Development of Low-Cost, Kirigami-inspired, Stretchable on Skin Strain Sensors using Tattoo Paper

The increased demand for highly sensitive body sensors have created a range of smart wearables. Strain sensors have evolved from semi-rigid to highly, stretchable, and flexible devices that can conform to the human skin. In contrast to complex conventional fabrication methods, this paper proposes a simple and cost-effective technique that combines stencil printing with kirigami cutting to produce flexible, stretchable, linear, disposable sensors using temporary tattoo paper and conductive carbon paste. Here, two sensor designs (straight line and serpentine) were fabricated and analyzed. The number of carbon-ink coatings were also varied to study the effect of number of coating layers to the sensitivities of the sensor. A total of117 samples were fabricated and tested. When tested on skin, the maximum strain that could be measured was 20% for the straight-line patterned sensors and 35% for the Kirigami structured sensors. Both designs demonstrated good adhesion to skin, are stretchable, and flexible. The best performing designs with the most reliable data were straight-line type sensor with width 9 mm and three-layer carbon ink coatings, and Kirigami sensor with width 8 mm and two-layer coatings of carbon ink. Both sensors exhibited high linearity of 0.9956 and 0.9813, but low sensitivities of 0.25 and 0.28. These sensors have potential applications in the biomedical field.