Hierarchical structures allow one to improve device performance by exploiting the synergistic effects of micro/nano multiscale components. However, the structural complexity of hierarchical ...structures places limits on their fabrication and applications. Herein, a novel morphology-controllable wrinkled micro/nano hierarchical structure (WHS) was developed by integrating micropatterns, nanopatterns, and wrinkles on a single substrate to overcome these limitations. Each structure could be individually controlled, which offers unlimited design diversity. The produced WHS was used as a superhydrophobic triboelectric nanogenerator. Compared to a nanogenerator with on a film structure, the WHS-based nanogenerator showed a superior contact angle of 152.5°, which is indicative of high hydrophobicity, and an enhanced (by 608%) triboelectric effect, which was ascribed to the highly rough surface of the WHS. The WHS-based nanogenerator was used to fabricate a self-powered and water-repellent cough detection sensor with an entirely superhydrophobic structure and stable superior sensing performance during repeated water spraying.
This study describes a novel fabrication method of hierarchical structures, which can integrate micropatterns, nanopatterns, and wrinkles on a single substrate. This method allows one to independently control three different structures and thus fabricate the wrinkled micro/nano hierarchical structures (WHS). The WHS is utilized as a self-powered and water-repellent cough detection sensor that maintains detection performance during repeated water spraying. Display omitted
•A novel fabrication method for wrinkled hierarchical structures (WHSs) is described.•Micropatterns, nanopatterns, and wrinkles can be integrated on a single substrate.•WHSs is utilized as a superhydrophobic triboelectric nanogenerator (S-TENG).•We demonstrate S-TENG as self-powered and water-repellent cough detection sensors.•The sensor maintains superior detection performance during repeated water spraying.
The growing demand for complex three-dimensional (3D) micro-/nanostructures has inspired the development of the corresponding manufacturing techniques. Among these techniques, 3D fabrication based on ...mechanically guided assembly offers the advantages of broad material compatibility, high designability, and structural reversibility under strain but is not applicable for nanoscale device printing because of the bottleneck at nanofabrication and design technique. Herein, a configuration-designable nanoscale 3D fabrication is suggested through a robust nanotransfer methodology and design of substrate's mechanical characteristics. Covalent bonding-based two-dimensional nanotransfer allowing for nanostructure printing on elastomer substrates is used to address fabrication problems, while the feasibility of configuration design through the modulation of substrate's mechanical characteristics is examined using analytical calculations and numerical simulations, allowing printing of various 3D nanostructures. The printed nanostructures exhibit strain-independent electrical properties and are therefore used to fabricate stretchable H
and NO
sensors with high performances stable under external strains of 30%.
With machine learning (ML) and artificial intelligence (AI) becoming increasingly refined and accessible, computer engineers and materials scientists are utilizing these data-driven techniques to ...design new functional materials more efficiently. Additionally, the advancement of simulation software and computing power has substantially lowered the cost of obtaining training data. However, using only simulation data presents a difficulty in the eventual realization of a material design due to possible misalignment of the simulation setup and physical laboratory conditions. Therefore, it is mutually beneficial to also improve the experimental aspect of functional materials development using ML and AI techniques. In this article, we survey the current state of ML/AI involvement in functional materials design, focusing specifically on acoustic/mechanical metamaterials, piezoelectric materials, and biological materials. The macroscopic nature of these functional materials lends well to additive manufacturing fabrication, which makes optimizing the synthesis process of these materials highly desirable. We conclude by pointing out a few promising directions for future investigation of functional materials and their place in societal applications.
