Shining a Light on Nature’s Superfast Movements

Shining a Light on Nature’s Superfast Movements

Evolution has achieved some pretty amazing feats.

By Mary Russell-Roberson

Take trap-jaw ants, for example. When they snap their mandibles together to grab prey, the motion takes a mere ten-thousandth of one second and the mandibles move at more than a hundred miles an hour. That adds up to a force equal to 300 times the ant’s body weight.

This ability to strike fast has evolved separately in at least four different groups across the ant evolutionary tree. Some species even propel themselves in the air by lowering their heads to the ground before snapping, jumping 20 times the length of their bodies to escape predators.

How can a tiny, fragile ant create forces of this magnitude?

Biologist Sheila Patek, PhD, would like to know. “We don’t know how the energy is distributed or how this happens without [the exoskeleton] breaking,” says Patek, who is the Mrs. Alexander Hehmeyer Professor of Biology.

Engineers would like to know too. “Engineers are interested in things biology can do that engineering can’t,” Patek says.

To delve into these questions, Patek has begun a new collaboration with Roarke Horstmeyer, PhD, assistant professor of biomedical engineering, who designs new tools to observe biological processes.

What they discover could help engineers design tiny devices to channel small amounts of energy over extremely short durations with precise timing and aim.

“The key physics trick these [ants] are performing is to take a small amount of energy and release it over a vanishingly short period of time,” Patek says. “This gives them tremendous power density, meaning a large amount of power per mass of the storage device.” The storage device, in this case, is the ant’s head, which deforms when the mandibles are latched into place before snapping.

Trap-jaw ants do all this using lightweight and biodegradable materials. Engineers could potentially use a wider range of materials to create similar devices. “That means we have barely tapped into engineering translation,” Patek said.

Imagine ultra-tiny robots that could deliver precise bursts of energy at exact times, perhaps even in the human body as a way of injecting medicine into specific tissues.

Patek has been studying trap-jaw ants for years, recording and quantifying their movements. The ants lock their mandibles in place and store elastic potential energy in their heads, like energy stored in a compressed spring. Then they use a trigger system to release that energy all at once in a mandible snap. But to understand how the ant’s body survives all that without breaking, Patek needs to be able to analyze the deformation of the head before, during, and after the snap.

Available cameras aren’t up to the task. Patek has a million-frames-per-second camera in her lab that can capture the movement, but only in one plane. Cameras that can record three-dimensional deformations at the scale of an ant head are too slow.

Patek needs both speed and dimensionality, but the technology to capture both didn’t exist–until Horstmeyer got involved.

When Patek and Horstmeyer first met, Horstmeyer understood right away what she needed and why it wasn’t yet possible. But he had some ideas for how he might make it so.

A few minutes into the conversation, Patek realized that Horstmeyer might be the perfect person to team up with. On his way to becoming a biomedical engineer, Horstmeyer majored in physics at Duke and did a lot of work with optics. Today, he uses his expertise to design new optical instruments that can help researchers in a variety of fields investigate thorny questions.

“In biology, there is a huge need for [new] methods for imaging, or just optical detection in general,” Horstmeyer says. “It’s so fascinating, all these different measurements and unknowns that people are after, whether it’s in ants, zebrafish, fruit flies, or the human brain.”

After that first meeting, Patek and Horstmeyer put their heads together with graduate students Clare Cook and Justin Jorge to come up with a design that uses multiple lenses in front of Patek’s million-frames-per-second camera. “You have a big lens to capture the scene and you have a lot of little lenses behind that to create angular perspectives,” Horstmeyer says. And the million-frames-per-second camera records it all.

Each little lens in the array behind the big lens has a slightly different angle on the action, which, when combined, gives a three-dimensional view. But combining all that data is no easy task. Horstmeyer and his lab members wrote software that uses machine learning to produce a video that displays measurements of the high-speed deformation of an ant’s head during a mandible snap.

With a DST Launch seed grant, the pair are working to refine the optical instrument and prove that it works for the task.

“For us or for anybody in my field,” Patek says, “it would be a total game changer because we could finally understand how biological systems have evolved to slowly load energy into a three-dimensional structure and then rapidly channel it into an extremely precise ultrafast movement.”

The new optical instrument will likely will find applications in other fields where researchers want to learn more about ultrafast processes at small scales, whether in living organisms, industrial processes, or chemical reactions.

While there are many possible applications of both the optical instrument and the biological engineering of trap-jaw ants, Patek is driven by something deeper–adding to the knowledge about how nature works.

“For me, I just think that we all have better lives if we have more knowledge about the world we live in,” she says. “I think it’s a fundamental piece of human happiness.”