Carbon Nanotubes/Hydrophobically Associated Hydrogels as Ultrastretchable, Highly Sensitive, Stable Strain, and Pressure Sensors

Abstract

Conductive hydrogels have become one of the most promising materials for skin-like sensors because of their excellent biocompatibility and mechanical flexibility. However, the limited stretchability, low toughness, and fatigue resistance lead to a narrow sensing region and insufficient durability of the hydrogelbased sensors. In this work, an extremely stretchable, highly tough, and anti-fatigue conductive nanocomposite hydrogel is prepared by integrating hydrophobic carbon nanotubes (CNTs) into hydrophobically associated polyacrylamide (HAPAAm) hydrogel. In this conductive hydrogel, amphiphilic sodium dodecyl sulfate was used to ensure uniform dispersion of CNTs in the hydrogel network, and hydrophobic interactions between the hydrogel matrix and the CNT surface formed, greatly improving the mechanical properties of the hydrogel. The obtained CNTs/HAPAAm hydrogel showed excellent stretchability (ca. 3000%), toughness (3.42 MJ m −3 ), and great anti-fatigue property. Moreover, it exhibits both high tensile strain sensitivity in the wide strain ranges (gauge factor = 4.32, up to 1000%) and high linear sensitivity (0.127 kPa −1 ) in a large-pressure region within 0−50 kPa. The CNTs/HAPAAm hydrogelbased sensors can sensitively and stably detect full-range human activities (e.g., elbow rotation, finger bending, swallowing motion, and pronouncing) and handwriting, demonstrating the CNTs/HAPAAm hydrogel's potential as the wearable strain and pressure sensors for flexible devices.

Gelatin Methacryloyl‐Based Tactile Sensors for Medical Wearables

“…Compared to previously reported hydrogel‐based pressure sensors, it shows a higher sensitivity and a lower limit of detection (LOD). [ 25–28 ] Furthermore, our GelMA pressure sensor shows high durability over 3000 cyclic tests, and long‐term stability up to 3 days’ exposure to air, demonstrating the robustness of the device structure and the reliability of the encapsulation. Furthermore, we demonstrate successful monitoring of human physiological signal, pulse, and vocal cord vibration using the developed GelMA hydrogel tactile sensors, encouraging their practical use in medical wearable applications.…”

Silicone‐Ionic Liquid Elastomer Composite with Keratin as Reinforcing Agent Utilized as Pressure Sensor

“…[ 3 ] The ability to sense low pressure (1–10 kPa), which is an important range covering intra‐body pressure, is particularly important for pressure sensors. [ 4 ] In recent years, vast efforts have been made to improve the performance of pressure sensors:, for example, via the integration of polymers with various nanomaterials including carbon nanotubes (CNT), [ 5 ] gold/silver nanowires, [ 6 ] graphene nanosheets, [ 7 ] and metal nanoparticles. [ 8 ] While the structures and materials of these novel pressure sensors are different, they all typically operate based on force‐induced changes in piezoresistivity, capacitance, piezoelectricity, and iontronic.…”

“…prepared a pressure sensor by integrating hydrophobic CNT into hydrophobically associated polyacrylamide hydrogel, reaching a sensitivity of 0.127 kPa −1 in the large‐pressure region of 0–50 kPa. [ 5 ] Lee et al. realized an ultra‐robust, wide‐range pressure sensor based on thermoplastic polyurethane (TPU) foam coated with both conformal silicone rubber and CNT/TPU nanocomposite islands, the sensitivity of which was controlled from 0.013 to 0.032 kPa −1 .…”

“…The 3D chart presented in Figure a shows a sensing characteristics comparison of the pressure sensor developed within this study and pressure sensors with different fillers reported previously. [ 5,7,10,16,18 ] By the overall evaluation of the sensitivity, response time and linearity range, the novel pressure sensor in this work is an overall better sensor. While it does not have the highest sensitivity, its response time is 75× faster than that of a CNT/hydrophobically associated hydrogel sensor, [ 5a ] 15× faster than that of the graphene‐paper pressure sensor, [ 7b ] and three times faster than that of the ionic gel pressure sensor.…”

MWCNTs reinforced conductive, self‐healing polyvinyl alcohol/carboxymethyl chitosan/oxidized sodium alginate hydrogel as the strain sensor

“…Meanwhile, CNTs have outstanding electrical stability, so the conductive network constructed by CNTs can endow hydrogel with good electrical stability and ensure its long‐term usability. For example, Qin et al 18 successfully prepared a kind of conductive hydrogel by integrating hydrophobic CNTs into hydrophobically associated polyacrylamide (HAPAAm) hydrogel. The obtained CNTs/HAPAAm hydrogel showed wonderful stretchability, toughness, and high‐tensile strain sensitivity in the wide strain ranges.…”