Jennifer Chu | MIT News Office - December 5, 2017

MIT engineers have devised a 3-D printing technique that uses a new kind of ink made from genetically programmed living cells.

The cells are engineered to light up in response to a variety of stimuli. When mixed with a slurry of hydrogel and nutrients, the cells can be printed, layer by layer, to form three-dimensional, interactive structures and devices.

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

The researchers, led by Xuanhe Zhao, the Noyce Career Development Professor in MIT’s Department of Mechanical Engineering, and Timothy Lu, associate professor of biological engineering and of electrical engineering and computer science, say that their technique can be used to fabricate “active” materials for wearable sensors and interactive displays. Such materials can be patterned with live cells engineered to sense environmental chemicals and pollutants as well as changes in pH and temperature.

What’s more, the team developed a model to predict the interactions between cells within a given 3-D-printed structure, under a variety of conditions. The team says researchers can use the model as a guide in designing responsive living materials.

Zhao, Lu, and their colleagues have published their results today in the journal Advanced Materials. The paper’s co-authors are graduate students Xinyue Liu, Hyunwoo Yuk, Shaoting Lin, German Alberto Parada, Tzu-Chieh Tang, Eléonore Tham, and postdoc Cesar de la Fuente-Nunez.

A hardy alternative

In recent years, scientists have explored a variety of responsive materials as the basis for 3D-printed inks. For instance, scientists have used inks made from temperature-sensitive polymers to print heat-responsive shape-shifting objects. Others have printed photoactivated structures from polymers that shrink and stretch in response to light.  

Zhao’s team, working with bioengineers in Lu’s lab, realized that live cells might also serve as responsive materials for 3D-printed inks, particularly as they can be genetically engineered to respond to a variety of stimuli. The researchers are not the first to consider 3-D printing genetically engineered cells; others have attempted to do so using live mammalian cells, but with little success.

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

Instead, the team identified a hardier cell type in bacteria. Bacterial cells have tough cell walls that are able to survive relatively harsh conditions, such as the forces applied to ink as it is pushed through a printer’s nozzle. Furthermore, bacteria, unlike mammalian cells, are compatible with most hydrogels, gel-like materials that are made from a mix of mostly water and a bit of polymer. The group found that hydrogels can provide an aqueous environment that can support living bacteria.

The researchers carried out a screening test to identify the type of hydrogel that would best host bacterial cells. After an extensive search, a hydrogel with pluronic acid was found to be the most compatible material. The hydrogel also exhibited an ideal consistency for 3-D printing.

“This hydrogel has ideal flow characteristics for printing through a nozzle,” Zhao says. “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.”

From tattoos to living computers

Lu provided the team with 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,” Zhao says. “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 that they built using standard elements combined with fixtures they machined themselves. To demonstrate the technique, the team printed a pattern of hydrogel with cells in the shape of a tree on an elastomer layer. After printing, they solidified, or cured, the patch by exposing it to ultraviolet radiation. They then adhere the transparent elastomer layer with the living patterns on it, to skin.

To test the patch, the researchers smeared several chemical compounds onto the back of a test subject’s hand, then pressed the hydrogel patch over the exposed skin. Over several hours, branches of the patch’s tree lit up when bacteria sensed their corresponding chemical stimuli.

The researchers also engineered bacteria to communicate with each other; for instance they programmed some cells to light up only when they receive a certain signal from another cell. To test this type of communication in a 3-D structure, 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. They found the output filaments lit up only when they overlapped and received input signals from corresponding bacteria .

Yuk says in the future, researchers may use the team’s technique 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.

Photo: MIT engineers have devised a 3-D printing technique that uses a new kind of ink made from genetically programmed living cells. Courtesy of the researchers

“This is very future work, but we expect to be able to print living computational platforms that could be wearable,” Yuk says.

For more near-term applications, the researchers are aiming to fabricate customized sensors, in the form of flexible patches and stickers that could be engineered to detect a variety of chemical and molecular compounds. They also envision their technique may be used to manufacture drug capsules and surgical implants, containing cells engineered produce compounds such as glucose, to be released therapeutically over time.

“We can use bacterial cells like workers in a 3-D factory,” Liu says. “They can be engineered to produce drugs within a 3-D scaffold, and applications should not be confined to epidermal devices. As long as the fabrication method and approach are viable, applications such as implants and ingestibles should be possible.”

This research was supported, in part, by the Office of Naval Research, National Science Foundation, National Institutes of Health, and MIT Institute for Soldier Nanotechnologies.

Source: MIT News

Read more

Comments

No comments to display.

Related posts

Intel Artificial Intelligence and Rolls-Royce Push Full Steam ahead on Autonomous Shipping

Rolls-Royce builds shipping systems that are sophisticated and intelligent, and eventually it will add fully autonomous to that portfolio, as it makes commercial shipping safer and more efficient.

Call for Applications: 2019 RoboMaster Robotics Competition

The RoboMaster 2019 Robotics Competition is open to international universities. As long as you love robots and hope to show your talent and wisdom on the RoboMaster Robotics Competition, you can apply for registration!
Application Deadline in 24 days

EU's Call for Proposals: Pilot lines for modular factories

Modular production equipment can create highly adaptable production lines to enable efficient production of small series tailored to customer demands.
Application Deadline in 4 months

Overseas investment falling, developing countries largely unscathed: UN trade agency

Foreign direct investment (FDI) has dropped 40 per cent year-on-year so far, the UN Conference on Trade and Development (UNCTAD) said on Monday, but the $470 million decline is happening mainly in wealthy, industrialized nations, especially in North America and Western Europe.

EU's Call for Proposals: Alternatives to anti-microbials in farmed animal production

Activities shall focus on developing and testing new, efficient and targeted alternatives to anti-microbials in farmed animal production.
Application Deadline in 3 months

Aerial Mapping of Forests Affected by Pathogens Using UAVs, Hyperspectral Sensors, and Artificial Intelligence

The method integrates unmanned aerial vehicles (UAVs), hyperspectral image sensors, and data processing algorithms using machine learning.

EU's Call for Proposals: Blue economy

This topic aims to support demonstration projects based on innovative technologies testing/deploying/scaling-up of new industrial or service applications and solutions for the blue economy.
Application Deadline in 3 months

Exciting Possibilities in the Visible Light Communications Market & Their Potential

The Global Visible Light Communication market is valued of $ 6.9mn during the forecast period 2017 -2023. As the developments pertaining to VLC are being executed incessantly complimented by the exponential rise in the data transfer due to on-going IoT wave will boost the market. Europe remained a significant market for VLC developments in 2017. The access and station point’s shipments in this region totaled around 4.7 thousand units in 2017 and is forecast to advantage at a CAGR of 153.6% while Americas evaluated to witness the highest CAGR of nearly 178% in the forecast period.

EU's Call for Proposals: Blue Labs

The focus of this action is to support young scientists supported by experienced researchers, industry and local stakeholders, to team up and develop innovative technologies, products and services in support of a sustainable blue economy, preserving marine resources and ecosystems.
Application Deadline in 3 months

A Close Look At The Latest Research Trends Within The Uninterruptible Power Supply Market

The Global Uninterrupted power supply market has a market revenue of $10,369.8 million in 2017 and is estimated to grow at a CAGR of 3.6% during the forecast period 2018-2023. Growing demand for continuous power supply and protecting equipment from voltage fluctuations is driving the market.