A review of flexible force sensors for human health monitoring

Abstract

Background: In recent years, health monitoring systems (HMS) have aroused great interest due to their broad prospects in preventive medicine. As an important component of HMS, flexible force sensors (FFS) with high flexibility and stretch-ability can monitor vital health parameters and detect physical movements.

Aim of review: In this review, the novel materials, the advanced additive manufacturing technologies, the selective sensing mechanisms and typical applications in both wearable and implantable HMS are discussed.

Key scientific concepts and important findings of review: We recognized that the next generation of the FFS will have higher sensitivity, wider linear range as well as better durability, self-power supplied and multifunctional integrated. In conclusion, the FFS will provide powerful socioeconomic benefits and improve people's quality of life in the future.

Keywords: Flexible force sensors; Health monitoring; Implantable; Preventive medicine; Wearable.

Graphical abstract

Fig. 1

Illustration of the structure of this review.

Fig. 2

The schematic of (a) DIW , (b) SLA, (c) DLP, (d) FDM and (e) SLS .

Fig. 3

Manufacturing process of EGaIn soft sensor based on DIW: (a) spin-coat the silicone layer on the wafer; (b) writing EGaIn on the silicone layer; (c) spreading uncured silicone material on the printed trace by rod coating; (d) trimming the silicone body into a desired shape by laser cutting, and (e) direct insertion and fixation of electrodes .

Fig. 4

Schematic diagram of the manufacturing process of micro-architected graphene (MAG) .

Fig. 5

(a) Structure diagram of the sensor (b) DLP-based desktop 3D printer (c) Optical photo of the sensor after UV curing .

Fig. 6

3D printed schematic of multi-axis force sensor based on FDM .

Fig. 7

Manufacturing process of the CB /PA12 composite parts .

Fig. 8

The working principle of (a) resistive, (b) capacitive, (c) piezoelectric and (d) triboelectric sensors.

Fig. 9

(a) The change of the resistance of the wearable sensor under different bending degrees of the finger, that is, the change of the brightness of the LED ; (b) Schematic diagram of the change in the extension of the glove-type wearable sensor ;(c) The sensor collecting throat muscle movement signals ;(d) The image of the plantar sensor array .

Fig. 10

(a) Wearable sensors for monitoring wrist activity and breathing during sports ; (b) Wireless sensor for heart rate monitoring through the wrist ;(c) BSN system application demonstration .

Fig. 11

(a) Manufacturing method of AB ; (b) Sensors were implanted into the porcine heart and femoral arteries to monitor micro-pressure changes ; (c) Photo of the polymer scaffold with integrated wireless sensor .

Fig. 12

(a) The schematic diagram of a cell stimulation device ; (b) Schematic diagram of a wireless symbiotic cardiac pacemaker system .