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Okada K, Horii T, Yamaguchi Y, Son K, Hosoya N, Maeda S, Fujie T. Ultraconformable Capacitive Strain Sensor Utilizing Network Structure of Single-Walled Carbon Nanotubes for Wireless Body Sensing. ACS APPLIED MATERIALS & INTERFACES 2024; 16:10427-10438. [PMID: 38375854 DOI: 10.1021/acsami.3c19320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/21/2024]
Abstract
Capture and real-time recording of precise body movements using strain sensors provide personal information for healthcare monitoring and management. To acquire this information, a sensor that conforms to curved irregular surfaces, including biological tissue, is desired to record complex body movements while acting like a second skin to avoid interference with the movements. In this study, we developed a thin-film-type capacitive strain sensor that is flexible and stretchable on the surface of a living body. We fabricated conductive polymeric ultrathin films ("nanosheets") comprising polystyrene-block-polybutadiene (SB) elastomers and single-walled carbon nanotubes (SWCNTs) (i.e., SWCNT-SB nanosheets) via gravure coating; the SWCNT-SB-coated nanosheets were used as the flexible electrode in a capacitive strain sensor. The dielectric (DE) layer was then prepared using the silicone elastomer Ecoflex 00-30 because its Young's modulus is comparable to that of the epidermis. The normalized capacitance changes (ΔC/C0) in the sensor increased with increasing tensile strain over a range from 0-100%, indicating that the proposed sensor can measure the strain of biological movements, including those of skin and blood vessels. To improve sensor conformability further, the effect of sensor thickness on the gauge factor (GF) was investigated using thinner DE layers by focusing on their flexural rigidity. As a result, the GF increased from 0.64 to 1.13 as the DE layer thickness decreased from 260 to 40 μm. Finally, we evaluated the fabricated sensor's signal stability and mechanical durability, including during wireless sensing when applied to human skin and a vascular model. The ΔC/C0 values varied in response to the bending motion of a finger, dilation of a blood vessel, and the swallowing movement of the throat. These results indicate that our capacitive strain sensor is conformable and functional on biological tissue to enable monitoring of dynamic biological movements (e.g., pulse rate and arterial dilation) without wearer discomfort.
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Affiliation(s)
- Kei Okada
- School of Life Science and Technology, Tokyo Institute of Technology, B-50, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan
| | - Tatsuhiro Horii
- School of Life Science and Technology, Tokyo Institute of Technology, B-50, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan
| | - Yuya Yamaguchi
- Mechanical Dynamics Laboratory, Shibaura Institute of Technology, 3-7-5, Toyosu, Koto-ku, Tokyo 135-8548, Japan
| | - Kon Son
- School of Life Science and Technology, Tokyo Institute of Technology, B-50, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan
| | - Naoki Hosoya
- Mechanical Dynamics Laboratory, Shibaura Institute of Technology, 3-7-5, Toyosu, Koto-ku, Tokyo 135-8548, Japan
| | - Shingo Maeda
- Department of Mechanical Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
- Living Systems Materialogy (LiSM) Research Group, International Research Frontiers Initiative (IRFI), Tokyo Institute of Technology, R3-23, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
| | - Toshinori Fujie
- School of Life Science and Technology, Tokyo Institute of Technology, B-50, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan
- Living Systems Materialogy (LiSM) Research Group, International Research Frontiers Initiative (IRFI), Tokyo Institute of Technology, R3-23, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
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Picomolar, Electrochemical Detection of Paraoxon Ethyl, by Strongly Coordinated NiCo2O4-SWCNT Composite as an Electrode Material. J Electroanal Chem (Lausanne) 2023. [DOI: 10.1016/j.jelechem.2023.117175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Nanotube Functionalization: Investigation, Methods and Demonstrated Applications. MATERIALS 2022; 15:ma15155386. [PMID: 35955321 PMCID: PMC9369776 DOI: 10.3390/ma15155386] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 07/28/2022] [Accepted: 08/01/2022] [Indexed: 02/04/2023]
Abstract
This review presents an update on nanotube functionalization, including an investigation of their methods and applications. The review starts with the discussion of microscopy and spectroscopy investigations of functionalized carbon nanotubes (CNTs). The results of transmission electron microscopy and scanning tunnelling microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, Raman spectroscopy and resistivity measurements are summarized. The update on the methods of the functionalization of CNTs, such as covalent and non-covalent modification or the substitution of carbon atoms, is presented. The demonstrated applications of functionalized CNTs in nanoelectronics, composites, electrochemical energy storage, electrode materials, sensors and biomedicine are discussed.
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