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Stretchable electronics have increasingly gained interest both in the academic and industrial communities owing to its potential to enable a wide variety of applications, especially ...wearable and implantable devices for biomedical applications. As the key component for electronic devices, the design of a suitable semiconductor is essential, while the solution processability and structural tunability of polymer semiconductor make it a promising candidate. Along this line, it is important to consider the mechanical properties of polymer semiconductors in the design of flexible and stretchable devices placed on soft and curved surfaces to accommodate the constant movement of the human body. However, achieving high mechanical deformability and high charge transport properties simultaneously in polymer semiconductors remains a major challenge. In this trend article, we survey various approaches in designing intrinsically stretchable conjugated polymers, focusing on structure-property relationships from a molecular perspective, such as molecular weight, regioregularity, backbone and side chain modifications. Understanding the influence of these molecular structure parameters on thin film morphology may provide general guidelines for achieving desired microstructures that allow mechanical deformation without interrupting charge transport. Beyond highlighting recent key work in this field, we will discuss future prospects of stretchable conjugated polymers.
Electronic second skin is touted as the next interface to expand applications of electronics for natural and seamless interactions with humans to enable smart health care, the Internet of Things, and ...even to amplify human sensory abilities. Thus, electronic materials are now being actively investigated to construct “second skin.” Accordingly, electronic devices are desirable to have skin‐like properties such as stretchability, self‐healing ability, biocompatibility, and biodegradability. This work reviews recent major progress in the development of both electronic materials and devices toward the second skin. It is concluded with comments on future research directions of the field.
Second skin enabled by advanced electronics is emerging as a next interface of electronics to expand applications of electronics from smart health care to even amplification of human's sensing abilities. Recent progress in fields of materials and devices with noble capabilities for the second skin are highlighted and its perspectives are also suggested.
Flexible electronics offer a wide-variety of applications such as flexible circuits, flexible displays, flexible solar cells, skin-like pressure sensors, and conformable RFID tags. Carbon nanotubes ...(CNTs) are a promising material for flexible electronics, both as the channel material in field-effect transistors (FETs) and as transparent electrodes, due to their high intrinsic carrier mobility, conductivity, and mechanical flexibility. In this feature article, we review the recent progress of CNTs in flexible electronics by describing both the processing and the applications of CNT-based flexible devices. To employ CNTs as the channel material in FETs, single-walled carbon nanotubes (SWNTs) are used. There are generally two methods of depositing SWNTs on flexible substrates-transferring CVD-grown SWNTs or solution-depositing SWNTs. Since CVD-grown SWNTs can be highly aligned, they often outperform solution-processed SWNT films that are typically in the form of random network. However, solution-based SWNTs can be printed at a large-scale and at low-cost, rendering them more appropriate for manufacturing. In either case, the removal of metallic SWNTs in an effective and a scalable manner is critical, which must still be developed and optimized. Nevertheless, promising results demonstrating SWNT-based flexible circuits, displays, RF-devices, and biochemical sensors have been reported by various research groups, proving insight into the exciting possibilities of SWNT-based FETs. In using carbon nanotubes as transparent electrodes (TEs), two main strategies have been implemented to fabricate highly conductive, transparent, and mechanically compliant films-superaligned films of CNTs drawn from vertically grown CNT forests using the "dry-drawing" technique and the deposition or embedding of CNTs onto flexible or stretchable substrates. The main challenge for CNT based TEs is to fabricate films that are both highly conductive and transparent. These CNT based TEs have been used in stretchable and flexible pressure, strain, and chemical and biological sensors. In addition, they have also been used as the anode and cathode in flexible light emitting diodes, solar cells, and supercapacitors. In summary, there are a number of challenges yet to overcome to optimize the processing and performance of CNT-based flexible electronics; nonetheless, CNTs remain a highly suitable candidate for various flexible electronic applications in the near future.
The distributed network of receptors, neurons, and synapses in the somatosensory system efficiently processes complex tactile information. We used flexible organic electronics to mimic the functions ...of a sensory nerve. Our artificial afferent nerve collects pressure information (1 to 80 kilopascals) from clusters of pressure sensors, converts the pressure information into action potentials (0 to 100 hertz) by using ring oscillators, and integrates the action potentials from multiple ring oscillators with a synaptic transistor. Biomimetic hierarchical structures can detect movement of an object, combine simultaneous pressure inputs, and distinguish braille characters. Furthermore, we connected our artificial afferent nerve to motor nerves to construct a hybrid bioelectronic reflex arc to actuate muscles. Our system has potential applications in neurorobotics and neuroprosthetics.
