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Technical Briefs

In Situ Deformations in the Immature Brain During Rapid Rotations

[+] Author and Article Information
Nicole G. Ibrahim, Rahul Natesh, Spencer E. Szczesny, Karen Ryall, Stephanie A. Eucker, Brittany Coats

Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd Street, Philadelphia, PA 19104-6321

Susan S. Margulies

Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd Street, Philadelphia, PA 19104-6321margulie@seas.upenn.edu

J Biomech Eng 132(4), 044501 (Mar 10, 2010) (4 pages) doi:10.1115/1.4000956 History: Received September 21, 2009; Revised October 08, 2009; Posted January 06, 2010; Published March 10, 2010; Online March 10, 2010

Head trauma is the leading cause of death and debilitating injury in children. Computational models are important tools used to understand head injury mechanisms but they must be validated with experimental data. In this communication we present in situ measurements of brain deformation during rapid, nonimpact head rotation in juvenile pigs of different ages. These data will be used to validate computational models identifying age-dependent thresholds of axonal injury. Fresh 5 days (n=3) and 4 weeks (n=2) old piglet heads were transected horizontally and secured in a container. The cut surface of each brain was marked and covered with a transparent, lubricated plate that allowed the brain to move freely in the plane of rotation. For each brain, a rapid (20–28 ms) 65 deg rotation was applied sequentially at 50 rad/s, 75 rad/s, and 75 rad/s. Each rotation was digitally captured at 2500 frames/s (480×320pixels) and mark locations were tracked and used to compute strain using an in-house program in MATLAB . Peak values of principal strain (Epeak) were significantly larger during deceleration than during acceleration of the head rotation (p<0.05), and doubled with a 50% increase in velocity. Epeak was also significantly higher during the second 75 rad/s rotation than during the first 75 rad/s rotation (p<0.0001), suggesting structural alteration at 75 rad/s and the possibility that similar changes may have occurred at 50 rad/s. Analyzing only lower velocity (50 rad/s) rotations, Epeak significantly increased with age (16.5% versus 12.4%, p<0.003), which was likely due to the larger brain mass and smaller viscoelastic modulus of the 4 weeks old pig brain compared with those of the 5 days old. Strain measurement error for the overall methodology was estimated to be 1%. Brain tissue strain during rapid, nonimpact head rotation in the juvenile pig varies significantly with age. The empirical data presented will be used to validate computational model predictions of brain motion under similar loading conditions and to assist in the development of age-specific thresholds for axonal injury. Future studies will examine the brain-skull displacement and will be used to validate brain-skull interactions in computational models.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Diagram of the horizontal transection set-up. The transected brain and skull are potted in the canister with the exposed brain facing out and visible through the transparent lid.

Grahic Jump Location
Figure 2

(a) Original cropped frame excluding extraneous background and (b) perimeters of identified objects superimposed on cropped image shown in (a)

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