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Tian et al. Soft Sci 2023;3:30 https://dx.doi.org/10.20517/ss.2023.21 Page 7 of 27

Figure 4. Overview of interconnect materials of pressure and temperature sensors towards e-skin. (A) All-printed, interdigitated, and
freestanding serpentine interconnect-based flexible solid-state supercapacitors for self-powered wearable electronics. Reproduced with
permission [45] . Copyright 2019, Elsevier B.V. (B) Metallic and non-metallic interconnect materials. Reproduced with permission [47-52] .
Copyright 2020, Springer Nature [47] . Copyright 2020, John Wiley & Sons, Inc [48] . Copyright 2022, Springer Nature [49] . Copyright 2011,
Springer Nature [50] . Copyright 2022, MDPI [51] . Copyright 2017, American Association for the Advancement of Science [52] . (C)
Graphene/silver nanowire hybrid fillers on highly stretchable strain sensors based on spandex composites. Reproduced with
permission [54] . Copyright 2020, MDPI. (D) Conductive hydrogel-based elastic microelectronics for localized low-voltage
neuromodulation. Reproduced with permission [55] . Copyright 2019, Springer Nature. (E) Wearable microfluidic diaphragm pressure
sensors for health and tactile touch monitoring. Reproduced with permission [56] . Copyright 2017, John Wiley & Sons, Inc.

from single signal detection on the rigid substrate to multi-sensing integration combined with flexible
electronics, connected intelligence, and advanced algorithms to implement enhanced biocompatible and
conformal advantages [1-3,57] . In contrast to conventional rigid and fragile sensing materials, soft electronics
towards e-skin makes additional requirements for sensing materials, which include the highly physical and
biochemical sensitivity and structural compatibility with the whole system.

Variations exist in the conductive properties of materials between interconnects and sensing elements,
which means that rapid data transmission can be ensured owing to interconnects with high electrical
conductivity, whereas it is not ideal for active sensing applications. In fact, sensing materials that are
sensitive to aimed physical parameters, namely pressure and temperature, are needed. It is noteworthy that
lots of carbon-based materials or CPs exhibit an excellent multi-sensing capacity. Hence, Table 1 briefly
summarizes common active sensing materials based on different pressure and temperature
mechanisms [58-64] . In brief, active materials sensitive to pressure and temperature cover metal or metal oxides
(e.g., Ag/Au/Cu nanomaterials [14,15,17,20,22,25] , BaTiO ), carbon nanomaterials (CNTs [11,12,14,25] , graphene [18,65] ,
[23]
3
[23]
reduced graphene oxide (rGO) ), CPs {e.g., Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)
(PEDOT: PSS) [13,14,17,19,22,25] , poly(vinylidene difluoride and trifluoroethylene) [P(VDF-TrFE)] }, ionic
[20]
[13]
liquid [66,67] , and MXene . Clearly, multiple active materials tend to be utilized for simultaneous pressure and