Computational Modeling of Primary Blast Effects on the Human Brain by Michelle K. Nyein S.B., Chemistry, Massachusetts Institute of Technology (2004) J.D., Harvard University (2007) S.M., Aeronautics and Astronautics, Massachusetts Institute of Technology (2010) Submitted to the Department of Aeronautics and Astronautics in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Aeronautics and Astronautics at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2013 c Massachusetts Institute of Technology 2013. All rights reserved. Author............................................. ...................................... Department of Aeronautics and Astronautics March 4, 2013 Certified by.......................................... ..................................... Ra´ul Radovitzky Professor of Aeronautics and Astronautics Thesis Supervisor Certified by.......................................... ..................................... Dava J. Newman Professor of Aeronautics and Astronautics Certified by.......................................... ..................................... Laurence R. Young Apollo Program Professor of Aeronautics and Astronautics Certified by.......................................... ..................................... Simona Socrate Principal Research Scientist, Institute for Soldier Nanotechnologies Certified by.......................................... ..................................... David F. Moore Attending Neurologist, Baylor University Medical Center Accepted by......................................... ..................................... Eytan H. Modiano Professor of Aeronautics and Astronautics Chair, Committee on Graduate Students 2 Computational Modeling of Primary Blast Effects on the Human Brain by Michelle K. Nyein Submitted to the Department of Aeronautics and Astronautics on March 4, 2013, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Aeronautics and Astronautics Abstract Since the beginning of the military conflicts in Iraq and Afghanistan, there have been over 250,000 diagnoses of traumatic brain injury (TBI) in the U.S. military, with the majority of incidents caused by improvised explosive devices (IEDs). Despite the urgent need to understand blast-induced TBI in order to devise strategies for protection and treatment, much remains unknown about the mechanism of injury, the effects of personal protective equipment (PPE) such as helmets, and injury metrics and thresholds. In order to help address these gaps, this thesis has four objectives: 1) to present a comprehensive computational framework for investigating the mechanical response of the human head to blasts that includes blast-structure interaction codes, a detailed, three-dimensional model of a human head generated from high-resolution medical imaging data, and an experimentally-validated constitutive model for brain tissue; 2) to validate the framework against a broad range of experiments, including free-field blast tests involving physical human head surrogates and laboratory-scale shock tube tests involving animals and human cadavers; 3) to use the computational framework to investigate the effect of PPE on the propagation of stress waves within the brain following blast events and evaluate their blast protection performance; and 4) to develop interspecies scaling laws for the blast response of the brain that would allow translation of injury metrics from animals to humans. Thesis Supervisor: Ra´ul Radovitzky Professor of Aeronautics and Astronautics Committee Member: Dava J. Newman Professor of Aeronautics and Astronautics Committee Member: Laurence R. Young Apollo Program Professor of Aeronautics and Astronautics 3 Committee Member: Simona Socrate Principal Research Scientist, Institute for Soldier Nanotechnologies Committee Member: David F. Moore Attending Neurologist, Baylor University Medical Center 4 Acknowledgments I am immensely grateful to my advisor, Professor Ra´ul Radovitzky, for his support and guidance over the years. If he had not believed in me when I was a third-year law student who was curious about computational mechanics, I never would have had the privilege of conducting the research presented in this thesis. None of this research would have been possible without financial support from the Joint Improvised Explosive Device Defeat Organization (JIEDDO), the Office of Naval Research (ONR), and the MIT Institute for Soldier Nanotechnologies (ISN). I thank these organizations for their generous support. I would also like to express my gratitude to my thesis committee members. I owe so much to Dr. David F. Moore, who has contributed to almost every aspect of this research. Not only did he provide the segmented geometry that served as the basis of the DVBIC/MIT Full