title: Mechanical Characterization of Immature Porcine Brainstem in Tension at Dynamic Strain Rates.
abstract: BACKGROUND
  Many brain injury cases involve pediatric road traffic accidents, and among these, brainstem injury causes disastrous outcomes. A thorough understanding of the tensile characterization of immature brainstem tissue is crucial in modeling traumatic brain injury sustained by children, but limited experimental data in tension is available for the immature brain tissue at dynamic strain rates.
  
  
  METHODS
  We harvested brainstem tissue from immature pigs (about 4 weeks old, and at a developmental stage similar to that of human toddlers) as a byproduct from a local slaughter house and very carefully prepared the samples. Tensile tests were performed on specimens at dynamic strain rates of 2/s, 20/s, and 100/s using a biological material instrument. The constitutive models, Fung, Ogden, Gent, and exponential function, for immature brainstem tissue material property were developed for the recorded experimental data using OriginPro 8.0 software. The t test was performed for infinitesimal shear modules.
  
  
  RESULTS
  The curves of stress-versus-stretch ratio were convex in shape, and inflection points were found in all the test groups at the strain of about 2.5%. The average Lagrange stress of the immature brainstem specimen at the 30% strain at the strain rates of 2, 20, and 100/s was 273±114, 515±107, and 1121±197 Pa, respectively. The adjusted R-Square (R2) of Fung, Ogden, Gent, and exponential model was 0.820≤R2≤0.933, 0.774≤R2≤0.940, 0.650≤R2≤0.922, and 0.852≤R2≤0.981, respectively. The infinitesimal shear modulus of the strain energy functions showed a significant association with the strain rate (p<0.01).
  
  
  CONCLUSIONS
  The immature brainstem is a rate-dependent material in dynamic tensile tests, and the tissue becomes stiffer with increased strain rate. The reported results may be useful in the study of brain injuries in children who sustain injuries in road traffic accidents. Further research in more detail should be performed in the future.
authors.affiliation: Chongqing Key Laboratory of Vehicle/Biological Crash Security, Research Institute for Traffic Medicine, Daping Hospital, Third Military Medical University, Chongqing, China (mainland).
authors.forename: Hui
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Chongqing Key Laboratory of Vehicle/Biological Crash Security, Research Institute for Traffic Medicine, Daping Hospital, Third Military Medical University, Chongqing, China (mainland).
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Yin
authors.affiliation: Chongqing Key Laboratory of Vehicle/Biological Crash Security, Research Institute for Traffic Medicine, Daping Hospital, Third Military Medical University, Chongqing, China (mainland).
authors.forename: Kui
authors.initials: K
authors.lastname: Li
authors.affiliation: Chongqing Key Laboratory of Vehicle/Biological Crash Security, Research Institute for Traffic Medicine, Daping Hospital, Third Military Medical University, Chongqing, China (mainland).
authors.forename: Zhikang
authors.initials: Z
authors.lastname: Liao
authors.affiliation: Chongqing Key Laboratory of Vehicle/Biological Crash Security, Research Institute for Traffic Medicine, Daping Hospital, Third Military Medical University, Chongqing, China (mainland).
authors.forename: Hongyi
authors.initials: H
authors.lastname: Xiang
authors.affiliation: Bioengineering Center, Wayne State University, Detroit, MI, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhu
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D001930:Brain Injuries / Q000473:pathology; D001933:Brain Stem / Q000033:anatomy & histology / Q000293:injuries / Q000473:pathology / Q000502:physiology*; D004195:Disease Models, Animal; D008954:Models, Biological; D013314:Stress, Mechanical; D013552:Swine; D013718:Tensile Strength; D055682:Viscoelastic Substances
chemical_list: D055682:Viscoelastic Substances