Tardigrades, also known as water bears, have survived outer space, high pressure, near starvation, freezing temperatures, etc. As if that wasn’t cool enough, these tiny animals, resilient to almost every extreme, have now received the tiniest tattoo possible. The picture of the tattooed critter has found its place amongst the best pictures of April, hand-picked by experts at Nature. Turns out, the near indestructible nature of tardigrades has a large part to play in it. All this is being done to test a microfabrication technique to build microscopic, biocompatible devices. According to Ding Zhao, co-author of the paper, these micro-tattoos are not just for water bears, but also for other living organisms like bacteria.
Microfabrication has brought new life to electronic and photonic technologies, from developing micro- and nanoscale instruments like microprocessors and solar panels, to biosensors that detect food contamination or cancer cells. If biologists succeed in making microfabrication techniques more compatible with living organisms, it can lead to advances in biomedical engineering and medicine.
To carve the tattoo, the scientists directed an electron beam into a thin layer of ice coating on the tardigrade, or on other living tissue. This process leaves behind a design when the ice sublimates. The process is known as ice lithography. While most other organisms will face troubles surviving this process, near-indestructible tardigrades manage to survive being frozen, coated in ice, and hit with electron beams, making them the perfect fit for this experiment. These tattoos are also quite stable, showing no change even after stretching, solvent immersion, rinsing, and drying.
The tardigrades were put in a state of half-death, known as the cryptobiotic state. The team slowly dehydrated the microscopic critters, and then placed a single tardigrade onto a carbon-composite paper, cooled the sheet below -226°F (-143°C), and covered the water bear with a protective layer of frozen anisole. This frozen anisole protected the surface of the tardigrade from getting damaged by the focused electron beam, which drew the pattern.
The electron beam reacted with the frozen anisole to form a new biocompatible compound that stuck to the tardigrade’s surface when warmed. In fact, as the tardigrade warmed to room temperature and was rehydrated, it sported its new tattoo, unbothered. The unreacted anisole sublimated, leaving behind the pattern drawn on it using the beam of electrons.
The precision of this technique allowed the team to create a variety of micropatterns, like squares and lines that were 72 nanometers wide, and even the university’s logo. 40% of the tardigrades that underwent the procedure survived, and the research team is hopeful about better survival rates once the process has been fine-tuned. The tardigrades didn’t mind their new tattoos and showed no change in behavior either. The results are promising, and scientists are hopeful that the technique will help devise micro-electronics or sensors onto living tissue without harm.
Gavin King, a researcher credited with inventing the ice lithography technique who was not involved in this study, concludes, “It is challenging to pattern living matter, and this advance portends a new generation of biomaterial devices and biophysical sensors that were previously only present in science fiction.”
Zhao and Qiu hope this work will enable advancements, such as the development of microbial cyborgs after further research. Biomedical applications in the future can also benefit from this process. Fields like cryopreservation and astrobiology are expected to gain new knowledge from this series of microfabrication experiments.
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