Abstract
Despite the tremendous efforts dedicated to developing various wearable piezoresistive sensors with sufficient stretchability and high sensitivity, challenges remain pertaining to fabrication scalability, cost, and efficiency. In this study, a facile, scalable, and low-cost coaxial printing strategy is employed to fabricate stretchable and flexible fibers with a core–sheath structure for wearable strain sensors. The highly viscous silica-modified silicone elastomer solution is used to print the insulating sheath layer, and the silicone elastomer solutions containing multi-walled carbon nanotubes (CNTs) are used as the core inks to print the conductive inner layer. With the addition of silica powders as viscosifiers, silica-filled silicone ink (sheath ink) converts to printable ink. The dimensions of the printed coaxial fibers can be flexibly controlled via adjusting the extrusion pressure of the inks. In addition, the electro-mechanical responses of the fiber-shaped strain sensors are investigated. The printed stretchable and wearable fiber-like CNT-based strain sensor exhibits outstanding sensitivities with gauge factors (GFs) of 1.4 to 2.5 × 106, a large stretchability of 150%, and excellent waterproof performance. Furthermore, the sensor can detect a strain of 0.1% and showed stable responses for over 15,000 cycles (high durability). The printed fiber-shaped sensor demonstrated capabilities of detecting and differentiating human joint movements and monitoring balloon inflation. These results obtained demonstrate that the one-step printed fiber-like strain sensors have potential applications in wearable devices, soft robotics, and electronic skins.
Highlights
Soft and flexible piezoresistive sensors, as a key component of soft electronic devices, have recently become prevalent in various research fields, such as soft robotics, wearable electronics, healthy monitoring, and human–machine interfaces [1]
A fibrous or wire-shaped device can be integrated into stretchable fabrics to fulfill a more practical demand of wearable electronics in our daily life [3]
The surface morphology of carbon nanotubes (CNTs) was characterized by a field-emission scanning electron microscope (SEM) (Zeiss GenimiSEM 500, Oberkochen, Germany)
Summary
Soft and flexible piezoresistive sensors, as a key component of soft electronic devices, have recently become prevalent in various research fields, such as soft robotics, wearable electronics, healthy monitoring, and human–machine interfaces [1]. Tremendous efforts have been made to develop fiber-like piezoresistive sensors [4,5,6,7] Conductive materials such as carbon nanotubes (CNTs) [8], graphene [9], liquid alloy [10], and metal nanowire solutions [11] infiltrated into or coated on stretchable elastomer fibers have been widely used to fabricate fiber-shaped sensors. Most conducting fibers in previous studies were fabricated by physically deposited fillers or solution-coated conducting materials [7,8,9,12] The common methods such as dip-coating, spray-coating, and a layer-by-layer assembly method have some limitations, such as complex processes, high costs, and manual interventions. The combination of one-dimensional (1D) coaxial fiber design and the easy, low-cost, and scalable DIW printing technology can offer a promising solution for wearable and high-performance electronic devices
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