Soft Actuator with Biomass Porous Electrode: A Strategy for Lowering Voltage and Enhancing Durability.

Electroactive artificial muscles with deformability have attracted widespread interest in the field of soft robotics. However, the design of artificial muscles with low-driven voltage and operational durability remains challenging. Herein, novel biomass porous carbon (BPC) electrodes are proposed. The nanoporous BPC enables the electrode to provide exposed active surfaces for charge transfer and unimpeded channels for ion migration, thus decreasing the driving voltage, enhancing time durability, and maintaining the actuation performances simultaneously. The proposed actuator exhibits a high displacement of 13.6 mm (bending strain of 0.54%) under 0.5 V and long-term durability of 99.3% retention after 550,000 cycles (∼13 days) without breaks. Further, the actuators are integrated to perform soft touch on a smartphone and demonstrated as bioinspired robots, including a bionic butterfly and a crawling robot (moving speed = 0.08 BL s-1). This strategy provides new insight into the design and fabrication of high-performance electroactive soft actuators with great application potential.

Multi-Level Structural Enhancement Mechanism of the Excellent Mechanical Properties of Dung Beetle Leg Joint.

The multi-level structure is a strategy to enhance the mechanical properties of dung beetle leg joints. Under external loads, the microstructure facilitates energy dissipation and prevents crack extension. The macrostructure aids in transferring the load to more reliable parts. The connection established by the two hemispheres is present in the dung beetle leg joint. The micron-layered and nanoscale crystal structures further constitute the leg joint with excellent mechanical properties. The maximum compression fracture force is ≈101000 times the weight of the leg. Here, the structural design within the dung beetle leg joints and reveal the resulting mechanical response and enhancement mechanisms is determined. A series of beetle leg joints where the macrostructure and microstructure of the dung beetle leg provide mechanical strength at critical strains while avoiding catastrophic failure by transferring the load from the joint to the exoskeleton of the femur is highlighted. Nanocrystalline structures and fiber layers contribute to crack propagation of the exoskeleton. Based on this, the bionic joint with multi-level structures using resin and conducted a series of tests to verify their effectiveness is prepared. This study provides a new idea for designing and optimizing high-load joints in engineering.

Continuous 3D Printing of Biomimetic Beetle Mandible Structure with Long Bundles of Aramid Fiber Composites.

Fiber-reinforced composites are an ideal high-performance composite material made from a combination of high-strength continuous fibers and a polymer matrix. Compared to short cut fibers, continuous long strand fibers can improve the mechanical properties of fiber composites more effectively. Herein, continuous aramid fiber-reinforced PLA filaments with fiber centering were prepared by modifying the outlet design of a desktop-grade thermoplastic single-screw melt extruder. Inspired by the cross-laminated structure of a beetle's mandible fibers, a biomimetic structure composite was printed, which demonstrates a significant influence on the mechanical properties. The G-code printing program was developed, and the microstructure of the fracture surface of the specimen was analyzed. The uniform and orderly arrangement of aramid fibers within the PLA resin-based 3D-printed specimen was found. Consequentially, the bionic composites exhibits a 12% increase in tensile strength and a 5% increase in impact toughness, confirming the feasibility of utilizing continuous 3D printing to manufacture long bundles of aramid fiber composite filaments for enhanced mechanical performances.

Composite Flexible Sensor Based on Bionic Microstructure to Simultaneously Monitor Pressure and Strain.

To achieve the human sense of touch, a strain sensor needs to be coupled with a pressure sensor to identify the compliance of the contacted material. However, monitoring the pressure-strain signals simultaneously and ensuring no coupling effect between the two signals is the technical bottleneck for the flexible tactile sensor to. Herein, a composite flexible sensor based on microstructures of lotus leaf is designed and manufactured, which integrates the capacitive pressure sensor and the resistance strain sensor into one pixel to realize the simultaneous detection of pressure and strain. The electrode layer of the capacitance sensor also plays the role of the resistance strain sensor, which greatly simplifies the structure of the composite flexible sensor and obtains the compact size to integrate more easily. The device can simultaneously detect pressure and deformation, and more importantly, there is no coupling effect between the two kinds of signals. Here, the sensor has high pressure sensitivity (0.784 kPa-1 when pressure less than 100 kPa), high strain sensitivity (gauge factor = 4.03 for strain 0-40%), and can identify materials with different compliance, which indicates the tactile ability as the human skin performs.

Impact of human contact patterns on epidemic spreading in time-varying networks.

