Aligned Ni nanowires towards highly stretchable electrode

Easy fabrication of super-stretchable electrodes can pave the way for smart and wearable electronics.Using drop casting unidirectional nickel nanowires with polyurethane matrix,we fabricated a super-stretchable film with high electric conductivity.The as-fabricated film can withstand a 300%tensile strain in the direction perpendicular to nanowires,owing to the transformation of percolating nanowire network from 2D to 3D.In contrast to the decreased film conductivities under large tension in most stretchable electrodes,which usually associate with fractures and irreversible deformations,our film conductivity can increase with the applied strain.This probably benefits from the enhanced electrical contacts between twisted nanowires under tension.The developed super-stretchable film with unprecedented behavior in this work sheds light on the facile fabrication of super-stretchable electrodes with durable performance.

Ultra-robust stretchable electrode for e-skin:In situ assembly using a nanofiber scaffold and liquid metal to mimic water-to-net interaction

The development of stretchable electronics could enhance novel interface structures to solve the stretchability-conductivity dilemma,which remains a major challenge.Herein,we report a nano-liquid metal(LM)-based highly robust stretchable electrode(NHSE)with a self-adaptable interface that mimics water-tonet interaction.Based on the in situ assembly of electrospun elastic nanofiber scaffolds and electrosprayed LM nanoparticles,the NHSE exhibits an extremely low sheet resistance of 52 mΩsq^(-1).It is not only insensitive to a large degree of mechanical stretching(i.e.,350%electrical resistance change upon 570%elongation)but also immune to cyclic deformation(i.e.,5%electrical resistance increases after 330000 stretching cycles with 100%elongation).These key properties are far superior to those of the state-of-the-art reports.Its robustness and stability are verified under diverse circumstances,including long-term exposure to air(420 days),cyclic submersion(30000 times),and resilience against mechanical damages.The combination of conductivity,stretchability,and durability makes the NHSE a promising conductor/electrode solution for flexible/stretchable electronics for applications such as wearable on-body physiological signal detection,human-machine interaction,and heating e-skin.

A review on structures,materials and applications of stretchable electrodes

With the rapid development of wearable smart devices,many researchershave carried out in-depth research on the stretchable electrodes.As one of the corecomponents for electronics,the electrode mainly transfers the electrons,which plays animportant role in driving the various electrical devices.The key to the research for thestretchable electrode is to maintain the excellent electrical properties or exhibit theregular conductive change when subjected to large tensile deformation.This articleoutlines the recent progress of stretchable electrodes and gives a comprehensiveintroduction to the structures,materials,and applications,including supercapacitors,lithium-ion batteries,organic light-emitting diodes,smart sensors,and heaters.Theperformance comparison of various stretchable electrodes was proposed to clearly showthe development challenges in this field.We hope that it can provide a meaningfulreference for realizing more sensitive,smart,and low-cost wearable electrical devices inthe near future.

Highly conductive and transparent carbon nanotube-based electrodes for ultrathin and stretchable organic solar cells

In this work, we have presented a freestanding and flexible CNT-based film with sheet resistance of 60 ？/ and transmittance of 82% treated by nitric acid and chloroauric acid in sequence. Based on modified CNT film as a transparent electrode, we have demonstrated an ultrathin, flexible organic solar cell（OSC） fabricated on 2.5-μm PET substrate. The efficiency of OSC, combined with a composite film of poly（3-hexylthiophene）（P3HT） and phenyl-C61 butyric acid methyl ester（PCBM） as an active layer and with a thin layer of methanol soluble biuret inserted between the photoactive layer and the cathode, can be up to 2.74% which is approximate to that of the reference solar cell fabricated with ITO-coated glass（2.93%）. Incorporating the as-fabricated ITO-free OSC with pre-stretched elastomer, 50% compressive deformation can apply to the solar cells. The results show that the as-prepared CNT-based hybrid film with outstanding electrical and optical properties could serve as a promising transparent electrode for low cost, flexible and stretchable OSCs, which will broaden the applications of OSC and generate more solar power than it now does.