Graphical abstract
In this work, a model for predicting the leakage rate was developed to investigate the effect of irradiation on the sealing performance of ethylene propylene diene monomer (EPDM) O-rings. The model ...is based on a mesoscopic interfacial gap flow simulation and accurately predicts the sealing performance of irradiated and non-irradiated materials by utilizing the gap height as an indicator in a mechanical simulation of the O-ring under operating conditions. A comparison with vacuum test results indicates that the model is a good predictor of leak initiation. The positive pressure leakage of the O-rings was investigated numerically. The results show the following. The sealing performance of the non-irradiated O-ring is much better than that of the irradiated one. The sealing performance is the worst at 0. 713 MGy and the best at 1.43 MGy, and the seal is maintained at an absorbed dose of 3.55 MGy. A theoretical analysis of the non-monotonic variation using the proposed model shows that the leakage behavior of the O-rings depends not only on the material properties but also on the roughness and prestressing properties. Finally, a method was proposed to classify the sealing performance, using the maximum allowable leakage rate as an indicator.
Abstract
Individuals who are unable to walk independently spend most of the day in a wheelchair. This population is at high risk for developing pressure injuries caused by sitting. However, early ...diagnosis and prevention of these injuries still remain challenging. Herein, we introduce battery-free, wireless, multimodal sensors and a movable system for continuous measurement of pressure, temperature, and hydration at skin interfaces. The device design includes a crack-activated pressure sensor with nanoscale encapsulations for enhanced sensitivity, a temperature sensor for measuring skin temperature, and a galvanic skin response sensor for measuring skin hydration levels. The movable system enables power harvesting, and data communication to multiple wireless devices mounted at skin-cushion interfaces of wheelchair users over full body coverage. Experimental evaluations and numerical simulations of the devices, together with clinical trials for wheelchair patients, demonstrate the feasibility and stability of the sensor system for preventing pressure injuries caused by sitting.
A number of flexible and stretchable strain sensors based on piezoresistive and capacitive principles have been recently developed. However, piezoresistive sensors suffer from poor long-term ...stability and considerable hysteresis of signals. On the other hand, capacitive sensors exhibit limited sensitivity and strong electromagnetic interference from the neighboring environment. In order to resolve these problems, a novel stretchable strain sensor based on the modulation of optical transmittance of carbon nanotube (CNT)-embedded Ecoflex is introduced in this paper. Within the film of multiwalled CNTs embedded in the Ecoflex substrate, the microcracks are propagated under tensile strain, changing the optical transmittance of the film. The proposed sensor exhibits good stretchability (ε ≈ 400%), high linearity (R 2 > 0.98) in the strain range of ε = 0–100%, excellent stability, high sensitivity (gauge factor ≈ 30), and small hysteresis (∼1.8%). The sensor was utilized to detect the bending of the finger and wrist for the control of a robot arm. Furthermore, the applications of this sensor to the real-time posture monitoring of the neck and to the detection of subtle human motions were demonstrated.
Wearable pressure sensors have been attracting great attention for a variety of practical applications, including electronic skin, smart textiles, and healthcare devices. However, it is still ...challenging to realize wearable pressure sensors with sufficient sensitivity and low hysteresis under small mechanical stimuli. Herein, we introduce simple, cost-effective, and sensitive capacitive pressure sensor based on porous Ecoflex-multiwalled carbon nanotube composite (PEMC) structures, which leads to enhancing the sensitivity (6.42 and 1.72 kPa–1 in a range of 0–2 and 2–10 kPa, respectively) due to a synergetic effect of the porous elastomer and percolation of carbon nanotube fillers. The PEMC structure shows excellent mechanical deformability and compliance for an effective integration with practical wearable devices. Also, the PEMC-based pressure sensor shows not only the long-term stability, low-hysteresis, and fast response under dynamic loading but also the high robustness against temperature and humidity changes. Finally, we demonstrate a prosthetic robot finger integrated with a PEMC-based pressure sensor and an actuator as well as a healthcare wristband capable of continuously monitoring blood pressure and heart rate.
•The critical heat transfer coefficient (hcr) is defined to indicate that the heat dissipation capability is equal to the heat generated by the battery.•A quantitative criterion (h < hcr) is proposed ...to predict the over-temperature risk of batteries.•The intervention time (τintv) is specified as the time when the battery reaches the over-temperature threshold.•A response surface analysis is conducted to determine intervention methods to prevent over-temperature risk.
