How do you study concussion without tearing skulls? Try using an egg maker.
In a new study, which appeared in the journal on January 19 Physics of liquids, scientists drew inspiration from how egg scallops mix egg whites and yolks through without first cracking the shell. The device simply rotates the unbroken egg at a very high speed, and the power is transferred to the liquid inside and the dropper is dropped. Similarly, in most concussion brain injury, the skull does not crack, but the brain is still injured, the scientists thought.
Disclaimer: No human brain was involved during the study. Instead, the researchers used egg yolks as a model for the human brain.
Related: From Dino Brain to Mind Control – 10 Fascinating Brain Findings
“I would say this is a very wild comparison,” said senior author Qianhong Wu, director of the Cellular Biomechanics and Sports Science Laboratory at Villanova University in Pennsylvania. “These are completely different systems, in terms of material properties.” Eggs contain only one substance – yolk – while brains contain a variety of cell types arranged in complex structures, he said.
That said, eggs and brains of humans have a handful of important similarities, which can give some insight into the fundamentals physics of concussion, he said.
When we look at the brain, we have an insertion organ surrounded by a fluid called cerebrospinal fluid (CSF) and encased in a solid container, the skull. An egg yolk is also made from soft, squishy material, surrounded by liquid and encased in a hard container, the shell. Wu and his colleagues spotted these similarities and ran with them, designing experiments to see how the egg yolk would deform under different forces. They tested two types of collisions seen in concussion, including rotational impact, which causes the skull to rotate, and translational impact, which simply moves the skull into space without rotating it.
Their lab experiments began with a trip to the grocery store, where they picked up fresh chicken eggs. To see how power changes the egg yolk, they discard the eggshell and place the white and yellow in a clear container; in this way they could observe the insides of the egg directly while still holding it in a sturdy vessel. To test the translation impact, the team dropped a 1.7-kilogram hammer on the 1-meter-high container; for their rotational impact experiments, they rotated the container with an electric motor, up to 64 revolutions per second.
The team recorded these tests using a high-speed camera and found that the rotational impact caused the egg yolk to change dramatically, while the translation impact did not cause any visible change in comparison. When the container begins to rotate, the spherical yellow stretches horizontally and forms an ‘ellipsoid’. But the most intense change occurred when the turn slowed. As the rotational speed decreases, the center of the egg yolk pinches inward and pulls the horizontal ellipsoid into the vertical plane. Within one second, the rounded shape was pressed into a flat disk.
When the rotation stopped completely, it took the egg yolk about a minute to relax again in an atmosphere. “This great distortion can, of course, seriously damage the egg yolk,” the authors noted.
The conclusion? Extreme rotational influences can also destroy the brain. For example, if boxers are socked on the chin, their heads quickly clap backwards on their necks and then slow down quickly when the head cannot turn further. This may explain why boxers can easily faint if they are beaten in this way, Wu noted.
While the rotational impact destroyed the egg yolk, the hammer-drop experiment did not change at all. “It’s very surprising, it’s counterintuitive,” because you would expect the power to be transmitted through the hard container and egg whites and into the yolk, Wu said. This surprising result can be explained by the fact that egg whites and yolks have a very similar density, so under a hammer strike the two can move together as a unit, he said. This will prevent the yolk from changing shape.
Since the brain has a different density than the surrounding CSF, a solid head on the head will probably pull the brain a little crooked. But based on their experiments, the brain can be more sensitive to rotational influences, Wu said.
During an actual concussion, translation and rotation impacts occur simultaneously. “You really can not completely separate … It’s always a combination of both,” Wu said.
Now that Wu and his colleagues have worked out the physics of concussion in eggs, they plan to verify their results in the brain. The laboratory recently developed an artificial brain, based on scans of human brains and surrounded by a transparent skull, which they did through impact experiments. The team also studies brains harvested from mice, but Wu said they want to work with the brains of live animals in the future.
They also worked with physicians at Thomas Jefferson University Hospital to compare the results of laboratory experiments with data from patients who had experienced traumatic brain injury, he added. It can help connect the points between the physics observed in eggs, and the actual injuries that humans sustained.
Originally published on Live Science.