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Page 14 of 34 Ma et al. Soft Sci 2024;4:26 https://dx.doi.org/10.20517/ss.2024.20

biophysical signals collection and intelligent healthcare. Chen et al. reported a high-performance porous
[58]
LIG composites-based sensor for strain and temperature detection fabricated by a simple laser process
[Figure 8A]. The developed dual-mode sensor showcased a remarkable strain sensitivity (GF: 2,212.5) in a
wide linear range of 0%-65%, ultralow detection limit (< 0.0167%), and temperature sensitivity of
0.97 × 10 °C in a broad linear range of 10-185 °C. Owing to this high performance, the proposed dual-
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mode sensor could simultaneously record the heat stress and human pulse waves when integrated into the
wrist skin surface [Figure 8B].

To track the sleeping status of vulnerable populations, Xu et al. exhibited a wireless sensing patch based on
LIG, which could detect multimodal indicators (sleeping postures, respiration rate, and diaper moisture)
and feedback alarms [Figure 8C]. In this study, the LIG was utilized as active porous sensing materials in
[97]
strain sensors for respiration rate detection and was employed as highly conductive electrodes in tilt and
humidity sensors for sleeping postures and diaper moisture perception, respectively. The tilt sensor was
created by confining a GaInSn (Galinstan) droplet within a cavity integrated with patterned LIG electrodes,
achieving the perception of 18 slanting directions. Originating from the various slanting orientations, the
contact and separation between the liquid metal droplets and conductive LIG electrodes determine the
“ON” and “OFF” states. As a proof-of-concept, a volunteer wore an intelligent diaper integrated with the
proposed multimodal sensor device with feedback tracking functions, achieving real-time monitoring of
sleeping posture, respiration, and wetness.

Similarly, Babatain et al. reported fully standalone LIG-based multifunctional skin electronics for multiple
parameters (inertial, temperature, humidity, and breathing) detection [Figure 8D]. The proposed inertial
[98]
sensor comprised graphene-coated liquid metal droplets and 3D circular channels. This creative design
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rendered an inertial sensor with an excellent sensitivity of 6.52% m ·s in a wide range (1-30 m/s ) and
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outstanding stability (> 12,500 cycles). After integrating optimized multifunctional sensors with a wireless
programmable system on a programmable system on a chip (PSoC) signal processing circuit, a fully
standalone platform was created, which achieved monitoring of human healthcare and soft human-machine
interfaces in a real-time manner.

Electronic gloves (e-gloves) integrated with multifunctional sensing capabilities can render robotic/
prosthetic hands with excellent perception performance to feel the physical aspects of the real world.
Sharma et al. reported an all-directional strain-insensitive e-glove through laser engraving techniques,
realizing real-time pressure monitoring, temperature, humidity, and ECG signals [Figure 8E] . To avoid
[72]
the influence of external stretch on the performance of e-gloves, the sensing area and interconnections were
designed as ripple-like meandering patterns. In addition, the crosslinking network of the CNT in the porous
LIG could reduce the stress effect. The developed e-glove could simultaneously assess the temperature and
humidity of objects, pressure profile on the fingers, ECG signals, hand movements, and gestures, exhibiting
great potential application in prosthetic hands.

Although various multifunctional skin electronics have been fabricated, seamlessly integrating multiple
functional sensors into a common stretchable substrate without interfering remains challenging. To
overcome this shortcoming, Zhang et al. developed a multifunctional soft skin electronic system by
integrating strain, temperature, and ECG sensors into a stretchable and soft SEBS substrate without
[74]
interfering with each other [Figure 8F] . The heterogeneity of these three different sensors was enabled by
electrophoretically depositing MXene-Ti C Tx@EDOT onto porous LIG, forming LIG/MXene-
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Ti C Tx@EDOT composites. As expected, the fabricated device successfully exhibited synchronous strain,
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temperature, and ECG detection.