Artist's impression of a bacteria cell engineered to incorporate particles such as quantum dots (red and green spheres) and gold nanoparticles [Credit: Yan Liang]

Engineers create 'living materials'

Engineers have coaxed bacterial cells to produce biofilms that can incorporate non-living materials, such as gold nanoparticles and quantum dots.

Taking from bone – a matrix of minerals and other substances, including living cells – researchers at MIT have created "living materials" that combine the advantages of live cells with non-living materials and could one day be used to design complex devices such as solar cells, self-healing materials or diagnostic sensor.

The materials combine the benefits of cells, which can respond to their environment, produce complex biological molecules, and span multiple length scales, with the benefits of non-living materials, which add functions such as conducting electricity or emitting light.

"Our idea is to put the living and the nonliving worlds together to make hybrid materials that have living cells in them and are functional," said Timothy Lu, an assistant professor of electrical engineering and biological engineering and senior author of a paper published in Nature Materials yesterday.

"It's an interesting way of thinking about materials synthesis, which is very different from what people do now, which is usually a top-down approach."

The team modified ‘curli fibers’ – proteins found in biofilms created by the bacterium E. coli that help it attach to surfaces – with protein fragments called peptides, which can capture non-living materials such as gold nanoparticles, incorporating them into the biofilms.

By programming cells to produce different types of curli fibers when different chemicals are introduced to their environment, the researchers were able to control the biofilms' properties and create gold nanowires, conducting biofilms, and films studded with quantum dots, or tiny crystals that exhibit quantum mechanical properties.

They also engineered the cells so they could communicate with each other and change the composition of the biofilm over time, by designing cells that produced the chemicals that determine the properties of the biofilm.

“It shows that indeed you can make cells that talk to each other and they can change the composition of the material over time," Lu said. "Ultimately, we hope to emulate how natural systems, like bone, form. No one tells bone what to do, but it generates a material in response to environmental signals."

These hybrid materials could be worth exploring for use in energy applications such as batteries and solar cells, Lu says.

The researchers are also interested in coating the biofilms with enzymes that catalyse the breakdown of cellulose, which could be useful for converting agricultural waste to biofuels. Other potential applications include diagnostic devices and scaffolds for tissue engineering.

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