Human contact behaviors involve both dormant and active processes. The dormant (active) process goes from the disappearance (creation) to the creation (disappearance) of an edge. The dormant (active) time is the elapsed time since the edge became dormant (active). Many empirical studies have revealed that dormant and active times in human contact behaviors tend to show a long-tailed distribution. Previous researches focused on the impact of the dormant process on spreading dynamics. However, the epidemic spreading happens on the active process. This raises the question of how the active process affects epidemic spreading in complex networks. Here, we propose a novel time-varying network model in which the distributions of both the dormant time and active time of edges are adjustable. We develop a pairwise approximation method to describe the spreading dynamical processes in the time-varying networks. Through extensive numerical simulations, we find that the epidemic threshold is proportional to the mean dormant time and inversely proportional to the mean active time. The attack rate decreases with the increase of mean dormant time and increases with the increase of mean active time. It is worth noting that the epidemic threshold and the attack rate (e.g., the infected density in the steady state) are independent of the heterogeneities of the dormant time distribution and the active time distribution. Increasing the heterogeneity of the dormant time distribution accelerates epidemic spreading while increasing the heterogeneity of the active time distribution slows it down.

Nitrogen-doped hydrochar prepared by biomass and nitrogen-containing wastewater for dye adsorption: Effect of nitrogen source in wastewater on the adsorption performance of hydrochar.

Dye wastewater has become one of the main risk sources of environmental pollution due to its high toxicity and difficulty in degradation. Hydrochar prepared by hydrothermal carbonization (HTC) of biomass has abundant surface oxygen-containing functional groups, and therefore is used as an adsorbent to remove water pollutants. The adsorption performance of hydrochar can be enhanced after improving its surface characteristics through nitrogen-doping (N-doping). In this study, wastewater rich in nitrogen sources such as urea, melamine and ammonium chloride were selected as the water source for the preparation of HTC feedstock. The N atoms were doped in the hydrochar with a content of 3.87%-5.70%, and mainly in the form of pyridinic-N, pyrrolic-N and graphitic-N, which changed the acidity and basicity of the hydrochar surface. The N-doped hydrochar adsorbed methylene blue (MB) and congo red (CR) in wastewater through pore filling, Lewis acid-base interaction, hydrogen bond, and π-π interaction, and the maximum adsorption capacities of those were obtained with 57.52 mg/g and 62.19 mg/g, respectively. However, the adsorption performance of N-doped hydrochar was considerably affected by the acid-base property of the wastewater. In a basic environment, the surface carboxyl of the hydrochar exhibited a high negative charge and thus an enhanced electrostatic interaction with MB. Whereas, the hydrochar surface was positively charged in an acid environment by binding H+, resulting in an enhanced electrostatic interaction with CR. Therefore, the adsorption efficiency of MB and CR by N-doped hydrochar can be tuned by adjusting the nitrogen source and the pH of the wastewater.

Low-Voltage Driven Ionic Polymer-Metal Composite Actuators: Structures, Materials, and Applications.

With the characteristics of low driving voltage, light weight, and flexibility, ionic polymer-metal composites (IPMCs) have attracted much attention as excellent candidates for artificial muscle materials in the fields of biomedical devices, flexible robots, and microelectromechanical systems. Under small voltage excitation, ions inside the IPMC proton exchange membrane migrate directionally, leading to differences in the expansion rate of the cathode and the anode, which in turn deform. This behavior is caused by the synergistic action of a three-layer structure consisting of an external electrode layer and an internal proton exchange membrane, but the electrode layer is more dominant in this process due to the migration and storage of ions. The exploration of modifications and alternatives for proton exchange membranes and recent advances in the fabrication and characterization of conductive materials, especially carbon-based materials and conductive polymers, have contributed significantly to the development of IPMCs. This paper reviews the progress in the application of proton exchange membranes and electrode materials for IPMCs, discusses various processes currently applied to IPMCs preparation, and introduces various promising applications of cutting-edge IPMCs with high performance to provide new ideas and approaches for the research of  new generation of low-voltage ionic soft actuators.

Bouncing dynamics of impact droplets on bioinspired surfaces with mixed wettability and directional transport control.

