Our bones are remarkable feats of engineering; strong and yet light, shot through with holes and yet able to bear incredible loads. This super-strong natural material is built as cells incorporate hard minerals like calcium into living tissue. Now, scientists at the Massachusetts Institute of Technology are borrowing this idea from nature: They've created living cells that incorporate inorganic matter like gold and quantum dots.
These bacterial factories, described in the journal Nature Materials, could one day help create fully functional hybrid "living materials" that could be integrated into everyday objects and devices, from solar panels to adjustable furniture.
"This work lays a foundation for synthesizing, patterning, and controlling functional composite materials with engineered cells," the study authors wrote.
The scientists used E. coli bacteria as their cellular factory, because they naturally create a biofilm that contains "curli" fibers that allow the bacteria to stick to surfaces. Curli fibers are made up of long protein chains that can pick up protein subunits called peptides. These peptides then grab non-living materials and then incorporate them into the biofilm's structure.
The scientists managed to program these E. coli cells to produce different flavors of curli fibers. One kind of curli fiber worked with a type of peptide called histidine, which could pick up little bits of gold. By alternating the E. coli containing gold-grabbing curli fibers with a different version of the bacteria, the scientists were able to create rows of gold nanowires and an electrically conducting network.
The researchers also managed to create a curli fiber that used a different peptide (which they called SpyTag) that would bind to a substance they called SpyCatcher. When they coated quantum dots in SpyCatcher, the modified curli fiber grabbed the quantum dots and pulled them in. Quantum dots are tiny, semiconductor nanocrystals with a range of properties and potential applications. And since the scientists could grow slightly different strains of E. coli together in the same spot, they say they can create a multitalented material made of both quantum dots and gold nanoparticles.
Depending on what you can engineer the bacteria to pick up, these kinds of hybrid materials could be useful to create batteries and solar cells, or even biomedical devices and scaffolds for tissue engineering. Such hybrid materials could also be smart materials, able to respond to the environment or even self-heal after they're damaged, just as natural living materials do.
This research "will enable the realization of smart composite materials that combine the properties of living and non-living systems," the study authors wrote.