Although tattoos are some of humanity’s most ancient art forms, millennials have embraced them in a way that has come to surprise previous generations. In 2018, a market research firm estimated that growth of the tattoo industry will expand 7.7% a year, reflecting a booming desire. Beyond statements of self-identity, new technology could make having a tattoo useful in an emergency. A new development in flexible temporary electronic displays could make glowing tattoos a real thing.
The secret ingredient is biodegradable and easy enough to come by, according to a new study from out of Nanjing Tech University, based in China and published in the journal ACS Nano: gelatin derived from collagen in fish scales.
These flexible displays are a type of alternating current electroluminescent (ACEL) device. As a reminder, there’s alternating current (AC) and direct current (DC). A direct current flows only in one direction—often used in either very big or very small applications, like transmission wires, semiconductors, or the battery cell of a flashlight. But in an alternating current, the current regularly reverses its direction. That means, among other things, that it needs less insulation. That flexibility has led it to be commonplace, used in everyday items like lamps and food mixers.
“One critical requirement for wearable electronic devices is the flexibility, which allows the devices to be adaptive to mechanical changes, such as bending, folding or twisting,” write the authors in their paper, led by Xiaopan Zhang.
There already are thin, flexible substrates that are widely used, but these come with a huge disadvantage: they’re made out of raw oil, a classic nonrenewable source. Given that over 20 million tons of plastic are thrown into American landfills alone each year, according to the EPA, the need to ween this cutting edge technology off of future garbage as soon as possible is critical.
Fish gelatin isn’t the only possible renewable source for these substrates, it’s just the one that makes the most sense. Silk proteins from silkworms, for example, have tremendous potential as a material. But there are a number of problems with attaining it, which consists of treating silkworm cocoons with hot air in a process known as “stifling.” Obtaining fish gelatin is much easier, and cheaper, by comparison.
Fish wouldn’t need to be specially harvested to obtain fish scales, as would be the case in silkworms. Fish scales are already inedible, and according to the scientists already are around 3% of 70.5 million metric tons of fish that are consumed worldwide each year. Depending on the fish, anywhere between 40 to 55% of their fish scales can be used to obtain the gelatin needed for the flexible substrates.
So they’re easy enough to obtain, but what makes them so good? And what makes them possible tattoos? The team breaks down their reasoning with four categories: recyclability, which we’ve already discussed, light transparency, flexibility, and surface roughness.
For an ACEL device, like a smartwatch, transparency is the name of the game. The scientists placed flowers and films under fish gelatin, and during testing they report that “they could be seen clearly, and no blurring or darkening was observed.” That means that FG material would be transparent enough to be placed on top of an already-existing tattoo, without any casual observer ever noticing the difference.
Then there’s flexibility. For tattoos or any other stylish design that could be made digital, it’s crucial. Scientists were able to squish their fish gelatin material into the shape of a tiny frog. “Inks could also be deposited on the film by direct handwriting,” the scientists note, directly opening the door for potential tattoos. And in addition to that flexibility, they’re sturdy: the fish gelatin material held its “original shape without any damage after being immersed in various organic solvents for 24 hours, showing a good chemical stability,” the scientists write in their paper.
But what good what all of that be if it was uncomfortable to the skin? Luckily, testing showed that the fish gelatin material had a surface roughness par with the currently used oil-based products. “Low surface roughness makes it a promising candidate for integrating with other components in [the] field of electronics.”
That promise could open up a world of possibilities.
The Inverse Analysis
When the coronavirus epidemic finally ends, the economic recession it brought forward will likely still be wreaking havoc on commercial fisheries, who will have seen serious losses. The further development of these fish scales into materials used for electronics, as well as potential tattoos in the future, could open up a whole new market.
Abstract: In the past decades, various alternating current electroluminescent (ACEL) devices, especially the flexible ones, have been developed and used in flat panel display, large-scale decorating, logo display lighting, optical signaling, etc. Transparent plastics are usually used as substrates in ACEL devices; however, they are undegradable and may cause serious environmental pollution. Herein, we have developed a flexible transient ACEL device based on transparent fish gelatin (FG) films. The FG films were made from fish scales, which are sustainable, cost-efficient, and eco-friendly. These films could dissolve in water within seconds at 60 °C and degrade completely within 24 days in soil. The transmittance of these FG films was up to 91.1% in the visible spectrum, comparable to that of polyethylene terephthalate (PET) (90.4%). After forming a composite with silver nanowires (Ag NWs), the Ag NWs-FG film showed a transmittance up to 82.3% and a sheet resistance down to 22.4 Ω sq–1. The fabricated ACEL device based on the Ag NWs-FG film exhibited high flexibility and luminance up to 56.0 cd m–2. The device could be dissolved in water within 3 min. Our work demonstrates that the sustainable, flexible, and transparent FG films are a promising alternative for green and degradable substrates in the field of flexible electronics, including foldable displays, wearable devices, and health monitoring.