Fig. 5.

Sensing materials with porous hierarchical structures. a Aerogel-based [104]. Copyright (2022) The Authors. b Wood-based porous aerogel with nanochannels in the cellular walls [61]. Copyright (2018) Wiley–VCH. c Porous structures fabricated by coating and depositing of sponge-based [37] (Copyright (2018) American Chemical Society), d foam-based [105] (Copyright (2016) Wiley–VCH), e paper-based [34] (Copyright (2019) American Chemical Society), f fabric-based [106] (Copyright (2020) Wiley–VCH). g Piezoresistive sensor based on SFP-based CF. h SEM image of hollow hierarchical structure [225]. Copyright (2017) Elsevier