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At the same time, the continuous innovation and application of these technical means will also provide a
broader space and prospect for the development of wearable IoT sensors.

Self-powered wearable IoT sensors have a wide range of applications as human-machine interfaces,
including e-skins, fabrics, and integrated clothing. Electronic skin can integrate sensors into the surface of
the human body to realize real-time perception and interaction of the human-machine interface, thus being
widely used in medical monitoring, virtual reality, sports, and other fields. In terms of fabrics, sensors can
be integrated into smart clothing to monitor and analyze human health, posture, and movement status,
which have great application prospects. In addition, integrated clothing is also an important application
direction of self-powered wearable IoT sensors. It can integrate sensors into clothing to realize intelligent
monitoring and control and has a wide range of commercial and life application prospects. The continuous
expansion and innovation of these application fields will provide a broader market and application space for
the development of self-powered wearable IoT sensor technology.

Overall, our review highlights the potential of self-powered wearable IoT sensors as human-machine
interfaces and identifies several key areas for future research.

DISCUSSION
Materials of sensors
In order to realize various performances of wearable self-powered sensors, the sensor material is carefully
designed [74-80] . The materials used in self-powered wearable sensors typically include flexible materials,
nanomaterials, and degradable materials [50,81-84] .

Flexible materials
Flexible materials are materials that can bend, twist, or deform without breaking [32,74,85] . In the context of
wearable technology, flexible materials are commonly used to make wearable devices more comfortable,
lightweight, and durable [86,87] . Flexible materials can bend, twist, and deform without breaking. This allows
them to fit the body shape of the wearer and provide a comfortable fit . Flexible materials are usually
[88]
designed for durability and wear resistance which can withstand repeated bending and twisting without
[89]
losing shape or breaking . What is more, flexible materials are usually light in weight, compact in shape,
and comfortable to wear for a long time . Many flexible materials can be stretched under continuous
[90]
cracking, which is very important for wearable devices that need to move and stretch with the wearer’s
body. Some flexible materials, such as textiles, are breathable and allow air to flow . This helps prevent
[91]
overheating and discomfort. Some flexible materials are designed to be waterproof, which helps protect
electronic components from damage caused by exposure to moisture . Some flexible materials, such as
[92]
thin films, can be transparent or translucent, which is very important for manufacturing displays and other
[93]
electronic components . Yi et al. showed a self-powered keyboard with biometric recognition capability,
which was characterized by extensibility and flexibility . It was a sensor based on fabric and
[38]
triboelectricity, which can record physiological signals and human percussion input, achieving self-powered
operation. Specifically, it can identify individual typing characteristics to achieve the effect of information
security. As shown in Figure 3A, Ma et al. manufactured a wearable fuel cell-type self-powered motion
intelligent sensor. The sensor used methanol steam as the target fuel and has a core-shell structure. Porous
carbon networks were used as catalysts for methanol oxidation and oxygen reduction reactions, while
alkaline hydrogels with high conductivity were used as solid electrolytes . They have excellent sensing and
[94]
mechanical properties and can be used as wearable equipment to supply power for strain sensors. As shown
in Figure 3B, Wang et al. developed a hybrid nanogenerator (HNG) composed of triboelectric-
electromagnetic for self-powered gas and motion monitoring . It can turn on the light (3W) and charge
[95]