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Could Infrastructure Grow and Heal Itself?

By Kevin Wilcox

A new program seeks to capitalize on advances in biological engineering to develop living building materials.

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DARPA is inviting researchers to develop biology-based construction materials—for both defense and civil applications—that can be “grown” on-site and repair themselves if damaged. DARPA

August 23, 2016—What if such building materials as structural beams or roofing tiles could be grown on the work site and repair themselves when they are damaged over the entire design life of a structure? That's the bold question that researchers are asking through a new project headed by the Defense Advanced Research Projects Agency (DARPA).

DARPA is an agency of the U.S. Department of Defense charged with developing new technologies to ensure that the U.S. military maintains a technological advantage in the world. This new program, known as engineered living materials (ELM), seeks to capitalize on scientific advances in biological engineering to create a new class of building materials that is, essentially, a living system.

This will represent a significant step forward from the current state-of-the-art in biological engineering, which typically employs such microbes as bacteria and yeast to produce fuel oil, chemicals, fragrances, flavorings, or pharmaceuticals, according to Justin Gallivan, Ph.D., a program manager in DARPA's Biological Technologies Office. In those applications, the living system functions as a novel means of production that is powered by such inexpensive energy sources as sugar or solar power.

A step closer to what DARPA hopes to produce with the ELM program is the packing material created when mycelium fungus is introduced into a molded form filled with a substrate of agricultural waste products. The mycelia consume part of the substrate, bind the rest together, and fill the mold. But in that instance, the mycelia are subjected to heat to stop growth.

"You take something that is alive, with potentially many great properties, and then you turn them all off by heat curing it and rendering it inert," Gallivan explains. "So we started thinking about, 'What if we could leverage the living system as actual building blocks themselves?' We're futurists here—we like to think about what ultimately might be possible."

Growth and self-healing are two natural properties that the ELM program is especially interested in harnessing for this new generation of building materials. Gallivan likens the former quality to the ability to ship a plywood "seed" to a remote site and grow the finished product rapidly. Because the Department of Defense ships large quantities of heavy, low-value materials, the time and expense saved would be significant. It could also reduce the number of convoys transporting supplies across dangerous terrain. Self-healing building materials would further reduce the need for shipping materials that might be used to repair or replace damaged materials and could extend the life span of infrastructure.

The ELM program also seeks to incorporate into this new type of building material the efficiencies of strength and structure that many natural materials—think spider's silk or butterfly wings—possess. Some natural materials made from weak proteins are, pound for pound, stronger than steel. "Biology is very crafty," Gallivan says. "We don't have to build things out of steel or titanium to get these incredible properties."

The first step to developing such a material is likely to involve a hybrid in which researchers develop a more conventional scaffolding material that will support the living matter that provides the growth and healing properties of the component. Eventually, however, the goal of the ELM program is to control how cells grow, divide, and organize to produce the desired three-dimensional structures.

A central question that researchers will face as they move toward that goal is how best to control and eventually stop the growth of living cells while leaving them alive. Another key question is how "alive" the living material might be. For instance, a material might contain spores that are dormant in a dry state and become active when sprayed with water, or could contain plant matter that needs a steady supply of nutrition and sunlight.

"We are not being particularly prescriptive," Gallivan explains. "A lot of that is going to be determined by the performers who ultimately do the work. At DARPA we often say that we are looking for a capability. We know what capability it is that we want, but we are not going to prescribe how you have to produce it.

"I suspect we will see a mixture of people who are approaching this from different angles," he says. "Some will be interested in using plant cells, some will be interested in using microbes. We are interested, really, in all potential approaches to the problem."

DARPA released a broad agency announcement  earlier this month describing the goals of the program, and the deadlines for abstracts and full proposals from researchers and developers, which vary by phase and research track. Potential researchers are expected to focus on solutions that are scalable for production.

DARPA is not interested in very expensive, one-time-only, or small-scale solutions, Gallivan emphasizes. "There must be a potential to scale it up to something that would be useful for building," Gallivan says.

"At DARPA, we think about what is possible. We try to develop advanced capabilities. We are comfortable with absorbing the technical risk," he says. "This is a really, really hard thing to do. We know that. That's why we are doing it. We think that if it's successful, [it] really opens up a new space for how we design and build."


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