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Page 20 of 43 Wang et al. Soft Sci 2024;4:41 https://dx.doi.org/10.20517/ss.2024.53

Capacitive fibric pressure sensors are known for their high accuracy, wide detection range, and reliability.
For effective performance, the fiber electrodes must maintain stable conductivity during stretching and
[149]
bending . Additionally, microstructures can be incorporated to enhance sensing capabilities and reduce
[150]
response time . Furthermore, one-dimensional conductive fibers, such as gel fibers, CNT fibers, graphene
fibers, and polyaniline fibers, can be used as electrodes for capacitive pressure sensors, forming fiber
electrode pairs. For example, fiber pressure sensors made with hydrogel exhibit high sensitivity, a wide
operating range, and stable proximity sensing .
[65]

When piezoelectric materials such as ZnO, BaTiO , and polyvinylidene fluoride (PVDF) are subjected to
3
pressure, deformation of their crystal structure occurs, resulting in charge separation and the generation of
voltage across the material. These piezoelectric materials are widely used in the development of piezoelectric
fiber-based pressure sensors. For instance, integrating a fibric triboelectric sensor array into clothing enables
simultaneous monitoring of arterial pulse and respiratory signals , facilitating non-invasive and long-term
[151]
health surveillance [Figure 8L]. Additionally, a piezoelectric PVDF nanofiber membrane (PVDF/ZnO
NFM) was utilized as the pressure sensing layer . This textile was used for external pressure detection,
[152]
human pulse monitoring, and tactile spatial mapping. Despite the high durability and flexibility of
piezoelectric fibric pressure sensors, they are generally limited to dynamic measurements. However, by
integrating a rectifier component, continuous measurements can be achieved.

Fibric thermal sensors
Body temperature monitoring is essential for assessing health conditions. However, traditional temperature
sensors are unsuitable for wearable applications due to their rigidity and inability to provide continuous
body temperature monitoring over extended periods [153,154] . Fibric temperature sensors, by contrast, offer
[5]
high sensitivity, rapid response, along with the flexibility and compliance to the skin , making them widely
applicable in e-skin and healthcare . Based on the temperature sensing mechanisms of the
[155]
[156]
temperature-sensitive materials, fibric temperature sensors can be categorized into thermoresistive and
thermoelectric types. The functional materials, structural designs, performance, and application areas of
these two types of fibric temperature sensors will be discussed in detail in the following sections.

The principle of thermoresistive fibric temperature sensors is that resistance changes with temperature .
[157]
The conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) shows
strong potential for wearable temperature sensing due to its excellent flexibility, good electrical conductivity
and high sensitivity [153,158] . Furthermore, to mitigate the impact of additional stress, various specialized
structural designs have been employed in the development of strain-insensitive fibric temperature sensors.
One option is that a strain-insensitive fibric temperature sensor with periodic and uniform micro-wrinkles
[159]
can be fabricated by applying pre-strain . Another feasible option is to sew PEDOT-thermoplastic
polyurethane (TPU) composite fibers into normal textiles in an S-shape, which allows the sensor to measure
skin temperature accurately during daily activities [Figure 9A]. However, as a polymer, PEDOT fibers are
[160]
vulnerable to humidity, leading to inaccurate measurements, especially after perspiration. To address this
issue, temperature-sensitive fibers have been developed by encapsulating PEDOT with a PU/graphene
[153]
composite [Figure 9B]. Carbon-based materials are also widely employed in fibric temperature sensors
due to their high electrical conductivity and thermal stability, such as graphene oxide (GO)-based fibers ,
[161]
[162]
[163]
rGO/PU composite freestanding stretchable fibers , and graphene-based fibers . Additionally,
temperature-sensitive fabrics made from textile yarns coated with graphene-based inks offer both good
[163]
washability and high flexibility [Figure 9C]. Fibric temperature sensors based on conductive polymers
achieve high sensitivity, owing to their tunable semiconductor properties [164,165] . When these sensors were
integrated into textiles, they offered stable performance in detecting both body temperature changes and