Future electronics will take on more important roles in people's lives. They need to allow more intimate contact with human beings to enable advanced health monitoring, disease detection, medical ...therapies, and human-machine interfacing. However, current electronics are rigid, nondegradable and cannot self-repair, while the human body is soft, dynamic, stretchable, biodegradable, and self-healing. Therefore, it is critical to develop a new class of electronic materials that incorporate skinlike properties, including stretchability for conformable integration, minimal discomfort and suppressed invasive reactions; self-healing for long-term durability under harsh mechanical conditions; and biodegradability for reducing environmental impact and obviating the need for secondary device removal for medical implants. These demands have fueled the development of a new generation of electronic materials, primarily composed of polymers and polymer composites with both high electrical performance and skinlike properties, and consequently led to a new paradigm of electronics, termed "skin-inspired electronics". This Account covers recent important advances in skin-inspired electronics, from basic material developments to device components and proof-of-concept demonstrations for integrated bioelectronics applications. To date, stretchability has been the most prominent focus in this field. In contrast to strain-engineering approaches that extrinsically impart stretchability into inorganic electronics, intrinsically stretchable materials provide a direct route to achieve higher mechanical robustness, higher device density, and scalable fabrication. The key is the introduction of strain-dissipation mechanisms into the material design, which has been realized through molecular engineering (e.g., soft molecular segments, dynamic bonds) and physical engineering (e.g., nanoconfinement effect, geometric design). The material design concepts have led to the successful demonstrations of stretchable conductors, semiconductors, and dielectrics without sacrificing their electrical performance. Employing such materials, innovative device design coupled with fabrication method development has enabled stretchable sensors and displays as input/output components and large-scale transistor arrays for circuits and active matrixes. Strategies to incorporate self-healing into electronic materials are the second focus of this Account. To date, dynamic intermolecular interactions have been the most effective approach for imparting self-healing properties onto polymeric electronic materials, which have been utilized to fabricate self-healing sensors and actuators. Moreover, biodegradability has emerged as an important feature in skin-inspired electronics. The incorporation of degradable moieties along the polymer backbone allows for degradable conducting polymers and the use of bioderived materials has led to the demonstration of biodegradable functional devices, such as sensors and transistors. Finally, we highlight examples of skin-inspired electronics for three major applications: prosthetic e-skins, wearable electronics, and implantable electronics.
Deformable energy storage devices are needed to power next‐generation wearable electronics that interface intimately with human skin. Currently, deformable energy storage devices demonstrate poor ...performance compared to their rigid lithium‐ion counterparts, forcing wearable manufacturers to design their devices around bulky battery compartments. However, technological advances to create deformable batteries at the component and device level have yielded continuous improvement in stretchable batteries over the last five years. In this Essay, the major strategies at the component and device level that have been successfully employed to create stretchable batteries are reviewed. The outstanding challenges facing deformable energy storage are also discussed, namely, energy density, packaging, delamination, device integration, and manufacturing. This Essay will give researchers who are interested in contributing to the development of deformable batteries a cursory understanding of the most successful strategies to date, and provide insights into the most important directions to pursue in the future.
Deformable batteries are needed to enable the next generation of skin‐conformable electronics. This Essay describes past strategies to enable stretchable batteries at the device and component level. These strategies demonstrate significant advances in stretchable battery technology; however, there are still limitations that must be overcome. This Essay also describes the five main challenges that the development of deformable batteries encounters.
Recent progress in electronic skin or e‐skin research is broadly reviewed, focusing on technologies needed in three main applications: skin‐attachable electronics, robotics, and prosthetics. First, ...since e‐skin will be exposed to prolonged stresses of various kinds and needs to be conformally adhered to irregularly shaped surfaces, materials with intrinsic stretchability and self‐healing properties are of great importance. Second, tactile sensing capability such as the detection of pressure, strain, slip, force vector, and temperature are important for health monitoring in skin attachable devices, and to enable object manipulation and detection of surrounding environment for robotics and prosthetics. For skin attachable devices, chemical and electrophysiological sensing and wireless signal communication are of high significance to fully gauge the state of health of users and to ensure user comfort. For robotics and prosthetics, large‐area integration on 3D surfaces in a facile and scalable manner is critical. Furthermore, new signal processing strategies using neuromorphic devices are needed to efficiently process tactile information in a parallel and low power manner. For prosthetics, neural interfacing electrodes are of high importance. These topics are discussed, focusing on progress, current challenges, and future prospects.
Recent progress in electronic skin research is broadly reviewed, focusing on the technologies required in the following three applications: skin‐attachable electronics, robotics, and prosthetics. Topics such as stretchability, self‐healing, biocompatibility, tactile sensing, chemical and electrophysiological sensing, wireless communication, large‐area integration, neuromorphic signal processing, and neural interfaces are discussed.
There is often a trade-off between mechanical properties (modulus and toughness) and dynamic self-healing. Here we report the design and synthesis of a polymer containing thermodynamically stable ...whilst kinetically labile coordination complex to address this conundrum. The Zn-Hbimcp (Hbimcp = 2,6-bis((imino)methyl)-4-chlorophenol) coordination bond used in this work has a relatively large association constant (2.2 × 10
) but also undergoes fast and reversible intra- and inter-molecular ligand exchange processes. The as-prepared Zn(Hbimcp)
-PDMS polymer is highly stretchable (up to 2400% strain) with a high toughness of 29.3 MJ m
, and can autonomously self-heal at room temperature. Control experiments showed that the optimal combination of its bond strength and bond dynamics is responsible for the material's mechanical toughness and self-healing property. This molecular design concept points out a promising direction for the preparation of self-healing polymers with excellent mechanical properties. We further show this type of polymer can be potentially used as energy absorbing material.
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