An All‐Nanofiber‐Based, Breathable, Ultralight Electronic Skin for Monitoring Physiological Signals

Abstract

materials [11,12] and sensing performances of flexible pressure sensors, such as high sensitivity, [13,14] fast response speed, [15,16] and low detection limit. [17,18] However, for practical long-term wearable applications, the wearability of pressure sensors also needs to be considered.At present, flexible, elastic, and lightweight e-skins based on polymers, especially hydrogels, have been widely investigated, but their sweat volatility, oxygen permeability, and thermal diffusivity have often been ignored. As the largest organ of the body, the skin can respire, excrete sweat, and regulate body temperature. E-skins without air permeability will insulate oxygen and prevent moisture evaporation as well as heat dissipation, causing skin discomfort and even inflammation and itching during long-term wearing. [19][20][21] Therefore, some reported studies developed e-skins with textile structures to achieve flexibility and air permeability. Yang et al. introduced graphene into polyester fabric to fabricate a graphene textile strain sensor. [22] Fu et al. reported a high-performance textile structural strain sensor by coating reduced graphene oxide (rGO) onto a glass fabric/ silicone composite. [23] Cao et al. developed a wearable piezoresistive sensor based on cotton fiber coated by rGO and silver nanowire (Ag NW) via a simple hydrothermal method. [24] The use of commercial textiles in e-skins is beneficial to simplifying the fabrication process and realizing batch manufacturing.Since 2020, electrospinning techniques that can fabricate fabric with nanostructures flexibly, economically, and quickly have gained wide attention in the field of e-skins. [25] A nanofiber (NF) network can enhance the gas permeability and reduce the effective mass density of e-skin. Peng et al. developed all-NF triboelectric nanogenerators, which were fabricated by sandwiching Ag NW between polylactic-co-glycolic acid and polyvinyl alcohol, for real-time and self-powered physiological signal monitoring. [26] Someya et al. reported the design of an all-NF triboelectric mechanoacoustic sensor by sandwiching polyvinylidene fluoride film in two pieces of Au-coated polyurethane film for continuous long-term heart monitoring. [27] Triboelectric nanogenerators are an ideal device for the self-powered monitoring of periodic physiological signals or vibrations, such as pulses, heartbeats, respiration, and vocal cord vibrations. In Electronic skins (e-skins) are a promising design paradigm for health care systems and human-machine interactions. Piezoresistive sensors made with simple structures, high sensitivity, mass production methods, light weight, and comfort for long-term wearing and physiological signal monitoring remain a challenge and are urgently desirable. Here, a breathable and lightweight all-nanofiber piezoresistive (ANFP) sensor is presented, which is composed of three layers of electrospun nanofibers (NFs). A specific interpenetrating network of conductive polyvinylpyrrolidone NFs coated by polypyrrole (PVP@PPy) and insulating polyacrylon...

Nature-Driven Biocompatible Epidermal Electronic Skin for Real-Time Wireless Monitoring of Human Physiological Signals

“…These properties involve flexibility, heat dissipation ability, and air permeability. Thus, the air permeability of PCFF has been studied . As illustrated in Figure i, different samples, such as tissue, neat PVDF, and PCFF were applied to cover the mouth of a glass bottle, which is being filled with hot water (85 °C).…”

“…57 During the monitoring of different joint bendings, the sensor will suffer from both pressure and strain, but the effect of pressure is predominant. 26 However, in addition to the sensing of the joint bending and different muscle movements, the e-skin is also capable of sensing those physiological signals generated under the action of weak pressure or vibrations. One such weak signal is swallowing; interestingly, this is the most complicated body reflection of the human body.…”

“…Rapid progress in development of thin, soft, and conformal electronics supported by Internet of Things (IoT) is enabling the move toward skin-worn biomonitoring patches and wearable e-textiles. − This has applications in wearable monitoring of human health, athlete’s performance, human motion monitoring, human–machine interaction, and e-skins for robotics and prostheses. − To be used for body-worn applications, these e-skins are desired to be flexible, breathable, and biocompatible. − A wide range of polymers and hydrogels were used in the fabrication of these flexible and stretchable e-skins . However, without efficient air permeability, these e-skins will insulate oxygen and prevent moisture evaporation, resulting in skin discomfort, i.e., inflammation or itching during long-term wearing. − Previous efforts for the fabrication of electronic skins with air permeability include a textile structure with reduced graphene oxide and a cotton fiber-based piezoresistive sensor …”

Breathable Electronic Skins for Daily Physiological Signal Monitoring

“…Tactile sensing is one of the human body's most important abilities. In recent years, tactile sensors have played an important role in human-machine interaction, robotics, and medical health development [56]. To meet the needs of longterm physiological signal monitoring in daily life, a variety of tactile sensors with good breathability and high performances have been developed in recent years [14,[57][58][59].…”

How Far for the Electronic Skin: From Multifunctional Material to Advanced Applications

“…[1] Inspired by human skin, an electronic device that imitates the characteristics and functions of human skin to sense various external signals and record them as different electrical signals, named as electronic skin, has appeared. [2][3][4][5][6][7] The origin of electronic skin stems from people's pursuit of artificial skin.…”