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Figure 1. Self-powered wearable sensors used in various parts of the human body. They are EEG. Reproduced with permission [40] .
Copyright 2015, IOP Publishing Ltd; Breath. Reproduced with permission [41] . Copyright 2019, Elsevier Ltd; ECG. Reproduced with
permission [42] . Copyright 2018, American Chemical Society; Feet. Reproduced with permission [43] , Copyright 2022, Advanced Materials
Technologies; Eyes, Reproduced with permission [44] , Copyright 2018, Elsevier Ltd; Sweat, Reproduced with permission [45] , Copyright
2022, Elsevier Ltd; Pulses, Reproduced with permission [46] Copyright 2022, Licensee MDPI, Basel, Switzerland; Legs, Reproduced with
permission [47] Copyright 2022, American Chemical Society. ECG: Electrocardiogram; EEG: electroencephalogram.

The overall purpose of this review is to comprehensively sort out and summarize the application of self-
powered wearable IoT sensors as human-machine interfaces in order to discuss their development and
prospects in the future. With the continuous development and popularization of wearable devices and IoT
technology, self-powered sensors, as an emerging technology, have broad application prospects in realizing
intelligence, automation, and human-computer interaction. In this context, the purpose of this review is to
comprehensively analyze and summarize the progress and innovations achieved in the current research,
demonstrate the application of self-powered sensors in the human-machine interface in terms of their role
in materials, working modes, technologies used, application scenarios, and advantages, and discuss future
development directions and challenges in this field.

Here, the materials of sensors, sensor operation modes, and techniques used in sensors are the focus of our
discussion, which are shown in Figure 2. The selection of sensor materials mainly involves degradable
materials, flexible materials, and nanomaterials. Degradable materials are of great significance in wearable
devices to protect the environment, and under certain conditions, degradable materials are safer and
healthier. The use of flexible materials allows the sensor to fit the human body better and provide a more
comfortable experience. Nanomaterials, on the other hand, can provide excellent electrical, optical, and
mechanical properties, enabling sensors to efficiently and accurately sense and measure various
physiological parameters. In terms of the working mode of the sensor, the common ones include chemical,
physical, and binding modes. Chemical sensors enable data acquisition primarily by detecting and
responding to changes in specific chemicals, such as monitoring the concentration of specific molecules in