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Every day you walk around with your brain moving gently inside your skull. A bit like a soft egg yolk floating in a cloud of clear egg whites.
All it takes is a sudden jerk or bang, and your brain is pushed aside with surprising speed. Whether it’s hitting the skull or making a whirlwind, the damage can be terrible, as we know from people who have suffered traumatic brain injury.
But what exactly happens to the brain at this moment of impact? How does it move?
Research into the biomechanics of brain injury typically involves crash test dummies, athletes wearing mouthguards or helmets equipped with motion sensors, or models simulating the human brain.
Now the scientists have thrown eggs into the mix.
How an egg yolk reacts when different forces are applied. (Lang et al., Fluid physics, 2021)
What started as a kitchen curiosity for a team of engineers, with an egg scrambling instrument for home cooks, led them to study the fundamental physics governing the movement of soft matter in a liquid environment, by using an egg to mimic the brain.
“Critical thinking, coupled with simple cooking experiments, has led to a series of systematic studies to examine the mechanisms that cause egg yolk to deform,” said biomedical engineer Qianhong Wu of Villanova University. in Pennsylvania.
While their approach is somewhat unusual, the results of this study help us understand how soft matter, like brain tissue, moves and deforms when exposed to outside forces.
The more we know about the forces of concussion and can take them into account, the more researchers will be able to improve vehicle safety systems, design protective helmets, and help athletes improve their technique to prevent injury.
Inside the skull, the brain sits in a shock-absorbing fluid called cerebrospinal fluid.
The most common and mild form of head trauma (TBI) is concussion, and the term actually comes from a Latin word meaning “to shake violently”. But even a single sub-concussion hit to the head is enough to trigger changes in how brain cells work, studies have shown.
https://www.youtube.com/watch?v=Rk_375SG-kM
Regarding the causes of brain damage, the rotation of the head as a mechanism of brain damage was proposed in the 1940s. Easy to imagine if you think of a punch in the chin that throws the head back, or someone who gets whipped by a tackle.
But there is often confusion about the mechanics of concussions, as there are different ways to measure head impacts and use that information to predict brain damage.
Early research efforts looked at linear or “linear” impacts, where the brain is struck in one direction and bounces off the skull. Then the attention turned to the rotational forces that twist the brain within the skull.
Needless to say, it’s hard to measure how the brain can actually twist in such an impact, because we can’t look inside people’s moving heads.
But scientists can still learn something by recreating the brain, tightly adjusted in its cerebrospinal fluid, using similar materials.
In this study, the researchers started by measuring the physical characteristics of an egg yolk and its outer membrane, so that they could later quantify the stress the eggs were subjected to in laboratory experiments, which involved two configurations. .
“To damage or warp an egg yolk, one would try to shake and spin the egg as fast as possible,” the study authors write in their paper, so the eggs were cracked in a container transparent and subject to three types of impact.
The team observed how the egg yolks understood each other and stretched in different directions with accelerated rotational impact, and how they barely changed at all with a direct hit on the container.
When a rotating container filled with eggs was abruptly stopped, the yolk deformed “tremendously” with the deceleration rotational impact, and it took about a minute for the deformed yolk to return to its round shape. origin.
“We suspect that the rotation, in particular [decelerating] rotational, the impact is more harmful to brain matter, ”Wu said.
The results of this study correspond to previous research involving vehicle crash testing and pendulum head impacts, which found that rotating head impacts were a better indicator of head injury risk than linear acceleration.
These findings echo the general consensus that the brain is more sensitive to rotational movement than linear movement.
But that doesn’t mean we should ignore linear impacts altogether, as other researchers have proposed new measures of injury combining measures of linear and rotational head acceleration to assess concussion risk.
Brain damage is surely complicated and unfortunately many go undetected. At least with this intelligent experience, we can see the raw impact for ourselves.
The study was published in Fluid physics.
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