Can bacteria make stronger cars, airplanes and armor?
Researchers harness the power of living organisms to make materials that
are strong, tolerant and resilient

Date:
February 22, 2021
Source:
University of Southern California
Summary:
Biological systems can harness their living cells for growth and
regeneration, but engineering systems cannot. Until now.Researchers
are harnessing living bacteria to create engineering materials
that are strong, tolerant, and resilient.



FULL STORY ========================================================================== Biological systems can harness their living cells for growth and
regeneration, but engineering systems cannot. Until now.


========================================================================== Qiming Wang and researchers at the USC Viterbi School of Engineering
are harnessing living bacteria to create engineering materials that are
strong, tolerant, and resilient. The research is published in Advanced Materials.

"The materials we are making are living and self-growing," said Wang,
the Stephen Schrank Early Career Chair in Civil and Environmental
Engineering and assistant professor of civil and environmental engineering
in the Sonny Astani Department of Civil and Environmental Engineering
(CEE). "We have been amazed by the sophisticated microstructures of
natural materials for centuries, especially after microscopes were
invented to observe these tiny structures.

Now we take an important step forward: We use living bacteria as a tool
to directly grow amazing structures that cannot be made on our own."
The researchers work with specific bacteria -- S. pasteurii -- known
for secreting an enzyme called urease. When urease is exposed to urea
and calcium ions, it produces calcium carbonate, a fundamental and
strong mineral compound found in bones or teeth. "The key innovation
in our research," said Wang, "is that we guide the bacteria to grow
calcium carbonate minerals to achieve ordered microstructures which are
similar to those in the natural mineralized composites." Wang added:
"Bacteria know how to save time and energy to do things. They have their
own intelligence, and we can harness their smartness to design hybrid
materials that are superior to fully synthetic options.

Borrowing inspiration from nature is not new in engineering. As one would suspect, nature has great examples of complex mineralized composites
that are strong, fracture resistant, and energy damping -- for example
nacre or the hard shell surrounding a mollusk.



==========================================================================
Wang said: "Although microorganisms such as bacteria, fungi and viri are sometimes detrimental in causing diseases -- like COVID-19 -- they can
also be beneficial. We have a long history of using microorganisms as
factories -- for example, using yeast to make beer. But there is limited research on using microorganisms to manufacture engineering materials." Combining living bacteria and synthetic materials, Wang said this new
living material demonstrates mechanical properties superior to that of
any natural or synthetic material currently in use. This is largely
due to the material's bouligand structure, which is characterized by
multiple layers of minerals laid at varying angles from each other to
form a sort of "twist" or helicoidal shape. This structure is difficult
to create synthetically.

Wang worked in collaboration with USC Viterbi researchers An Xin,
Yipin Su, Minliang Yan, Kunhao Yu, Zhangzhengrong Feng, and Kyung Hoon
Lee. Additional support was provided by Lizhi Sun, professor of civil engineering at the University of California, Irvine, and his student
Shengwei Feng.

What's in a Shape? One of the key properties of a mineralized composite,
Wang said, is that it can be manipulated to follow different structures or patterns. Researchers long ago observed the ability of a mantis shrimp to
use his "hammer" to break open a muscle shell. Looking at his "hammer" --
a club-like structure or hand -- more closely, they found it was arranged
in a bouligand structure. This structure offers superior strength to
one arranged at more homogenous angles -- for example alternating the
lattice structure of the material at 90 degrees with each layer.



========================================================================== "Creating this structure synthetically is very challenging in the field,"
Wang said. "So we proposed using bacteria to achieve it instead."
In order to build the material, the researchers 3-D printed a lattice
structure or scaffolding. This structure has empty squares within it and
the lattice layers are laid at varying angles to create scaffolding in
line with the helicoidal shape.

The bacteria are then introduced to this structure. Bacteria intrinsically
like to attach to surfaces and will gravitate to the scaffolding,
grabbing on to the material with their "legs." There the bacteria will
secrete urease, the enzyme which triggers formations of calcium carbonate crystals. These grow from the surface up, eventually filling in the tiny squares or voids in the 3-D printed lattice structure. Bacteria like
porous surfaces, Wang said, allowing them to create different patterns
with the minerals.

The Trifecta "We did mechanical testing that demonstrated the strength
of such structures to be very high. They also were able to resist crack propagation -- fractures - - and help dampen or dissipate energy within
the material," said An Xin, a CEE doctoral student.

Existing materials have shown exceptional strength, fracture resistance,
and energy dissipation but the combination of all three elements has
not been demonstrated to work as well as in the living materials Wang
and his team created.

"We fabricated something very stiff and strong," Wang said. "The immediate implications are for use in infrastructures like aerospace panels and
vehicle frames." The living materials are relatively lightweight, also offering options for defense applications like body armor or vehicle
armor. "This material could resist bullet penetration and dissipate
energy from its release to avoid damage," said Yipin Su, a postdoc
working with Wang.

There's even potential for these materials to be reintroduced to bacteria
when repairs are needed.

"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." ========================================================================== Story Source: Materials provided by
University_of_Southern_California. Original written by Avni Shah. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. An Xin, Yipin Su, Shengwei Feng, Minliang Yan, Kunhao Yu,
Zhangzhengrong
Feng, Kyung Hoon Lee, Lizhi Sun, Qiming Wang. Growing Living
Composites with Ordered Microstructures and Exceptional Mechanical
Properties.

Advanced Materials, 2021; 2006946 DOI: 10.1002/adma.202006946 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/02/210222095038.htm

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