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Ma et al. Soft Sci 2024;4:26 https://dx.doi.org/10.20517/ss.2024.20 Page 21 of 34

precisely classify respiratory disease patients from healthy human subjects by analyzing clinical breath
samples [Figure 10L].

LIG-based skin electronics for multiple biochemical signals detection
Multiple biochemical signals recording or incorporating biochemical information with biophysical
information could enhance the device’s performance for intelligent healthcare. Yang et al. reported an
entirely laser-engraved sensing system, which contained LIG-based physical sensors for temperature and
respiration rate monitoring, a highly sensitive chemical sensor based on LIG for low concentrations of UA
[42]
and Tyr detection, and a laser-fabricated chip for dynamic sweat collection . The sensing system was
composed of five layers, i.e., multimodal sensors prepared on a flexible PI film, microfluidic channels
engraved on a double-sided medical adhesive layer, and inlet-patterned polyethylene terephthalate (PET)
layer, and a medical adhesive layer. When the sweat flowed into the sensing system, the LIG-CS monitored
sweat UA and Tyr and LIG-PS evaluated the temperature and strain-related physiological signals
[Figure 11A and B]. As expected, the fully standalone sensing system could be attached to different human
body parts, the signals of which were displayed on a mobile terminal [Figure 11C]. The high performance
enabled this sensing system to monitor the variations in sweat UA and Tyr, skin temperature and
respiration rate, responding to cycling exercise experienced by a healthy individual [Figure 11D]. A
noticeable decrease in UA and Tyr concentrations was probably due to profuse sweat secretion. Wang et al.
exhibited a wearable multifunctional skin electronics system based on porous LIG and double-side
configurations, which enabled avoiding signal interferences among different modal modules
[107]
[Figure 11E] . This wearable system could simultaneously record various physiological signals, including
electrophysiological signals (such as ECG, EMG, etc.), mechanical signals (i.e., strain, pressure, temperature,
+
proximity, etc.), and concentration variations of various biochemical signals containing sodium ion (Na ),
hydrogen ion (H ), acetone gas, and nitrogen dioxide (NO ). Besides, it could produce and store energy
+
2
through integrated energy harvesters and storage units. The experimental results showcased that the
fabricated device could precisely monitor the physiological status variations in subjects caused by exercise,
including body temperature fluctuations, Na concentration increase, and rapid breathing and heartbeat
+
[Figure 11F and G]. Typical LIG-based biochemical sensors for healthcare are summarized in Table 4.

2
LIGS E as bio-actuators
Besides biosensors, the LIG facilitates the development of bio-actuators as an interface for further stimulus
generation (for instance, sound, heat, etc.) and healthcare. Most existing soft skin electronics focus on the
monitoring of physiological signals without the capability of sounding an alarm. Developing self-alarm
health management devices integrated with two functions of physiological signals monitoring and sound
alarm synchronously could further improve intelligent healthcare. Chen et al. showcased a LIG-based dual
functional electric skin (E-skin) for simultaneous real-time health monitoring and alarm [Figure 12A] .
[44]
The developed E-skin with shutter pattern achieved excellent overall performance, with a GF of 316.3,
capable of detecting various physiological indicators, such as respiration monitoring, voice recognition, and
wrist pulse perception. Meanwhile, the fabricated shutter-patterned E-skin could sound an alarm at 200 Hz
to 20 kHz in a broadband frequency. Benefiting from its outstanding mechanical and acoustic performance,
the E-skin exhibited wide applications in health monitoring and alarm of diseases, for instance, sleep apnea
[Figure 12B].

In addition, Huang et al. demonstrated a soft multifunctional (detection and warning) sensing patch,
[45]
utilizing mechanical and thermal effects of LIGs [Figure 12C] . The strain sensor with a mesh pattern
exhibited a mechanical sensitivity of up to 950 (GF), which could detect human motions and monitor weak
physiological signals, such as pulse waves. The prepared heater without patterned LIG exhibited better
heating performance than the device with a mesh pattern. Then, the developed device was integrated into