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Page 6 of 34 Ma et al. Soft Sci 2024;4:26 https://dx.doi.org/10.20517/ss.2024.20

[54]
scanning speed could compensate for this defect while benefiting large-scale production .

To enhance the conductivity further, researchers have proposed a blended strategy. It can be divided into
two types: laser engraving substrates blended with conductive sources and LIG with conductive sources.
Before laser engraving treatment, doping the substrate with conductive nanoparticle sources is an effective
approach to improve the electrical properties of LIG. For instance, Zang et al. developed a mechanically
stable Mo C @LIG electrode by laser engraving a fibrous paper soaked with gelatin-mediated inks rich in
3
2
molybdenum ions [Figure 3B]. The prepared Mo C @LIG electrodes showcased high conductivity
[69]
2
3
(~30 Ω/sq) and fascinating porous structures, exhibiting potential applications, including biochemical
sensors, energy harvesters and supercapacitors.
[39]
Meanwhile, modification of fabricated porous LIG with conductive nanoparticles (such as Ag paste , silver
[41]
[70]
[72]
[40]
nanowires (AgNWs) , Au [40,47,71] , Ni , polyaniline (PANI) , carbon nanotubes (CNT) , MXene , and
[73]
MXene-Ti C Tx@3, 4-ethylene dioxythiophene (EDOT) ) or conductive polymers [for example, poly(3,4-
[74]
2
3
[75]
ethylenedioxythiophene) (PEDOT) ] can significantly improve the conductivity of electrodes. For
instance, Huang et al. reported a gold nanoparticles (AuNPs)@LIG electrode prepared by coating a
chloroauric acid (HAuCl ) onto the porous LIG electrode and then baked in the thermostatic oven
[71]
4
[Figure 3C]. The fabricated AuNPs@LIG electrodes showcased a low impedance of 16 Ω, facilitating the
electron transfer between the enzyme active center and electrode surface, endowing the device’s better
performance. Meanwhile, Yang et al. developed a stretchable AgNWs electrode by spray-coating an AgNWs
solution on a prestressed LIG/polydimethylsiloxane (PDMS)-Ecoflex substrate and then releasing the
substrate . Profited from the evenly distribution AgNWs on the 3D porous LIG/PDMS-Ecoflex substrate
[70]
and a pre-strain (30%) design, the conductivity of the LIG electrodes reduced from 48.6 to 3.2 Ω/sq.
Stretchability enhancement
Human skin exhibits natural strain up to 50%-80% . Therefore, stretchability is important in soft skin
[76]
electronics to withstand daily skin deformations while maintaining stable performance. Several engineering
strategies are utilized to realize high stretchability [Figure 4A]. Due to the thermoplastic property of the PI
film, the LIG directly fabricated on PI sheets showcased limited stretchability (up to 10%) [42,44,77] . This limited
stretchability hinders the development of high-fidelity soft skin electronics. To tackle this problem,
researchers have attempted several mechanical strategies to improve the stretchability of LIG/PI composites,
[41]
[78]
including kirigami , serpentine patterns , and 3D architectures . For example, Ling et al. reported a
[79]
straightforward and practical strategy for developing LIG’s 3D hierarchical architectures with designed
configurations through mechanically guided and 3D assembly . The resulting device with 3D helical coils
[79]
exhibited negligible variations in electrical resistance when stretched to 150%. The electrical resistance only
increased by approximately 0.3%, even after undergoing 1,000 biaxial stretching cycles with a strain of 50%.
To further improve the stretchability of LIG functional composites, the elastomers containing carbon
[80]
sources were employed to be thermal treatment with laser to prepare LIG, such as PDMS directly, PDMS/
[82]
PI composites , PDMS/photosensitive PI (PSPI) composites , etc. For instance, Wang et al. utilized
[81]
PDMS/PI composites, prepared by blending PI particles in PDMS precursors, to develop LIG-based
stretchable and soft electronics . Benefiting from the flexible and stretchable properties of the PDMS/PI
[81]
composites, the fabricated LIG-based flexible electronics exhibited outstanding mechanical stretchability
(> 15%).

Finally, transferring prepared LIG from the PI substrate to a stretchable elastomer substrate provides a
practical approach to developing soft skin electronics. The stretchability of resulting LIG/elastomer