AsianScientist (Aug. 22, 2019) – In a study published in Nano Letters, scientists in South Korea developed a transfer-printing technology that uses hydrogel and nano ink to create flexible sensors.
Interest in wearable devices, including smartwatches and fitness bands, is increasing rapidly. With the scope of such devices expanding from types that are worn like clothing to those that are attached directly to the skin, there is growing demand for technologies that allow for the production of high-performance sensors on surfaces of various shapes and types.
Transfer printing works in a way similar to that of a tattoo sticker: by placing a tattoo sticker against the skin, then removing the paper component, an image is left behind on the skin. The most notable advantage of transfer printing is that it largely avoids the difficulties involved in creating devices directly on substrates that are thermally and chemically sensitive. This is why the technique is widely used for manufacturing flexible devices. On the other hand, the primary disadvantage of current transfer printing processes is that they can usually only be used for substrates with flat surfaces.
Seeking to overcome these limitations, researchers led by Dr. Yi Hyunjung at the Korea Institute of Science and Technology (KIST), South Korea, inkjet-printed an aqueous solution-based nano ink onto a porous and hydrophilic hydrogel layer which was solidified onto a surface bearing specific topological structures. The surfactant and water in the nano ink passed quickly through the hydrogel’s porous structure, leaving only the nanoparticles in the ink on the hydrogel. This allowed the scientists to lay down a specific electrode pattern.
The amount of nano ink used for this printing process was very small, allowing for the rapid formation of electrodes. Moreover, the electrical performance of the electrodes was high due to the high levels of purity and uniformity of the resulting nanonetworks. Also, because of the hydrophobic nature of the nanomaterial, there was an extremely low degree of interaction between the nanomaterial and the hydrogel, allowing for the easy transfer of the electrodes to diverse topographic surfaces.
To demonstrate the easy application of their technology, the researchers transferred nanoelectrodes directly onto a glove to create a modified sensor that can immediately detect finger movements. They also created a flexible, high-performance pressure sensor that can measure the pulse in the wrist.
“The outcome of this study is a new and easy method for creating flexible, high-performance sensors on surfaces with diverse characteristics and structures. We expect that this study will be utilized in the many areas that require the application of high-performance materials onto flexible and non-traditional substrates, including digital healthcare, intelligent human-machine interfaces, medical engineering and next-generation electrical materials,” said Yi.
Source: National Research Council of Science & Technology; Photo: Korea Institute of Science and Technology.
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