Abstract
Electrospun nanofiber mats have been used as sensing elements to construct piezoresistive devices due to their large surface area and high porosity. However, they have not been utilized as skin-contact supporting layers to package conductive nanofiber networks for the fabrication of piezoresistive sensors. In this work, we developed a sandwich-structured pressure sensor, which can sensitively monitor human motions and vital signs, with electrospun nanofiber mats as supporting, sensing, and packaging layers. The nanofiber mats were prepared by electrospinning with biocompatible poly (l-lactide) (PLA), silk fibroin (SF), and collagen (COL) as raw materials. The synthesized PLA–SF–COL mat possesses a non-woven structure with a fiber diameter of 122 ± 28 nm and a film thickness of 37 ± 5.3 μm. Polypyrrole (PPy) nanoparticles were grown in-situ on the mat to form a conductive layer. After stacking the pristine and conductive mats to form a PLA–SF–COL mat/(PPy-coated mat)2 structure, another layer was electrospun to pack the multilayers for the construction of a sandwich-structured piezoresistive sensor. The as-prepared device can sensitively detect external pressures caused by coin loading and finger tapping/pressing. It can also tolerate more than 600 times of pressing without affecting its sensing capability. The human body-attached experiments further demonstrate that the sensor could real-time monitor finger/arm bending, arterial pulse, respiration rate, and speaking-caused throat vibration. The electrospinning-based fabrication may be used as a facile and low-cost strategy to produce flexible piezoresistive sensors with excellent skin-compatibility and great pressure sensing capability.
Highlights
A wearable electronic device has been regarded as the best choice for everyday health monitoring due to its superior capability to real-time detect vital signs such as pulse rate, respiration rate, body temperature, and blood pressure [1,2,3,4,5,6,7,8,9]
The thickness of the collected mat was about 37.0 ± 5.3 μm (Figure S2), indicating that the mat could be utilized as a freestanding film for the following PPy modification and sensor assembly
In comparison to the relatively smooth surface of PLA–silk fibroin (SF)–COL fibers, a number of nanoparticles were uniformly coated on the modified fibers (Figure 1D), causing significant increment of the fiber diameter
Summary
A wearable electronic device has been regarded as the best choice for everyday health monitoring due to its superior capability to real-time detect vital signs such as pulse rate, respiration rate, body temperature, and blood pressure [1,2,3,4,5,6,7,8,9]. A microfabrication technique is needed to precisely control the opposite area and distance between the two electrodes in capacitive pressure sensors [10] These sensors may provide relative high sensitivity, the complicated fabrication process greatly hinders their large-scale production and practical applications. Piezoelectric materials such as ZnO nanorod arrays and polyvinylidene fluoride (PVDF) films are used to functionalize flexible substrates for the preparation of piezoelectric sensors [5,11,12,13,14,15], which can generate electric charges in response to the applied mechanical stress
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