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Wearable bioelectrical monitoring devices can provide long-term human health information such as electrocardiogram and other physiological signals. It is a crucial part of the remote medical system. These can provide prediction for the diagnosis and treatment of cardiovascular disease and access to timely treatment. However, the patch comfort of the wearable monitoring devices in long-term contact with the skin have been a technical bottleneck of the hardware. In this study, the biomimetic patch with wicking-breathable and multi-mechanism adhesion performance to achieve adaptability and comfortability to human skin has been reported. The patch was designed based on a conical through-hole and hexagonal microgroove to directionally transport sweat from skin to air which gives the patch the breathable performance. The breathable and drainage capability of the biomimetic patch was experimentally verified by analyzing the conical through-hole and hexagonal microgroove with the structural mechanism of wicking. Multi-mechanism adhesion of the Ag/Ni microneedle array and PDMS-t adhesion material ensures the stability of patch signal acquisition. This study provides a new way for enhancing the breathability and adaptability of the patch to realize accurate bioelectrical signal monitoring under sweat conditions on human skin.

Adhesive materials have many potential applications for daily life such as soft robotics, wearable devices and transfer printing, however the robust and reversible adhesion, especially under extreme environments including space and polar environment, has rarely been studied and poses an inevitable challenge. We report a new design rule to fabricate an adhesive structure, which possesses the two orders of highest adhesive strength at -100 ℃, excellent reversible adhesion under thermal cycling (from − 100 to 100 ℃) and on ultra-low temperature ice surface (-98.5 ℃). We believe that this new strategy will have wide applications not limited to extreme environments to deploy space exploration and glacier rescue.

As the most efficient perception system in nature, the perception mechanism of the insect (such as honeybee) antennae is the key to imitating the high-performance sensor technology. An automated experimental device suitable for collecting electrical signals (including antenna reaction time information) of antennae was developed, in response to the problems of the non-standardized experimental process, interference of manual operation, and low efficiency in the study of antenna perception mechanism. Firstly, aiming at the automatic identification and location of insect heads in experiments, the image templates of insect head contour features were established. Insect heads were template-matched based on the Hausdorff method. Then, for the angle deviation of the insect heads relative to the standard detection position, a method that calculates the angle of the insect head mid-axis based on the minimum external rectangle of the long axis was proposed. Eventually, the electrical signals generated by the antennae in contact with the reagents were collected by the electrical signal acquisition device. Honeybees were used as the research object in this study. The experimental results showed that the accuracy of template matching could reach 95.3% to locate the bee head quickly, and the deviation angle of the bee head was less than 1°. The distance between antennae and experimental reagents could meet the requirements of antennae perception experiments. The parameters, such as the contact reaction time of honeybee antennae to sucrose solution, were consistent with the results of the manual experiment. The system collects effectively antenna contact signals in an undisturbed state and realizes the standardization of experiments on antenna perception mechanisms, which provides an experimental method and device for studying and analyzing the reaction time of the antenna involved in biological antenna perception mechanisms.生物（如蜜蜂）触角作为自然界最高效的感测系统，研究其感知机制是仿制高性能传感技术的关键。针对触角感知机制研究过程中存在的实验过程非标准化、手动操作干扰与效率低等问题，本文开发了一种适用于采集生物触角电信号（含触角反应时间信息）的自动化实验装置。首先，针对实验中昆虫头部的自动识别定位问题，建立了昆虫头部轮廓特征的图像模板，对昆虫头部实现了基于豪斯多夫（Hausdorff）法的模板匹配。然后，针对昆虫头部相对于标准检测位置的角度偏差问题，提出了基于长轴最小外接矩形的昆虫头部中轴线角度计算方法。最终，通过生物触角电信号采集装置采集得到昆虫触角接触试剂时产生的电信号。本文以蜜蜂为研究对象，实验结果表明：利用模板匹配可实现对蜜蜂头部准确率95.3%的快速匹配定位，蜜蜂头部的位姿角度纠正误差小于1°；触角与实验试剂的接触距离能够满足触角感知机制实验的要求；采集得到蜜蜂触角对蔗糖溶液的接触反应时间等参数与人工实验得到的结果一致。该系统在无人干扰的状态下实现了生物触角接触信号的有效采集，提高了生物触角感知机制实验的标准化水平，为研究与分析生物触角感知机制中所涉及的生物触角反应时间提供一种实验方法与装置。.

Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads. Their mainstream manufacturing method is molding. Due to most molds are made of silicon or silicon-based soft templates, and have poor wear resistant or vulnerability to high temperature, limiting their use in large-scale manufacturing. Nickel is widely used as an embossing mold in the micro/nano-imprint industrial process owing to its good mechanical properties. However, the processing of metal molds for the fabrication of tip-expanded microstructural arrays is extremely challenging. In this study, using electrodeposition techniques, the shape of the micropores is modified to obtain end-controlled pores. The effect of the non-uniformity of the electric field on the microporous morphology in the electrodeposition process is systematically investigated. Furthermore, the mechanism of non-uniformity evolution of the microporous morphology is revealed. The optimized microporous metal array is used as a mold to investigate the cavity evolution laws of the elastic cushions under pre-load during the manufacturing process. As a result, typical bionic adhesives with tip-expansion are obtained. Moreover, corresponding adhesion mechanics are analyzed. The results show that electrochemical modifications have broad application prospects in the fabrication of tip-expanded microstructures, providing a new method for the large-scale fabrication of bionic adhesives based on metal molds.

Electrostatic cumulative discharges from the surfaces of polyurethane elastomers are often the primary cause of accidents and disasters, such as equipment failures, fires, and explosions, in industries. In this study, in order to improve the electrostatic protection performance of PU as well as to enhance the wear resistance of the PU matrix, copper foam was embedded in polyurethane to form a copper foam-based polyurethane composite with a three-dimensional connected metal skeleton. The mechanical properties, wear resistance, and antistatic capability of the composite were experimentally investigated. The results indicated that the connected metal skeleton structure forms a good conductive network and reduces the static electricity on the polyurethane composite surface to less than 1/10 of that on polyurethane. Moreover, owing to the mechanical support offered by metal skeletons with pore densities greater than 50 pores per inch, the wear resistance of the polyurethane composite is also enhanced, and consequently, its degree of wear is reduced to ∼1/5 of that of polyurethane under the same conditions.

Biologically inspired adhesives microstructure requires enough flexibility to make a conformal attachment to the surface as well as high rigidity to maintain the mechanical stability of structure against buckling. To tackle these conflicting factors for the synthetic adhesives is a challenge towards large-scale production and utilizing in practical applications. Addressing this problem, we have fabricated a honeycomb structure with a soft elastic film, partially covering the cavity of the honeycomb pattern. Honeycomb structure provides enough support to maintain the structural stability of the microstructure and soft PDMS film over the pattern provides sufficient flexibility to form a strong attachment with the target surface. Meanwhile, the resemblance of the designed structure to the octopi's sucker generates a negative pressure resulting in suction forces. To justify this suction effect, we compared our results with other controlled honeycomb microstructures (1) without any elastic film (2) with elastic film covering the whole cavity of the honeycomb pattern. Experimental results and theoretical prediction demonstrate the synergistic role of van der Waals and suction forces in the proposed partial-film honeycomb microstructure. The synergistic role of adhesive forces makes this structure a stronger, durable, and surface adaptable adhesive. We also investigated the critical role of the viscous forces for our proposed microstructure in water and silicon oil wetting conditions which signify the contribution of capillary forces.

The resistance of Ionic Polymer Metal Composite (IPMC) electrodes plays an important role in the actuation performance of IPMC actuators. Owing to crack formation on the surface of platinum electrode, the surface resistance of the electrode increases, which greatly limits its actuating performance. In this paper, we proposed a new method of dynamic self-repair electrodes by exchanging Cu2+ into the IPMC basement membrane. IPMC actuators with Cu2+ were prepared and the actuation performance in the air was subsequently measured. Compared with conventional IPMC actuators containing Li+ counter ions, those containing Cu2+ counter ions exhibited 2 times –3 times larger displacement and 2 times–3 times bigger blocking force. In the morphology observation, we found that many small copper particles scattered in the middle of cracks after several bending cycles, which leads to an obvious decrease in electrode resistance. In the Cyclic Voltammetry (CV) scan measurement, we observed that the oxidation reaction of copper alternates with reduction reaction of copper ions with the change of voltage polarity, which was a dynamic process. Based on these analyses, it is concluded that the presence of Cu2+ can repair the damaged electrodes and induce lower electrode resistance, thus leading to the performance improvement of actuation.

This study focused on the application of vertically aligned carbon nanotubes (VACNTs) grown by thermal chemical vapor deposition as a gecko-inspired dry adhesive material. The adhesive properties of VACNTs comprising Fe and Al2O3 layers of different thicknesses were evaluated by scanning electron microscopy, Raman spectroscopy, transmission electron microscopy, and atomic force microscopy. Owing to the surface energy difference between metallic Fe and alumina, the wetting influence of the latter enabled the conversion of the iron film into metal islands (nanoparticles) at high temperature. The bionic morphological characteristics of the produced VACNTs (e.g., alignment, density, diameter, growth rate, and defects) and thus their adhesive properties were determined by the size and distribution of the catalyst particles. With respect to variable adhesion test angles, VACNTs were sensitive to peeling angles and showed high tangential but low normal adhesion strength, thereby providing controlled strong adhesion characteristics in combination with easy peel-off.

