## 2 LIG-Based Wearable Systems for Multifunctional and Intelligent Health Care
### Self-Powered Sensing System  
Wearable systems have consistently been the focus of research due to the need for a stable energy supply. For a LIG-based wearable system to be used for extended periods of daily life, it must possess a dependable self-powering capability. While some studies have shown that combining a stretchable energy harvester, power management circuit, and energy storage unit can lead to self-charging capability [26; 27], many systems still struggle with low and inconsistent energy output, particularly during body movements that cause deformation.  
To realize a simple and stable self-powered health monitoring system, [PERSON] et al. proposed a LIG-based self-powered sensing system driven by human motion [15]. Figure 4 shows the concept diagram, structure, photos, preparation process, and circuit schematic of the self-powered sensing system. The 3D porous structure of LIG with high specific surface area and excellent charge transport ability provide effective flows of triboelectric electrons in the triboelectric nanogenerator (TENG). To enhance energy density, the LIG foam can be surface coated or doped to form MSC arrays. For instance, the addition of Au nanoparticles in LIG results in a TENG with an output voltage of 320 V, and the output power was as high as 0.022 W, even when subjected to a strain of 40%, which exceeds the stretching limit of human skin. The LIG-based MSC arrays have a PVA/H2 SO4 gel electrolyte and the LIG foam acts as the active material, the current collector, and the conductive substrate. The MSC arrays can deliver a maximum energy density of 0.569 \(\mu\)Wh cm\({}^{-2}\) at a power density of 0.014 mW cm\({}^{-2}\). To achieve a stable energy supply module, a power management circuit was used to integrate the LIG-based TENG and the LIG-based MSC arrays.  
Figure 3: Self-alarm health-monitoring system. Reproduced with permission from [14]. Copyright 2019 Wiley.  
This self-powered system can collect energy from human movements and convert it into a consistent energy source for sensors and other electrical devices. Key LIG-based physiological sensors such as strain sensors, temperature sensors, and electrodes are integrated into the self-powered system to monitor various physiological signals such as pulse, motion, temperature, blood pressure, blood oxygen, and ECG. Furthermore, using Bluetooth, the physiological signals can be transferred wirelessly to mobile devices for display and further processing. These typical physiological signals can be used to assess the health condition of people and can help realize the early diagnosis of cardiovascular diseases, chronic wounds, diabetes, hyperuricemia, etc. This early detection helps in reducing the cost of medical examinations and alleviates the pressure on the health care system.  
The realized innovative health monitoring system, which is self-powered, wireless, and multi-functional, enables the simultaneous monitoring and transmission of multiple physiological signals in an integrated and cost-effective manner, providing a platform for the future of self-powered wearable technologies. This is crucial to solving the problem of power supply for the daily long-term use of wearable health monitoring systems. Next, we will look at the value of empowering wearable systems with intelligence for high-performance health care applications.