Updated: Mar 22, 2021
A car accident, a sports game, a fall, there are many instances where a bump on the head can seem insignificant but has caused damage within the brain. Our brains consist of liquid matter bathed within a rigid skull in watery cerebrospinal fluid (CSF). An effect on the hard skull is transferred to the soft brain matter through the thin layer of CSF inside the subarachnoid space.
Wu and co-authors Ji Lang and Rungun Nathan describe researching another device with the same characteristics, an egg, in Physics of Fluids, from AIP Writing, to look for answers. An egg resembles the brain because, inside a hard shell, the delicate yolk is bathed in a liquid egg white. Given that the skull would not crack in most concussive brain trauma, Wu tried to figure out if it was possible to break or deform the egg yolk without destroying the eggshell. Using an egg scrambler, the researchers did a straightforward experiment, from which they could see that rotational force would quickly split the egg yolk and make it blend with the white of the egg.
Something very counterintuitive and quite shocking was found by the researchers. The egg deformation is not caused by direct translational effects, although rotational deceleration causes considerable egg yolk deformation. When the head is subject to unexpected external effects, this observation shines light on the motion and deformation of our brain.
"We suspect that the impact of rotation, particularly deceleration rotation, is more harmful to brain matter," Wu said. "During this process, the large deformation of brain matter induces neuronal stretching and causes damage.
This thesis offers a fresh insight as the first research of its kind to consider the reaction of a membrane-bound soft object to unexpected external impacts. Those designing helmets would be involved in this new outlook.