Engineers learn lessons from nature to devise better devices and materials.
Courtney Humphries
After long lagging behind MIT and other schools in engineering, Harvard has been beefing up its engineering research efforts over the last 10 years. A major area of growth has been at the interface between engineering and biology. Harvard’s bioengineering faculty members, many of them young recruits, span disciplines and draw on biology, engineering, computer science, and materials science. Some look to nature, which has evolved ways to create complex materials and organisms, to guide their efforts in coming up with novel materials and devices. Here are a few examples.
Following the herd
Radhika Nagpal, a computer scientist with a longstanding interest in biology, joined the Harvard faculty as an assistant professor in computer science in 2004 after completing a PhD and postdoc at MIT. Nagpal studies self-organizing systems in nature—where individual entities such as cells, insects, or people cooperate to accomplish a larger task—and looks for ways to apply that knowledge to the design of new technologies, such as groups of robots that work together.
The cells of the heart, for instance, contract together to create a single heartbeat, and fireflies synchronize their flashes of light. Nagpal and her colleagues drew upon these principles of self-organizing synchronization to address the simple problem of computers that operate out of synch with each other. Using algorithms derived from the activity of heart cells, her team programmed a network of computers to gradually reach synchronization, one step towards getting them to perform tasks in a coordinated fashion. Using a reverse approach, they programmed computers to desynchronize into a “round robin” pattern as they sent information over a wireless network; by taking turns, the computers avoided network traffic jams.
Drew Endy, a bioengineer at MIT, says that Nagpal’s work adds a new dimension to computer programming. “Most computer programs don’t change the physical world; they operate over time,” he says. “Radhika is thinking about programs that operate in space,” like the biological program that allows a tree to grow from a seed. This distinction, he adds, makes Nagpal one of only “a handful of people in the world who recognize that this is an important problem to solve.”
Studying nature’s materials
Joanna Aizenberg, who left Bell Laboratories to become a professor of materials science at Harvard last summer, also sees biology as an inspiration. Aizenberg uses engineering tools to study materials in nature and then exploits that knowledge to develop better materials. Biological materials have several properties that manmade ones lack: they can respond to the environment, heal themselves after injury, and rearrange dynamically.
She is interested in the inorganic materials that biological organisms create, such as skeletons and shells. These structures do more than just provide structure and strength. A few years ago, Aizenberg and colleagues found that the outer skeleton of brittlestars, a close relative of starfish, contains near-perfect arrays of tiny lenses that sense light. In this case, she says, “nature can teach us serious lessons about how to design inorganic materials with optical properties that are well beyond what we make.” The lenses are equipped with, in effect, their own built-in sunglasses: a network of channels through which the brittlestar pumps pigments to cover the lenses during the day, and removes the pigments at night. Based on their studies of the brittlestar, Aizenberg and colleagues created arrays of tiny lenses with microfluidic pigment systems. Microlens arrays are currently used in digital photography and many other technologies; these “tunable” lens arrays could one day use dyes to change their optical properties or reduce their transmission of light.
Shaping an environment for stem cells
Debra Auguste studies a key question in developmental biology—how embryonic stem cells differentiate into various cell types—from an engineering perspective. Many stem cell biologists focus on identifying the chemical signals that guide a stem cell down different paths. But Auguste looks at the cells’ physical environment to figure out how those signals vary over time and space and how those variations may be causing stem cells to specialize into such a variety of cell types. Auguste, who did postdoctoral work at MIT before coming to Harvard two years ago, uses microfluidics technology to test how stem cells respond to varying gradients of biochemical signals.
The goal is to find ways to control stem cell differentiation and increase the yield of the desired cell type. Rather than just identifying chemical signals, Auguste focuses on developing scaffolds on which to grow cells; these structures would imitate the cells’ natural physical environment, including the delivery of the chemical signals at just the right place and time.
(All photos courtesy of Harvard School of Engineering and Applied Sciences)
