ILP Institute InsiderAugust 8, 2012
Envisioning Silk Stronger Than Steel
Modeling novel materials for a new era in engineering.
Markus J. Buehler likes studying the composition of things. It could be the skeletal system, orchestral music or spider webs. They all provide insight into a driving force of his work: how structures can be designed, work, and respond to challenges. With that knowledge, the Associate Professor of Civil and Environmental Engineering, Director of the Laboratory for Atomistic and Molecular Mechanics, co-Director of the Computation for Design and Optimization Program and Director of the MIT-Germany Program gains understanding into creating stronger, more accessible and less expensive building materials. The development work will ultimately be done in the lab or a factory, but the blueprint is in the outside world. “In almost anything it builds, nature uses nanotechnology,” Buehler says. “We can learn about nanoscience by studying the environment, which has helped us to find radically new solutions to design better materials by merging the concepts of ‘structure’ and ‘material’ through hierarchical architectures.”
Buehler has spent a good deal of research on spider webs, as they’re a prime example of using nanoscale science to generate heightened function at the macroscale. At first glance, the design of a web shouldn’t work, he says. It uses hydrogen bonds, which are weak. But through the use of nanostructured beta-sheet protein crystals, the threads work synergistically, stretching and then strengthening to resistant breaking. The web survives wind storms. It catches prey. And when one strand breaks, the rest stays intact. Buehler likens it to a tough piece of meat – a part can be broken off, but the majority of the steak remains.
It’s in the study of webs that Buehler uses a fundamental aspect of his work, computational modeling. Buehler has pioneered this materiomics approach in which engineering properties of a material, such as strength, toughness, or how it fails, can be predicted from the scale of a material’s building blocks, and how they are combined. The method allows engineers to probe new material architectures “in silico” – on the computer – thereby saving time and money in the design and development phases. “With the biggest computers available, it’s now possible to predict the engineering performance solely based on the chemical structure of its molecules,” Buehler says. “We can then focus on manufacturing the designs that appear most promising for applications.”
The challenge is actualizing the findings. While the spider anticipates failure and builds in resilience, modern design takes almost the opposite approach. As Buehler says, buildings, computer chips, cars or airplanes tend to be over-engineered with stress spread throughout an entire structure, making it susceptible to sudden collapse if unanticipated conditions occur. Engineers can use nanotechnology, but, as of now, it’s usually only on a basic level, a single particle in the lab. Through materiomics the understanding is there, but scientists still lack the ability to put a large structure together from the nanoscale up, Buehler says.
The hope could be in carbon nanostructures such as nanotubes, rolled two-dimensional carbon atom sheets from a layer of graphene. They’re stronger than anything in nature with reliable electrical, thermal and mechanical properties that could mimic the natural world in how they respond to failure. “They would heal itself. When they break, they will re-organize, but they will perform much better than the natural analogs from which the architecture of the materials was derived,” Buehler says. Such hierarchically organized materials would offer flexibility to numerous industries. Steel, ceramics or concrete would no longer be the only answers, and materials could be customized to a specific project. Since not as much would be needed, products would be cheaper and more efficient, such as a lighter, more economical car. “You could improve the strength by a factor of two and reduce the weight by a similar amount,” Buehler says.
Understanding the Mechanics of Disease
Buehler also looks at the processes of failure in biology. Often, a weakness and fragility develop in the progression of a disease, and, again using materiomics, Buehler studies the underlying molecular changes in order to understand how to fix them. One specific area is brittle bone disease. In his research, Buehler has worked with mice, using healthy and diseased models of bone, containing the abundant protein collagen. By creating mutations, he can see developments, such as the effects of loading, how stress is distributed and cracks eventually form.
Another study focuses on rapid aging disease. In this condition, structures in the cell become rigid since proteins end up sticking together too tightly as they become more strongly bonded. When the cell’s structure isn’t as flexible as it used to be, gene expression may be affected. Like with the bones, the hope is to understand the systemic breakdown and be able to prevent or, at least, control it. With both conditions, what Buehler is hoping to import is a different approach and perspective on handling illness, one that would allow for more focused, less invasive therapies. “It’s a mechanistic way of understanding and treating disease,” Buehler says. “If we understand the mechanics, we can target that through tailored biomaterials. Computational modeling provides that strategy to solve these complex problems.”
Listening to Words and Music
In his quest for increasing the possibilities in nanotechnology, Buehler also studies music and language. Both disciplines have building blocks that work in an abstract space but have surprising commonalities with the physical world of materials. Music has notes that when arranged in certain ways create a multitude of tones, melodies and sounds. Language uses letters that when combined with inflection and nuance result in various meanings. But while both have hierarchical structures, they’re not rigid systems, he says. People of differing abilities can play different instruments and still produce the same, recognizable piece of music. A person who doesn’t know a certain word can use others and still convey the intended meaning.
Buehler would like to take that approach and utilize the concepts in the development and organization of new, raw materials. Currently, it’s merely a concept, subject to trial and error. But Buehler says that, as with his work on spider webs and disease, it’s about connecting disparate concepts and imagining what could be, of taking this theory and developing it in a designed, repeatable, reliable way.
“You wouldn’t need iron and carbon atoms for steel. If you could use silica, you can just collect some sand from the beach and assemble the silica molecules in a clever way,” he says. If that happens, the possibilities open up – a bigger pool of raw materials to draw from; more combinations to create the best material for a project; and more efficiency. “We can now reach the ultimate limit of your materials,” Buehler says. “A lot of materials are wasted in the current engineering world. The natural world is better at that, utilizing all the pieces. We are beginning to mimic this in our designed materials and open exciting doors to innovation where the design and manufacturing of materials are tightly coupled.”