ms and reliability in detecting tiny pressures.

A flexible neural implant with ultrathin substrate for low-invasive brain–computer interface applications

Implantable brain–computer interface(BCI)devices are an effective tool to decipher fundamental brain mechanisms and treat neural diseases.However,traditional neural implants with rigid or bulky cross-sections cause trauma and decrease the quality of the neuronal signal.Here,we propose a MEMS-fabricated flexible interface device for BCI applications.The microdevice with a thin film substrate can be readily reduced to submicron scale for low-invasive implantation.An elaborate silicon shuttle with an improved structure is designed to reliably implant the flexible device into brain tissue.The flexible substrate is temporarily bonded to the silicon shuttle by polyethylene glycol.On the flexible substrate,eight electrodes with different diameters are distributed evenly for local field potential and neural spike recording,both of which are modified by Pt-black to enhance the charge storage capacity and reduce the impedance.The mechanical and electrochemical characteristics of this interface were investigated in vitro.In vivo,the small cross-section of the device promises reduced trauma,and the neuronal signals can still be recorded one month after implantation,demonstrating the promise of this kind of flexible BCI device as a low-invasive tool for brain–computer communication.

Stretchable Parylene-C electrodes enabled by serpentine structures on arbitrary elastomers by silicone rubber adhesive

The delicate serpentine structures are widely used in high-performance stretchable electronics over the past decade.The metal interconnects encapsulated in biocompatible polymer Parylene-C film is a superior choice for long-term implantation in vivo,especially as neural interface to acquire electrophysiological signals or apply electrical stimulation.To avoid the physical contact damages from the neural tissues such as the brain or peripheral nerves,serpentine interconnects are utilized as stretchable electrodes and usually bonded to the soft elastomer substrate.The adhesion strength between the serpentine interconnects and the elastomer substrate becomes a considerable issue to ensure reliability and structural integrity.In this paper,the stretchable Parylene-C electrodes can be transfer printed onto arbitrary elastomer substrates by a thin layer of silicone rubber adhesive with low modulus for electrocorticogram(ECoG)recording.Mechanical simulation of serpentine structures consisting of same periodic arcs and different straight segments is investigated by uniaxial stretching.Then,the elastic stretchability of serpentine electrodes is further studied by simulation and experiments.After 5000 repetitive stretching cycles,the electrochemical impedance of microelectrodes remains in steady states.These results prove that the silicone rubber adhesive facilitates the interfacial bonding in the structure of stretchable electrodes as the compliant and reliable neural interface.

Stimulated emission at 1.54 μm from erbium/oxygen-doped silicon-based light-emitting diodes

Silicon-based light sources, including light-emitting diodes(LEDs) and laser diodes(LDs) for information transmission, are urgently needed for developing monolithic integrated silicon photonics. Silicon with erbium ions(Er^(3+)) doped by ion implantation is considered a promising approach, but it suffers from an extremely low quantum efficiency. Here we report an electrically pumped superlinear emission at 1.54 μm from Er/O-doped silicon planar LEDs, which are produced by applying a new deep cooling process. Stimulated emission at room temperature is realized with a low threshold current of ~6 mA(~0.8 A∕cm^(2)). Time-resolved photoluminescence and photocurrent results have revealed the complex carrier transfer dynamics by relaxing electrons from the Si conduction band to the Er^(3+) ion. This picture differs from the frequently assumed energy transfer via electron–hole pair recombination of the silicon host. Moreover, the amplified emission from the LEDs is likely due to a quasi-continuous Er/O-related donor band created by the deep cooling technique. This work paves the way for fabricating superluminescent diodes or efficient LEDs at communication wavelengths based on rare-earth-doped silicon.