The human desire to create larger and more impressive structures is insatiable. The Egyptian pyramids, the Great Wall of China and Burj Khalifa in Dubai are the tallest structures in the world today (828 meters) - all this is the result of the work of people who squeeze the maximum out of the engineering possibilities of their time. However, high buildings are not only monuments to human ambitions: they can play a key role in the development of mankind in the epoch of the space age.
Today, proposals for building a "space elevator" are being widely discussed: a freestanding tower capable of reaching the Earth's geostationary orbit. Such a tower could become an alternative to rocket transport and significantly reduce the energy costs required to get into space. Moreover, we can imagine the emergence of multikilometre solar-powered space mega-engineering facilities, possibly covering entire planets or even stars.
In recent years, engineers have been able to build much larger structures thanks to the strength and reliability of modern materials, particularly new steel alloys. But when it comes to mega-structures - buildings a thousand kilometers high and higher - maintaining safety and structural integrity becomes a diabolical challenge. This is due to the fact that the higher the structure, the more mechanical stress it experiences because of its size and weight. ("Mechanical stress" arises, for example, when you stretch or compress something. "Strength" is the maximum mechanical stress that a building can withstand before it collapses.)
It turns out that biological design, the result of almost four billion years of experience, can help solve the problem. Prior to material science, engineers had to observe nature in search of unusual solutions to overcome the limitations of their materials. Thus, ancient civilizations built their military equipment, recreating the structure of tendons with the help of stretched animal skins. The obtained mechanism could be stretched and compressed to launch a projectile into the enemy. But then came materials such as steel and concrete, which were much stronger and lighter than their predecessors.
All this led to the emergence of a sub-discipline of "reliability engineering". The designers began to develop structures that were much stronger than the maximum possible load for which they were designed, which meant that the mechanical stress in the materials remained in a range where the possibility of breakage was as low as possible. But, according to the calculations, as soon as the structures are turned into mega structures, the risk reduction and safety approach imposes a limit on the possible size of the building. Mega-structures necessarily squeeze the maximum out of the materials used, which does not allow to keep the mechanical stress at an acceptable level.
However, neither bones nor tendons in our bodies are within the limits of permissible risk. In fact, they are often squeezed and stretched beyond the level at which they are supposed to break. Nevertheless, the parts of the human body are still more "reliable" than the strength of the materials suggests. For example, even a simple run can load an Achilles tendon by more than 75% of its strength, and weightlifters can load the lumbar spine by 90% when they lift hundreds of kilograms.
How does biology handle such loads? The answer is that our body is constantly repairing and reproducing the materials it consists of. Collagen fibres in the tendons are replaced in such a way that as long as some of the fibres are damaged, the tendon is generally intact. This permanent self-healing is efficient, cost effective, and can vary depending on the load. Of course, all the structures and cells in our bodies are constantly being replaced; according to some estimates, almost 98% of the atoms in the human body change within a year.
Recently, we have applied this self-healing paradigm in practice to find out if it is possible to build a reliable space elevator using available materials. Our proposed design is based on a ninety one thousand kilometer long cable (rope) that starts at the equator and ends in space, where the counterweight will be located. The rope will consist of bundles of parallel fibers that follow the structure of collagen fibers in the bones, but are made of Kevlar, the material used to create body armour. Using sensors and artificial intelligence software, it will be possible to recreate the model so that it can mathematically predict when, where, and how the fibers will break. In this case, when this happens, special robots moving along the entire rope will be able to replace them according to the level of damage and maintenance required, imitating the sensitivity of the biological process. Although the tower will be subjected to more mechanical stress than the materials it consists of can withstand, the structure will be reliable and will not require excessive replacement costs. Moreover, the necessary material strength required to maintain structural stability has been reduced by an impressive 44%.
This biology-inspired approach to engineering can also be useful on Earth, for example in the construction of bridges and skyscrapers. By "challenging" our materials and equipping systems with stand-alone replacement and repair mechanisms, we can both go beyond the constraints of construction and improve the reliability of future buildings. To understand all the advantages of working with materials that are on the verge of their mechanical stress limit, take a look at the suspension bridges with their wavy iron ropes. The main problem with increasing the length of this bridge is that as the length of the ropes increases, their weight increases, resulting in their breaking under their own weight. If the rope is stretched no more than 50% of its ultimate strength, the maximum length of the bridge is four kilometres; but if the tensile stress is increased to 90%, the possible length will increase significantly and can reach more than seven and a half kilometres. However, in such a case, in order to maintain the safety of the bridge, it is necessary to establish the process of replacement of steel wire rope fibers according to the principle of biological systems.
Mega-structures are no longer science fiction. The fall of the Tower of Babel, as described in the Old Testament, never stopped people. We continued to build and build more, higher and faster, thanks to the new opportunities that science and technology give us. And yet, according to the standards of classical engineering in terms of reliability, we are still far from building structures with a height of space. We need to use a new paradigm that focuses not so much on the strength of the materials as on the inherent regenerative potential of the systems. There is no need to follow it far: it is enough to simply study the gift that biological life around us has given us. And believe me, people have something to learn from the long history of evolution.