A Living Tattoo That Uses Genetically Programmed Bacteria

  • Researchers create a cell sensitive, thin tattoo that glows when comes in contact with the skin cells. 
  • The tattoo ink is made of hydrogel and mixture of nutrients to keep the cells alive.
  • The ink can be printed at a high resolution – approximately 30 micrometers.
  • A 3D printed living tattoo features 3 different sensors, which can endure compression, stretching and twisting.

Researchers at MIT have found a new method to use a special kind of ink made of genetically programmed living cells. They have devised a temporary tattoo, and its prototype looks like thin, transparent, stick-on patch with a tree-shape pattern.

It is divided into several sections that are cell sensitive to a different chemical compound. When this tattoo comes in contact with the skin, it is exposed to particular compound (present in human skin), making corresponding regions of the tree to light up in response.

This happens, because cells are designed to light up in response to different kinds of stimuli. When combined with a slurry of nutrients and hydrogen, the cells could be printed layer by layer in order to form a 3D interactive structure.

Previous Studies In The Same Field

Stimuli responsive material is not something new – research and development has been going on for more than a decade. For instance, a material that well responds to chemicals can be used to create a chemical sensor, or a material that responds to high-temperature can be used to develop self-assembling robots

Since the 3D printing is now widely accessible and available at much cheaper prices, it has become a common method for developing experimental objects, including stimuli responsive materials.

However, this time, researchers realized a way to use living cells that can be programmed and obtained in a 3D printed reactive material. Researches done till date suggest that at least mammalian cells would not be feasible for this. They cannot work in the harsh conditions of 3D printing – ultraviolet exposure during cross-linking, shear force during extrusion and much more. Since the mammalian cells are lipid bilayer balloons, the cells die during the printing process.

On the other hand, bacterial cells with a protective cell wall are much stronger. They are compatible with most hydrogels – material made of polymer and water, and used in a wide range of medical applications.

The New Living Responsive-Ink

MIT researchers use a new technique to fabricate ‘active’ material for interactive displays and wearable sensors. In fact, these materials could be combined with live cells to sense environmental chemical and pollutants as well as slight alterations in temperature and pH.

Using genetically programmed bacterial cells, the team built an ink made of hydrogel and mixture of nutrients to keep the cells alive.

More specifically, they’ve engineered a range of bacterial cells that can generate green fluorescent protein (GFP) or secrete chemicals in response to four different signaling chemicals, which diffuse freely throughout the hydrogel. Bio-ink containing pure pluronic F127 diacrylate micelles recovers to a packing state after printing, which is stabilized by ultraviolet cross-linking.

Reference: Advanced Materials | 10.1002/adma.201704821 | Via MIT News 

They’ve also built a model to forecast the interactions between cells within a 3D printed structure, under different conditions. This model could be used by other scientists as a guide for creating responsive living materials.

The ink they’ve developed can be printed at a high resolution – approximately 0.03 millimeters or 30 micrometers. Even pyramid-like connections of analyte and sensor are easily achieved. Multi-ink 3D printing enables the construction of several logic gates using GFP fluorescence as output. They have already printed the test pattern onto elastomer and stuck it to skin, which had been smeared with chemicals.

Spatiotemporally controlled patterning is achieved because of well-defined spatial distribution of hydrogel, time dependence of the signal molecule diffusion and GFP production.

The gel that consists of bacteria responsive to N-acyl homoserine lactone, can be printed in intricate patterns. Connection to N-acyl homoserine lacton-containing gel induces GFP production of the bacteria, which scatters throughout the whole sensor overnight.  

A 3D printed living tattoo developed using this methodology features 3 different sensors, which can endure compression, stretching and twisting. Application of analytes causes precise local responses only in respective sensor area.  

For a few hours, different sections of the tree pattern in the tattoo lit up as the bacteria came into direct contact with its chemical stimuli. Bacterial cells can also communicate with each other, and fluoresce after getting a specific signal from another cell.

Researchers have tested it in a 3D structure, overlaying two hydrogel filaments printed sheets. They lit up when they came in contact with each other and got the specific communication signal.

Read: Magnesium-Ion Batteries Are More Efficient and Safer Than Lithium

What’s Next?

In near future, researchers expect to be able to print living, wearable computational platform, and structures with several different kinds of cells that can pass signals back and forth, much like transistors on a microchip.

They are working to develop drug delivery systems and chemical sensors, which can be programmed to deliver drugs into the body over time. 

Written by
Varun Kumar

Varun Kumar is an experienced science and technology journalist interested in machines, AI, and space exploration. He received a Master's degree in computer science from Indraprastha University. To find out what his latest project is, feel free to directly email him at [email protected] 

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