It’s no yolk — egghead experiment simulates concussion

Scientists used raw eggs to simulate the damaging effects on the brain from strikes to the head, with surprising results.

If someone calls you an egghead, they are not too far off. Think about it: an egg has a hard outer shell; a liquid interior, which is the white of the egg; and liquid yolk surrounded by a membrane suspended in the centre. Your head also has a hard outer skull and liquid, called the cerebrospinal fluid, inside of it — which, among other things, acts as a shock absorber around the squishy brain.

In a research paper in the journal Physics of Fluids, scientists from Villanova University in Pennsylvania conducted rather simple kitchen style experiments on raw eggs to simulate strikes to the head that could lead to concussion. 

They wanted to determine how much shock absorbing protection the egg white would provide the yolk and how much the yolk would be distorted out of shape during an impact.  

The results were not what they expected.

Applying force to monitor yolk deformation

In order to see the yolks in action, the egg material was placed in a clear plastic container that was mounted on springs and filmed with high speed cameras. 

First, they hit it in a straight line by dropping a 1.77 kg weight on it from a height of one metre. representing a direct blow to the head.

To their surprise, the yolk remained suspended in the egg white and did not change shape or break as the container suddenly accelerated downwards. This could be because liquids cannot be compressed, and since the two liquids are almost the same density, both of them moved together as one unit.

Next, the egg material was placed in another clear container that could rotate to simulate a knock to the side of the head that causes sudden rotation, like a boxer taking a hit to the jaw in a knockout punch.  

Cameron Dantzler #27 of the Minnesota Vikings is taken off the field in a stretcher after a neck injury and evaluated for a concussion during the second quarter against the Green Bay Packers at Lambeau Field on November 01, 2020. (Dylan Buell / Getty Images)

When the egg was spun up from zero to 400 radians per second (3820 rpm) in just one second, the yolk, when viewed in slow motion, lagged behind slightly, which changed its shape from a sphere to a wobbly blob, but it did not break.

The most dramatic results came when the spinning egg material was suddenly stopped from high speed down to zero in a second. The yolk continued to rotate, becoming elongated like a football and squeezed flat with a large ridge running along the centre. 

These findings suggest it is the action of stopping a rotation that does the most damage, not the initial strike. The researchers speculate that such a distortion in the brain could stretch brain neurons and cause damage.

Protecting your precious ‘yolk’

Of course, a raw egg is not exactly like a brain and concussions are far more complicated than just the physical motions. But they are a serious issue in contact sports, especially for young people whose brains are still developing.

This experiment showed that concussions from hits that cause the head to quickly rotate and then suddenly stop could be causing physical stresses on the brain. 

The researchers suggest that sports helmets be as round and smooth as possible to avoid any protrusions, like the ridges on many hockey helmets, that could act as lever arms and accelerate the rotation. 

It’s all part of a continuing effort to protect our precious grey matter so we don’t accidentally “scramble” our brains as we engage in rough activities.

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