Inertia effects on characterization of dynamic response of brain tissue

Sanborn, Brett; Nie, Xu; Chen, W.; Weerasooriya, Tusit

doi:10.1016/j.jbiomech.2011.12.017

Cited by 13 publications

(8 citation statements)

References 19 publications

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“…Mean flow rate was estimated from the measured data following established theory. 29 The wall shear stress, s, was calculated using the empirical equation, s ¼ 6lQ=wh 2 , where l is the dynamic viscosity of the fluid, Q is the volume flow rate, and w and h are the width and the height of the chamber, respectively. 30 Viscosity was assumed to be 10 -3 Pa s.…”

Section: Flow Chamber and Pressure Servo Pumpmentioning

confidence: 99%

“…Traumatic injury is normally classified as a focal injury that results in cerebral contusions at a specific location or diffuse axonal injury over a widespread area, probably resulting from shear forces. [1][2][3][4] The deformation caused by the shear forces in diffuse TBI is difficult to define because it occurs throughout the brain and is often mixed with secondary injuries resulting from subsequent biochemical and metabolic dysfunction. 5,6 Most TBI patients exhibit mild or minimal observable damage upon the initial shock.…”

Section: Introductionmentioning

confidence: 99%

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A Threshold Shear Force for Calcium Influx in an Astrocyte Model of Traumatic Brain Injury

Maneshi

Sachs

Hua

2015

Journal of Neurotrauma

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Traumatic brain injury (TBI) refers to brain damage resulting from external mechanical force, such as a blast or crash. Our current understanding of TBI is derived mainly from in vivo studies that show measurable biological effects on neurons sampled after TBI. Little is known about the early responses of brain cells during stimuli and which features of the stimulus are most critical to cell injury. We generated defined shear stress in a microfluidic chamber using a fast pressure servo and examined the intracellular Ca 2 + levels in cultured adult astrocytes. Shear stress increased intracellular Ca 2 + depending on the magnitude, duration, and rise time of the stimulus. Square pulses with a fast rise time (*2 ms) caused transient increases in intracellular Ca 2 + , but when the rise time was extended to 20 ms, the response was much less. The threshold for a response is a matrix of multiple parameters. Cells can integrate the effect of shear force from repeated challenges: A pulse train of 10 narrow pulses (11.5 dyn/cm 2 and 10 ms wide) resulted in a 4-fold increase in Ca 2 + relative to a single pulse of the same amplitude 100 ms wide. The Ca 2 + increase was eliminated in Ca 2 + -free media, but was observed after depleting the intracellular Ca 2 + stores with thapsigargin suggesting the need for a Ca 2 + influx. The Ca 2 + influx was inhibited by extracellular Gd 3 + , a nonspecific inhibitor of mechanosensitive ion channels, but it was not affected by the more specific inhibitor, GsMTx4. The voltage-gated channel blockers, nifedipine, diltiazem, and verapamil, were also ineffective. The data show that the mechanically induced Ca 2 + influx commonly associated with neuron models for TBI is also present in astrocytes, and there is a viscoelastic/plastic coupling of shear stress to the Ca 2 + influx. The site of Ca 2 + influx has yet to be determined.

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Section: Flow Chamber and Pressure Servo Pumpmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Threshold Shear Force for Calcium Influx in an Astrocyte Model of Traumatic Brain Injury

Maneshi

Sachs

Hua

2015

Journal of Neurotrauma

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“…Models continue to advance in biofidelity by incorporating an increased level of anatomic detail [4], [13], [14], improved representation of the material behavior at various loading rates [15]–[20], and advanced measures and predictions of injury [8], [21], [22]. Finite element models are commonly used to understand the biomechanics of brain and skull deformation when the head is subjected to insult, leading to improved insight into mechanisms of acute injury.…”

Section: Introductionmentioning

confidence: 99%

Combining the Finite Element Method with Structural Connectome-based Analysis for Modeling Neurotrauma: Connectome Neurotrauma Mechanics

et al. 2012

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This article presents the integration of brain injury biomechanics and graph theoretical analysis of neuronal connections, or connectomics, to form a neurocomputational model that captures spatiotemporal characteristics of trauma. We relate localized mechanical brain damage predicted from biofidelic finite element simulations of the human head subjected to impact with degradation in the structural connectome for a single individual. The finite element model incorporates various length scales into the full head simulations by including anisotropic constitutive laws informed by diffusion tensor imaging. Coupling between the finite element analysis and network-based tools is established through experimentally-based cellular injury thresholds for white matter regions. Once edges are degraded, graph theoretical measures are computed on the “damaged” network. For a frontal impact, the simulations predict that the temporal and occipital regions undergo the most axonal strain and strain rate at short times (less than 24 hrs), which leads to cellular death initiation, which results in damage that shows dependence on angle of impact and underlying microstructure of brain tissue. The monotonic cellular death relationships predict a spatiotemporal change of structural damage. Interestingly, at 96 hrs post-impact, computations predict no network nodes were completely disconnected from the network, despite significant damage to network edges. At early times () network measures of global and local efficiency were degraded little; however, as time increased to 96 hrs the network properties were significantly reduced. In the future, this computational framework could help inform functional networks from physics-based structural brain biomechanics to obtain not only a biomechanics-based understanding of injury, but also neurophysiological insight.

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“…Studies utilizing compression Kolsky bar techniques purportedly removed radial inertia effects by switching from disk-shaped specimens to annular specimens [Chen and Song 2011]. It was later shown that annular specimens are also plagued by radial inertia effects and that the observed increases in axial stress at high strain-rates were falsely attributed to viscoelastic properties of the specimen [Scheidler and Kraft 2010;Sanborn 2011;Sanborn et al 2012].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, a variation of the torsional Kolsky bar test has been developed for studying the strain-rate sensitivity of very soft materials and applied to bovine brain tissue [Nie et al 2013;Sanborn et al 2012]. In this modified torsion test, the transmission bar is replaced with a torque load cell in order to generate a stronger signal than could be obtained from strain gage measurements on a transmission bar; see Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Nonuniform shear strains in torsional Kolsky bar tests on soft specimens

Sokolow

Scheidler

2014

J. Mech. Mater. Struct.

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We investigate inertial effects in torsional Kolsky bar tests on nearly incompressible, soft materials. The results are relevant for materials with instantaneous elastic shear modulus on the order of 1-1000 kPa and density on the order of water. Examples include brain tissue and many other soft tissues and tissue surrogates. We have conducted one-and three-dimensional analyses and simulations to understand the stress and strain states that exist in these materials in a torsional Kolsky bar test. We demonstrate that the short loading pulses typically used for high strain-rate (e.g., 700/s) tests do not allow the softer specimens to "ring-up" to uniform stress and strain states and that consequently the shear stress versus shear strain data reported in the literature are erroneous. We also show that normal stress components, which are present even in quasistatic torsion of nonlinear elastic materials, can be amplified in dynamic torsion tests on soft materials.

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Inertia effects on characterization of dynamic response of brain tissue

Cited by 13 publications

References 19 publications

A Threshold Shear Force for Calcium Influx in an Astrocyte Model of Traumatic Brain Injury

A Threshold Shear Force for Calcium Influx in an Astrocyte Model of Traumatic Brain Injury

Combining the Finite Element Method with Structural Connectome-based Analysis for Modeling Neurotrauma: Connectome Neurotrauma Mechanics

Nonuniform shear strains in torsional Kolsky bar tests on soft specimens

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