High conductivity, large mechanical strength, and elongation are important parameters for soft electronic applications. However, it is difficult to find a material with balanced electronic and mechanical performance. Here, a simple method is developed to introduce ion-rich pores into strong hydrogel matrix and fabricate a novel ionic conductive hydrogel with a high level of electronic and mechanical properties. The proposed ionic conductive hydrogel is achieved by physically cross-linking the tough biocompatible polyvinyl alcohol (PVA) gel as the matrix and embedding hydroxypropyl cellulose (HPC) biopolymer fibers inside matrix followed by salt solution soaking. The wrinkle and dense structure induced by salting in PVA matrix provides large stress (1.3 MPa) and strain (975%). The well-distributed porous structure as well as ion migration–facilitated ion-rich environment generated by embedded HPC fibers dramatically enhances ionic conductivity (up to 3.4 S m −1 , at f = 1 MHz). The conductive hybrid hydrogel can work as an artificial nerve in a 3D printed robotic hand, allowing passing of stable and tunable electrical signals and full recovery under robotic hand finger movements. This natural rubber-like ionic conductive hydrogel has a promising application in artificial flexible electronics.

Vertical aligned carbon nanotube (VACNT) arrays used as dry adhesive materials have broad prospects in the applied fields of space, medicine and electronics. The adhesion of VACNT arrays is believed to be related not only to the nano-array structure and a clean surface, but also to chemical composition. Here, radio-frequency (RF) carbon dioxide (CO2) plasma treatment is introduced as an effective method for purifying and functionalizing the surface to improve the dry adhesive performance of VACNT arrays. Scanning electron microscopy showed that the VACNT arrays retained the alignment architecture with minimal damage at low power. X-ray photoelectron spectroscopy and contact angle tests revealed that the content of non-polar components (C = C bonds) decreased after treatment, while the content of polar groups (C = O and O-C = O bonds) increased, which changed the surface polarity of the VACNT arrays. Raman analyses and transmission electron microscopy demonstrated that amorphous carbon can be selectively removed with increasing time (0-18 min), but was continuously generated with increasing power (30-90 W). The best adhesive strength of 18 N cm-2 (increased by 39%) was obtained after CO2 plasma treating for 10 min at 30 W power, which was attributed to the combined action of purification and polarization.

Vertically-aligned carbon nanotubes (VACNTs) have extraordinary structural and mechanical properties, and have been considered as potential candidates for creating dry adhesives inspired by adhesive structures in nature. Catalytic chemical vapor deposition is widely used to grow VACNTs; however, the influential mechanism of VACNT preparation parameters (such as H2 concentration) on its adhesion property is not clear, making accurate control over the structure of VACNTs adhesive an ongoing challenge. In this article, we use electron beam-deposited SiO2/Al2O3 as a support layer, Fe as catalyst, and C2H4/H2 gas mixtures as a feed gas to prepare VACNTs, while varying the ratio of the reducing atmosphere (H2) from 0% to 35%. VACNTs synthesized at a 15% H2 concentration (5 mm × 5 mm in size) can support a maximal weight of 856 g, which indicates a macroscopic shear adhesive strength of 34 N/cm2. We propose a hydrogen-concentration-dependent model for the shear adhesive performance of VACNTs. By adjusting the amount of hydrogen present during the reaction, the morphology and quality of the prepared VACNTs can be precisely controlled, which significantly influences its shear adhesive performance. These results are advantageous for the application of carbon nanotubes as dry adhesives.

The development of selective-wettability surfaces of porous materials is important for oil spill cleanup. A new type of oil–water separation material has been prepared through a three-dimensional (3-D) extension of a biologically inspired two-dimensional (2-D) material. In this, a simple solution-immersion method is used to construct a super-oleophilic and super-hydrophobic surface on the metallic skeleton of a copper foam, onto which a nanosheet structure is formed that differs greatly from previous nanoscale needle-based materials. This 3-D copper foam is demonstrated to be capable of supporting a maximum height of accumulated water of 5.5 cm prior to oil wetting and 1.5 cm after oil wetting. Furthermore, the foam is capable of efficient oil–water separation, despite losing its super-hydrophobicity during the process. This has given important new insight into the mechanism of separation, in that super-oleophilicity is clearly important to achieving good separation. The selective-wettability of this porous metal foam is expected to extend the range of metal-based oil–water separation materials from 2D metal meshes to more complex 3-D metal structures.

