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Flexible and Stretchable Liquid Metal Electronics
Published in Katsuyuki Sakuma, Krzysztof Iniewski, Flexible, Wearable, and Stretchable Electronics, 2020
Dishit P. Parekh, Ishan D. Joshipura, Yiliang Lin, Christopher B. Cooper, Vivek T. Bharambe, Michael D. Dickey
While flexible electronics can be bent, stretchable electronics can be elongated. Thus, stretchable electronics can be used in a wider application space while providing increased durability. To build a stretchable electronic device, in addition to having the backbone of a soft polymer matrix, it is required to pattern interconnects that are intrinsically stretchable. Using multiple patterning processes such as chemical vapor deposition, sputtering, soft lithography, and 3D printing, researchers have fabricated a variety of stretchable electronics such as optoelectronic skin for sensing and display,[55–57] soft neural implants that sustain millions of mechanical stretch cycles and assist in drug delivery,[58–60] stretchable batteries with wireless recharging capabilities,[61–63] stretchable displays,[64–66] soft silicon integrated circuits using wavy metal films,[67–70] and epidermal electronics for the skin.[71–73] Some of these examples are shown in Figure 8.4.[54,55,61,65]
Flexible On-Chip Interdigital Micro-Supercapacitors: Efficient Power Units for Wearable Electronics
Published in Run-Wei Li, Gang Liu, Flexible and Stretchable Electronics, 2019
Guozhen Shen, Kai Jiang, Di Chen
During the past years, stretchable electronics, as a kind of “soft” electronic devices that can be stretched, deformed, and wrapped onto nonplanar curved surfaces, have attracted tremendous attention due to their potential applications in wearable electronics, implantable biomedical devices, and artificial electronic skin. Besides flexibility, on-chip MSCs must also have the feature of stretchability in some cases, to fit for stretchable electronic systems.
Artificial Skin
Published in Muhammad Mustafa Hussain, Nazek El-Atab, Handbook of Flexible and Stretchable Electronics, 2019
The characteristics and capabilities of a sensor are majorly affected by the mechanical properties of the platform [1]. The low elastic modulus of skin allows it to conform to the surface of objects by altering the distribution of forces and strains at different points [19]. For example, a good grip is achieved by inducing friction, which is in turn realized by increasing contact area with the object [20]; this latter mechanism can be made feasible only if the platform is flexible. Only flexible electronics that can be bent over curved surfaces can provide additional degrees of movement [21–24]. State-of-the-art silicon electronics are stiff and brittle, therefore alternative materials are embraced to simulate the soft mechanical properties of skin. Evidently, organic materials became the first attraction due to their intrinsically flexible and stretchable nature. However, they exhibit limited performance, complex integration strategies, as well as thermal instability, which compelled investigation into 1D materials (e.g., nanowires, nanotubes, and nanorods), 2D material composites, and the use of unconventional substrates such as paper [2]. Although flexibility alone of an E-skin can satisfy many of the requirements desired in robotic applications and smart wearables, stretchable materials with low elastic moduli can further augment the functionality of a prosthetic, making it closer to the feel of real skin. For example, the free movement of joints in the human body is assisted by our naturally stretchable biological skin, capable of withstanding strains up to 75% on average [1]. Making electronics stretchable requires new materials such as intrinsically stretchable organic and hybrid elastomers, or design approaches to transform brittle and inelastic metals and semiconductors into physically deformable materials [22,23,25], providing the desired additional degrees of movement. Biological skin is characterized by a network of touch fibers that governs its soft, yet tough nature. In contrast, elastomers often present a settlement between softness and durability [1]. Elastomers with an elastic modulus comparable to human skin often lack the robustness needed in prosthetics [26]. One common approach to overcome this matter is to adopt a network of a low-modulus materials mixed within a network of a high-modulus materials [1,27]. The elasticity of the resulting composite would be contingent on the applied strain, in such a way to avoid rupture. Moreover, our biological skin displays various designs essential to the perception of force and texture discrimination, such as intermediate ridges and fingerprint ridges found on the surface of our fingers [20,28,29] (Figure 10.1). These are a few of the biomimetic designs that researchers aim to implement into their sensors to improve their performance and get closer to skin sensations [30,31].
Hydrogel-elastomer-based stretchable strain sensor fabricated by a simple projection lithography method
Published in International Journal of Smart and Nano Materials, 2021
Zhenqing Li, Xiangnan He, Jianxiang Cheng, Honggeng Li, Yuan-Fang Zhang, Xiaojuan Shi, Kai Yu, Hui Ying Yang, Qi Ge
Stretchable strain sensor is a type of sensor that is highly stretchable and capable of detecting a wide range of strain variations. Therefore, it is a key component in various emerging fields including soft robots [1–4], wearable devices [5–7], smart prosthetics [8,9], and others [10–12]. In the past years, many efforts have been made to develop stretchable strain sensors, and the approaches mainly rely on two types: elastomer-based strain sensors and liquid-based strain sensors. The elastomer-based strain sensors are made of elastomers doped with conductive components such as silver nanoparticles/nanowires, carbon nanotubes, and graphene. However, the conductivity of such strain sensors degrades remarkably as a result of the separation of doped wires or particles [13,14]. Therefore, they are not ideal for sensing large deformations. Liquid-based strain sensors are fabricated with liquid conductors such as liquid metal and grease. While such type of strain sensors can sustain large deformations, the accumulated localized plastic deformation resulting from cyclic loading deteriorates the conductivity and leads to signal drifts [15,16]. More importantly, many of those liquid conductors are not biocompatible, and the efforts to prevent them from leakage result in additional design complexity and manufacturing costs [14].
Stretchable electronics: functional materials, fabrication strategies and applications
Published in Science and Technology of Advanced Materials, 2019
As a newly developed technology, flexible and stretchable electronics is emerging and achieving a great variety of applications, because its components can be compressed, twisted and conform to complex non-planar surfaces [1]. Currently, wearable electronics applications have positive effects on various aspects of daily life, leading to economic growth and the rapid development of stretchable electronic devices and related manufacturing technologies. Flexible, soft and stretchable forms of electronic devices enable next-generation wearable electronic applications, opening up various applications for healthcare, energy and military purposes.