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Ma et al. Soft Sci 2024;4:26 https://dx.doi.org/10.20517/ss.2024.20 Page 7 of 34

Figure 4. Stretchability enhancement strategies of LIG. (A) Schematic illustration exhibits LIG’s stretchability regulation strategies; (B)
Serpentine LIG is transferred onto a soft, stretchable hydrogel layer [27] . Copyright 2023, Springer Nature; (C) A kirigami-patterned
PDMS sponge with transferred porous LIG [83] . Copyright 2020, WILEY-VCH; (D) Electromechanical response comparison of typical LIG
composites. LIG: Laser-induced-graphene; PDMS: polydimethylsiloxane.

composites depends on the material properties of the elastomer. For example, a commercial medical
polyurethane film (MPU) is widely used for wound healthcare, exhibiting several advantages, including high
stretchability (> 100%), long-term and conformal attachment on the skin (> 72 h), gas permeability, etc.
These features enable it to be a potential substrate for skin electronics development. Motivated by this,
Dallinger et al. transferred porous LIG from a PI substrate onto an ultrathin MPU film (~50 μm in
thickness), achieving a remarkable stretchability (> 100%) and long-term stability in electromechanical
tensile tests (> 200 cycles) . Furthermore, introducing mechanical design in elastomer enhances the
[34]
[27]
stretchability of LIG/elastomer composites, such as serpentine design and kirigami configuration . For
[83]
instance, Lu et al. transferred prepared serpentine LIG onto a soft and stretchable hydrogel layer, achieving
[27]
a high stretchability up to approximately 220% [Figure 4B] . In addition, Sun et al. transferred porous LIG
onto a PDMS sponge with a kirigami pattern to improve the stretchability, originating from the fact that the
[83]
kirigami cuts could tolerate the applied strains . As expected, the electrical resistance of the LIG/PDMS
sponge only increased by approximately 6%, even when stimulated by a tensile strain of 1,000% [Figure 4C].
Figure 4D illustrates the strain range and electromechanical sensitivity of typical LIG
composites [3,26,33,36,40,41,43,44,68,74,77,81-89] .

Role design of LIG in soft skin electronics
For the development of soft skin electronics, versatile LIG plays three leading roles, including sensing
materials, electrodes, and conductors [Figure 5]. The densely interconnected graphene flakes endow porous