Human Head Model and supply material property values for a number of head structures, but throughout the years he was a source of medical insight and excellent advice. I also owe much of the success of this project to Dr. Simona Socrate. She developed the experimentally-validated brain tissue constitutive model used in the simulations presented in this thesis, and she patiently met with me to help implement the model in our code; her support has been invaluable. I would also like to thank Professor Dava Newman for her insightful suggestions, particularly relating to interspecies scaling. Also, thanks to Professor Newman, I was able to attend a Harvard Medical School anatomy class for one day and see what real human brains (including one with Pick’s disease!) look and feel like – it was an experience I won’t soon forget. Thank you also to Professor Larry Young for his thoughtful comments throughout the process. I would also like to thank the other members of my Thesis Defense Committee, Professors Krystyn Van Vliet and John Gabrieli, for their valuable feedback. I am also grateful to our collaborators at Duke University – Professor Dale Bass and his students, particularly Jay Shridharani – and our collaborators at the Naval Surface Warfare Center, Carderock Division – Phil Dudt and Alyssa Littlestone – for 5 providing experimental data for our validation efforts. I would like to express my appreciation to Professor John Joannopoulos for par- ticipating in my thesis proposal defense and providing financial support through ISN, and to Professor Wes Harris for allowing me to take Unified Engineering when I was in my third year of law school. I would also like to thank the wonderful Aero-Astro administrators. I am truly grateful to Barbara Lechner, Beth Marois, and Marie Stuppard for their assistance throughout my graduate career. Of course, my grad school experience would not have been the same without the members, past and present, of the RR Group. Special thanks to Dr. Antoine Jerusalem for teaching me how to do pretty much everything when I first started grad school. Also, I would be remiss if I did not thank Li Yu, Amira guru and designer extraordinaire, for developing the computational pig head model, and Amanda Jason, Ansys expert, for developing the face shield model. I would also like to acknowledge Lei Qiao, Andy Seagraves, Mike Tupek, and Brandon Talamini for their friendship and support through many, many years of navigating through classes, quals, research, paperwork, and information security trainings together. Thank you also to Bob and Jan Randolph for being such wonderful housemasters and to everyone at Bexley for providing a unique, colorful home for me and David forfouryears. Deepest and most heartfelt thanks to my amazing husband, Dr. David Carpenter, who has been by my side through every step of my journey through law school and grad school. He has brought so much joy and love into my life, and we have experi- enced such wonderful adventures over our 9.5 years together – I cannot wait to see what the future holds in store for us. Thanks also to our cat, Truffle, for providing much-needed amusement and fluffiness over the last 4.5 years. 6 Contents 1 Introduction 19 1.1TraumaticBrainInjury.......................... 23 1.1.1 Definition............................. 23 1.1.2 Screening,Symptoms,andTreatment.............. 24 1.1.3 Pathophysiology.......................... 30 1.2BlastInjuryMechanisms......................... 35 1.3ComputationalModelsofBlast-InducedTBI.............. 39 1.4ThesisOverview.............................. 45 2 Modeling Framework 47 2.1ComputationalFramework........................ 47 2.1.1 SolidMechanicsofDeformingTissues.............. 47 2.1.2 AMROC.............................. 52 2.1.3 Fluid-StructureInteraction.................... 53 2.2MeshGeneration............................. 53 2.3MaterialModelsandProperties..................... 55 2.3.1 Neo-HookeanModel....................... 55 2.3.2 SimpleViscoelasticModel.................... 58 2.3.3 SocrateBrainTissueConstitutiveModel............ 59 2.3.4 MaterialProperties........................ 62 2.4Summary................................. 67 7 3 Validation: Physical Surrogate Tests 69 3.1Introduction................................ 69 3.2Methods.................................. 72 3.2.1 Experiments............................ 72 3.2.2 ComputationalSimulations................... 75 3.3Results................................... 76 3.3.1 Round1.............................. 76 3.3.2 Round2.............................. 80 3.4Discussion................................. 84 4 Validation: Live Pig and Human Cadaver Tests 89 4.1Introduction................................ 89 4.2Experiments...............................