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Arab Hassani. Soft Sci 2023;3:31 https://dx.doi.org/10.20517/ss.2023.23 Page 19 of 33

of mucin as a secreted protein, lithium chloride (LiCl) as an electrolyte, and polyacrylamide (PAAm) as the
3D porous polymer network to facilitate facile electrolyte flow, as illustrated in Figure 11B. Additionally, a
tannic acid (TA) solution was used to prepare the hydrogel layer because it could induce the formation of

Figure 11. (A) Schematic illustration of wipe-and-detection of the human tongue; (B) an image of the artificial tongue and schematic
illustration of the astringency-sensing principle of the artificial tongue; and (C) application of five drops of 1 wt.% TA to the artificial
tongue array (left panel) and two drops of 0.1 and 1 wt.% TA to the array (right panel), along with the corresponding taste mapping
[124]
data . TA: Tannic acid.

hydrophobic aggregates and enhance ionic conductivity. Direct UV polymerisation of the hydrogel on a
poly(ethylene naphthalate) (PEN) substrate with patterned Au IDEs was realised using
3- (trimethoxysilyl)propyl methacrylate (TMSPMA) as the chemical anchoring agent. When 0.1 and 1 wt.%
TA solutions were applied at five different spots on the array, the sensor measured the corresponding
current changes to generate taste maps [Figure 11C]. The largest current changes were observed at the spots
where 1 wt.% solution was applied, whereas the spots where 0.1 wt.% solution was applied exhibited smaller
current changes. This artificial tongue could be used as a platform for future applications involving portable
taste-monitoring devices and humanoid robots.