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Most of the resistive-type stretchable strain sensors exhibit large sensing ranges and high sensitivity but suboptimal repeatability and linearity because of the contact-resistance mechanism. To achieve high repeatability and linearity, several sensors with contact-resistance-free structures are proposed. However, due to the different geometric layouts of the conductive materials and the insulating substrates, the patterning of these sensors requires multiple processes including photolithography and etching, which may cause high costs and are not suitable for consumer wearable applications. Here, we report a design for stretchable strain sensors based on a one-step patterned contact-resistance-free structure, i.e., the independent-sensing-and-stretchable-function structure (ISSFS). The stretchability mainly comes from the overall large deformation of the wide curved segments (the stretchable parts), while the resistance variation is mainly attributed to the tensile strain of the narrow straight segments (the sensing parts). High linearity (R2 = 0.999) and repeatability (repeatability error = 1.44%) are achieved because neither unstable contact resistance nor nonlinear constitutive and geometric behaviors occur during the sensing process. The conductive materials and the insulating substrates do not need to have different geometric layouts; thus, they can be patterned by only one-step laser cutting. The proposed sensors show great potential in body-motion detection for wearable devices.

The flexible piezoelectric energy harvester (FPEH), as an effective strategy for long-term power supply of implantable and wearable electronics, requires high areal output energy density, low mechanical stiffness, and high energy efficiency, simultaneously. The widely adopted sandwich FPEH, consisting of one relatively hard substrate sandwiched between two piezoelectric films, can provide a high areal output energy density, but also high mechanical stiffness and low energy efficiency due to its energy-wasting deformation of the hard substrate. Here, we propose a novel optimal soft-substrate sandwich FPEH with designs of sufficient length and optimized Young’s modulus of the substrate, which is much smaller than that of the piezoelectric film. A sandwich beam model considering both the bending and shearing of the soft substrate and the one-way coupling of the piezoelectric effect was adopted for the theoretical analysis and optimal design. The optimal soft-substrate sandwich FPEH exhibits greatly improved overall performance with a 33% increase in areal output energy density, a 51% reduction in mechanical stiffness, and a 177% increase in energy efficiency, simultaneously. Systematic theoretical analysis is performed to illustrate the mechanism and guide the optimal design. The novel optimal soft-substrate sandwich FPEH is then applied to harvesting energy from various living subjects. This optimal design can be extended to other types of mechanical energy harvesters with a similar laminated structure.

Most of the existing stretchable strain sensors are based on the contact-resistance mechanism, where the stretchability and resistance variation depend on the change of the contact relationship of the conductive microstructures. These sensors usually exhibit large sensing ranges and gauge factors but unsatisfactory repeatability and linearity of the electrical responses because the contact is unstable. Here, we report a completely different design for stretchable strain sensors based on a contact-resistance-free structure, i.e., the off-axis serpentine sandwich structure (OASSS), with the mechanism of the stretch-bending-stretch transformation (SBST). Neither unstable contact resistance nor nonlinear constitutive and geometric behaviors occur for the OASSS while the sensor undergoes a large applied strain (50%), which guarantees high repeatability (repeatability error = 1.58%) and linearity (goodness-of-fitgt;0.999). Owing to such performances, the present sensors are not only applied to monitoring human activities and medical surgery but also to the ground tests of Tianwen-1, China's first Mars exploration mission.

We introduce a stretchable electronic facial mask (SEFM) as a platform for facial healthcare, which can integrate with various sensors and actuators. As a demonstration, an SEFM for sonophoresis enabling the promotion of the delivery effect of a drug mask is developed. To overcome the technique challenges, several approaches including the design of the joined silicone layer by two planar half-face portions and the single-side soft pressing (SSSP) technique for encapsulation are exploited in this work, which could be extended to the design and fabrication of other stretchable electronics. The mechanical, thermal, electrical, and ultrasonic characteristics of the SEFM are all verified by the finite element analysis and experiments. Finally, we prove the effect of the SEFM on accelerating the delivery of hyaluronic acid (HA) through animal experiments and confirm that the SEFM can enhance the skin moisture content by 20% via human facial experiments.

