Every day you walk with your brain fluttering slightly inside the skull. Like a soft yolk floating in a cloud of clear whites.
All it takes is a sudden blow or a blow, and your brain is set aside with astonishing speed. Whether it hits the skull or spins, the injury can be serious, as we know from people who have suffered a traumatic brain injury.
But exactly what happens to the brain at that moment of impact? How does it move?
Research investigating the biomechanics of brain injury typically involves mannequins heading for an accident, athletes wearing mouth guards or headphones equipped with motion sensors or models that simulate the human brain.
Now, scientists have thrown eggs into the mixture.
How an egg yolk reacts when different forces are applied. (Lang et al., Fluid Physics, 2021)
What started as a curiosity in the kitchen for a team of engineers, with an egg mixing tool for home cooks, led them to study the fundamental physics that governs the motion of soft matter in a liquid environment, using an egg to mimic the brain. .
“Critical thinking, along with simple experiments in the kitchen, has led to a series of systematic studies to examine the mechanisms that cause egg yolk deformity,” said biomedical engineer Qianhong Wu of Villanova University in Pennsylvania.
Although their approach has been somewhat unusual, the results of this study help us understand how soft matter, such as brain tissue, moves and deforms when exposed to external forces.
The more we know about and explain the concussive forces that affect the brain, the more researchers can improve vehicle safety systems, design headgear for protection, and help sports players improve their technique to prevent injury.
Inside the skull, the brain leans in a shock-absorbing fluid called cerebrospinal fluid.
The most common and mild form of traumatic brain injury (TBI) is concussion, and the term actually comes from a Latin word meaning “to shake violently.” But even a single sub-concussive blow to the head is enough to trigger changes in the way brain cells work, studies have shown.
As for what causes brain damage, head rotation as a mechanism for brain damage was proposed in the 1940s. Easy to imagine if you think of a fist on the chin that throws the head back or someone who gets whipped from an attack.
But there is often confusion about the mechanics of contusion because there are different ways to measure the impact of the head and use this information to predict brain damage.
Early research efforts looked at linear or “linear” impact, where the brain is hit in one direction and bounces off the skull. Then the focus turned into rotational forces that twist the brain inside the skull.
Needless to say, it is difficult to measure how the brain can turn in such an impact, because we cannot look inside people’s moving heads.
But scientists can learn something by recreating the brain, immersing itself in cerebrospinal fluid, using similar materials.
In this study, the researchers began by measuring the material characteristics of an egg yolk and its outer membrane so that they could later quantify the stress of the eggs during laboratory experiments, which presented two settings.
“In order to damage or deform an egg yolk, they would try to shake and rotate the egg as quickly as possible,” the study authors write in their paper, so that the eggs were cracked in a clear container and subjected to three types. of impact.
The team observed how the egg yolks compressed and stretched in different directions with an accelerated rotational impact and also how they changed at all with a direct hit of the container.
When a rotating container filled with egg was suddenly stopped, the yolk deformed “extraordinarily” with the decelerating rotational impact and lasted about a minute until the deformed yolk regained its original round shape.
“We suspect that the rotation is mostly [decelerating] rotational, the impact is more harmful to brain matter, “Wu said.
The results of this study are parallel to previous research involving vehicle crash tests and pendulum head impacts, which found that rotating head impacts are a better indicator of the risk of brain trauma than linear acceleration.
These findings echo the general consensus that the brain is more sensitive to rotational motion than linear motion.
But this does not mean that we should completely reduce the linear impact, as other researchers have proposed new injury metrics that combine measures of linear acceleration and head rotation to assess the risk of concussion.
Brain injuries are complicated and, unfortunately, many are undetected. At least, with this clever experiment, we can see the gross impact for us.
The study was published in Fluid physics.