Building
stimulus-responsive units in the hydrogel coatings remains
challenging for film sensors consisting of alternated layers of inert
substrates and hydrogel coatings. An interesting film sensor with
a carboxymethyl starch-based hydrogel coating was developed here.
The cross-linking networks of carboxymethyl starch play the roles
of structure-constructing units and stimulus-controlling units simultaneously,
endowing the coatings with thermal sensing and strain sensing capabilities.
The dynamic cross-links formed via the boronic ester bonds are temperature-sensitive,
releasing or consuming additional acid ions with temperature alteration,
and also as primary networks give the hydrogel strength and stretchability
with the assistance of semi-penetrated polyacrylamide chains. Therefore,
as-prepared flexible film sensors can be used to detect the periodic
changes of human temperature and small-scale motion with multiple
working modes, discriminating the physical states related to human
health. Moreover, this kind of starch-based coating is degradable
in a strongly alkaline solution and the inert substrate layer can
protect the skin from erosion caused by direct hydrogel-skin contact,
and thereby the film sensor is human- and environmentally friendly.
This work also proposes a strategy of building temperature-sensitive
units in the film sensor via regulating the chemical networks, instead
of tuning physical structures.
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