Kingfishers stand on a branch, and raindrops tumble translationally from feathers during raining, enlightening functional surfaces design and liquid transport control. Far-ranging studies on oriented transportation are confined to vertical impacting, which is, to date, in-depth philosophy of horizontal droplets transport on motionless surface deems to be rather serviceable. This study, employed mixed-wettability surface inspired by kingfishers' feather, occurs on directional transportation issues, such as the synergies of wettability-controlled, driving force and transportation capability. Here we conduct both experimental testing and CFD-aided numerical modelling to reproduce the asymmetric bouncing and directional transport phenomena. We found that the anisotropic surface manipulates to convert normally vertical impacting to horizontal droplets transport. Law of the thrown droplet, on the other hand, is predominated by the wettability-controlled surface, while the coexistence of contact angle difference and surface offset location cooperatively dictates the intensity and patterns of the thrown droplet. Of all these factors, the post-optimized surfaces are designed first and then the regime map of transportation pattern is elaborated. Results manifest that the elements induce the maximum horizontal transport distance by up to 6.2D0, and first desorption time is only 7.8 ms. The findings shed light on engineering design principles that can pave the way for novel applications in anti-icing, lubrication, and spray cooling.

Ethanol Phase Change Actuator Based on Thermally Conductive Material for Fast Cycle Actuation.

Artificial muscle actuator has been devoted to replicate the function of biological muscles, playing an important part of an emerging field at inter-section of bionic, mechanical, and material disciplines. Most of these artificial muscles possess their own unique functionality and irreplaceability, but also have some disadvantages and shortcomings. Among those, phase change type artificial muscles gain particular attentions, owing to the merits of easy processing, convenient controlling, non-toxic and fast-response. Herein, we prepared a silicon/ethanol/(graphene oxide/gold nanoparticles) composite elastic actuator for soft actuation. The functional properties are discussed in terms of microstructure, mechanical properties, thermal imaging and mechanical actuation characteristics, respectively. The added graphene oxide and Au nanoparticles can effectively accelerate the heating rate of material and improve its mechanical properties, thus increasing the vaporization rate of ethanol, which helps to accelerate the deformation rate and enhance the actuation capability. As part of the study, we also tested the performance of composite elastomers containing different concentrations of graphene oxide to identify GO-15 (15 mg of graphene oxide per 7.2 mL of material) flexible actuators as the best composition with a driving force up to 1.68 N.

Bionic Design and 3D Printing of Continuous Carbon Fiber-Reinforced Polylactic Acid Composite with Barbicel Structure of Eagle-Owl Feather.

Inspired by eagle-owl feather with characteristics of light weight and high strength, the bionic continuous carbon fiber-reinforced polylactic acid composite with barbicel structure was successfully 3D printed. Under the action of external load, angles between barbicels and rachis structure of eagle-owl feather decreased, which consumed a part of energy and built structure base of bionic feather structure model with a certain arrangement angle of continuous carbon fiber. Variation of bionic structure model design parameters significantly affected the mechanical properties of the 3D printing bionic composites. The relatively low continuous carbon fiber content on tensile force direction restricted enhancement of tensile strength of bionic composite. However, attributed to different angle arrangement of continuous carbon fiber, the propagation of cracks in bionic composite was hindered, exhibiting high impact resistance. The effective and feasible bionic feather design and 3D printing of continuous carbon fiber-reinforced polylactic acid composite extended the corresponding application in the areas with high impact loads.

Investigation of microstructure and dissimilar materials connection patterns of mantis shrimp saddle.

The microstructure and dissimilar materials connection patterns of mantis shrimp saddle were investigated. The outer layer with layered helical structure and inner layer with slablike laminae structure constructed the microstructure characteristics of saddle. The merus and membrane were characterized by layered structure. The lamina of saddle connected the corresponding lamina in merus and membrane, building the continuous and smooth coupling connection patterns. The entitative "hard-hard" and "hard-soft" transitions of dissimilar materials at micro level enhanced the steady transmit of driven force. The saddle exhibited high mechanical strength. With the increase of in-situ tensile displacement, the number of fractured fragments on saddle outer layer surface increased, which subjected to tensile load and defused the damage in the form of mineralized surface fragmentation. In the inner part of saddle, the fracture of mineralized laminae and crack deflection mechanisms bore the tensile load influence. The combination of microstructure with high mechanical strength and continues micro lamina connection endowed the concise dissimilar materials connection and efficient elastic energy storage property of saddle, which can be treated as the bionic models for design and preparation of fiber reinforced resin composite, hyperelastic material and so on.

Study on the heterogeneous material coupling connection characteristics and mechanical strength of Oratosquilla oratoria mantis shrimp saddle.

