Forensic physics and the stretchy brain

For such a vital organ, the brain is surprisingly soft and stretchy. Often, the brain is modeled with hydrogels which have similar rheological properties. Formulating an accurate replica is difficult, but essential in helping crime scene investigators understand the nature of a traumatic brain injury.

Yarin and Kosmerl developed a rheological model of the brain from experimental data and comparable to hydrogel models. This model could be particularly useful in identifying staged suicides (homicides) and analyzing blast-induced traumatic brain injuries.

The authors integrated the brain’s key rheological parameters into their model.

“The brain is much more resistant to compression than to stretching,” said author Alexander Yarin. “In addition, there is a potentially strongly nonlinear response to shear stress, accompanied by the appearance of normal stresses in parallel to the shear stress.”

In a companion publication, they apply their model to bullet penetration in the brain tissue. The model exhibited realistic compression and rarefaction waves.

“We present the first of its kind, rigorously constructed rheological model of brain tissue based on the hydrogel stress-energy function,” Yarin said. “It not only describes the hyperelastic features of brain tissue — important in short-time phenomena such as bullet penetration — but also is generalized to include viscoelasticity, which is important on much longer time scales characteristic of blast-induced traumatic brain injuries.”

This model can help guide further experimentation into the brain’s material properties. As experimental data improves, the authors plan to refine their model accordingly. They are also interested in collaborating with evolutionary biologists and biomedical researchers to investigate why the brain is more resistant to compression than stretching.

Source: “Rheology of brain tissue and hydrogels: A novel hyperelastic and viscoelastic model for forensic applications,” by A. L. Yarin and V. Kosmerl, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0173127 .

This paper is part of the Flow and Forensics Collection, learn more here .