At Wake Forest University in North Carolina, scientists recently grew a human ear in a petri dish. They first used cellular material and a 3D printer to create the cartilage for the ear.
Then they grew the ear – complete with the blood vessels needed to keep it alive – using a synthetic material designed to mimic human skin.
The breakthrough, a major step forward for medical science, promises to help people injured in accidents or suffering from severe burns. But the Wake Forest ear also significantly advanced the science of engineered materials: In many respects, the scientists produced the ear in the same way nature does, first by growing a scaffold out of rigid material and then by giving instructions to the synthetic skin material to assemble itself in response to various chemical triggers.
For those of us who work in materials science, the combination of organic and synthetic materials, 3D printing and natural growth, all arranged by a set of instructions encoded like human DNA, is the realization of a long-held goal. But the potential uses of engineered materials stretch far beyond the world of medicine.
A wide range of high-tech manufacturing industries is creating demand for made-to-measure materials that can be engineered to deliver a level of targeted performance that existing materials simply can’t match. And now materials science and computer science are teaming up to help researchers answer the call, fast and sustainably.
THE SUSTAINABILITY IMPERATIVE
Humanity’s creations require tremendous amounts of energy and generate massive amounts of waste. Think of the rubble generated during construction of a new skyscraper or the energy consumed in manufacturing a product. In contrast, nature creates new organisms with minimal energy and waste, optimizes them to their environments and makes them fully recyclable. If we can draw clues from nature, we can better position ourselves to solve most of the man-made sustainability issues threatening our planet and provide abundance for a rapidly growing population.
Of course, it took nature 4 billion years to develop amazing materials such as wood and lobster shells through the painfully slow, trial-and-error process of evolution. Obviously, it’s not practical to wait 4 billion years to develop the new materials that can help humanity be less wasteful.
Instead, scientists have created software that mimics evolution in a virtual environment, a process we call in silico because the simulations happen in a computer. Instead of the time-consuming trial-and-error approach that tests thousands of possible combinations in a laboratory and discards what doesn’t work, the software’s sophisticated machine-learning capabilities identify the most promising combinations for a specific purpose in a matter of minutes.
“IF WE CAN DRAW CLUES FROM NATURE, WE CAN BETTER POSITION OURSELVES TO SOLVE MOST OF THE MAN-MADE SUSTAINABILITY ISSUES THREATENING OUR PLANET AND PROVIDE ABUNDANCE FOR A RAPIDLY GROWING POPULATION.”
Nature has given us the blueprint; the confluence of supercomputing and data science has given us the means to accelerate the process and to direct it toward a set of pre-defined characteristics. Together, material scientists at the Institute for Materials at the Georgia Institute of Technology (Georgia Tech) and experts at Dassault Systèmes are teaming up to enable this new science.
LIMITED BUILDING BLOCKS, ENDLESS VARIATIONS
One of nature’s wonders is that it builds millions of different configurations of molecules and associated material systems from just four primary elements: carbon, hydrogen, nitrogen and sulfate (plus minute amounts of a few common metals). Nature combines these elements to create 20 amino acids. From this small toolset, it engineers more than 100,000 different proteins, which it assembles into millions of wildly varied life forms with billions of unique characteristics.
By studying how nature assembles its organisms, scientists are learning how to engineer new materials with similar characteristics from these same basic building blocks. For example, scientists have long been fascinated by the sea cucumber, a marine animal that changes its leathery skin from soft to hard in response to the changing temperatures and acidity of its ocean environment. Now, a US government lab is working to mimic this capability in aircraft design, enabling the wings of a plane to be rigid for takeoffs and landings, then become more pliable when it encounters turbulence. Increased wing pliability will allow the aircraft to glide smoothly through rough air, improving passenger comfort.
Another common quality of natural materials is self-healing. Break a bone and it becomes inflamed. In reaction, the body sends blood and stem cells to the fracture site, lays down a compound called callus and begins the healing process. Similarly, scientists have created synthetic materials with a vascular system that pumps “healing” agents to damaged parts of the material. Fluids such as resin and a hardener, which react when they mix, automatically seal the cracks to execute the repair.
CLOSING THE KNOWLEDGE GAP
Today, new solutions to old challenges are being created in mind-boggling ways. For example, developing more powerful, longer-lasting battery technologies is critical to many fields, including electric-powered cars. Current battery technologies, however, rely on corrosive chemicals and become dangerous waste at the end of their useful lives.
Rather than look for a new combination of current-generating metals, Angela Belcher and her colleagues at the Massachusetts Institute of Technology (MIT) engineered a harmless virus to “grow” high-powered batteries. The team used a bactirophage, a special kind of virus that infiltrates bacteria. Instructions implanted in the phage’s DNA instructed the bacteria to collect carbon tubes a billionth of an inch wide and then use them to grow a battery electrode. For the first time, Belcher and her colleagues succeeded in creating batteries that can be “grown” at room temperature on a biological scaffold.
Although experiments like these are yielding significant advances, much work remains. We understand how basic compounds assemble at the nano level, but we need to discover more at the meso-level, the in-between range of length scales where cells exist. Using a combined strategy of multiscale modeling and experimentation, and by advancing the new field of materials data science and informatics, Georgia Tech’s Institute for Materials is leading efforts to model relations among synthesis, processing and accessible material structures at the meso-level, as well as effects of these meso-level structures on material properties and performance.
Numerous properties and responses emerge from the meso-level structure of materials, including strength, ductility, fracture resistance and toughness, energy emissivity, friction, light and color. Georgia Tech’s Center for Biologically Inspired Design, meanwhile, explores evolutionary adaptation as a source for materials design inspiration.
Spider thread is a good example of the potential benefits of meso-scale research. The material is incredibly strong and tough but very flexible. Engineers have created synthetic spider silk, but only in volumes sufficient for small structures. With more understanding of the meso-level, we can create algorithms that will show us how to “scale” spider silk for use in massive structures such as bridges and scaffolding.
IN PURSUIT OF A LIMITLESS FUTURE
Our world faces constraints on energy, raw materials and methods of waste disposal, requiring more efficient alternatives to traditional materials and methods.
“BY STUDYING HOW NATURE ASSEMBLES ITS ORGANISMS, SCIENTISTS ARE LEARNING HOW TO ENGINEER NEW MATERIALS WITH SIMILAR CHARACTERISTICS FROM THESE SAME BASIC BUILDING BLOCKS.”
In response, scientists are asking: Can we find materials that assemble themselves and self-repair when damaged, using only minimal energy? Can we create biomaterials that help the planet become a better place to live rather than adding to the poisonous load of environmental toxins? Can we mimic nature’s processes to develop a class of truly sustainable materials? What can we learn from evolutionary adaptation to guide the way new and improved materials are made?
Increasingly, powerful computing technologies coupled with machine learning are helping scientists to discover and create new materials in months or years, not eons. Humanity and nature are the clear beneficiaries of this grand mission.
David L. McDowell is Regents’ Professor, Carter N. Paden Jr. Distinguished Chair and Executive Director of the Institute for Materials at the Georgia Institute of Technology. Reza Sadeghi is Chief Strategy Officer for Dassault Systèmes’ BIOVIA brand, which develops solutions for the process and life sciences industries.