The city that Mother Nature built

Unfortunately, we’ve chosen to build our cities out of two completely unsustainable materials: steel and concrete. If we want to lower carbon emissions we are going to have to invent new materials pretty quickly. Could looking to nature hold the key? We find out more

Pretty much ever since we stopped using branches and twigs to build homes, we’ve thought of concrete and steel as the materials of choice when it comes to construction. But these materials are responsible for as much as a tenth of worldwide carbon emissions, so we have two choices: either we start producing steel and concrete in more energy-efficient ways, or we create new building materials to take their place.

Ask the US’ Defence Advanced Research Projects Agency (DARPA) or University of Cambridge bioengineer Michelle Oyen what they think the cities of tomorrow will be made of, and they might answer bone, bark, egg shells or spider’s silk.

DARPA and Oyen are part of a growing movement that sees biomimicry, or the principle of seeking sustainable solutions to human challenges by emulating nature’s time-tested patterns and strategies, as the future of construction.

The benefit of letting nature guide our construction techniques is obvious. For example, despite knowing its cost to the environment we use steel because it’s really good at taking tension, but spider’s silk is stronger than steel and more flexible – because it is a perfectly designed composite of proteins. It makes sense then that we stop using steel and prop buildings up with spider’s silk; apart from anything else who wouldn’t want to live in a city that looks like Spiderman has had a particularly busy night of webslinging. The reason we don’t is because the construction industry is set in its ways, and we believe we can ‘green’ steel. But why bother when nature has already given us a better alternative?

Disrupting construction

“The construction industry is a very conservative one,” said Oyen in a statement. “All of our existing building standards have been designed with concrete and steel in mind. Constructing buildings out of entirely new materials would mean completely rethinking the whole industry. But if you want to do something really transformative to bring down carbon emissions, then I think that’s what we have to do. If we’re going to make a real change, a major rethink is what has to happen.”

Featured image courtesy of eVolo

Featured image courtesy of eVolo

If we want to move to a more sustainable future then some of our preconceptions about construction are going to have to be disrupted. The principal assumption that has to change is: just because we can make buildings out of concrete and steel, doesn’t mean we have to or we should. The cement industry, for example, is one of the world’s most polluting, accounting for 5% of man-made carbon-dioxide emissions each year, as making and transporting concrete puts a massive burden on the environment.

There seems to be little desire to change. Retrofitting old kilns to improve thermal efficiency could lower concrete manufacturers’ energy usage by two-fifths, according to the Carbon Disclosure Project, but even this would only represent symbolic greening.

What is needed is drastic change, and what could be more dramatic than replacing concrete and steel with bone? While bone cities may seem haunting at first glance, bone is stronger than steel, and just one cubic inch of it can bear a load four times greater than concrete. Bone gets its strength from having a roughly equal ratio of proteins and minerals – the minerals give bone stiffness and hardness, while the proteins give it toughness or resistance to fracture. Bones also have the advantage of being self-healing, which is another feature that engineers are trying to bring to biomimetic materials.

DARPA’s living materials

The US’ research agency, DARPA, has already realised that living materials provide many advantages, as they can be grown where needed, self-repair when damaged and respond to changes in their surroundings. The agency has recently launched the Engineered Living Materials (ELM) programme to create a new class of materials that combine the structural properties of traditional buildings with the added benefits that living systems provide.

Imagine that instead of shipping finished materials, we can ship precursors and rapidly grow them on site using local resources

“The vision of the ELM programme is to grow materials on demand where they are needed,” said ELM programme manager, Justin Gallivan. “Imagine that instead of shipping finished materials, we can ship precursors and rapidly grow them on site using local resources. And, since the materials will be alive, they will be able to respond to changes in their environment and heal themselves in response to damage.”

Being able to construct with living materials could offer significant benefits; however, DARPA has commenced its ELM programme because it concluded that scientists and engineers are currently unable to easily control the size and shape of living materials in ways that would make them useful for construction. But Oyen and her team at the Oyen Lab (which came into being in 2006 at Cambridge University’s Engineering Department) have been constructing small samples of artificial bone and eggshell, which they believe could be scaled up and used as low-carbon building materials.

Oyen’s laboratory

“What we’re trying to do is to rethink the way that we make things,” said Oyen. “Engineers tend to throw energy at problems, whereas nature throws information at problems – they fundamentally do things differently.”

