Massachusetts Institute of Technology (MIT) engineers have created a new ink from genetically programmed living cells. While many engineers are experimenting with a variety of responsive materials the MIT team wondered if live cells could be co-opted into a functional use.
The team used the ink to print a 3D layered structure onto a transparent elastomer patch.
The researchers designed the tattoo to make it more tree-like, with each section of the tree’s branches containing bacteria sensitive to certain types of chemicals.
Over several hours, branches of the patch’s tree lit up when bacteria sensed their corresponding chemical stimuli.
“We found this new ink formula works very well and can print at a high resolution of about 30 micrometers per feature. We can also print relatively large-scale structures, measuring several centimeters”, he said. While right now that means they light up when they come in contact with particular molecular compounds, there are exciting potential applications: the tattoos could be designed so that they respond to environmental pollutants or changes in temperature.
The MIT team chose to revisit the concept using bacterial cells instead because they are hardier and able to survive relatively harsh conditions.
The living tattoo itself was produced using a 3D printer custom-made for the bioprinting application.
Here’s how it works: First the bacterial cells are programmed to respond to different compounds. “You need the ink to flow out of a nozzle like toothpaste, and it can maintain its shape after it’s printed”.
Yuk says their technology could be developed further to, one day, build “living computers” made up of different types of bacteria cells that communicate with each other by passing signals back and forth – “much like transistors on a microchip”. Again, unlike mammalian cells, bacteria are compatible with most hydrogels – mixes of water and some polymer. To test this system, scientists printed a thin sheet of hydrogel filaments with input (signal-producing) bacteria and chemicals, and overlaid that with another layer of filaments of output (signal-receiving) bacteria.
The new tattoo goes beyond conventional smart devices and uses genetically modified bacterial cells to serve as a living sensor. The output filaments only lit up when they overlapped with the input layer and received a signal from them. This breakthrough opens the door to living tattoos that are able to monitor for different chemicals when worn.
Authors of the study include Xinyue Liu, Hyunwoo Yuk, Shaoting Lin, German Alberto Parada, Tzu-Chieh Tang, Eléonore Tham, Cesar de la Fuente-Nunez, Timothy K. Lu and Xuanhe Zhao. They’re also looking into creating drug capsules and surgical implants containing cells engineered to produce compounds such as glucose, which could be released over time. “As long as the fabrication method and approach are viable, applications such as implants and ingestibles should be possible”.
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