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Published on: May 18, 2015
Mechanical Characterization of Immature Porcine Brainstem in Tension at Dynamic Strain Rates
Hui Zhao1, Zhiyong Yin1, Kui Li1
1Chongqing Key Laboratory of Vehicle/Biological Crash Security, Research Institute for Traffic Medicine, Daping Hospital, Third Military Medical University, Chongqing, China (mainland).
Insights
Pediatric brainstem tissue is rate-dependent, stiffening with increased strain rates in dynamic tensile tests. These findings aid in modeling traumatic brain injuries in children from road traffic accidents.
Area of Science:
- Biomechanics
- Neuroscience
- Pediatric Traumatology
Background:
- Pediatric road traffic accidents frequently cause brain injuries, with brainstem injuries leading to severe outcomes.
- Understanding the tensile properties of immature brainstem tissue is vital for modeling pediatric traumatic brain injury.
- Limited experimental data exists on the tensile behavior of immature brain tissue at dynamic strain rates.
Purpose of the Study:
- To characterize the tensile properties of immature brainstem tissue.
- To develop constitutive models for immature brainstem tissue under dynamic loading.
- To investigate the relationship between strain rate and tissue stiffness.
Main Methods:
- Immature piglet brainstem tissue (developmentally similar to human toddlers) was used.
- Tensile tests were conducted at dynamic strain rates of 2/s, 20/s, and 100/s.
- Constitutive models (Fung, Ogden, Gent, exponential) were developed and validated against experimental data.
Main Results:
- Stress-strain curves exhibited convex shapes with inflection points around 2.5% strain.
- Lagrange stress increased significantly with strain rate, reaching 1121±197 Pa at 100/s and 30% strain.
- All tested constitutive models showed good to excellent fit (R² values up to 0.981), with infinitesimal shear modulus significantly associated with strain rate (p<0.01).
Conclusions:
- Immature brainstem tissue demonstrates rate-dependent behavior in dynamic tensile tests.
- Tissue stiffness increases proportionally with higher strain rates.
- These findings are valuable for developing computational models of pediatric brain injuries in road traffic accidents.
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.
Material And 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.
