Biological Tissue-Inspired Ultrasoft,Ultrathin,and Mechanically Enhanced Microfiber Composite Hydrogel for Flexible Bioelectronics

Hydrogels offer tissue-like softness,stretchability,fracture toughness,ionic conductivity,and compatibility with biological tissues,which make them promising candidates for fabricating flexible bioelectronics.A soft hydrogel film offers an ideal interface to directly bridge thin-film electronics with the soft tissues.However,it remains difficult to fabricate a soft hydrogel film with an ultrathin configuration and excellent mechanical strength.Here we report a biological tissue-inspired ultrasoft microfiber composite ultrathin(<5μm)hydrogel film,which is currently the thinnest hydrogel film as far as we know.The embedded microfibers endow the composite hydrogel with prominent mechanical strength(tensile stress~6 MPa)and anti-tearing property.Moreover,our microfiber composite hydrogel offers the capability of tunable mechanical properties in a broad range,allowing for matching the modulus of most biological tissues and organs.The incorporation of glycerol and salt ions imparts the microfiber composite hydrogel with high ionic conductivity and prominent anti-dehydration behavior.Such microfiber composite hydrogels are promising for constructing attaching-type flexible bioelectronics to monitor biosignals.

Effects of deformation twins on microstructure evolution,mechanical properties and corrosion behaviors in magnesium alloys-A review

Due to lattice reorientation,grain segmentation,induced recrystallization,twins play a very important role in regulating texture,refining grains,improving mechanical properties and corrosion resistance,and has received more extensive attention.Numerous studies have shown that{10-12}<10-11>tensile twins(TTWs)are easily activated in large quantities due to the lower critical resolve shear stresses(CRSS).Introduction of TTWs under uniaxial compression improved the strength,ductility,and formability of magnesium(Mg)alloys.Moreover,TTWs produced by multi-directional impact forging(MDIF)can optimize the microstructure by dividing grains and promoting recrystallization,resulting in significant improvement of mechanical properties.Although{10-11}<10-12>compressive twins(CTWs)and{10-11}-{10-12}double twins(DTWs)can promote dynamic recrystallization(DRX),they are also favorable nucleation sites for cracks.In addition,the type and volume fraction of twins can affect the corrosion resistance,and they also play different roles in the corrosion process of different Mg alloys.Twins have shown great potential for improving structure and properties,but a comprehensive and critical discussion of twins in Mg alloys is still lacking.Therefore,based on previous studies,this article reviews the common types and variants of twins in Mg alloys,influencing factors,and their effects on the microstructure,mechanical properties and corrosion resistance.In addition,some interesting ideas are being proposed for further research.

Investigation on microstructures and mechanical properties of Mg-6Zn-0.5Ce-xMn(x=0 and 1)wrought magnesium alloys

The microstructure evolution and mechanical properties of Mg–6Zn–0.5Ce–xMn(x=0 and 1 wt.%)wrought magnesium alloys were researched,and the morphologies and role of Mn element in the experimental alloys were analyzed.The research shows that all of Mn elements form theα-Mn pure phases,which do not participate in the formation of other phases,such as theτ-phases.The mechanical properties of Mn-containing alloys in as-extruded and aged states are superior to Mn-free alloys.During the hot extrusion process,the dispersed fineα-Mn particle phase hinders the migration of grain boundaries and inhibits dynamic recrystallization,which mainly takes effect of grain refining and dispersion hardening.During the aging treatments,the dispersed fineα-Mn particle phase not only hinders the growth of the solution-treated grains,but also becomes the nucleation cores ofβ1 rod-like precipitate phase,which is conducive to increasing the nucleation rate of the precipitate phase.For the aged alloy,the Mn addition mainly takes effect of grain refining and promoting aging strengthening.