Tuning the microstructures of electrodes plays a vital role in enhancing the electrochemical performance of supercapacitors. In this work, we have developed a simple and effective way to tune the microstructures of graphene-based electrode by assembling different sizes of graphene sheets under vacuum filtration and freeze drying. It is found that the large-sized reduced graphene oxide (RGO) sheets (e.g., RGO-50) are assembled in large and nearly parallel structures showing poor capacitive performance due to the long transfer length of electrolyte ions in the layered structure, while the RGO film with small-sized RGO sheets (e.g., RGO-8000) has relatively small pores, thus showing low capacitance on account of low electrical conductivity. The RGO film with moderate RGO sheets shows proper porous and honeycomb-like network and thus has the largest capacitance (260.2 F g−1), ascribed to the balance of electrical conductivity, ion diffusion and reaction interface. By considering their microstructures, a theoretical model is developed which can describe the electrical conductivity of RGO films assembled by different sizes of RGO sheets. The results presented herein exploring structure–capacitance relation of graphene-based electrode may provide useful insight for designing high-performance energy storage devices.

Wearable and stretchable electronics including various conductors and sensors are featured with their lightweight, high flexibility, and easy integration into functional devices or textiles. However, most flexible electronic materials are still unsatisfactory due to their poor recoverability under large strain. Herein, we fabricated a carbon nanotubes (CNTs) and polyurethane (PU) nanofibers composite helical yarn with electrical conductivity, ultrastretchability, and high stretch sensitivity. The synergy of elastic PU molecules and spring-like microgeometry enable the helical yarn excellent stretchability, while CNTs are stably winding-locked into the yarn through a simple twisting strategy, making good conductivity. By virtue of the interlaced conductive network of CNTs in microlevel and the helical structure in macrolevel, the CNTs/PU helical yarn achieves good recoverability within 900% and maximum tensile elongation up to 1700%. With these features, it can be used as a superelastic and highly stable conductive wire. Moreover, it also can monitor the human motion as a rapid-response strain sensor by adjusting the content of the CNTs simply. This general and low-cost strategy is of great promise for ultrastretchable wearable electronics and multifunctional devices.

Organic semiconducting polymers have opened a new paradigm for soft electronics due to their intrinsic flexibility and solution processibility. However, the contradiction between the mechanical stretchability and electronic performances restricts the implementation of high-mobility polymers with rigid molecular backbone in deformable devices. Here, we report the realization of high mobility and stretchability on curvilinear polymer microstructures fabricated by capillary-gradient assembly method. Curvilinear polymer microstructure arrays are fabricated with highly ordered molecular packing, controllable pattern, and wafer-scale homogeneity, leading to hole mobilities of 4.3 and 2.6 cm2 V−1 s−1 under zero and 100% strain, respectively. Fully stretchable field-effect transistors and logic circuits can be integrated in solution process. Long-range homogeneity is demonstrated with the narrow distribution of height, width, mobility, on-off ratio and threshold voltage across a four-inch wafer. This solution-assembly method provides a platform for wafer-scale and reproducible integration of high-performance soft electronic devices and circuits based on organic semiconductors., Though stretchable semiconducting polymers are advantageous for electronic applications requiring low cost, the low performance of patterned microstructures remains a challenge. Here, the authors realize high mobility, stretchable polymer microstructures via a capillary-gradient assembly method.

