Page 40 - Read Online

Ma et al. Soft Sci 2024;4:26 https://dx.doi.org/10.20517/ss.2024.20 Page 17 of 34

Table 2. Summary of typical LIG-based multimodal biophysical sensors for healthcare
LIG composites Signals Sensitivity Intelligent applications Ref.
(role)/substrate
LIG (S)/PDMS foam Strain; temperature GF: 2,212.5; Simultaneously record heat stress and pulse waves [58]
-2
TCR: 0.97 × 10 °C -1
LIG (S, E)/PDMS Tilt; strain; humidity GF: ~10; Sleeping safety monitoring for vulnerable populations (e.g., [97]
humidity: -0.667/% elderly, infants, disabled)
-1 2
LIG (S, E)/PI Inertial; temperature; I: 6.52% m ·s ; Monitoring of human physical and health activities, legged-robot [98]
humidity; TCR: 215.2 m·Ω·°C -1 activities, and the control of the robotic arm via a human
breath rate
-1
LIG/CNT (S, E)/SEBS Pressure; temperature; P: 0.506 kPa ; Simultaneously assess the temperature and humidity of an [72]
-1
humidity; ECG TCR: 0.212% °C ; object, pressure distribution on the fingers, ECG signals, hand
H: 0.053%/%; movements, and gestures
ECG: 35 ± 3 dB
MXene-Ti C Tx@EDOT Strain; temperature; S: 2,075; Simultaneous measurement of strain, temperature, and ECG [74]
3 2
@LIG (S, E)/SEBS ECG TCR: 0.86%;
ECG: 20.14 dB
LIG (S, E)/PPH/PDMS Mechanical; M: 30; 5 detected indicators reflected the corresponding health status [27]
-1
temperature; humidity; TCR: 0.35% °C ; during movements
ECG H: 0.81%/%
LIG: Laser-induced-graphene; PDMS: polydimethylsiloxane; GF: gauge factor; TCR: temperature coefficient of resistance; PI: polyimides; CNT:
carbon nanotubes; SEBS: polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene; ECG: electrocardiography; EDOT: 3, 4-ethylene
dioxythiophene; PPH: polyvinyl alcohol-phytic acid-honey.

validation, and real-time cardiovascular disease (CVD) events diagnostics, which hinder their population-
wide practical applications. To tackle this challenge, Ma et al. reported a cheap, clinically validated, smart,
and soft pulse monitoring system (termed FlexiPulse) based on porous LIG for CVD management and
[3]
diagnostics . The ultrathin FlexiPulse can conform to the skin surface [Figure 9G]. The FlexiPulse was
highly sensitive to deform with the pulse waves when adhered to the epidermis above the artery
[Figure 9H]. The developed intelligent pulse sensor exhibited a high sensitivity of 2,336, an extreme-low
strain detection limit of 0.0056%, excellent stability (> 24,000 cycles), and clinical accuracy (> 93%).
Integrated with machine learning, the FlexiPulse realized clinical evaluation of actual CVD events
[containing atrial fibrillation (AF) and atrial septal defect (ASD)] with a high accuracy of approximately
98.7% [Figure 9I]. Typical machine learning-assisted soft biophysical sensors based on LIG for intelligent
healthcare are summarized in Table 3.

2
LIGS E for biochemical signals detection
Biochemical signals detection
The porous structures endow LIG electrodes with large contact areas with surrounding chemical stimuli,
[75]
resulting in high performance in biochemical sensors . Rahimi et al. demonstrated a stretchable
electrochemical pH sensor consisting of a pH-sensitive working electrode and a liquid-junction-free
[41]
reference electrode for wearable healthcare applications [Figure 10A] . The electrodes were developed by
bonding LIG/PI composites to soft Ecoflex substrates. The porous LIG electrodes were modified with PANI,
which functioned as the conductive filler and pH-sensitive film. Meanwhile, introducing serpentine
patterned interconnections rendered the pH sensor with excellent stretchability, which withstood
elongations of up to 135%. The experimental results validated that the developed pH sensor presented a
linear -53 mV/pH sensitivity in a pH 4-10 physiological range. The sensing performance remained stable
even under a tensile strain of 100% [Figure 10B].