Special materials let tiny critters deliver big pain

"Human engineers might learn from this biological trick used by small organisms in developing their sharp fangs, stings, and mandibles," says Robert Schofield. (Credit: Getty Images)

Ant mandibles, spider fangs, and scorpion sting tips are made of special materials that deliver sharpness for penetrating prey that the limited forces of their small muscles don’t otherwise allow, research shows.

That knowledge won’t ease the pain of puncture in human skin, but it may be useful for designing new precision cutting tools, says Robert Schofield, a researcher in the physics department at the University of Oregon.

Schofield, lead author of the paper in Scientific Reports, and colleagues used miniature testing machines to explore the sharp tools of such small organisms as ants, bristle worms, scorpions, and spiders. In all, the team completed 1,500 hand-positioned measurements on 150 organisms from 10 different species.

The sharp tools contain what researchers call heavy element biomaterials, enriched with zinc and manganese.

“Using atom probe tomography, an advanced type of microscope, we observed the distribution of zinc and proteins in ant teeth at subnanometer scale, which helped us understand why these cutting ‘tools’ are so strong,” says Arun Devaraj, a materials scientist who applied the specialized atomic probe tomography techniques developed at Pacific Northwest National Laboratory.

They also represent a third class of structural biomaterials, different than the plain organic materials found in claws and fingernails and mineralized substances in teeth and bones, the researchers say.

“We found that, if these small organisms made their tools of the same organic material as other stiff parts of their exoskeletons, the sharp edges would deform more, they would not be as hard, and they would often wear away much faster,” Schofield says.

“On the other hand,” he says, “if they used the calcified material that human teeth are made from, their tools would be hard enough, but they wouldn’t be sharp enough because of the large crystal size.”

This class of biomaterials, Schofield says, create sharper, damage-resistant tools that allow scorpions, for example, to use about a fifth of the force relative to that for plain organic materials.

With their testing machines and related techniques, the researchers measured the ability of the organisms’ puncturing tools to resist impact and fracture. They also gathered measurements on the abrasion resistance and damping, or mechanical energy, properties of the materials.

With atom probe tomography, the team created 3D maps of the molecular fragments in the protein structures, achieving a resolution of better than seven nanometers. They used other precision instruments to disassemble the materials almost atom by atom to study their composition.

“Human engineers might learn from this biological trick used by small organisms in developing their sharp fangs, stings, and mandibles,” Schofield says. “The hardness of ant teeth, for example, increases from about the hardness of plastic to that of aluminum when zinc is added. While there are much harder engineering materials, they are often more brittle or ductile.”

Additional coauthors are from Lane Community College, Pacific Northwest National Laboratory, Oregon State University, and the University of Oregon. The National Science Foundation funded the work.

Source: University of Oregon