Microplastics (MPs) pollution in Tangxun Lake, the largest urban lake in China, was investigated. The average MPs pollution in sediment (1.81 ± 1.75 × 10

Fabricating ultrathin organic semiconductor nanostructures attracts wide attention towards integrated electronic and optoelectronic applications. However, the fabrication of ultrathin organic nanostructures with precise alignment, tunable morphology and high crystallinity for device integration remains challenging. Herein, an assembly technique for fabricating ultrathin organic single-crystal arrays with different sizes and shapes is achieved by confining the crystallization process in a sub-hundred nanometer space. The confined crystallization is realized by controlling the deformation of the elastic topographical templates with tunable applied pressures, which produces organic nanostructures with ordered crystallographic orientation and controllable thickness from less than 10 nm to ca. 1 μm. The generality is verified for patterning various typical solution-processable materials with long-range order and pure orientation, including organic small molecules, polymers, metal-halide perovskites and nanoparticles. It is anticipated that this technique with controlling the crystallization kinetics by the governable confined space could facilitate the electronic integration of organic semiconductors., Fabrication of ultrathin organic semiconductor nanostructures with precise alignment, tuneable morphology and high crystallinity remains challenging. Here the authors use an assembly technique with dewetting process controllability for patterning organic single-crystal arrays in a sub-hundred nanometer space.

The prebuckling deformation of structures is usually very small in conventional concepts, and is always neglected in the conventional buckling theory (CBT) and numerical method (CNM). In this paper, we find a class of structures from the emerging field of stretchable electronics, of which the prebuckling deformation becomes large and essential for determining the critical buckling load. Although great progress has been made for the buckling theory in the past hundred years, it is still challenging to analyze the buckling problems with finite prebuckling deformation (FPD buckling) straightforwardly. Here, the experimental stretch of a series of serpentine interconnects was firstly conducted as a representative example to show the FPD buckling behaviors and inapplicability of the CBT and CNM. The CNM can yield a huge error of 50% on the critical buckling load for the case with thickness-to-width ratio of the cross section h/b = 0.6. Most importantly, a systematic and straightforward theory (FPD buckling theory) is developed to analyze the FPD buckling behaviors of beams with the coupling of bending, twist and stretch/compression. As a comparison, various theoretical and numerical methods are applied to three classic problems, including lateral buckling of a three-point-bending beam, lateral buckling of a pure bending beam and Euler buckling. Our FPD buckling theory for beams is able to give a good prediction, while the CBT (by Timoshenko et al.) and CNM (by commercial program packages) yield unacceptable results (with 70% error for a three-point-bending beam with h/b = 0.8, for example). Discussion on the FPD buckling of bulk structures is deferred to a following paper.

The global pollution of microplastics (MPs) has attracted widespread attention, and the atmosphere was an indispensable media for the global transmission of MPs. With the growing awareness of MPs, atmospheric microplastics (AMPs) have been proposed as a new topic in recent years. Compared with the extensive studies on MPs in Marine and terrestrial environments, the studies of AMPs remain limited. In this study, sampling and analysis methods, occurrence, source analysis and health risk of AMPs were summarized and discussed. According to the different sampling methods, AMPs can be divided into suspension microplastics (SAMPs) and deposition microplastics (DAMPs). Previous studies have shown that SAMPs and DAMPs differ in composition and abundance, with SAMPs generally having a higher fraction of fragments. The mechanism of the migration of AMPs between different media was not clear yet. We further collated global data on the composition characteristics of MPs in soil and fresh water, which showed that the fragment MPs in soil and fresh water was higher than that in the atmosphere. Polymers in soil and fresh water were mainly PP and PE, while AMPs in the atmosphere were mainly PET. The shape composition of the MPs in both atmospheric and freshwater systems suggests that there may be the same dominant factor. The transport of AMPs and source apportionment were the important issues of current research, but both of them were at the initial stage. Therefore, AMPs needs to be further studied, especially for the source and fate, which would be conducive to understand the global distribution of AMPs. Furthermore, a standardized manual on sampling and processing of AMPs was also necessary to facilitate the comparative analysis of data between different studies and the construction of global models.

