
(Nanowerk News) The coming decades present many challenges for our built environments: the rising global population coupled with increasing urbanization; crumbling infrastructure and dwindling resources to rebuild it; and the increasing pressure of a changing climate, to name a few.
To become more livable to more people, cities themselves must become smarter, with buildings, bridges and infrastructure that are no longer static but dynamic, able to adapt and respond to what is happening around them. If not exactly alive, these structures must be life-like, in important ways. And for that, they need to include living materials.
“Engineers and scientists have been working for hundreds of years using so-called smart materials,” said Zoubeida Ounaies. “Piezoelectricity was discovered in the 1880s.” Smart materials can understand and respond to their environment, he explained, “but they often require an external control system or power source. Living materials that adapt, respond to the environment, self-energize, and regenerate -or—the way nature’s materials are made—is the next logical step.”
Ounaies, a professor of mechanical engineering at Penn State, is the director of the Convergence Center for Living Multifunctional Material Systems, a research partnership between Penn State and the University of Freiburg in Germany. Known as LiMC2, the center is one of only a few in the world focused on this emerging field.
A new paradigm: Materials inspired by nature
Living materials, Ounaies explained, are engineered materials inspired by nature. Sometimes they even include biological elements. Their dynamic properties, at any rate, enable them to adapt to changes in their environment, responding to external stimuli. They can change, heal themselves, even make simple decisions.
Ounaies’ counterpart in Freiburg is Jurgen Ruhe, director of the Cluster of Excellence in Living, Adaptive and Energy-autonomous Materials Systems (livMatS). In a webinar last summer Ruhe said this way: “When we look at materials today, one of the most important features is that materials have properties that do not vary with time. But if we return to our view of nature, nothing is constant. For living systems, adaptation is the key to survival. The goal of our livMatS cluster is to create systems of materials that can adapt to changes the environment based on sensory input and then develop throughout their lives.
Importantly, Ounaies says, living materials are multifunctional. Not only does it provide strength or elasticity or hardness, it reduces environmental impacts and improves health; they monitor their own condition, and when used up they can be recycled or reabsorbed. They harvest energy from their environment, store it, and use it for what they need. They do these things, at best, while moving themselves and without external sensors or motors.
Above all, perhaps, engineered living materials aim to be sustainable. “The concept requires us to look at the entire life cycle,” Ounaies said. “To think about the starting material, the extraction and manufacturing processes, the waste generated, the energy required.” Design should account for everything. Therefore, unlike many smart materials, living materials do not place a harmful load on the environment.

“If you think about it,” he said, “adaptive behaviors happen in nature all the time. Maybe not in material form, but certainly in systems. There are plant systems that do it. There are animals that do it. in it.” Nature does the original work of design. “For example, when one investigates the hierarchical pattern of a mollusk shell or the intricate structure of a bird’s wings, one is inspired to use it in the human structures in ways that combine multiple uses.”
Thomas Speck has been fascinated by biomimetics for 30 years. Trained as a biophysicist, Speck is now professor of botany at the University of Freiburg. He studies the functional morphology of plants—the relationship between structure and function—and how these “biological role models” can be applied to the world of technology. As the director of the University’s Botanic Garden, he has over 6,000 species from which to find his inspiration.
Plants, says Speck, have important lessons to offer. “First, they are mobile, although their movements are often hidden from us,” he explained. “Many plant movements are beautiful—think of the opening of a flower. We want to transfer these aesthetics to our architectural solutions. ”

Plus, Speck says, plants work their magic with a limited amount of structural materials. “Cellulose, hemi-cellulose, lignin, a little pectin. Three polysaccharides and a complex polyaromatic polymer. With these materials, all of which are easy to recycle, they are able to create unique structures, unique systems that work very well.
A simple example is the pine cone, whose paddle-shaped scales open and close in response to changes in ambient humidity. At the Botanic Garden, Speck and his colleagues analyzed fossilized pinecones that were 50 million years old and found that they still performed like modern specimens. “And it doesn’t cost energy, because changes in humidity are carried by sunlight,” he said.
As surprisingly robust as a natural mechanism is, the pinecone is only reactive, Speck said. “If it’s wet, it’s closed. If it’s dry, it’s open.” Adapting this principle, he said, “We want to design systems that are interactive, that can combine actions, that make decisions. Biomimetics for us means that we get inspiration from nature and then reinvent nature too. We don’t copy it. We want to combine the best of both worlds: living nature and technologies.
A center for living materials was born
Engineering living materials requires a daunting combination of skills: in biology, materials, engineering, and design, to name a few. This is exactly the kind of problem Penn State’s interdisciplinary institutions are set up to solve. LiMC2 began when the directors of two of the institutes, Tom Richard of the Institutes for Energy and the Environment and Clive Randall of the Materials Research Institute, saw this emerging field as one in which the University could excel.