Skin is the largest organ in the human body and has a wide variety of interesting properties such as stretchability, self-healing ability, high mechanical toughness, and tactile sensing capability. Devices that mimic such properties of human skin along with additional features are commonly referred to as electronic skin or e-skin. The applications of e-skin vary widely, however, the key application areas are in the wearable or skin attachable devices, robotics, and prosthetics. This article will review the recent progress in the field of e-skin, focusing on the latest research results over the past 6 years since our last review paper,[1] and on the necessary technologies to enable the aforementioned three applications. The topics to be discussed in this review will generally apply to all three applications, while the importance of the topics to each application will vary. This is a broad review covering a wide variety of topics. Our purpose is to introduce the key concepts and key papers for each topic. For a more focused review, we guide the reader to review papers referenced in each of the topics. Figure 1 summarizes the on-going research in the three application areas. Table 1 lists the requirements and their relative importance in each of the three applications. Below, we briefly summarize the contents of this review with the motivation underlying the discussion of each topic.
When e-skin is attached to human skin or is functioning as skin in robotics or prosthetics, first, they need to be well adhered to moving surfaces. For instance, at the joints, the surface will undergo lateral tension, compression, and twisting. In order for the e-skin to be adhered to the body under such conditions, stretchability is of critical matter. Without stretchability, the e-skin is likely to be delaminated from the surface. Here we note that the conformal contact to a given surface is also dependent on geometrical factors of the device and the strength of the adhesive layers. Furthermore, for skin-attachable applications, since stretchable materials can stretch along with the surface of the skin, the user will experience higher comfort. In addition, stretchability is needed to provide the necessary mechanical degrees of freedom to prevent the breakage of e-skin duringusage. When e-skin is attached to human skin or is replacing skin in prosthetics, the daily human motion will generate strain values up to 30%.[2] Hence, without stretchability, the e-skin will likely undergo serious damage. In the case of robotics, stretchability of e-skin will enable the robot to take on a variety of shapes and enable high degrees of freedom in movement. Section 2.1 will discuss the recent progress in the fabrication of stretchable devices, and intrinsically stretchable materials and devices. Even with the necessary mechanical properties, since e-skin will be exposed to repeated and prolonged mechanical stresses. Hence, 
e-skin may experience wear and tear over time, which significantly limits its long-term durability. In this regard, self-healing ability is important. Section 2.2 will hence discuss self-healable materials and devices. Furthermore, since e-skin will interact closely with humans, biocompatibility is also critical. In Section 2.3, biocompatibility of e-skin materials will be discussed.
Tactile sensing is also necessary to enable skin-like functionality. Broadly speaking, tactile sensing refers to the detection of temperature and physical stimuli such as pressure, strain, shear, and slip. In skin attachable devices, these sensors can be used to detect human motion, and vital signs such as heart rate, respiration, and body temperature for health monitoring. For robotics and prosthetics, tactile sensors will enable critical functions such as object manipulation. Various types and current challenges of tactile sensors will be covered in Section 3. Other types of sensors such as chemical and electrophysiological sensors are particularly important for health monitoring in skin attachable devices. These sensors will be covered in Section 4.
The development of materials and the fabrication of individual sensors and devices must be accompanied by their large-area fabrication and integration. First, enabling spatial tactile sensing is important. Also, particularly for robotics and prosthetics, large-area fabrication of e-skin on 3D surfaces is critical. Sections 5.1 and 5.2 will discuss these aspects, focusing mainly on solution-based processing. For skin-attachable devices, wireless communication is of high importance to enable portability and user comfort. Section 5.3 will discuss the recent progress in wireless tactile signal communication. To enable human-like tactile sensing in robotics and prosthetics, signal coming from a large number of sensors needs to be processed. This becomes a serious challenge as the number of sensors increases, due to various issues such as complex wiring, high power consumption, and time delay of external read-out circuitry. In this regard, neuromorphic computing based on artificial synaptic devices offers a promising solution as it can potentially enable low power parallel signal processing, with added features such as learning-based noise elimination and classification. Section 5.4 will address the recent progress in tactile sensors integrated with artificial synaptic devices. For prosthetic applications, the tactile signal needs to be transmitted to neurons. Therefore, electrodes for neural interface are of high importance. Section 5.5 will discuss the recent progress in this area. Finally in Section 6, summary and future prospect of e-skin will be discussed.分析这句话的内容组成、结构、以及语言特点（包括常用词汇、句型、时态存在问题以及相关拓展）