Biodegradable, Breathable Leaf Vein‐Based Tactile Sensors with Tunable Sensitivity and Sensing Range

Abstract

natural skin, which has significant applications in wearable health care devices, intelligent robotics, implantable medical devices, and human-machine interfaces. [4][5][6][7] Different sensing mechanisms including capacitance, [8] piezoresistivity, [9] piezoelectricity, [10] and triboelectricity, [11] have mainly been used to convert external stimuli into electronic impulses for quantitative and spatial detection. Among them, piezoresistive effect has been widely used in the design and fabrication of tactile sensor due to the advantages of large detection, simple signal processing, and strong anti-interference capability. [12][13][14][15][16][17][18][19] Novel materials and structure have been applied in the design of high performance tactile sensors in recent researches. A hybrid 3D structure based on ultralight and superelastic MXene/ reduced graphene oxide aerogel is adopted to design a piezoresistive sensor by Yihua Gao etc., which exhibits the sensitivity of 22.56 kPa −1 , and limit detection (10 Pa). [20] Kai Pan's group reported a piezoresisitive pressure sensor based on aPANF/GA aerogel with a 3D interconnected hierarchical microstructure to monitor the real time movement of wrist pulse and main joints of human body. [21] Tactile sensors with high performance containing high sensitivity, wide detection range, fast response, flexibility, and mechanical durability are most concerned in the recent progress of e-skin. [22] Additionally, special functional properties such as self-healing, self-powered, biodegradable, biocompatible, and Resistive pressure sensors have been widely studied for application in flexible wearable devices due to their outstanding pressure-sensitive characteristics. In addition to the outstanding electrical performance, environmental friendliness, breathability, and wearable comfortability also deserve more attention. Here, a biodegradable, breathable multilayer pressure sensor based piezoresistive effect is presented. This pressure sensor is designed with all biodegradable materials, which show excellent biodegradability and breathability with a three-dimensional porous hierarchical structure. Moreover, due to the multilayer structure, the contact area of the pressure sensitive layers is greatly increased and the loading pressure can be distributed to each layer, so the pressure sensor shows excellent pressuresensitive characteristics over a wide pressure sensing range (0.03-11.60 kPa) with a high sensitivity (6.33 kPa −1 ). Furthermore, the sensor is used as a human health monitoring equipment to monitor the human physiological signals and main joint movements, as well as be developed to detect different levels of pressure and further integrated into arrays for pressure imaging and a flexible musical keyboard. Considering the simple manufacturing process, the low cost, and the excellent performance, leaf vein-based pressure sensors provide a good concept for environmentally friendly wearable devices.

Natural ginkgo tree leaves as piezo-energy harvesters

“…The ultrahigh linear piezo-sensitivity, especially at very low stress ranges, is particularly desirable in sensing subtle human physiological signals and small external forces, thus making the natural ginkgo leaf based device more appealing in networked wearable/implantable green electronics. 9–12,66–82…”

Breathable Electronic Skins for Daily Physiological Signal Monitoring

“…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]. In this section, we will introduce some recently developed representative breathable e-skins for tactile sensing.…”

Flexible Pressure Sensors with Combined Spraying and Self-Diffusion of Carbon Nanotubes

“…1−4 For example, in the field of healthcare monitoring, flexible pressure sensors can monitor human breathing, 5−7 heartbeat, 2 pulse, 3,6 limb movement, 6−8 and other signals in real time, which is of great significance for the timely detection and real-time monitoring of diseases. 5 According to the working principle, pressure sensors can be divided into four kinds, namely, piezoresistive, 6−10 capacitive, 11−16 piezoelectric, 17,18 and triboelectric. 19,20 Among them, the piezoresistive has gradually been recognized as a qualified candidate for the next generation of flexible pressure sensors owing to the advantages of good data readability, high reliability, simple process, low cost, fast response, and wide detection range.…”

“…Over the past decades, flexible pressure sensors have made great progress in medical monitoring, biomedical research, human–machine interaction, smart home, smart agriculture, and other fields due to their typical properties of converting mechanical stimulation signals into electrical signals that can be directly measured. − For example, in the field of healthcare monitoring, flexible pressure sensors can monitor human breathing, − heartbeat, pulse, , limb movement, − and other signals in real time, which is of great significance for the timely detection and real-time monitoring of diseases . According to the working principle, pressure sensors can be divided into four kinds, namely, piezoresistive, − capacitive, − piezoelectric, , and triboelectric. , Among them, the piezoresistive has gradually been recognized as a qualified candidate for the next generation of flexible pressure sensors owing to the advantages of good data readability, high reliability, simple process, low cost, fast response, and wide detection range. − Research in recent years has greatly promoted the development of pressure sensors, especially piezoresistive pressure sensors; however, various application scenarios have high requirements for all kinds of performances of sensors.…”