Tag Archives: living materials

Semi-living gloves as sensors

Researchers at the Massachusetts Institute of Technology (MIT) are calling it a new ‘living material’ according to a Feb. 16, 2017 news item on Nanowerk,

Engineers and biologists at MIT have teamed up to design a new “living material” — a tough, stretchy, biocompatible sheet of hydrogel injected with live cells that are genetically programmed to light up in the presence of certain chemicals.

Researchers have found that the hydrogel’s mostly watery environment helps keep nutrients and programmed bacteria alive and active. When the bacteria reacts to a certain chemical, the bacteria are programmed to light up, as seen on the left. Courtesy of the researchers

A Feb. 15, 2017 MIT news release, which originated the news item, provides more information about this work,

In a paper published this week in the Proceedings of the National Academy of Sciences, the researchers demonstrate the new material’s potential for sensing chemicals, both in the environment and in the human body.

The team fabricated various wearable sensors from the cell-infused hydrogel, including a rubber glove with fingertips that glow after touching a chemically contaminated surface, and bandages that light up when pressed against chemicals on a person’s skin.

Xuanhe Zhao, the Robert N. Noyce Career Development associate professor of mechanical engineering at MIT, says the group’s living material design may be adapted to sense other chemicals and contaminants, for uses ranging from crime scene investigation and forensic science, to pollution monitoring and medical diagnostics.

“With this design, people can put different types of bacteria in these devices to indicate toxins in the environment, or disease on the skin,” says Timothy Lu, associate professor of biological engineering and of electrical engineering and computer science. “We’re demonstrating the potential for living materials and devices.”

The paper’s co-authors are graduate students Xinyue Liu, Tzu-Chieh Tang, Eleonore Tham, Hyunwoo Yuk, and Shaoting Lin.

Infusing life in materials

Lu and his colleagues in MIT’s Synthetic Biology Group specialize in creating biological circuits, genetically reprogramming the biological parts in living cells such as E. coli to work together in sequence, much like logic steps in an electrical circuit. In this way, scientists can reengineer living cells to carry out specific functions, including the ability to sense and signal the presence of viruses and toxins.

However, many of these newly programmed cells have only been demonstrated in situ, within Petri dishes, where scientists can carefully control the nutrient levels necessary to keep the cells alive and active — an environment that has proven extremely difficult to replicate in synthetic materials.

“The challenge to making living materials is how to maintain those living cells, to make them viable and functional in the device,” Lu says. “They require humidity, nutrients, and some require oxygen. The second challenge is how to prevent them from escaping from the material.”

To get around these roadblocks, others have used freeze-dried chemical extracts from genetically engineered cells, incorporating them into paper to create low-cost, virus-detecting diagnostic strips. But extracts, Lu says, are not the same as living cells, which can maintain their functionality over a longer period of time and may have higher sensitivity for detecting pathogens.

Other groups have seeded heart muscle cells onto thin rubber films to make soft, “living” actuators, or robots. When bent repeatedly, however, these films can crack, allowing the live cells to leak out.

A lively host

Zhao’s group in MIT’s Soft Active Materials Laboratory has developed a material that may be ideal for hosting living cells. For the past few years, his team has come up with various formulations of hydrogel — a tough, highly stretchable, biocompatible material made from a mix of polymer and water. Their latest designs have contained up to 95 percent water, providing an environment which Zhao and Lu recognized might be suitable for sustaining living cells. The material also resists cracking even when repeatedly stretched and pulled — a property that could help contain cells within the material.

The two groups teamed up to integrate Lu’s genetically programmed bacterial cells into Zhao’s sheets of hydrogel material. They first fabricated layers of hydrogel and patterned narrow channels within the layers using 3-D printing and micromolding techniques. They fused the hydrogel to a layer of elastomer, or rubber, that is porous enough to let in oxygen. They then injected E. coli cells into the hydrogel’s channels. The cells were programmed to fluoresce, or light up, when in contact with certain chemicals that pass through the hydrogel, in this case a natural compound known as DAPG (2,4-diacetylphloroglucinol).

The researchers then soaked the hydrogel/elastomer material in a bath of nutrients which infused throughout the hydrogel and helped to keep the bacterial cells alive and active for several days.

To demonstrate the material’s potential uses, the researchers first fabricated a sheet of the material with four separate, narrow channels, each containing a type of bacteria engineered to glow green in response to a different chemical compound. They found each channel reliably lit up when exposed to its respective chemical.

Next, the team fashioned the material into a bandage, or “living patch,” patterned with channels containing bacteria sensitive to rhamnose, a naturally occurring sugar. The researchers swabbed a volunteer’s wrist with a cotton ball soaked in rhamnose, then applied the hydrogel patch, which instantly lit up in response to the chemical.

Finally, the researchers fabricated a hydrogel/elastomer glove whose fingertips contained swirl-like channels, each of which they filled with different chemical-sensing bacterial cells. Each fingertip glowed in response to picking up a cotton ball soaked with a respective compound.

The group has also developed a theoretical model to help guide others in designing similar living materials and devices.

