Why bother to manufacture materials if you can grow them organically?
Researchers have produced "living" materials by nudging bacteria to grow biological films. In turn, this process could lead to the development of more complex and interactive structures programmed to self-assemble into specific patterns, such as those used on solar cells and diagnostic sensors, and even self-healing materials that could sense damage and repair it, a new study finds.
"In contrast to materials we use in modern life, which are all dead, living materials have the ability to self-heal, adapt to the environment, form into complex patterns and shapes, and generate new functional materials and devices from the bottom up," said study lead author Timothy Lu, a biological engineer at the Massachusetts Institute of Technology.
Such "living materials" are essentially hybrids that have the best of both worlds: the benefits of both living cells, which can organize and grow on their own, and nonliving materials, which add functions such as electricity conduction or light emission.
For instance, other researchers have looked at the possibility of organizing viruses into new materials. But Lu said his team's approach is different. "Previous systems do not leverage the characteristics of living organisms," he told Live Science. "Also, most modern materials' synthesis processes are energy-intensive, human-intensive endeavors. But we're suggesting to use biology to grow materials from the bottom up in an environmentally friendly fashion."
Learning from bones
To create the materials, Lu's team took inspiration from natural materials, such as bone and teeth, which contain a mix of minerals and living cells. Bones grow when cells arrange themselves into specific patterns and then excrete special proteins to produce the calcium phosphate structures.
Lu's team tried to do the same by reprogramming Escherichia colibacterial cells using genetic engineering to produce the proteins.
E. coli naturally produce biofilms that contain a special type of protein called curli fibers that help the bacteria attach to surfaces, and are known to have the strength of steel. Each curli fiber is composed of a chain of identical protein units called CsgA, which can be changed by adding protein fragments called peptides. These peptides can capture nonliving materials, such as gold nanoparticles, and incorporate them into the biofilms.
The researchers' goal was to get the bacteria to secrete the protein matrix in response to specific stimulants.
To do so, the researchers disabled the bacterial cells' natural ability to produce CsgA and replaced it with an engineered genetic code that produces CsgA proteins only under certain conditions — when a molecule called AHL is present.
The scientists could then adjust the amount of AHL in the cells' environment, and when AHL was present, the cells produced CsgA, making curli fibers that merged into a biofilm.
The team then modified E. coli in a different way, to make it produce CsgA with a specific peptide with many histidine amino acids, but only when a molecule called aTc was present.
Written By: Katia Moskvitch
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