Controlled blunt impact experiments on soft tissue simulants

Beavers, Timothy J.<sup>1,2</sup>; Chandra, Abhijit<sup>1</sup>; Bentil, Sarah A.<sup>1,2</sup>

Affiliations

¹Department of Mechanical Engineering, Iowa State University

²The Bentil Group, Department of Mechanical Engineering, Iowa State University

Abstract

Traumatic brain injury (TBI) following blunt force impact to the head yields symptoms that include confusion, headache, dizziness, and speech problems. The injury mechanism resulting in these symptoms is still not well understood, hindering the development of effective countermeasures. To increase our understanding of TBI (without skull fracture), we have designed an apparatus that can reproduce blunt impact forces in a controllable and repeatable manner. The apparatus consists of a simplistic cylindrical head system with tissue and fluid surrogates to represent the brain, cerebrospinal fluid (CSF), and skull. Resultant forces imparted on the outer layer of the skull are recorded using force transducers. A tri-axial accelerometer mounted on the brain and a laser vibrometer are used to measure the acceleration and velocity, respectively. A dedicated shaker is coupled with the head system (i.e. brain-CSF-skull apparatus) to allow for controlled and repeatable testing of blunt loading scenarios of variable complexities. The selection of the shaker’s frequency and applied force needed to simulate a TBI, such as a concussion, were guided by the Severity Index (SI) scale. The SI scale is used to rate the severity of skull impact. SI of 700 corresponds to a concussion sustained by a National Football League (NFL) player during gameplay. The duration of the blunt impact resulting in concussion is 15 ms, which translates to an acceleration of 74 g-force. Our preliminary results show that when the shaker’s period of oscillation was 15 ms, a maximum acceleration of 49 g-force and a measured resultant skull force of 196.6 N was recorded. At 15 ms, the percent difference for the acceleration measured using our head system and 74 g-force reported by the SI scale is 41%. To ensure that a TBI event is being reproduced using the brain-CSF-skull apparatus, the mass on the unbalanced shaker tray will be increased until the acceleration matches 74 g-force. Our brain-CSF-skull apparatus will facilitate research to identify the various frequencies and loading magnitudes that will yield a TBI. The results of the research will aid in the design of countermeasures to damping or offset the frequencies experienced by the brain resulting in TBI.

Links

URL: http://ibrc.osu.edu/wp-content/uploads/2018/05/Beavers_manuscript.pdf

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