In recent years, research on high-performance battery thermal management systems (BTMSs) has increased to improve the safety and reliability of electric vehicle (EV) batteries. However, some underlying concepts have not been clearly explained. For example, which conditions are considered safe, and what about not？ This study focuses on the prediction and prevention of battery over-temperature risk using the finite element method. The critical heat transfer coefficient (hcr) is proposed as a quantitative criterion for risk prediction since it provides sufficient information on the battery operation, such as the dynamic operating parameters and the battery’s safety temperature. The intervention time is specified, and intervention methods are suggested to prevent risky conditions. Three parameters were found to have a substantial impact on risk prevention, namely, the equivalent heat transfer coefficient (h), representing the maximum heat transfer capacity of the heat dissipation system, the ambient temperature (Tab), representing the coolant temperature of the heat dissipation system, and the discharge current rate (Crate), representing the current level during discharge. A response surface analysis was performed using the maximum operating temperature of the battery (Tmax) as the response variable and three influencing factors as the input variables. The results show that safety zones can be found for each of the three influencing factors. For example, for the case considered in this work, the optimum Tab is around 281.15 K and should not exceed 305.15 K; the Crate should be below under 5C and should never exceed 8C; h should be greater than 50 W·m−2·K−1. Suggestions are provided for choosing risk prevention methods according to the response characteristics of Tmax. The proposed method provides a novel approach for the research and design of intelligent BTMSs.
Soft strain sensors have attracted significant attention in wearable human motion monitoring applications. However, there is still a huge challenge for decoupled measurement of multidirectional ...strains. In this study, we have developed a biaxial and stretchable strain sensor based on a carbon nanotube (CNT) film and a microdome array (MA)-patterned elastomeric substrate. The MA structures lead to generating localized and directional microcracks of CNT films within the intended regions under tensile strain. This mechanism allows a single sensing layer to act as a strain sensor capable of decoupling the biaxial strains into axial and transverse terms. The ratio of resistance change between two perpendicular axes is about 960% under an x-directional strain of 30%, demonstrating the biaxial decoupling capability. Also, the proposed strain sensor shows high stretchability and excellent long-term reliability under a cyclic loading test. Finally, wearable devices integrated with the strain sensor have been successfully utilized to monitor various human motions of the wrist, elbow, knee, and fingers by measuring joint bending and skin elongation.
A biopsy needle integrated with a multi-modal physical/chemical sensor array for electrical conductivity, pH, and glucose concentration measurement was developed. A flexible device with an electrical ...conductivity sensor, a pH sensor, and a glucose sensor was fabricated on a flexible polyimide substrate with thickness less than 20 μm. Then, the sensor was directly integrated onto the surface of biopsy needle by attaching with a pressure sensitive adhesive. The performance factors of the sensor were examined, showing that it could properly measure the parameters in the ranges of human body conditions (conductivity = 0.0265 S/m - 1.027 S/m, pH = 6.6–7.4, and glucose concentration = 2 mM–13 mM). The capabilities of dual-modal and multi-modal sensing were demonstrated by tests with a liver cancer mimicking hydrogel phantom, a solution sample, and porcine liver tissue with exchanged parameters by perfusion of the phosphate buffer saline. Based on these results, we expect that the biopsy needle integrated with the multi-modal sensor array could help to increase the accuracy of the image-guided biopsy process by providing the information of tissue types at the needle tip.
•The biopsy needle with capability of multiplexed physical/chemical sensing (electrical conductivity, pH, and glucose concentration) is proposed.•Sensor integration onto the surface of biopsy needle (d = 1.2 mm) has been achieved by thin flexible biosensor (thickness < 20 μm).•Each sensor could cover the possible ranges in physiological condition for cancer vs. normal tissue discrimination.•Feasibility of tissue discrimination was demonstrated with solution samples, hydrogel phantom, and porcine liver sample.