“The model helps us to design living devices more efficiently,” Zhao says. “It tells you things like the thickness of the hydrogel layer you should use, the distance between channels, how to pattern the channels, and how much bacteria to use.”

Ultimately, Zhao envisions products made from living materials, such as gloves and rubber soles lined with chemical-sensing hydrogel, or bandages, patches, and even clothing that may detect signs of infection or disease.

Here’s a link to and a citation for the paper,

Stretchable living materials and devices with hydrogel–elastomer hybrids hosting programmed cells by Xinyue Liu, Tzu-Chieh Tang, Eléonore Tham, Hyunwoo Yuk, Shaoting Lin, Timothy K. Lu, and Xuanhe Zhao. PNAS February 15, 2017 doi: 10.1073/pnas.1618307114 Published online before print February 15, 2017

This paper appears to be open access.

Do you have a proposal for living building materials?

DARPA (US Defense Advanced Research Projects Agency) has launched a program called Engineered Living Materials (ELM) and issued an invitation. From an Aug. 9, 2016 news item on Nanowerk,

The structural materials that are currently used to construct homes, buildings, and infrastructure are expensive to produce and transport, wear out due to age and damage, and have limited ability to respond to changes in their immediate surroundings. Living biological materials—bone, skin, bark, and coral, for example—have attributes that provide advantages over the non-living materials people build with, in that they can be grown where needed, self-repair when damaged, and respond to changes in their surroundings. The inclusion of living materials in human-built environments could offer significant benefits; however, today scientists and engineers are unable to easily control the size and shape of living materials in ways that would make them useful for construction.

DARPA is launching the Engineered Living Materials (ELM) program with a goal of creating a new class of materials that combines the structural properties of traditional building materials with attributes of living systems. Living materials represent a new opportunity to leverage engineered biology to solve existing problems associated with the construction and maintenance of built environments, and to create new capabilities to craft smart infrastructure that dynamically responds to its surroundings.

An Aug. 5, 2016 DARPA news release, which originated the news item, explains further (Note: A link has been removed),

“The vision of the ELM program is to grow materials on demand where they are needed,” said ELM program manager Justin Gallivan. “Imagine that instead of shipping finished materials, we can ship precursors and rapidly grow them on site using local resources. And, since the materials will be alive, they will be able to respond to changes in their environment and heal themselves in response to damage.”

Grown materials are not entirely new, but their current manifestations differ substantially from the materials Gallivan envisions. For instance, biologically sourced structural materials can already be grown into specified sizes and shapes from inexpensive feedstocks; packing materials derived from fungal mycelium and building blocks made from bacteria and sand are two modern examples. And, of course, wood has been used for ages. However, these products are rendered inert during the manufacturing process, so they exhibit few of their components’ original biological advantages. Scientists are making progress with three-dimensional printing of living tissues and organs, using scaffolding materials that sustain the long-term viability of the living cells. These cells are derived from existing natural tissues, however, and are not engineered to perform synthetic functions. And current cell-printing methods are too expensive to produce building materials at necessary scales.

ELM looks to merge the best features of these existing technologies and build on them to create hybrid materials composed of non-living scaffolds that give structure to and support the long-term viability of engineered living cells. DARPA intends to develop platform technologies that are scalable and generalizable to facilitate a quick transition from laboratory to commercial applications.

The long-term objective of the ELM program is to develop an ability to engineer structural properties directly into the genomes of biological systems so that neither scaffolds nor external development cues are needed for an organism to realize the desired shape and properties. Achieving this goal will require significant breakthroughs in scientists’ understanding of developmental pathways and how those pathways direct the three-dimensional development of multicellular systems.

Work on ELM will be fundamental research carried out in controlled laboratory settings. DARPA does not anticipate environmental release during the program.

For anyone who’s interested in participating in the program, there’s an announcement (download the PDF for more details) featuring a Proposers Day event on Aug. 26, 2016 being held in Arlington, Virginia,

The Proposers Day objectives are:

1) To introduce the science and technology community (industry, academia, and government) to the ELM program vision and goals;

2) To facilitate interaction between investigators that may have capabilities to develop elements of interest and relevance to ELM goals; and

3) To encourage and promote teaming arrangements among organizations that have the relevant expertise, research facilities and capabilities for executing research and development responsive to the ELM program goals.

The Proposers Day will include overview presentations and optional sidebar meetings where potential proposers can discuss ideas for proposal submissions with the Government team.

The goal of the DARPA ELM program is to explore and develop living materials that combine the structural properties of traditional building materials with attributes of living systems, including the ability to rapidly grow, to self-repair, and to adapt to the environment. Living materials represent a new opportunity to leverage engineered biology to solve existing problems associated with the construction and maintenance of our built environments, as well as to create new capabilities to craft smart infrastructure that dynamically responds to our surroundings. The specific program objectives are to develop design tools and methods that enable the engineering of structural features into cellular systems that function as living materials, thereby opening up a new design space for building technology. These new methods will be validated by the production of living materials that can reproduce, self-organize and self-heal.

You can register for the event  here. Register by 12 pm (noon) ET on Aug. 23, 2016.