Polycyclic aromatic hydrocarbons (PAHs) are a kind of organic pollutants with carcinogenic, teratogenic, and mutagenic effects. This study aims to assess the effects of changes in China's socio-economic indicators represented by energy consumption and number of motor vehicles, on PAHs and black carbon (BC) deposition. For this, a 50-cm peat core from Dajiuhu peatland, Central China, was collected and divided into 50 subsamples to establish a sedimentary record of about 200 years with radioactive 210Pb. The Σ16PAH concentration ranged from 212.67 to 830.10 ng·g-1, mainly composed of 2- and 3-ring PAHs, and BC ranged from 7.89 to 36.48%. The deposition characteristics of BC first increased and then decreased from the core bottom to the top. The predominant of the carcinogenic PAHs (C-PAHs) was Dibenzo[a,h]anthracene (DBA) before 1949, and then changed to Benzo[b]fluoranthene (BbF). Ratio of Fla/Pyr, (3+4)-ring/(5+6)-ring PAHs, and BaA/(BaA+Chr), IcdP/(IcdP+BghiP) suggested that long-range atmospheric transmission (LRAT) and pyrogenic were the main PAHs sources, but that local PAH emission contribution gradually increased since 1990, and mixed (petroleum and combustion) sources were the dominant since 2000. The high concentration of Phenanthrene (Phe) and Naphthalene (Nap) were likely from plant product. Furthermore, increased concentrations of 4-, 5-, and 6-ring PAHs showed significant correlations with increased coal and petroleum consumption and the number of motor vehicles, respectively, and this influence has strengthened after 2000. These were caused by rapid urbanization and industrialization following the implementation of the reform and opening up policy in 1978, and a new round of urbanization after 2000.

The “island-bridge” mesh structure is widely adopted for flexible epidermal electronics to simultaneously achieve the electronic functions and mechanical flexibility. Mechanical intuition tells that the small size of the “island” is beneficial to the flexibility of the structure and the adaptability to complex geometric targets. Here, a plane-strain model and an axisymmetric model are established for square “island” and cycle “island,” respectively, to analyze the mechanical system consisting of the flexible epidermal electronics and the human skin. It is found that the pressure between the “island” and the human skin is positive at the inner region and reaches a peak value at the center, while is negative at the outer region and approaches infinite at the boundary of the contact region. With the increase in the size a/R0, the amplitude of the pressure significantly increases, as well as the singular degree of the pressure at the boundary. The reduction of the “island” size is beneficial for the optimization of the “comfort level” of the flexible epidermal electronics. The models degenerate into the famous Johnson-Kendall-Roberts (JKR) model for the limit case with extremely hard and thick “island.”

The development of constitutive models for shales has been a challenge for decades due to the difficulty of characterizing the strongly anisotropic macroscopic behavior related to the inherent mesostructure and damage mechanisms. In this paper, a spectral microplane damage model is developed for the anisotropic damage behavior of shales. The modeling challenge of the anisotropic elasticity in the microplane model is theoretically overcome by the spectral decomposition theory without limitation on the degree of the anisotropy compared with other microplane models. The stiffness tensor of anisotropic shales is effectively decomposed into four different eigenmodes with the activation of certain groups of microplanes corresponding to the specific orientation of the applied stresses. The inherent and the induced anisotropic behavior is thus characterized by proposing suitable microplane relations on certain eigenmodes directly reflecting the initial mesostructure and the failure mechanisms. For the challenge of the postpeak softening behavior, two-scalar damage variables are introduced to characterize the tensile and the shear damage related to the opening and the closure of microcracks under different stress conditions. Comparison between numerical simulation and experimental data shows that the proposed model provides satisfactory predictions for both weakly and highly anisotropic shales including prepeak nonlinear behavior, failure strengths, and postpeak softening under different confining pressures and different bedding plane orientations.

