Described in a paper titled “Hydrogel-Templated Transfer-Printing of Conductive Nanonetworks for Wearable Sensors on Topographic Flexible Substrates” published in the Nano Letters, the technique relies on the non-adherence, nanoporous structure, and molding capability of hydrophilic hydrogels.
In one implementation, the researchers inkjet-printed an aqueous solution-based ink containing carbon nanotubes (CNT) onto a hydrogel layer used as a flexible template. Both the surfactant and water in the nano ink pass through the hydrogel's porous structure, leaving only the hydrophobic CNT on the surface ready to be transferred to any curved surface by reversing the hydrogel onto it.
In another implementation, the researchers molded a curable elastomer fluid directly onto the printed electrodes (on their hydrogel substrate). Simply unmolding the solidified elastomer yields a flexible skin with the transferred electrodes.
Using this hydrogel-templated approach, the researchers designed flexible strain sensors onto a glove to monitor finger motions, They also designed pressure sensors able to measure arterial pulses at the wrist.
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