## 2 LIG-Based Wearable Systems for Multifunctional and Intelligent Health Care
### Electrothermally Controlled Soft Actuators for On-Demand Health Care  
A comprehensive wearable health care system should not only track physiological signals, but also provide \"physician-like intervention\" to allow for real-time physiological signal monitoring, feedback, and treatment capabilities, similar to a medical professional.  
To address this requirement, [PERSON] et al., proposed an electrochemally controlled, mechanically guided, 3D assembly actuator based on LIG [19]. The actuator consisted of three layers including the PI, LIG, and polydimethylsiloxane (PDMS). The LIG acts as a flexible heater to heat the PI layer and PDMS layer on demand. Due to the difference in the thermal expansion coefficient of PI and PDMS, the temperature change of LIG led to the deformation of the PI layer and PDMS layer in different degrees, thereby enabling the electrothermally controlled actuator to function. Inspired by kirigami and origami, the actuator can be customized to different shapes through precise structural design and modeling and forming a variety of actions and 3D structures under different control voltages. The LIG-based actuator could realize an excellent bending angle of 1080\({}^{\circ}\) and a bending curvature of 3.3 cm\({}^{-1}\). Furthermore, the actuator could bend from 0\({}^{\circ}\) to 180\({}^{\circ}\) in about 3 s and recover in about 4 s.  
In terms of physiological signal monitoring, the actuator could simulate a doctor's hand to achieve on-demand gesture interaction and ECG monitoring. As shown in Figure 6,  
Figure 5: The machine learning-based multi-modal electrochemical analytical system. Reproduced with permission from [17]. Copyright 2022 Elsevier.  
by using three LIG-based sensors to monitor the EMG signals of the skin, the structure of the flower-shaped LIG-based actuator could be controlled using hand gestures. Additionally, actuators can act as resonators with gesture-controlled bandgap behaviors. Furthermore, similar to a doctor's palpation, by controlling the deformation of the actuator like a human finger, the ECG electrodes on the actuator can selectively collect the ECG signal on demand. Moreover, the authors showed that the actuator could lift up to 110 times its weight when used as an artificial muscle.  
This study highlights the potential for wearable systems equipped with LIG-based actuators to perform on-demand health monitoring, disease diagnosis, and treatment. This opens the door for creating wearable systems that mimic a doctor's abilities, with the added ability to independently provide treatment. However, doctors often refer to multiple physiological signals in the actual diagnosis of diseases. How to collect various physiological information without interfering with each other is important to achieve accurate diagnosis with wearable systems. In the next section, we will describe how to give the multi-functional sensing system an anti-interference capability to achieve the high-quality acquisition of a variety of physiological signals.  
Figure 6: The electrothermally controlled soft actuators for on-demand gesture interaction and ECG monitoring. (**a**) Human gestures are used to control the 3D assembly of a (**b**) flower-like structure and (**c**) shape reconfiguration of an elastic metamaterial for (**d**) tunable bandgap behaviors. (**e**) A soft robotic finger which can wrap the human finger for ECG measurement in an on-demand and reversible fashion. Scale bars: 1 cm. Reproduced with permission from [19]. Copyright 2020 Wiley.