Silk Fibroin-Based Piezoelectric Sensor with Carbon Nanofibers for Wearable Health Monitoring Applications

Abstract

The continuous real-time monitoring of human health using biomedical sensing devices has recently become a promising approach to the realization of distant health monitoring. In this paper, the piezoelectric characteristics of the silk fibroin (SF) natural polymer were analyzed as the material used for obtaining sensing information in the application of distance health monitoring. To enhance the SF piezoelectricity, this paper presents the development of a novel SF-based sensor realized by combining SF with different carbon nanofiber (CNF) densities, and for such newly developed SF-based sensors comprehensive performance analyses have been performed. Versatile methods including the scanning electron microscope, Fourier transform infrared spectroscopy, Raman and X-ray diffraction measurements and impedance analysis were used to study the morphologic, mechanical and electrical properties of the developed SF-based sensor. The SF with CNF samples was analyzed for three different pressure loads (40 N, 60 N and 80 N) in 500 compression test cycles. The analyses thoroughly describe how combining natural polymer SF with different CNF densities impacts the piezoelectricity and mechanical strength of the proposed SF-based sensor. The developed piezoelectric SF-based sensors were further tested on humans in real medical applications to detect generated piezoelectric voltage in versatile body movements. The maximum piezoelectricity equal to 2.95 ± 0.03 V was achieved for the jumping movement, and the SF sample with a CNF density equal to 0.4% was tested. Obtained results also show that the proposed SF-based sensor has an appropriate piezoelectric sensitivity for each of the analyzed body movement types, and that the proposed SF-based sensor can be applied in real medical applications as a biomedical sensing device. The proposed SF-based sensor’s practical implementation is further confirmed by the results of cytotoxicity analyses, which show that the developed sensor has a non-toxic and biocompatible nature and can be efficiently used in skin contact for biomedical wearable health monitoring applications.

Silk fibroin-based flexible pressure sensors: processing and application

“…However, the lower temperature in freeze-drying will inhibit the formation of β-sheet folding in RSF, thus it is often necessary to incorporate other piezoelectric materials to improve its overall piezoelectric output owing to the low intrinsic piezoelectricity of RSF. For instance, Rathinasamy et al [118] freeze dried RSF solution with acidified CNFs to prepare nanocomposite sponges for the fabrication of piezoelectric pressure sensors, which showed a maximum piezoelectric voltage energy of 2.95 V. In order to reduce the structural damage of the material during freeze-drying, Ma et al [88] prepared the frozen RSF gel scaffold with a gradient freezing method, and applied an in-situ polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) on its surface to enhance the material electrical conductivity. The asprepared SF/PEDOT scaffold had good tensile properties and could remain stable under cyclic testing under 50% strain.…”

“…Silk proteins, as a natural polymer material with piezoelectric properties, are widely available, so they are often used to prepare flexible piezoelectric sensors for detecting pressure, especially for detecting human physiological activities and movements [74,95,121,132,142]. For example, Rathinasamy et al [118] developed an RSF/CNF composite piezoelectric sensor and attached it to the outside of socks, which can make different output signals for different physical states of the human body, such as walking, running, falling, etc., so this sensor can also be used to prepare fall alarms to monitor people who are prone to falls, such as the elderly or children. Gogurla et al [143] developed a RSF/FA/glycerol-based piezoelectric hydrogel EG-skin for monitoring human respiration and movements of muscles and elbow joints, as well as the response of chick tissue to external stimuli (figure 8(a)).…”

“…The maximum output voltage of the prepared SF film reached 20 mV. In addition to GNR, other carbon nanomaterials, such as carbon nanotubes (CNTs) [89,117], carbon nanofibers (CNFs) [118] and graphite nanoplatelets (GNPs) [16,119], are also used to mix SF for the fabrication of piezoelectric RSF-based materials. Compared with gold or carbon nanomaterials, BaTiO 3 particles with intrinsically high piezoelectric properties have more contribution for the improvement of piezoelectric output of RSF.…”

A Recent Review of Electrospun Porous Carbon Nanofiber Mats for Energy Storage and Generation Applications

“…Electrospun carbon nanofibers can be used as biosensors due to their high sensitivity, fast response, and biocompatibility, making them promising candidates for various biomedical and diagnostic applications [129]. Electrospun carbon nanofibers can be functionalized with specific biomolecules such as enzymes or antibodies, glucose, DNA, proteins, or other biomarkers by measuring changes in electrical conductivity or other electrical properties to create biosensors [130]. These biosensors can detect biological analytes.…”

Hierarchically Structured MXene Nanosheets on Carbon Sponges with a Synergistic Effect of Electrostatic Adsorption and Capillary Action for Highly Sensitive Pressure Sensors

“…Electronic skin (e-skin) emulates the tactile functionalities of human skin, − allowing for multiple sensing capabilities such as strain, , vibration, pressure, and temperature. As a result, this technology holds vast potential in applications such as smart robotics, prosthetics, human–machine interfaces, − and wearable medical systems. , The ideal electronic skin should possess multifunctional sensing capabilities, which means that it should be able to detect different types of stimuli simultaneously. In particular, an e-skin that can simultaneously sense pressure and temperature is important for self-protection, touch recognition, , and object manipulation.…”