May 14, 2021

They create bricks capable of regenerating themselves



The most surprising discoveries sometimes do not come from a single scientific field, but from several. For that reason, in today’s science multidisciplinarity is promoted, the coordinated work between scientists of different specialties to contribute new ideas to already established knowledge. A good example of this is what happens when biologists and engineers work as a team: a project to create cement and bricks that are “alive”.

It all started with the discovery of biomineralization, the process by which some living organisms are capable of generating minerals from the organic matter they consume. Said in this way it may seem like a strange process and limited to a few living beings, but it is quite common. In fact, some cells of our own body do it, such as osteoblasts that generate calcium carbonate crystals during the formation of our bones.

The most common minerals that form living beings are phosphates and calcium carbonates, which are mixed with proteins such as collagen and chitin to form shells and bones. But although they are the most frequent, they are not the only ones. Biologists have found up to 55 different minerals synthesized by some living being, some as strange as deposits of copper, gold or iron created by certain bacteria.

The materials created by biomineralization usually have defense or support applications, so they are especially hard and resistant. Through the microscope it is observed that they do not have a regular frame like that of a building, but rather resemble a chaotic conglomerate of crystals, something difficult to replicate in the construction.

And it was precisely this capacity that seduced engineers in search of new building materials. If it was possible to take advantage of a material with the lightness and strength of the biological materials it could give rise to more stable and durable constructions. But the first objective of this union between engineers and biologists was to obtain one of the holy grails of engineering: a building that will repair itself.

Microscopic workers

There are many materials with which a building can be built, but each has certain limitations. Buildings made of brick are usually quite heavy and have little resistance to earthquakes, which is why in Japan no building of this material is visible. There it is preferred to build with wood, a more flexible and lightweight material.

But these two materials have the same problem: they don’t allow you to easily build buildings over five stories high. The tall brick buildings weigh too much, their base sinks under the weight of the rest of the building, and the wood, which is not especially resistant, ends up commanding. To make tall buildings, we need materials that are both light and strong, and one of the best materials today is concrete.

In a construction site you can see the process. First a wrought iron skeleton is mounted that gives a structure and shape to the building. Its function is identical to the skeleton of our body: provide a place of stability in which to hold everything. The formwork technique is then applied, in which the concrete is added in molds while it is still wet, forming columns and floors around the iron skeleton.

Concrete is a very light but resistant element, capable of staying together around the metal structure and having a tall building without costing too much money or difficulties. The only problem is that it can deteriorate before earthquakes, the passage of time or an exaggerated damage (such as an explosion in a plant). In these cases, small internal cracks are generated which are difficult to access and fill, endangering the complete integrity of the building.

To solve this problem, the engineers thought of biomineralization. There are sea sponges capable of creating silicates from sand with a consistency similar to concrete, which would be useful for closing cracks. But instead of using sponges, our current genetic engineering advances allow us to create transgenic bacteria capable of having this ability.

In this way, a special concrete was created by mixing the spores of these bacteria with the concrete. The bacteria remain dormant inside the concrete until there is a fracture. At that time, you only need a little water and glucose to feed and you can now take care of transforming the sand from the concrete remains into a hardened silicate. We will have a concrete full of microscopic workers able to regenerate, and the operators would only have to pour water into the cracking area to see how it closes in a few hours.

But there is a weak point, and that is that cement is not the best place in the world for bacteria to grow. Although they are located in the crack and have food, the temperature is not ideal and the cement does not have a good humidity so that they can live easily. For this reason, when testing this cement in real conditions, bacteria usually die before the fracture is completely closed. Even so, it is still a useful cement for small cracks and works best in countries with high humidity and temperature.

But you don’t have to despair. It is clear that this limitation is important, but perhaps we can think of another application. What if we make bricks?

The attack of the living bricks

Recently, a team of American researchers has adapted this cement to make biological bricks. It is a smart change of approach, since the bricks can be manufactured in a different place from the work site and we can take care of the building bacteria while manufacturing the brick.

With this idea, they created a “crop” of bricks, to which sand, gelatin and the strain of building bacteria are added. Bacteria use gelatin as food and support to grow freely while creating silicate, generating a solid brick with a structure and strength similar to that of concrete. Then we can give a heat treatment to the brick to eliminate ingrate way to its builders and take it to the work.

The cultivation of bricks is a much cheaper and faster process than the traditional system. In addition, it is less polluting since it requires almost no energy. It is more similar to when we leave a cake with the yeast. We leave the brick material and the bacteria take care of the process.

But best of all, these bricks can “reproduce.” We can take a brick, cut it in half and put each part in a mold the size of the original brick. If we add more sand and jelly, and wait six hours, we will have two full bricks again. This multiplies the speed of obtaining bricks in a simple way.

The expectations are good. In the study, the scientists found that the bricks that are formed are light and stable enough to be used in construction. Now they are still looking for better strains of bacteria that allow faster brick formation. Currently they use cyanobacteria, a strain known for its low cost and high resistance to abnormal temperatures, which is an addition.

With these two studies the ban is opened to think realistically in buildings with biological properties. It is possible to create a material capable of changing color with light or responding to a contaminant by eliminating it. They are abilities that have always surprised biologists for their usefulness and misleading simplicity. Now we may be able to take advantage of them for home.

DON’T KEEP IT UP:

  • The transgenic bacteria used for the study are also controlled to limit their reproduction, avoiding any possible environmental contamination.
  • We almost never come into contact with the concrete of a building. There are multiple layers of brick, paint and plaster to protect it from possible damage and bad weather. The inhabitants of a building could not easily access these bacteria nor could they affect their condition.

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