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Zhu et al. Soft Sci 2024;4:17 https://dx.doi.org/10.20517/ss.2024.05 Page 27 of 38

galvanic skin response sensor. The wireless detection system communicates data with a plurality of wireless
devices mounted on the skin of the wheelchair user, enabling accurate and stable measurements of pressure,
temperature and hydration. Clinical trials with wheelchair patients demonstrated the feasibility and stability
of the monolithic integrated system in preventing injuries caused by sedentary behavior.

Intelligent machinery
E-skins also possess vast potential in the field of intelligent machinery [218,219] . The application of e-skins in
this area mainly includes two major aspects: remote control and mechanical haptics. For the former, the
basic implementation method is to use e-skins as convenient signal sources and realize the convenient
control of machinery by decoding the characteristics of the signals. Some scholars installed e-skins at the
joint positions of hands or gloves and achieved synchronized control of a robotic hand by decoding the
characteristic information transmitted by these e-skins in real time . For the latter, the basic strategy is to
[220]
install e-skins on the surface of the machinery so as to give the machinery tactile ability [221-223] [Figure 14A (i)
and Figure 14B (i)] [224-229] .

Zhang et al. designed a textile resistive pressure sensor, SPRET, consisting of a CNT network (conductive
layer) + polypyrrole-polydopamine-perfluorodecyltrlethoxysilane (PPy-PDA-PFDS) polymer layer
(hydrophobic layer) + a textile (substrate), exhibiting sparing to various reagents and high robustness .
[224]
This wearable e-skin can accurately, continuously, long-term and reliably detect human motion and
physiological signals in air/humid conditions or underwater and also enable synchronized remote control of
manipulators through a MCU [Figure 14A (i)].

Lu et al. developed hydroxypropyl cellulose (HPC)-based eutectic gels with high conductivity, transparency,
and anti-freezing properties with 98.1% resilience suitable for wearable applications by introducing HPC
[225]
into a metal salt-based deep eutectic solvent (MDES) . Self-powered e-skin composed of this Eutectic Gel-
Based Triboelectric Nanogenerator (E-TENG) prepared using this eutectic gel possesses excellent
performance. Realized by an Arduino nano MCU (using ATmega328P Chip) for gesture recognition and
robotic remote control, this highly resilient self-powered e-skin exhibits extraordinary potential for practical
HMI and cooperative operation of intelligent machinery [Figure 14A (ii)].

Liu et al. proposed a capacitive bimodal e-skin, silicone rubber/4-Methylbenzenesulfonhydrazide/Silok-
7455 Hyperdispersant/Polyphenylmethylsiloxane (SR/TSH/dispersant/PPMS), with 12 labyrinth-patterned
sensing units in a pyramidal porous multistage dielectric structure for proximity and pressure sensing in
HMI scenarios, which has a proximity detection range of 0-110 mm and a pressure detection range of
0-200 kPa, with a sensitivity of 0.464% kPa -1[226] . The e-skin was used as a “keyboard” to enable real-time
control of a robot arm through non-contact gestures and contact presses [Figure 14A (iii)].

Yang et al. report a self-healing high-performance flexible pressure sensor with MXene/PU (Sensitive Layer)
- MXene (interdigital electrode) that can be prepared by a low-cost spraying method, which can be prepared
on other arbitrary flexible substrates, with the hydrogen bonding of PU conferring self-healing functionality
to the device . The sensor exhibits high sensitivity (up to 509.8 kPa ) and good stability (10,000 cycles).
[228]
-1
This pressure sensor-based e-skin can be mounted on a robotic hand to give it haptic capabilities
[Figure 14B (ii)].

Luo et al. demonstrated a capacitive-dielectric integrated pressure sensor, micro-conformal electrode-
dielectric integration (MEDI), which has a complex structure of graphene nanowalls (pyramid-shaped top
electrode)/PDMS (pyramid-shaped dielectric layer)/ZnO (pyramid-shaped dielectric layer)/poly(methyl