Stretchable Electrochemical Sensors: From Electrode Fabrication to Cell Mechanotransduction Monitoring

Electrochemical sensing faces huge challenges in characterizing the transient release of biochemical molecules from deformed cells,due to the severely mechanical mismatch between rigid electrodes and soft cells.In recent years,the emergence of stretchable electrochemical sensors has made a breakthrough by complying with the deformation of living cells and simultaneous monitoring of mechanically evoked biochemical signals.This review first summarizes two fundamental strategies for the fabrication of stretchable electrodes from the points of structure and material.Next,recent progresses in construction of functionalized interface to improve the performance of stretchable electrochemical sensors are presented.Then,the application of stretchable electrochemical sensors in real-time monitoring of biomolecules released by mechanically sensitive cells is introduced.Finally,some perspectives and challenges of stretchable electrochemical sensors regarding cell detection are discussed.

Highly stable,stretchable,and transparent electrodes based on dualheaded Ag@Au core-sheath nanomatchsticks for non-enzymatic glucose biosensor

Stretchable and transparent electrodes(STEs)based on silver nanowires(AgNWs)have garnered considerable attention due to their unique optoelectronic features.However,the low oxidation resistance of AgNWs severely limits the reliability and durability of devices based on such STEs.The present work reports a type of core-sheath silver@gold nanowires(Ag@Au NWs)with a morphology resembling dual-headed matchsticks and an average Au sheath thickness of 2.5 nm.By starting with such Ag@Au NWs,STEs with an optical transmittance of 78.7%,a haze of 13.0%,a sheet resistance of 13.5Ω·sq.−1,and a maximum tensile strain of 240%can be formed with the aid of capillary-force-induced welding.The resultant STEs exhibit exceptional oxidation resistance,high-temperature resistance,and chemical/electrochemical stability owing to the conformal and dense Au sheath.Furthermore,non-enzymatic glucose biosensors are fabricated employing the Ag@Au NW STEs.The electrocatalytic oxidation currents are proportional to glucose concentrations with a high sensitivity of 967μA·mM−1·cm−2 and a detection limit of 125μM over a detection range of 0.6 to 16 mM.Additionally,the biosensors demonstrate an appealing robustness and antiinterference characteristics,high repeatability,and great stability that make them adequate for practical use.

Facile fabrication of stretchable Ag nanowire/polyurethane electrodes using high intensity pulsed light

Silver nanowires （AgNWs） have emerged as a promising nanomaterial for next generation stretchable electronics. However, until now, the fabrication of AgNW- based components has been hampered by complex and time-consuming steps. Here, we introduce a facile, fast, and one-step methodology for the fabrication of highly conductive and stretchable AgNW/polyurethane （PU） composite electrodes based on a high-intensity pulsed light （HIPL） technique. HIPL simultaneously improved wire-wire junction conductivity and wire-substrate adhesion at room temperature and in air within 50 μs, omitting the complex transfer-curing-implanting process. Owing to the localized deformation of PU at interfaces with AgNWs, embedding of the nanowires was rapidly carried out without substantial substrate damage. The resulting electrode retained a low sheet resistance （high electrical conductivity） of 〈10 Ω/sq even under 100% strain, or after 1,000 continuous stretching-relaxation cycles, with a peak strain of 60%. The fabricated electrode has found immediate application as a sensor for motion detection. Furthermore, based on our electrode, a light emitting diode （LED） driven by integrated stretchable AgNW conductors has been fabricated. In conclusion, our present fabrication approach is fast, simple, scalable, and cost- efficient, making it a good candidate for a future roll-to-roll process.

Localizing epileptic focus and assessing electrical stimulus effects on epilepsy in rats using stretchable micro electrocorticogram electrodes

Epilepsy is a chronic nervous disease with increasing incidence worldwide,while the accurate localization of epileptic focus and the corresponding treatment are still challenging due to the lack of effective tools to monitor and modulate the related brain neurological activities.In this work,stretchable micro electrocorticogram(mECoG)electrodes are developed and used to investigate penicillininduced epilepsy in rats.The electrodes possess excellent stretchability,conformality,anti-interference ability and sufficient resolution to successfully monitor electroencephalogram(EEG)signals,which is superior to traditional rigid polyimide-based electrodes.Characteristic epileptic spike waves are detected and analyzed to study the epileptic focus and electrical stimulus effects during epileptic seizures.It is found that the spike waves occur first in the visual cortex which is likely to be the epileptic focus.Epileptic spike wave frequency quickly increases to 1.07 Hz where it reaches a plateau and remains stable.There is no dominant brain hemisphere that would show early warning of epileptic seizures.Electrical stimuli for various times are applied after administering penicillin.It is found that 15 min of electrical stimulus has the best restraining effect on epileptic seizures.The mECoG electrodes developed in this study show potentials for applications in stretchable biomedical devices.