The microstructure, chemical composition and mechanical strength of heterogeneous materials of mantis shrimp (Oratosquilla oratoria) saddle were studied. As the key component of the striking system, the saddle comprised two distinct layers including outer layer and inner layer. The outer layer contained blocky microtubules and exhibited compact appearance. The inner layer presented a typical periodic lamellar structure. Due to the change of the thickness of the mineralized outer layer, the organic multilamellar structure became the foundation and enhanced the connection strength (4.55 MPa) at the connect regions between the saddle and merus exoskeleton and membrane, respectively. In the process of fracture, the lamellar structure dispersed the stress effectively by the change of the crack deflection direction and the microfibrils ordered arrangement. The exploration of mantis shrimp saddle region is beneficial to understand the striking system and provided the possibility for the stable connection of heterogeneous materials in engineering fields. The microstructure, heterogeneous material connection characteristics and high mechanical strength of saddle provide bionic models for the preparation of fiber-reinforced resin composites and soft composites.

Microstructure and in-situ tensile strength of propodus of mantis shrimp.

Effects of microstructure and phase component on mechanical property of spearer propodus of mantis shrimp were investigated. The spearer propodus consisted of three layers including epicuticle (outer layer), exocuticle (middle layer), and endocuticle (inner layer). The outer layer was composed of fluorapatite, which was treated as permeability barrier to environment. The compact middle layer and inner layer were constituted of chitin-protein fibers, which exhibited the layered spiral structure. Under the in-situ tensile test environment, spearer propodus owned high mechanical strength, which bore maximum tensile fore of 320 N. In the in-situ tensile process, cracks extended along with zigzag lines on spearer propodus surface. The middle layer and inner layer resisted the damage of force via the fracture and pulling of fibers. The crack deflection and delamination phenomena were the mechanical property mechanisms of spearer propodus of mantis shrimp. The investigations provided typical bionic models for the design and preparation of bionic structure materials, bionic anti-impact materials, and bionic soft materials in engineering fields.

Non-Markovian recovery makes complex networks more resilient against large-scale failures.

Non-Markovian spontaneous recovery processes with a time delay (memory) are ubiquitous in the real world. How does the non-Markovian characteristic affect failure propagation in complex networks? We consider failures due to internal causes at the nodal level and external failures due to an adverse environment, and develop a pair approximation analysis taking into account the two-node correlation. In general, a high failure stationary state can arise, corresponding to large-scale failures that can significantly compromise the functioning of the network. We uncover a striking phenomenon: memory associated with nodal recovery can counter-intuitively make the network more resilient against large-scale failures. In natural systems, the intrinsic non-Markovian characteristic of nodal recovery may thus be one reason for their resilience. In engineering design, incorporating certain non-Markovian features into the network may be beneficial to equipping it with a strong resilient capability to resist catastrophic failures.

Impact of contact preference on social contagions on complex networks.

Preferential contact process limited by contact capacity remarkably affects the spreading dynamics on complex networks, but the influence of this preferential contact in social contagions has not been fully explored. To this end, we propose a behavior spreading model based on the mechanism of preferential contact. The probability in the model that an adopted individual contacts and tries to transmit the behavioral information to one of his/her neighbors depends on the neighbor's degree. Besides, a preferential exponent determines the tendency to contact with either small-degree or large-degree nodes. We use a dynamic messaging method to describe this complex contagion process and verify that the method is accurate to predict the spreading dynamics by numerical simulations on strongly heterogeneous networks. We find that the preferential contact mechanism leads to a crossover phenomenon in the growth of final adoption size. By reducing the preferential exponent, we observe a change from a continuous growth to an explosive growth and then to a continuous growth with the transmission rate of behavioral information. Moreover, we find that there is an optimal preferential exponent which maximizes the final adoption size at a fixed information transmission rate, and this optimal preferential exponent decreases with the information transmission rate. The used theory can be extended to other types of dynamics, and our findings provide useful and general insights into social contagion processes in the real world.

Microstructure characteristics and mechanical properties of Meretrix lusoria shell.

The microstructure and mechanical properties of Meretrix lusoria shell were investigated. M. lusoria shell was comprised of three layers (outer layer, middle layer and inner layer). Outer layer with serried mastoid structure enhanced the connection strength with middle layer. The middle layer consisted of blocky pattern structure with porosity and crossed-lamellar structure. The inner layer exhibited the typical crossed-lamellar structure. Combined with structure characteristic, phase of aragonite confirmed the crossed-lamellar structure further, building material base for mechanical properties including flexure strength (296.26 MPa), compression strength (6.71 MPa) and crack arrest ability. Microstructure of the shell was the function base of crack deflection phenomenon, which dispersed and defused the applied load via the change of crack extension direction. The investigation of M. lusoria shell provided bionic models for the design and fabrication of bioinspired composites in engineering fields. RESEARCH HIGHLIGHTS: Microstructure and mechanical properties of Meretrix lusoria shell were investigated. Crossed-lamellar structure was the microstructure characterization. M. lusoria shell owned high flexure strength and crack arrest property.