Oyen cites eggshells as an example of nature doing something totally different that we can mimic. “If you look at a chicken, they go from zero to eggshell in 18 hours,” said Oyen in an interview with the Guardian. “It’s almost a millimetre thick, 95% ceramic and it has this organic component that makes it very tough. The whole thing has been put down in an extremely short period of time, at an ambient pressure and at body temperature, barely above ambient temperatures.”

Nature has already given us an idea of the kinds of resilient and sustainable materials that could be used to build the cities of the future. Oyen’s eggshells are already much more resistant to fracture than manmade ceramic. The experiments being carried out by Oyen and DARPA will hopefully contribute to the construction industry taking the way nature creates sustainable structures and putting this knowledge into practical use. Then we may well see skyscrapers made out of bone and eggshell.

factor-archive-28“From a timeline perspective,” said Oyen, “for the last 10 years we’ve been trying to figure these things out. We’ve probably still a few more years to go and then maybe the following decade will be taking all the things we’ve learned and being able to apply them to making new materials.”

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Beyond biomimicry: Scientists find better-than-nature run style for six-legged robots

Researchers have found a running style for six-legged robots that significantly improves on the traditional nature-inspired method of movement.

The research, conducted by scientists at the École Polytechnique Fédérale de Lausanne (EPFL) and the University of Lausanne (UNIL) in Switzerland, found that as long as the robots are not equipped with insect-like adhesive pads, it is faster for them to move with only two legs on the ground at any given time.

Robotics has in the past few years made heavy use of biomimicry – the practice of mimicking natural systems – resulting in six-legged robots being designed to move like insects. In nature, insects use what is known as a tripod gait, where they have three legs on the ground at a time, so it had been assumed that this was the most efficient way for similarly legged robots to move.

However, by undertaking a series of computer simulations, tests on robots and experiments on Drosophila melanogaster – better known as the common fruit fly – the scientists found that the two-legged approach, which they have dubbed the bipod gait, results in faster and more efficient movement.

The core goal of the research, which is published today in the journal Nature Communications, was to confirm whether the long-held assumption that a tripod gait was best was indeed correct.

“We wanted to determine why insects use a tripod gait and identify whether it is, indeed, the fastest way for six-legged animals and robots to walk,” said Pavan Ramdya, study co-lead and corresponding author.

Initially, this involved the use of a simulated insect model based on the common fruit fly and an algorithm designed to mimic different evolutionary stages. This algorithm simulated different potential gaits to create a shortlist of those that it deemed to be the fastest.

This, however, shed light on why insects have a tripod gait – and why it may not be the best option for robots. The simulations showed that the traditional tripod gait works in combination with the adhesive pad found on the ends of insects’ legs to make climbing over vertical surfaces such as rocks easier and quicker.

Robots, however, are typically designed to walk along flat surfaces, and so the benefits of such a gait are lost.

“Our findings support the idea that insects use a tripod gait to most effectively walk on surfaces in three dimensions, and because their legs have adhesive properties. This confirms a long-standing biological hypothesis,” said Ramdya. “Ground robots should therefore break free from only using the tripod gait”.

Study co-lead authors Robin Thandiackal (left) and Pavan Ramdya with the six-legged robot used in the research. Images courtesy of EPFL/Alain Herzog

To for always corroborate the simulation’s findings, the researchers built a six-legged robot that could move either with a bipod or tripod gait, and which quickly confirmed the research by being faster when moving with just two legs on the ground at once.

However, they went further by confirming that the adhesive pads were in fact playing a role in the insect’s tripod movement.

They did this by equipping the fruit flies with tiny polymer boots that would cover the adhesive pads, and so remove their role in the way the insects moved. The flies’ responses confirms their theory: they began moving with a bipod-like gate rather than their conventional tripod-style movement.

“This result shows that, unlike most robots, animals can adapt to find new ways of walking under new circumstances,” said study co-lead author Robin Thandiackal.

As bizarre as the research sounds, it provides valuable new insights both for roboticists and biologists, and could lead to a new standard in the way that six legged robots are designed to move.

“There is a natural dialogue between robotics and biology: Many robot designers are inspired by nature and biologists can use robots to better understand the behavior of animal species,” added Thandiackal. “We believe that our work represents an important contribution to the study of animal and robotic locomotion.”