To improve the thermal performance and wear resistance of epoxy–matrix polymers, foamed copper materials filled with a curable epoxy matrix have been developed for tribological studies. Graphite flakes were incorporated as friction additive in the epoxy matrix. The tribological properties of foamed-copper-reinforced composites were investigated using a UMT-2 friction and wear tester. The temperature of the frictional area was measured using an infra-red thermal camera, and the effect of metallic skeletons on temperature was calculated by the finite element analysis (FEA). The results show the foamed-copper-reinforced composites are effective in transmitting heat and sharing load along the interconnected metallic skeletons, and therefore possess better thermal conductivity and wear resistance.

Creating superhydrophobic surfaces is an important direction for porous materials used in water. We report a novel kind of super-floatable material fabricated from superhydrophobic metal foam as a three-dimensional extension of biologically inspired 1-D and 2-D materials. A simple and widely adaptable method is used to construct a superhydrophobic surface on the metallic skeleton of the copper foam with the pore sizes in the range of 0.5–4.2 mm. The force measurement procedure of the superhydrophobic copper foam in the process of sinking and floating is investigated. These 3D superhydrophobic surfaces are found to enable the metal foam to not only float freely on water, but also to exhibit a high loading capacity and sink resistance. The pore size of the sample is an important parameter reflecting the loading capacity. The smaller the pore size is, the higher the loading capacity. The maximal loading capacity of the sample is about 0.97 g cm−3, nearly equivalent to that generated by an air bubble of the same volume in water. Such porous metal foam mimicking the legs of water striders is expected to extend metal-based floatable materials from 1D metal threads and 2D metal meshes or sheets to 3D metal structures.

A lightweight multi-layered electromagnetic interference (EMI) shielding material made of open-cell foam of a Cu–Ni alloy integrated with carbon nanotubes (CNTs) was prepared by electroless copper plating, then nickel electroplating, and finally electrophoretic deposition of CNTs. The foamed Cu–Ni–CNT composite comprises, from inside to outside, Cu, Ni, and CNT layers. Scanning electron microscopy, energy dispersive spectroscopy, and EMI tests were employed to characterize the morphology, composition, and EMI performance of the composite, respectively. The results indicated that the shielding effectiveness (SE) of the composite increased with increasing pore density (indicated as pores per inch (PPI)) and increasing thickness. A specimen with a PPI of 110 and a 1.5-mm thickness had a maximum SE of up to 54.6 dB, and a SE as high as 47.5 dB on average in the 8–12 GHz range. Integrating the inherent superiority of Cu, Ni, and CNTs, the porous structure of the composite can attenuate the incident electromagnetic microwaves by reflecting, scattering, and absorbing them between the metallic skeleton and the CNT layer. The multiple reflections and absorptions make it difficult for the microwaves to escape from the composite before being absorbed, thereby making the composite a potential shielding material.

Open-cell foam of a Cu–Ni alloy integrated with graphene was used as a lightweight, multilayered, electromagnetic interference (EMI)-shielding material. It was prepared by electroless copper plating, then nickel electroplating, and finally electrophoretic deposition of a graphene nanosheet (GNS). The foamed Cu–Ni–GNS composite comprises, from the inside to the outside, Cu, Ni, and GNS layers. The morphology and EMI performance in the 8–12 GHz range were characterized and studied, respectively. The results indicate that the shielding effectiveness of the composite increased with increasing pore density (measured in pores per inch) and increasing thickness. The porous structure of the composite could attenuate the incident electromagnetic microwaves by reflecting, scattering, and absorbing them between the metallic skeleton and the GNS layer. This multilayered foamed composite is a potential material for applications in which shielding and ventilation are required.

Contemporary lead-acid batteries have a high internal resistance and a limited utilization of their positive active materials (PAM). In order to alleviate these problems, lead (alloy) foam-based positive electrodes for lead-acid batteries are prepared by electrodepositing lead on a copper-foam substrate. Using scanning electron microscopy, flame atomic absorption spectrometry, finite element analysis, cyclic voltammetry, and galvanostatic charge/discharge tests, the effect of the lead foam collectors on the electrochemical performance of the positive electrodes is characterized. The thickness of the lead coating has a strong effect on the corrosion-stability of the copper-foam substrate. In addition, the charge/discharge performance of the batteries is greatly improved by the lead-foam collectors. At the 20–2 h discharge rates, the utilization efficiency of the PAM of 40-PPI lead-foam battery is improved by 19–36% from the cast-grid battery. Combined with the finite element analysis, it appears that the 3D connected network structure of the positive lead foam electrode can reduce the surface current density, the polarization resistance, and the ohmic resistance of the battery because of its larger contact area with the active material. As a result, the lead foam battery has a higher utilization efficiency of the PAM.

