Using a newly developed 3D printing technique, researchers at MIT have engineered a “living tattoo” using ink composed of genetically programmed living bacteria cells.
The technique was demonstrated by printing a tree-shaped patch with branches lined with cells on a hand, with specific branches or cells responding based on which molecular compounds or chemicals the skin has been exposed to.
The research teamis led by Xuanhe Zhao, Noyce Career Development Professor in MIT’s Department of Mechanical Engineering, and Timothy Lu, an associate professor of biological engineering, electrical engineering, and computer science. The research team believes the technique could be important for providing useful information by sensing environmental conditions, for example, pollutants, temperature changes and pH levels.
The printing ink uses a mix of nutrients and hydrogel, which is printed in thin layers to create 3D structures and devices, with the cells capable of responding to the different external stimuli by lighting up. Cells can also be set up to interact with each other, reacting only after a signal is communicated from another cell.
The new developments have provided a more successful alternative to prior failed attempts to develop living materials. Previously, mammalian cells have been unsuccessfully utilized to create living devices mostly due to their inability to survive the printing process. Hyunwoo Yuk, a graduate student and co author of the MIT research, said, “It turns out those cells were dying during the printing process because mammalian cells are basically lipid bilayer balloons.”He added, "they are too weak, and they easily rupture.”
The bacterial cells have tougher cell walls with the ability to withstand much harsher conditions, including being pushed through the printer nozzle, something that the weaker mammalian cells were less capable of. Also, bacteria are more compatible with the majority of hydrogels, which consist mostly of water with a small amount of polymer, providing an aqueous environment for the bacteria to survive in and an ideal solution for printing.
Identifying the most suitable hydrogel for the printing process required an extensive search. Zhao said, “It's like squeezing out toothpaste. You need [the ink] to flow out of a nozzle like toothpaste, and it can maintain its shape after it's printed."
After finding the correct hydrogel and bacteria, nutrients are also added to the ink to aid in the bacteria’s sustainability and functionality. Zhao said, "We found this new ink formula works very well and can print at a high resolution of about 30 micrometers per feature…that means each line we print contains only a few cells. We can also print relatively large-scale structures, measuring several centimeters."
According the Yuk, there is an exciting future ahead with the potential to use the technique to print "living computers," structures with multiple types of cells that communicate with each other. The team are also aiming to develop flexible patches to function as customized sensors with the capability to detect various chemical and molecular compounds. There is also the potential to use the printing technology on drug capsules and surgical implants.
You can read more about the Zhao and Lu team’s research in its published journal article in Advanced Materials:3D Printing of Living Responsive Materials and Devices.
For an informative video summary of the research, click here.
For more information on this and other research at MIT, you can visit MIT’s news website: http://news.mit.edu/2017/engineers-3-d-print-living-tattoo-1205.
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