Dec 6, 2017 | By Tess

A team of MIT engineers have demonstrated the ability to 3D print what it calls a “living tattoo” from a bioink consisting of living cells and hydrogel. When adhered to human skin and exposed to certain chemicals, the tree-shaped “tattoo” lights up in response.

The research study, which was led by Xuanhe Zhao, from MIT’s Department of Mechanical Engineering, and Timothy Lu, associate professor of biological engineering, electrical engineering, and computer science, was very recently published in the journal Advanced Materials.

As the study outlines, the researchers have come up with a specialized bioprinting technique which has allowed them to create flexible and wearable structures made of genetically programmed biomaterials.

In their demonstration, the MIT researchers have 3D printed a multicolored tree-shaped tattoo made of live bacteria cells. The tree’s three different branch colors indicate a different cell type, and each branch has been engineered to react to a different chemical of molecular compound.

By exposing human skin to these particular chemical compounds and then placing the thin and transparent “tattoo” onto the skin, the 3D printed branches begin to light up when they come into contact with the chemicals.

Of course, while the 3D printed “living tattoos” are quite fun to look at, they have the potential to serve a more practical purpose. As the researchers explained, the process could be used to produce “active materials for wearable sensors and interactive displays” which could react and detect specific chemicals.

The 3D printed tattoos also have the potential to be adapted for applications in drug delivery and surgical implants as they could be built to contain “cells engineered to produce compounds such as glucose,” which could be released into the body gradually and even on demand.

Further down the line, the researchers say the innovative method could be used for 3D printing “living computers” (complex structures made up of multiple cell types which are capable of communicating with each other). “This is very future work, but we expect to be able to print living computational platforms that could be wearable,” explained Hyunwoo Yuk, an MIT graduate researcher and a co-author on the paper.

In developing the 3D bioprinted tattoos, the research team did have some hurdles to overcome. For one, the scientists had to find the right kind of cell which could withstand the printing process. As they explain, while scientists around the globe are working on printing mammalian cells, there has not been much success due to their fragility.

“It turns out those cells were dying during the printing process, because mammalian cells are basically lipid bilayer balloons,” said Yuk. “They are too weak, and they easily rupture.”

As a solution, the MIT research team turned to bacteria cells, which tend to have tougher cell walls than mammalian cells and can endure harsher environments. Interestingly, bacterial cells are more widely compatible with hydrogel materials, making them practically ideal for bioprinting applications.

Still, the researchers set out to find the best hydrogel mixture for printing the living tattoos and found that a hydrogel containing pluronic acid was the best fit. “This hydrogel has ideal flow characteristics for printing through a nozzle,” Zhao explained. “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.”

The final printable material consisted of a hydrogel base mixed with the bacterial cells, and nutrients to keep the cells alive. According to Zhao, the bioink was ideal for printing and even showcased its ability to be printed 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,” he said.

The living tattoo itself was produced using a 3D printer custom-made for the bioprinting application. Once printed, the tattoo was cured using UV radiation and was subsequently applied to human skin which had been exposed to various chemical compounds. As mentioned, the tattoo’s branches gradually began to light up when the particular cell types came into contact with the chemicals.

Though still in its early stages, the living tattoo research seems promising and we can’t wait to see what other types of living tattoos can be 3D printed in the future.



Posted in 3D Printing Technology



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