Skin inspired fractal strain sensors using a copper nanowire and graphite microflake hybrid conductive network

Adv Healthcare Materials

2017

471

296

humidity level, and concentration of harmful gases, and airborne particulates can provide valuable information for the prediction, management, and treatment of chronic diseases. [4,5] In addition to the applications in wearable health monitoring, continuous tracking of daily and sports activities can offer an efficient way to assess the well-being and athletic performances. [6] In order to ensure a robust and conformal contact with the curvilinear, coarse, and dynamic surface of skin without impeding daily activities, the wearable sensor should have low modulus and high stretchability. The epidermis has a modulus of 140-600 kPa while the dermis has an even lower modulus of 2-80 kPa. [7] Skin itself can be stretched elastically up to 15% and with the help of wrinkles and creases, the overall stretchability can reach as high as 100% during daily motions. [8] In addition to good wearability, wearable sensors should be highly sensitive, lightweight, low-cost, and with low power consumption. To achieve these features, nanomaterials that are compliant, possessing larger surface area and exceptional material properties, and compatible with low-cost fabrication processes are widely employed as building blocks for developing wearable sensors.In this review, we start from a brief overview of nanomaterials, their related structural designs and fabrication processes (Section 2). Following that, recent advances of nanomaterialenabled wearable sensors including temperature, electrophysiological, strain, tactile, electrochemical, and other sensors will be summarized (Section 3). A survey on the integration of multiple sensors and other components into wearable systems will be given in Section 4. The application of nanomaterialenabled wearable sensors for healthcare including health monitoring, activity tracking, and electronic skin will be presented in Section 5. The challenges and opportunities will be discussed at the end. Nanomaterials, Structural Designs, and Fabrication ProcessesNanomaterials can be classified into two categories-top-down fabricated ones and bottom-up synthesized ones. [9] The focus of this review is on the wearable sensors based on bottom-up synthesized nanomaterials. Nanomaterials can be synthesized into various dimensions, from 0D such as metallic nanoparticles (NPs), to 1D such as carbon nanotubes (CNTs), and metallic nanowires (NWs), to 2D such as graphene and transition metal Highly sensitive wearable sensors that can be conformably attached to human skin or integrated with textiles to monitor the physiological parameters of human body or the surrounding environment have garnered tremendous interest. Owing to the large surface area and outstanding material properties, nanomaterials are promising building blocks for wearable sensors. Recent advances in the nanomaterial-enabled wearable sensors including temperature, electrophysiological, strain, tactile, electrochemical, and environmental sensors are presented in this review. Integration of multiple sensors for multimodal sensing and integration with...

Section: Health Monitoringmentioning

confidence: 99%

Section: Daily Activity and Sports Performance Trackingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Nanomaterial‐Enabled Wearable Sensors for Healthcare

Yao

Swetha

Adv Healthcare Materials

2017

471

296

“…The related strain or stress/pressure sensors may serve as a vital component for advanced artificial intelligence de-vices, and an integral part in the future internet of things network [168]. Sensors are required to have high sensitivity, stability, reliability and robustness, which should be fulfilled by copper-based devices [88,101,[169][170][171][172][173]. Gauge factor, defined by the ratio of relative change of resistance to the mechanical strain, is one of the key factors judging the performance of resistive strain sensors.…”

Section: Electromechanical Sensorsmentioning

confidence: 99%

Copper nanomaterials and assemblies for soft electronics

Yang

2019

Sci. China Mater.

Soft electronics that can simultaneously offer electronic functions and the capability to be deformed into arbitrary shapes are becoming increasingly important for wearable and bio-implanted applications. The past decade has witnessed tremendous progress in this field with a myriad of achievements in the preparation of soft electronic conductors, semiconductors, and dielectrics. Among these materials, copper-based soft electronic materials have attracted considerable attention for their use in flexible or stretchable electrodes or interconnecting circuits due to their low cost and abundance with excellent optical, electrical and mechanical properties. In this review, we summarize the recent progress on these materials with the detailed discussions of the synthesis of copper nanomaterials, approaches for their assemblies, strategies to resist the ambient corrosion, and their applications in various fields including flexible electrodes, sensors, and other soft devices. We conclude our discussions with perspectives on the remaining challenges to make copper soft conductors available for more widespread applications.

“…Shengfei Shen, Wei Zhu,* Yuncheng Peng, Fengxun Hai, Jingjing Feng, and Yuan Deng* DOI: 10.1002/admi.201701038 also intensively investigated through techniques of spincoating, [15] screen printing, [16] and inkjet printing. [17] Besides, new novel printing inks that consist of low dimension metallic nanomaterials, such as Cu nanowires, [18,19] Ag nanowires, [20,21] and Au nanowires [22] have been widely explored. Although the emerging techniques have greatly boomed the application of the flexible electrode, inevitable organic solvents in the preparation process will bring on high porosity and weak adhesion of the prepared flexible thin film.…”

Section: Highly Conductive and Fatigue-free Flexible Copper Film Elecmentioning

confidence: 99%

Highly Conductive and Fatigue‐Free Flexible Copper Film Electrode Fabricated by a Facile Dry Transfer Technique

Shen

Peng

et al. 2017

Adv Materials Inter

also intensively investigated through techniques of spincoating, [15] screen printing, [16] and inkjet printing.[17] Besides, new novel printing inks that consist of low dimension metallic nanomaterials, such as Cu nanowires, [18,19] Ag nanowires, [20,21] and Au nanowires [22] have been widely explored. Although the emerging techniques have greatly boomed the application of the flexible electrode, inevitable organic solvents in the preparation process will bring on high porosity and weak adhesion of the prepared flexible thin film. [23] These demerits seriously limit the electrical conductivity and durability of the thin-film electrode, so in short-term future, PVD technology is still the best candidate to fabricate high-performance thin-film electrodes.Currently, there are mainly two key aspects restricting the popularity of metal thin film deposited on flexible substrates through PVD method. One is the weak adhesion strength of the interface between the metal thin film and flexible polymer substrates caused by the huge isomerism of materials. [24] On the other hand, owing to the poor heat resistance and unstable chemical properties of the polymer substrates, the deposition temperature is confined to a relatively low range, which is adverse to the crystallization of metal particles as well as the electrical performance. [25] The adhesive strength of the metalpolymer substrates can be improved by inserting a buffer interlayer, [26] varying the roughness of the interface, [27] and O 2 plasma treatment. [28] Nevertheless, it is still challenging to prepare high-performance metal films on flexible substrate even though the films deposited at low temperature could be slightly improved via postannealing process.Transfer printing is a unique approach that can be applied to integrate materials fabricated under harsh conditions onto plastic substrates. [29] In the transfer process, the essential issue is the detachment of rigid donor-film interface, which can be realized through etching the sacrificial layers, [30] functionalizing the donor surfaces with adhesion reduction layers, and stress-inducing delamination. [31] However, it is inevitable to corrode the transfer layer when the integration of donor-thin film system is immersed in the etching solutions. Functionalizing the donor surfaces with adhesion reduction layers cannot resist to high temperature process, for the coating material is organic. [32] As there is no heterogeneous material access in the transfer process, the method of stress inducing delamination is simple, nondestructive, and compatible with high temperature techniques, which is rather suitable for the transfer of The flexible electrodes with excellent electrical and mechanical performance play critical and fundamental roles in the wearable electronics. In this work, highly conductive and fatigue-free flexible copper thin-film electrodes on polyethylene terephthalate substrate are successfully fabricated by a facile, nondestructive, and heat-resistant dry transfer technique. Before the transfer proc...