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‘New paradigm’ in 3D printing uses genetically programmed cells

‘New paradigm’ in 3D printing uses genetically programmed cells

Technology News |
By Rich Pell



Designed to light up in response to a variety of stimuli, the cells – when mixed with a slurry of hydrogel and nutrients – can be printed, layer by layer, to form 3-D interactive structures and devices. Such a technique, the researchers say, could be used to fabricate “active” materials for wearable sensors and interactive displays.

The researchers have demonstrated the technique by printing a “living tattoo” — a thin, transparent patch patterned with “branches” of live bacteria cells in the shape of a tree. Each branch is lined with cells sensitive to a different chemical or molecular compound, and when the patch is adhered to skin that has been exposed to the same compounds, the corresponding regions of the “tree” light up in response.

The live cells can be engineered to sense environmental chemicals and pollutants, say the researchers, as well as changes in pH and temperature. In addition, the researchers have developed a model to predict the interactions between cells within a given 3-D-printed structure, under a variety of conditions, which they say can be used as a guide in designing responsive living materials.

Previously researchers have tried to use living mammalian cells as the basis for 3D-printed inks, which proved too fragile to survive the printing process. But the MIT researchers found bacteria cells that were able to survive those relatively harsh conditions, as well as a hydrogel – a gel-like material made from a mix of mostly water and a bit of polymer – with the proper consistency and environment that could be used as a transport medium for the cells.

Using bacterial cells engineered to light up in response to a variety of chemical stimuli, the researchers then came up with a recipe for their 3-D ink using a combination of bacteria, hydrogel, and nutrients to sustain the cells and maintain their functionality.

“We found this new ink formula works very well and can print at a high resolution of about 30 micrometers per feature,” says Xuanhe Zhao, who led the research team and who is the Noyce Career Development Professor in MIT’s Department of Mechanical Engineering. “That means each line we print contains only a few cells. We can also print relatively large-scale structures, measuring several centimeters.”

They printed the ink using a custom 3-D printer, which they built using standard elements combined with fixtures they machined themselves. After printing the patch, they solidified – or cured – it by exposing it to ultraviolet radiation.

They then adhered the transparent elastomer layer with the living patterns on it to skin that had been smeared with several chemical compounds. Over several hours, branches of the patch’s tree lit up when bacteria sensed their corresponding chemical stimuli.

The researchers also tested bacteria that had been engineered to communicate with each other – that is, to light up only when they receive a certain signal from another cell. To do so, they printed a thin sheet of hydrogel filaments with “input,” or signal-producing bacteria and chemicals, overlaid with another layer of filaments of an “output,” or signal-receiving bacteria, and found that the output filaments lit up only when they overlapped and received input signals from corresponding bacteria.

The researchers say that in the future this technique could be used to print “living computers” — structures with multiple types of cells that communicate with each other, passing signals back and forth, much like transistors on a microchip.

“This is very future work,” says Hyunwoo Yuk, a graduate student at MIT and co-author of a paper on the research, “but we expect to be able to print living computational platforms that could be wearable.”

In the shorter term, the researchers hope to fabricate customized sensors, in the form of flexible patches and stickers that could be designed to detect a variety of chemical and molecular compounds. They also see the potential for their technique to be used to manufacture drug capsules and surgical implants containing cells engineered to produce compounds such as glucose, to be released therapeutically over time.

For more, see “3D Printing of Living Responsive Materials and Devices.”

Related articles:
Wearable ‘living sensors’ light up in contact with chemicals
World’s smallest ‘tape’ recorder uses hacked microbes

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