Stretchable,self-healing,transient macromolecular elastomeric gel for wearable electronics

Flexible and stretchable electronics are emerging in mainstream technologies and represent promising directions for future lifestyles.Multifunctional stretchable materials with a self-healing ability to resist mechanical damage are highly desirable but remain challenging to create.Here,we report a stretchable macromolecular elastomeric gel with the unique abilities of not only self-healing but also transient properties at room temperature.By inserting small molecule glycerol into hydroxyethylcellulose(HEC),forming a glycerol/hydroxyethylcellulose(GHEC)macromolecular elastomeric gel,dynamic hydrogen bonds occur between the HEC chain and the guest small glycerol molecules,which endows the GHEC with an excellent stretchability(304%)and a self-healing ability under ambient conditions.Additionally,the GHEC elastomeric gel is completely water-soluble,and its degradation rate can be tuned by adjusting the HEC molecular weight and the ratio of the HEC to glycerol.We demonstrate several flexible and stretchable electronics devices,such as self-healing conductors,transient transistors,and electronic skins for robots based on the GHEC elastomeric gel to illustrate its multiple functions.

Biological receptor-inspired flexible artificial synapse based on ionic dynamics

The memristor has been regarded as a promising candidate for constructing a neuromorphic computing platform that is capable of confronting the bottleneck of the traditional von Neumann architecture.Here,inspired by the working mechanism of the G-protein-linked receptor of biological cells,a novel double-layer memristive device with reduced graphene oxide(rGO)nanosheets covered by chitosan(an ionic conductive polymer)as the channel material is constructed.The protons in chitosan and the functional groups in rGO nanosheets imitate the functions of the ligands and receptors of biological cells,respectively.Smooth changes in the response current depending on the historical applied voltages are observed,offering a promising pathway toward biorealistic synaptic emulation.The memristive behavior is mainly a result of the interaction between protons provided by chitosan and the defects and functional groups in the rGO nanosheets.The channel current is due to the hopping of protons through functional groups and is limited by the traps in the rGO nanosheets.The transition from short-term to long-term potentiation is achieved,and learning-forgetting behaviors of the memristor mimicking those of the human brain are demonstrated.Overall,the bioinspired memristor-type artificial synaptic device shows great potential in neuromorphic networks.

Bio-inspired flexible artificial synapses for pain perception and nerve injuries

Imitation of the perception system of living creatures is of great importance for the construction of artificial nerves and intelligent human-machine interfaces.However,a prominent challenge is to emulate the functions of the biological synapse,which is the basic building block of the neural system.Here,inspired by the pain perception mechanism of the living creatures,a flexible double-layer memristor was constructed,with 90%semiconducting single-wall carbon nanotubes(s-SWCNTs)covered by LiClO4 doped polyoxyethylene oxide(PEO:LiClO4)as the channel materials.The carriers(protons and Li+)from PEO:LiClO4 imitated the functions of Na+and K+in biological systems.A potentiation of the post-synaptic signal was observed with mild stimuli,while the post-synaptic signal was inhibited with severe stimuli with a pulse voltage larger than 1.4 V in this research.These behaviors resemble the sensation of pain,neuroprotection,and possible injuries to the neural system.To explore the underlying mechanism of the phenomenon,the fourier-transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),Raman spectrum,and current(IV)sweep were carried out.It was inferred that the observed results are attributable to the interaction between carriers in PEO:LiClO4 and functional groups and defects in the s-SWCNTs.The enhanced channel current results from the fulfillment of the traps by the carriers,and the suppression of the current is due to the intercalation of Li+in the s-SWCNTs.This flexible artificial synapse opens a new avenue for the construction of biocompatible electronic devices towards artificial intelligence systems.

