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Xi et al. Soft Sci 2023;3:26 https://dx.doi.org/10.20517/ss.2023.13 Page 3 of 34

medicine [24,31,39] .

As presented in Figure 1, self-powered wearable sensors can be used in all parts of the human body. These
[40]
sensors can be used to monitor electroencephalogram (EEG) signals of various brain activities . Using self-
powered wearable sensors for EEG measurement can improve the universality of this technology because it
allows measurement outside the clinical environment, which is more in line with people’s daily living
[41]
environment and habits. Additionally, self-powered wearable sensors can monitor respiratory function .
They can evaluate respiratory function from many aspects and have the ability to monitor respiration for a
long time, evaluate the effectiveness of respiratory therapy, and monitor respiratory function during
exercise or sleep. Self-powered wearable sensors also play a great role in ECG measurement . Through
[42]
long-term monitoring and out-of-hospital monitoring, they can greatly help the overall evaluation of
patients. Moreover, these sensors for foot monitoring can be used to monitor foot function and gait mode,
providing valuable information about foot and ankle joint function . Furthermore, self-powered wearable
[43]
sensors can be used to monitor eye movement, provide valuable information about eye function, monitor
eye disease, study visual perception and cognition, and track eye movement during tasks requiring visual
attention (such as reading or driving) . These sensors can also be used for sweat monitoring, aiding in the
[44]
diagnosis and management of various conditions such as dehydration, electrolyte imbalance, and skin
[45]
diseases, and tracking changes in body temperature and metabolic activity . In addition, self-powered
wearable sensors for pulse wave monitoring can be used for a variety of applications, such as diagnosis and
etc.
monitoring of hypertension, assessment of cardiovascular risk, . Lastly, intelligent exoskeletons enable
[46]
energy collection and angle sensing of joint movements, collecting energy from human joint movements
and supplying power to sensors, which can measure joint activity in real time and evaluate joint flexion .
[47]
Wearable sensors are IoT devices that can be worn on the body to collect and transmit data about physical
activity, vital signs, and other biometric information of the wearer [35,48,49] . They are often used with other IoT
devices to create a connected system that can provide real-time monitoring and feedback to the wearer [50,51] .
The IoT is a network composed of physical devices, vehicles, household appliances, and other objects
embedded in sensors, software, and network connections [52,53] . These devices can connect and exchange data
through the Internet, communicate with each other, collect data, and perform operations based on the data.
IoT devices are widely used, including in smart homes, wearable devices, industrial automation,
transportation, medical care, and agriculture [54,55] . By connecting everyday items to the Internet and
collecting data about them, IoT devices can provide valuable insights for optimizing processes, reducing
costs, and improving the overall quality of life [49,56] .

Compared with previous reviews, this review differs in the following ways [57-60] . First, this review focuses on
the application of self-powered wearable IoT sensors as human-machine interfaces rather than just
introducing and analyzing their fundamental principles [59,61,62] . We conducted a detailed analysis and
etc.
discussion of their application scenarios, including electronic skin, fabrics, integrated clothing, , and
deeply discussed their advantages and disadvantages in these application scenarios and future development
directions and challenges. Second, this review provides a more in-depth discussion of the working modes,
technologies, and materials used in self-powered wearable IoT sensors. We describe their different physical
sensing, chemical sensing, and hybrid sensing modes and introduce the technologies and materials used in
etc.
them, such as triboelectric nanogenerators (TENGs), piezoelectric nanogenerators (PENGs), , for each
technology and material detailed analysis and evaluation. Finally, this review combines the latest research
progress and practical application scenarios, conducts in-depth discussions and prospects for the future
development of this field, and puts forward some guiding suggestions. These suggestions not only provide
researchers with research directions and ideas but also provide useful enlightenment and guidance for the
industry, which has a certain role in promoting the development of this field.