## 2 LIG-Based Wearable Systems for Multifunctional and Intelligent Health Care
### Electronically Enhanced Paper-Based Green Wearable System  
The research of wearable systems has recently focused on the development of degradable green electronic devices. Some studies have attempted to replace non-degradable materials like PI with degradable ones to mitigate the environmental impacts of LIG-based wearable systems [3,4]. Although precursors like paper sheets or cardboard, which consist of aliphatic-rich cellulose, can serve as templates for graphitization, they do not possess the intrinsic aromatic carbon structure that can help the graphitization process. As a result, LIG made from cellulose-rich precursor materials does not perform electrical and chemical properties as well as LIG using common polymer precursors.  
Faced with this challenge, [PERSON] et al. increased the conductive properties of paper-based LIG by introducing external aromatic moieties and controlling the laser fluence meticulously [11]. Figure 2 shows the conceptual graph of the paper-based system. The manufacturing processes of the paper-based wearable system are as follows. First, the wax  
Figure 1: Gas-permeable and multifunctional on-skin system. Reproduced with permission from [10]. Copyright 2018 Wiley.  
treated paper substrate is irradiated using a laser with different spot-size focus profiles to depolymerize, deoxygenize, and dehydrate the aliphatic carbon rings within the cellulose and the hydrocarbon and aromatic structures in the wax. This pyrolysis process leads to the graphitization of the paper-based substrate and produces LIG. Second, once the LIG-based devices are made through laser treatment, they are separated from the paper substrate through deionized water as the cellulose fibers and fibrils have a higher affinity for water due to the hydrogen bonds they contain. The LIG-based devices are then transferred onto a medical-grade polyurethane tape with a polyacrylate glue surface, resulting in the creation of a multi-functional LIG-based wearable system.  
The paper-based LIG produced a Pt NP (platinum nanoparticle)-decorated electrochemical sensor, strain sensor, electrode, and micro-supercapacitor (MSC) with a polyvinyl alcohol (PVA)/H\({}_{2}\)SO\({}_{4}\) electrolyte that were able to perform four functions. These functions included detecting H\({}_{2}\)O\({}_{2}\) concentrations in human sweat, monitoring radial artery pressure wave and pulse, monitoring ECG signals, and energy storage.  
This work showed a sustainable LIG-based wearable system that could realize multi-modal health monitoring and kinetic energy harvesting and storage, and the system showed potential in self-powered daily autonomous health monitoring. Beyond that, recyclable or self-healing wearable systems are also a competitive development direction for green wearable systems.  
In addition to the above efforts in the material and fabrication process development of realizing gas-permeable and sustainable wearable systems, we will introduce the functional development direction of wearable systems for health care applications in the following sections including the realization of self-alarm and self-powered systems.