“Top-down” and “bottom-up” strategies for wafer-scaled miniaturized gas sensors design and fabrication

Manufacture of large-scale patterned nanomaterials via top-down techniques,such as printing and slurry coating,have been used for fabrication of miniaturized gas sensors.However,the reproducibility and uniformity of the sensors in wafer-scale fabrication are still a challenge.In this work,a“top-down”and“bottom-up”combined strategy was proposed to manufacture wafer-scaled miniaturized gas sensors with high-throughput by in-situ growth of Ni(OH)2 nanowalls at specific locations.First,the micro-hotplate based sensor chips were fabricated on a two-inch(2″)silicon wafer by micro-electro-mechanical-system(MEMS)fabrication techniques(“top-down”strategy).Then a template-guided controllable de-wetting method was used to assemble a porous thermoplastic elastomer(TPE)thin film with uniform micro-sized holes(relative standard deviation(RSD)of the size of micro-holes<3.5%,n>300),which serves as the patterned mask for in-situ growing Ni(OH)2 nanowalls at the micro-hole areas(“bottom-up”strategy).The obtained gas microsensors based on this strategy showed great reproducibility of electric properties(RSD<0.8%,n=8)and sensing response toward real-time H _(2)S detection(RSD<3.5%,n=8).

An artificial neuromorphic somatosensory system with spatio-temporal tactile perception and feedback functions

The advancement in flexible electronics and neuromorphic electronics has opened up opportunities to construct artificial perception systems to emulate biological functions which are of great importance for intelligent robotics and human-machine interactions.However,artificial systems that can mimic the somatosensory feedback functions have not been demonstrated yet despite the great achievement in this area.In this work,inspired by human somatosensory feedback pathways,an artificial somatosensory system with both perception and feedback functions was designed and constructed by integrating the flexible tactile sensors,synaptic transistor,artificial muscle,and the coupling circuit.Also,benefiting from the synaptic characteristics of the designed artificial synapse,the system shows spatio-temporal information-processing ability,which can further enhance the efficiency of the system.This research outcome has a potential contribution to the development of sensor technology from signal sensing to perception and cognition,which can provide a special paradigm for the next generation of bionic tactile perception systems towards e-skin,neurorobotics,and advanced bio-robots.

Superelastic alloy based electrical interconnects for highly stretchable electronics

To achieve stretchable inorganic electronics,improving elastic stretchability of the electrical interconnects becomes a bottleneck needed to be addressed.Here,we propose a material of Ni-Ti superelastic alloy for the design and fabrication of deformable interconnects,whose intrinsic elastic property overcomes the low intrinsic elastic strain limit of conventional metals.The serpentine interconnect made by Ni-Ti alloy with an intrinsic elastic strain limit of~7.5%represents a much higher elastic stretchability than conventional Cu interconnect.The deformation behavior of the interconnect is systematically investigated through finite element analysis(FEA)simulations and experiments.The results reveal that the interconnect exhibits an elastic stretchability up to 196%,and its resistance only changes by 0.4%with 100% strain.Moreover,the potentials and challenges of other superelastic alloys as electrical interconnects are discussed.The proposed superelastic alloys fundamentally boost the stretchable properties of electrical interconnects,which would open up opportunities for flexible and stretchable electronics.

Rational design of a laminate-structured flexible sensor for human dynamic plantar pressure monitoring

Flexible sensors are essential components in emerging fields such as epidermal electronics,biomedicine,and humancomputer interactions,and creating high-performance sensors through simple structural design for practical applications is increasingly needed.Presently,challenges still exist in establishing efficient models of flexible piezoresistive pressure sensors to predict the design required for achieving target performance.This work establishes a theoretical model of a flexible pressure sensor with a simple laminated and enclosed structure.In the modeling,the electrical constriction effect is innovatively introduced to explain the sensitization mechanism of the laminated structure to a broad range of pressures and to predict the sensor performance.The experimental results confirmed the effectiveness of the theoretical model.The sensor exhibited excellent stability for up to three million cycles and superior durability when exposed to salt solution owing to its simple laminated and enclosed structural design.Finally,a wearable sensing system for real-time collection and analysis of plantar pressure is constructed for exercise and rehabilitation monitoring applications.This work aims to provide theoretical guidance for the rapid design and construction of flexible pressure sensors with target performance for practical applications.