A novel foamed copper/epoxy (FCE) composite possessing improved wear resistance was developed as a rubbing pair material. The composites consist of an open-cell foamed copper skeleton and an epoxy resin and auxiliary additives, such as molybdenum disulfide (MoS2) and multi-walled carbon nanotubes (MWCNTs). A universal UMT-2 friction and wear tester was utilized to study the tribological properties of the FCE composites under dry lubrication conditions. We found that the amount of MoS2, the porosity of the copper foam, and the presence of the MWCNTs all have an effect on the friction and wear properties of the composite materials. The friction coefficient of the composite material gradually decreases as the amount of MoS2 increases; however, the wear rate initially decreases and then increases. When the MoS2 content is 30%, the wear rate reaches a minimum. The wear rate decreases as the porosity of copper foam decreases, but porosity has little effect on the friction coefficient. As the rotation speed of the grinding steel plate and the applied load on samples increase, the wear becomes more significant. The presence of MWCNTs also increases the strength and wear resistance of the epoxy resin matrix. Depth-of-field microscopy and scanning electron microscopy were employed to observe the worn-surface morphologies and wear mechanism. The worn surface of the FCE composite matrix is divided into three parts: the hollow metallic copper skeleton region, the polymer zone, and the transition zone copper skeleton that contains some polymer material. It is important to note that the wear mechanism of the various compositions is adhesive wear and slight abrasive wear, and the fatigue crack that runs perpendicular to the direction of movement begins to form at higher speeds, which results in a higher wear rate.

Four kinds of foamed metals (foamed Ni, FeNi, CuNi, and Cu) filled with polytetrafluoroethylene (PTFE) and graphite were developed as rubbing materials. These open-cell foamed metals had the same interconnected three-dimensional (3D) metallic skeletons. The friction and wear properties of the new composites were investigated on an M-2000 friction and wear tester. To study the influence of the metallic skeleton on the contact between the sample and the rotating ring, an electric field was imposed to monitor the formation of transfer film by means of contact resistance. A thermocouple was embedded into the sample to measure the temperature variation caused by friction. Optical and scanning electron microscopes were used to study the worn surface morphologies. The temperature field of the sample and the effect of the metallic skeleton on temperature were calculated using finite element analysis (FEA). It was found that the foamed metal–reinforced composites possessed better thermal conductivity and wear resi...

A copper foam–based (CFB) self-lubricating composite was developed as a friction pair material. The composite consists of copper foam with three-dimensionally interpenetrated pores and solid lubricant fillers (polytetrafluoroethylene [PTFE] and MoS2). The thermal and electrical conductivity, bending strength, and tribological properties of the new composite were investigated. The friction and wear properties were investigated on a M-2000 model ring-on-block test rig. An electric field was imposed between the sample and ring to monitor the tribochemical reaction and formation of transfer film by means of contact resistance. Measurement of friction temperature was carried out by means of three thermocouples embedded in the material. The friction coefficients of the CFB composite decrease slightly, and the wear rate substantially decreased overall compared with that of the homologous polymers. The optical and scanning electron micrographs (SEM) of the frictional surfaces show the worn surface of the CFB comp...

A novel foamed copper based (FCB) composite is developed as a rubbing pair material. The composites consist of the foamed copper and solid lubricants, such as polytetrafluoroethylene and graphite. Four kinds of FCB composites were fabricated by vacuum filtration, compression moulding, and sintering process in an orderly manner. The thermal and electrical conductivities and tribological properties of the new composites were investigated. Because the interconnected metal skeletons have been embedded in the polymers, the FCB composites possess excellent thermal and electrical conductivities, including nice self-lubricating property. The friction and wear properties were investigated on an M-2000 friction and wear tester. An electric field was imposed between the sample and ring to monitor the tribo-chemical reaction and formation of transfer film by means of ‘contact resistance’. The measurements of friction temperatures were carried out by means of three thermocouples embedded in the material. The friction tests show that the friction coefficients of the FCB composites decrease almost monotonically with the increase of graphite content under different conditions; and the wear rates decrease overall compared with that of the homologous polymers, more obvious especially under severe conditions. The optical microscope, SEM, and XPS were adopted to study the worn surface morphologies and the transfer films. The main wear mechanism of the new composite is a three-body abrasion, caused and promoted by the plastic deformation, abrasive wear, and fatigue spalling. The oxidation of copper is the dominant chemical processes which occurred during the sliding process.