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.

Patternable and transferable silver nanowire conductors via plasma-enhanced cryo-transferring process towards highly stretchable and transparent capacitive touch sensor array

Stretchable transparent electrode(STE)plays a key role in numerous emerging applications as an indispensable component for future stretchable devices.The embedded STE,as a promising candidate,possesses balanced performances and facile preparation procedures.However,it still suffers from the defects of conductive materials caused by the transferring,which results in the irreversible failure of devices.In this work,a patternable silver nanowire(AgNW)STE was fabricated by a plasma-enhanced cryo-transferring(PEC-transferring)process.Owing to the plasma-induced sintering,the AgNW network obtained remarkable improvement in robustness,which ensured the intact network after transferring and thus led to superior tensile electrical properties of the STE.Furthermore,serpentine patterns were utilized to optimize the tensile electrical properties of the STE,which achieved a figure of merit of 292.8 and 150%resistance changing under 50%strain.As a practical application,a 4×3 array of the mutual-capacitive type stretchable touch sensors was demonstrated for future touch sensors in stretchable devices.The PEC-transferring process opened a new avenue for patternable embedded STEs and exhibited its high potential in wearable electronics and the Internet of Thing devices.

Bio-inspired micro/nanostructures for flexible and stretchable electronics

The remarkable ability of biological systems to sense and adapt to complex environmental conditions has inspired the design of next-generation electronics with advanced functionalities.This review focuses on emerging bio-inspired strategies for the development of flexible and stretchable electronics that can accommodate mechanical deformations and integrate seamlessly with biological systems.We will provide an overview of the practical considerations in the materials and structure designs of flexible and stretchable electronics.Recent progress in bio-inspired pressure/strain sensors,stretchable electrodes,mesh electronics,and flexible energy devices are then discussed,with an emphasis on their unconventional micro/nanostructure designs and advanced functionalities.Finally,current challenges and future perspectives are identified and discussed.

Synergistic creation of highly stable strain-insensitive pressure sensors by in-plane strain modulation and quasi-homogenous interfacial design

The urgent requirement of electronic skin conformably attached to nonplanar surfaces to provide sta-ble monitoring in areas of healthcare,prosthetics,and robotics promotes the development of strain-insensitive/unperturbed pressure sensors.The main challenges lie in:(1)stretchability and conduc-tive stability of flexible electrodes and(2)mechanical stability of heterogeneous interfaces.This study presents a highly stable strain-insensitive pressure sensor achieved by in-plane strain modulation and quasi-homogenous interfacial design.Strain modulation of stretchable electrodes by both periodic mi-crostructured engineering and pre-stretching strategies(called“island-ripple”)was employed to suppress microcracks propagation.The improvement in stretchability and cyclic conductive stability of electrodes was identified by finite element analysis and experimental verification.The pre-stretched microconed stretchable electrode with a low sheet resistance of 0.546sq^(−1) shows a maximum deformation of up to 80%and excellent cyclic conductive stability over 10000 times under 30%strain.Quasi-homogenous interface strategy by the CNTs/PDMS system was employed to enhance the mechanical and electrical sta-bility of the electrode-active materials interface,demonstrating a strong peel strength and shear strength of>40.9 N/m and>124.8 kPa,respectively.The as-prepared strain-insensitive pressure sensor provides constant sensing performance over 5000 stretching-releasing cycles within 20%stretching.In addition,a 4×4 pixel strain-insensitive pressure sensor array with reduced cross-talk circuit design was further integrated to identify the shape and weight of different objects under strains.The stretchability and sta-bility of our sensor enable it to be applied in stretchable electronics with great potential.