Mild Traumatic Brain Injury - Helmet Material

PI: Prof. Bala Balachandran

The Mild Traumatic Brain Injury (MTBI) Committee of the Head Injury Interdisciplinary Special Interest Group of the American Congress of Rehabilitation Medicine has defined MTBI as traumatically induced physiological disruption of brain function manifested by at least one of the following: i) any period of loss of consciousness; ii) any loss of memory for events immediately before or after the accident; iii) any alteration in mental state at the time of the accident. We have formed a group consisting of engineers and scientists from the CECD, the ETC, and the Medical School in Baltimore to study this with the view of redesigning helmets that would mitigate the effects on the brain.

State of the Art
Pellman et al. (2006) investigated the performance of new NFL helmets under impact. It was shown that newer design improved the absorption of impact energy during normal conditions in a football match. However, better designs are still needed to overcome what is called the elite impact condition, normally at speeds above 11.2 m/s. Sensors have been implemented to measure real time impacts during college football matches. The collected data may help understand when concussions occur. Accelerometers have been used as sensors in these studies.

Continuing Studies
Our group is studying these issues in an effort to address gaps and questions, which include the following:
• Standard criteria used for establishing injury criteria consider only the motion of the center of mass of the head. Injury criteria are formulated as empirical relationships that depend on the acceleration of the head. While there is much discussion about the relative importance of linear acceleration versus angular acceleration in causing a brain injury, the approach suffers from the fundamental shortcoming that the relative motion of the brain with respect to the skull is not taken into account. Furthermore, despite the brain being a highly deformable entity, brain deformations are not taken into account in the models.
• While finite element models point to coup pressure and shear strain as failure criteria and also show that the use of helmets reduces the pressure and shear stress on the skull elements, they offer little insight into the actual mechanism of energy transfer to the brain as a result of impacts on the skull.
• A system approach could be useful in formulating the problem.
• Recent experimental work based on MRI methods has provided in vivo strain measurements on the brain. These results point to the importance of developing injury criteria that are based on brain deformation. Helmets could be designed as energy absorbing and redistributing mechanisms in the energy path to the brain (see figure).
• Perhaps a helmet with a harness should be considered to reduce the translational acceleration levels experienced by the brain (see figure).