The sedimentary history of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) over the past 140 years in a lake sediment core from Huixian karst wetland was reconstructed. The total PAHs and OCPs concentrations ranged from 40.0 to 210 ng g−1 and 0.98 to 31.4 ng g−1, respectively. The vertical distribution of PAHs and OCPs in different stages was great consistent with the history of regional socio-economic development and the usage of OCPs. As the indicators of socio-economic development, gross domestic product (GDP), population, energy consumption, highway mileage, and private vehicles correlated with the PAHs concentrations, indicating the impact of human activities on PAHs levels. The PAHs and OCPs concentrations were also affected by environmental changes in the wetland, as reconstructed by total organic carbon (TOC), sand, silt, clay, quartz, and calcite in sediments. Redundancy analysis (RDA) results showed TOC was the dominant factor to explain the concentrations of PAHs and OCPs with the explanation of 86.7% and 43.5%, respectively. In addition, TOC content had significantly positive correlation with PAHs (0.96, p

Pyroelectric energy harvesters (PyEHs) have been extensively developed for the energy supply to wireless, low-power advanced devices. Plenty of experiments show that the voltage–time curves for evaluating pyroelectric devices are alternatively positive and negative, while the fundamental pyroelectric theory gives a positive voltage without the negative portion. Here, this key confliction is addressed by both theoretical and experimental investigation. The voltage-time curves are recorded by three voltmeters with inner resistances of 10 MΩ, 150 GΩ, and 200 TΩ, respectively. Measured output voltages are found to be influenced greatly by the voltmeter’s resistance and capacitance, with peak voltages differing by a factor that exceeds 2200. The performance of the PyEH should be characterized by the intrinsic voltage rather than the open-circuit voltage. As a significant conclusion, the resistance and capacitance of voltmeters used should be reported in the literature, thus providing a rationale for comparing the performance of different devices.

Huanggang City in central China, is a regional site connect with the north air mass from Xiangyang and Suizhou in Hubei Province and the eastern air mass from Dabie-shan which located at the junction of Hubei and Anhui Province. To enrich the aerosol database in central China and provide reference for the control of air pollution in Huanggang City and surrounding cities in central China, totally 62 PM2.5 samples were collected during the year 2018 for season variation (January 2018–January 2019, once a week) and 16 priority PAHs were analyzed. The annual average concentrations of PM2.5 and PM2.5-bound PAHs were 60.4 ± 38.6 μg m−3 and 7.35 ± 6.79 ng m−3, respectively. Positive matrix factorization (PMF) model showed that the main sources of PM2.5-bound PAHs were vehicle emissions (56.8%), coal and biomass burning (29.5%) and petroleum sources (13.7%). PM2.5 and PM2.5-bound PAHs in Huanggang were mainly came from local emissions and relatively short-range transport and the high probability areas were concentrated in Hubei and Henan Province. The total incremental lifetime cancer risks (TILCR) values were ranged from 10−4 to 10−6, indicating the potential cancer risk for adults and children in Huanggang. However, ILCRing and ILCRdem were four orders of magnitude higher than ILCRinh, indicating that ingestion and dermal contact were the main exposure routes for cancer. Vehicle emission contributed the most to TILCR (70.9%), followed by coal and biomass combustion (21.8%) and petroleum sources (7.39%).

The output voltage is a key parameter to quantify the performance of piezoelectric devices, particularly for energy harvesters and sensors. Our recent work (Su et al., 2015) reported that the measured output voltage depends on the inner resistance of voltmeter used. It is contrary to the established concept that the measured results should be independent of the instruments used. Similar measurements, however, widely exist in recent published literature, which is actually not suitable to quantify the performance of piezoelectric devices. This paper proposes a universal and easy-to-use standard for the voltage measurement of piezoelectric devices. The output voltage measurements of a micro-fabricated, flexible lead zirconate titanate (PZT) mechanical energy harvester by two voltmeters with a resistance of 10 M Ω and 55 G Ω , present significantly different output voltage values ( ∼ 0.2 V vs. ∼ 2.0 V), which provide strong evidence for the unusual conclusion. A universal and easy-to-use standard of voltage measurement for piezoelectric devices requires that the inner resistance of voltmeter must be larger than a critical value in terms of effective capacitor, loading frequency and accuracy requirement of measured voltage. This standard is developed to obtain the open-circuit resistance-independent voltage. A self-developed electronic system meeting the standard requirement was built and the universality of all the findings was further validated by a commercial piezoelectric device.