Bacteria, fungus, and other living organisms have the ability to grow and regenerate themselves. Now, engineers are looking for ways to harness this ability and adapt it to make stronger, tolerant, and resilient engineering materials. The study is led by Qiming Wang of the USC Viterbi School of Engineering and published in the journal Advanced Materials.
Wang said that the materials they are making are living and self-growing. According to Science Daily, the researchers were inspired by the sophisticated microstructures of natural materials for centuries for their ability to grow and regenerate. Thanks to the microscopes scientists have been able to observe how microorganisms live and survive.
This time, living bacteria will be used as a tool to directly grow amazing structures that cannot be made by humans.
Harnessing Abilities of Bacteria to Design Engineering Materials
The researchers used the bacteria called Sporosarcina pasteurii (S. pasteurii). It is known to secrete an enzyme called urease. According to Biomed Central, this bacteria is also well-known for its ability to microbially induced calcite precipitation (MICP) that has great potential for construction and engineering materials.
That means when urease is exposed to urea and calcium ions it produces calcium carbonate, a strong mineral compound found in teeth. The researchers guide the bacteria to grow calcium carbonate minerals to make ordered microstructures that are the same as those in natural mineralized composites.
Since bacteria know how to save time and energy, harnessing these abilities will be helpful to design hybrid engineering materials that are superior to fully synthetic materials. This is not the first time that engineering has borrowed concepts from nature as it has great examples of complex mineralized, like the hard shell of mollusks.
The combination of living bacteria and synthetic materials creates the new living material that has properties superior to any natural or synthetic material currently in use, Wang said. This is because of the bouligard structure of the material that has several layers of minerals laid at varying angles from each other that forms a helicoidal shape that is hard to synthetically produce.
To create this material, the researchers 3D-printed a lattice structure that acts as scaffolding with empty squares and lattice layers that vary in angles that is inline with the helicoidal shape. The bacteria is then introduced, which intrinsically attached themselves to the surfaces. There they will release urease that will trigger the formation of calcium carbonate crystals that will eventually fill the tiny squares and create different patterns with the minerals.
Testing the Strength of the Living Materials
CEE doctoral student An Xin said that the living materials showed great strength when they were able to resist crack propagation or fractures and help dissipate energy within the material during the mechanical testing, Fooshya reported.
Wang noted that they were able to produce something so stiff and strong with immediate applications in infrastructures, like aerospace panels and vehicle frames. These living materials are lightweight and can be used as material for body or vehicle armors as they can resist bullet penetration and dissipate the energy to avoid being damaged.
Furthermore, the researchers also found a potential of reintroducing the bacteria once the living materials get damaged to repair it.
"An interesting vision is that these living materials still possess self-growing properties," Wang said. "When there is damage to these materials, we can introduce bacteria to grow the materials back. For example, if we use them in a bridge, we can repair damages when needed."
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