Wearable Stretchable Dry and Self‐Adhesive Strain Sensors with Conformal Contact to Skin for High‐Quality Motion Monitoring

Abstract

Wearable stretchable strain sensors can have important applications in many areas. However, the high noise is a big hurdle for their application to monitor body movement. The noise is mainly due to the motion artifacts related to the poor contact between the sensors and skin. Here, wearable stretchable dry and self‐adhesive strain sensors that can always form conformal contact to skin even during body movement are demonstrated. They are prepared via solution coating and consist of two layers, a dry adhesive layer made of biocompatible elastomeric waterborne polyurethane and a sensing layer made of a non‐adhesive composite of reduced graphene oxide and carbon nanotubes. The adhesive layer makes the sensors conformal to skin, while the sensing layer exhibits a resistance sensitive to strain. The sensors are used to accurately monitor both small‐ and large‐scale body movements, including various joint movements and muscle movements. They can always generate high‐quality signals even on curvilinear skin surface and during irregular skin deformation. The sensitivity is remarkably higher while the noise is saliently lower than the non‐adhesive strain sensors. They can also be used to monitor the movements along two perpendicular directions, which cannot be achieved by the non‐adhesive strain sensors.

Waterborne Polyurethane Enhanced, Adhesive, and Ionic Conductive Hydrogel for Multifunctional Sensors

“…According to previous literature reported, the shear strength between PU and glass could reach over 150 kPa. [23] However, not only the increase of PU content in the 20PUSAm hydrogel did not enhance its shear strength, but reduced step by step. This was mainly due to the hydrophobic segments of PU, which was also the hard segments (extremely important for the strong adhesion) gather together under hydrophobic interaction, which reduces the chance of contact between the adhesive functional group (C═O, -NH, etc.)…”

“…Due to the PU molecular chains contain lots of hard segments and soft segments, the performance about strength and flexible was usually excellent. [18,23] Hence, the PU was expected to improve the mechanical property of hydrogel. The carboxylate ions(-COO − )on PU chains lead to dispersion of PU in water.…”

Application of intrinsically conducting polymers in flexible electronics

“…In addition to the flexible and stretchable electrodes, ICPs have been investigated as the active materials of flexible strain sensors. The work principle of a strain sensor is the sensitivity of its resistance or capacitance to strain 22,23 . Because the resistance of a nanocomposite is determined by the charge transport across the conductive nanofillers, it is very sensitive to the separation among the nanofillers and thus the strain applied to the nanocomposite.…”

Soft Inductive Coil Spring Strain Sensor Integrated with SMA Spring Bundle Actuator

“…Until now, soft strain sensors of resistive and capacitive types have been mainly researched, and resistive soft strain sensors using liquid metals and silicone have been extensively researched. These sensors, which measure the strain by sensing changes in electrical resistance, show high sensitivity and stretchability [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. However, they are complex to produce, have large nonlinearity and hysteresis, and are highly sensitive to temperature changes.…”

“…However, they are complex to produce, have large nonlinearity and hysteresis, and are highly sensitive to temperature changes. As a result, these sensors cannot be easily used through a simple calibration only [ 4 , 8 , 9 , 10 , 15 , 16 , 17 , 18 ]. Because SSBAs are activated by water in the temperature range of 20–90 °C, it is unsuitable for application to resistive strain sensors that are sensitive to temperature changes [ 15 ].…”