It will still take a few more years before biodegradable organic molecules are used in our electronic devices - however, that day is inching closer with today's announcement of new results from Professor Clara Santato's laboratory in the Department of Engineering Physics at Polytechnique Montréal. In an article published in Nature Communications, Santato's research team demonstrates that its key molecule - eumelanin - rapidly degrades in an industrial context when exposed to bacteria.
The electronic products we use in our daily lives come with an environmental cost that is difficult, if not impossible, to sustain in the long term. In response to this, numerous researchers around the world - notably Professor Santato - are trying to identify sustainable alternatives to replace some of the currently-used metals and inorganic molecules, with compounds that have the same electro-activity characteristics, but that are "greener" and potentially biosourced, i.e. extracted from living matter.
"Our goal is to develop eco-responsible materials and electronic devices, with limited environmental impact and which can be composted at the end of their life cycle," she explains.
One such area of exploration was a family of molecules that are very abundant on the planet: melanins. Made of numerous carbon atom rings, among other functions these brownish-black pigments protect DNA from harsh UV rays. Melanins manifest as a blackish-brown pigment found in the peel of overripe bananas, but also in the skin, hair, and eyes of many mammals - including humans.
Melanins are also concentrated in the “ink” that cephalopods such as squid and cuttlefish expel when these animals feel threatened- and it's using that very same squid ink that Polytechnique researchers are conducting their experiments, says Professor Santato.
"When synthesized in the lab, the cost of this molecule is very high, so it's preferable to buy squid ink in a fish shop, then extract the components that are of interest - more precisely eumelanin," Santato explains. That being said, she also specifies that bioprocesses are currently being studied to ensure a cost-competitive supply of the molecule in the event that large quantities become necessary.
Toss your "squid" into the compost bin
In her article published in Nature Communications, Professor Santato's team looked at eumelanin's end of life period to estimate the amount of time that this molecule could take to degrade after its use in an electronic device.
To do this, researchers dipped squid ink samples into municipal waste treatment compost, then measured how quickly the eumelanin degraded under natural conditions at 25 degrees Celsius, or at 58 degrees in an industrial context.
After 98 days of incubation, the microorganisms in the warmed compost eliminated 37% of the eumelanin molecules, while only 4% had disappeared from the room temperature compost. Additional tests also showed that the resulting compost was non-toxic to plants and that it permitted both seed germination and plant growth.
“This is the first time that eumelanin's biodegradability has been tested in this way. The results we obtained suggest that this bio-based molecule could have a well-controlled life cycle that’s safe for the environment," notes Santato.
To demonstrate that the degradation of organic molecules in this context is something rather special, Santato’s team conducted a parallel biodegradation experiment on two synthetic organic compounds also being considered for use in electronic components: polyphenylene sulfide (PPS) and phthalocyanine blue (Cu-Pc). In both biodegradation experiments, the synthetic molecules performed poorly in terms of their environmental impact, and remained almost intact throughout the experiment. Further, PPS contaminated the compost, while Cu-Pc partially blocked the respiratory activity of microorganisms responsible for the composting process.
A genuinely future-forward material
While squid ink is still far from anyone's lips when it comes to manufacturing electronic components containing eumelanin, research teams have already demonstrated that it can be incorporated into supercapacitors, batteries, and even electrochemical transistors.
According to Professor Santato, several of this molecule's characteristics could make it a material of the future for biodegradable electronics. In addition to its abundance in nature and its non-toxicity, eumelanin also has appealing biodegradability potential, as demonstrated by the study the Professor has just concluded PhD graduate Eduardo Di Mauro, and collaborator Professor Denis Rho, researcher at the National Research Council of Canada (NRC).
"Eumelanin is a compound that's environmentally-friendly while also being suitable for sustainable organic electronics," she adds, specifying that it could, among other things, be incorporated into electronic devices intended for biomedical and environmental use.