PPAR Gamma Coactivator 1 Beta (PGC-1ß) Reduces Mammalian Target of Rapamycin (mTOR) Expression via a SIRT1-Dependent Mechanism in Neurons.

Mammalian target of rapamycin (mTOR) is a key regulator of metabolism, cell growth, and protein synthesis. Since decreased mTOR activity has been found to slow aging in many species, the aim of this study was to examine the activity of mTOR and its phosphorylated form in in vitro and in vivo models mimicking Alzheimer's disease (AD), and investigate the potential pathway of PGC-1ß in regulating mTOR expression. Primary neurons and N2a cells were treated with Aß25-35, while untreated cells served as controls. The expression of mTOR, p-mTOR (Ser2448), and PGC-1ß was determined with Western blotting and RT-PCR assay, and the translocation of mTOR was detected using confocal microscopy. Aß25-35 treatment stimulated the translocation of mTOR from cytoplasm to nucleus, and resulted in elevated expression of mTOR and p-mTOR (Ser2448) and reduced PGC-1ß expression. In addition, overexpression of PGC-1ß was found to decrease mTOR expression. The results of this study demonstrate that Aß increases the expression of mTOR and p-mTOR at the site of Ser2448, and the stimulation of Aß is likely to depend on sirtuin 1, PPARγ, and PGC-1ß pathway in regulating mTOR expression.

Effects of ADAM10 deletion on Notch-1 signaling pathway and neuronal maintenance in adult mouse brain.

A disintegrin and metalloproteinase 10 (ADAM10) has been demonstrated to regulate embryonic brain development by initiating Notch signaling. However, it is still unclear whether ADAM10 is required to activate the Notch signaling pathway in adult brain. To investigate the physiological role of ADAM10, we generated conditional knockout (cKO) mice lacking the Adam10 gene primarily in the cortex and hippocampus. We found that conditional disruption of ADAM10 resulted in a prominent decrease in the number of proliferating neuronal progenitor cells in the subgranular zone (SGZ), and a significant increase in the number of adult-generated postmitotic neurons in the hippocampal dentate gyrus (DG) due to premature neuronal differentiation. Moreover, the mutant mice also displayed an age-dependent reduction in the number of granule neurons in the hippocampal DG. It was further showed that the activation of Notch-1 and its downstream target genes Hes1, Hes5, Hey1, and Hey2 was impaired in ADAM10-deficient hippocampal tissues. Finally, Adam10 cKO mice had impaired learning and memory in the Morris water-maze. Thus, we provided experimental evidence to demonstrate that ADAM10 plays an essential role in the activation of Notch-1 signaling and has a remarkable effect on neuronal maintenance in adult mouse brain.

[Generation and characterization of the adult neuron-specific ADAM10 knock-out mice].

A disintegrin and metalloproteinase 10 (ADAM10) is a major sheddase for over 30 different membrane proteins and gets involved in such physiological processes and pathogenesis as embryonic development, cell adhesion, signal transduction, immune reaction, cancer, and Alzheimer's disease. Both ADAM10 knock-out mice and the neural progenitor cell-specific ADAM10 knock-out mice having been reported so far died in the embryonic or perinatal stage, respectively, thus resulting in the failure to investigate ADAM10 function in the adult mouse brain. Through a series of tests, we have succeeded in generating and characterizing the CaMKIIα-Cre/ADAM10(loxP/loxP) mice surviving until adulthood by means of crossing ADAM10(loxP/loxP) mice with newly generated CaMKIIα-Cre transgenic mice. PCR analysis of genomic DNAs from different regions of the ADAM10 cKO mouse brain shows that the deleted ADAM10 alleles are mainly found in the cortex and hippocampus. Real-time RT-PCR findings further confirm that ADAM10 mRNAs decrease in the cortex and hippocampus by 55.7% and 60.8%, respectively. Western-blotting analysis demonstrates 63% and 84.8% loss of mature ADAM10 proteins from the cortex and hippocampus. Immunohistochemical tests show that there is significantly less ADAM10- positive staining in the cortical and hippocampal neurons but not gliocytes of ADAM10 cKO mice compared with control mice. In summary, we established the adult neuron-specific ADAM10 knock-out (cKO) mice for the first time, which prevented ADAM10(-/-) mice from the embryonic and perinatal mortality and laid a firm foundation for the further study of ADAM10 function in the brain of adult mice in vivo.