Viscoelastic properties of shock wave exposed brain tissue subjected to unconfined compression experiments

Abstract

Traumatic brain injuries (TBI) affect millions of people each year. While research has been dedicated to determining the mechanical properties of the uninjured brain, there has been a lack of investigation on the mechanical properties of the brain after experiencing a primary blast-induced TBI. In this paper, whole porcine brains were exposed to a shock wave to simulate blast-induced TBI. First, ten (10) brains were subjected to unconfined compression experiments immediately following shock wave exposure. In addition, 22 brains exposed to a shock wave were placed in saline solution and refrigerated between 30 minutes and 6.0 hours before undergoing unconfined compression experiments. This study aimed to investigate the effect of a time delay on the viscoelastic properties in the event that an experiment cannot be completed immediately. Samples from both soaked and freshly extracted brains were subjected to compressive rates of 5, 50, and 500 mm/min during the unconfined compression experiments. The fractional Zener (FZ) viscoelastic model was applied to obtain the brain's material properties. The length of time in the solution statistically influenced three of the four FZ coefficients, E 0 (instantaneous elastic response), τ 0 (relaxation time), and α (fractional order). Further, the compressive rate statistically influenced τ 0 and α. AbstractTraumatic brain injuries (TBI) affect millions of people each year. While research has been dedicated to determining the mechanical properties of the uninjured brain, there has been a lack of investigation on the mechanical properties of the brain after experiencing a primary blast-induced TBI. In this paper, whole porcine brains were exposed to a shock wave to simulate blast-induced TBI. First, ten (10) brains were subjected to unconfined compression experiments immediately following shock wave exposure. In addition, 22 brains exposed to a shock wave were placed in saline solution and refrigerated between 30 minutes and 6.0 hours before undergoing unconfined compression experiments. This study aimed to investigate the effect of a time delay on the viscoelastic properties in the event that an experiment cannot be completed immediately. Samples from both soaked and freshly extracted brains were subjected to compressive rates of 5, 50, and 500 mm/min during the unconfined compression experiments. The fractional Zener (FZ) viscoelastic model was applied to obtain the brain's material properties. The length of time in the solution statistically influenced three of the four FZ coefficients, E 0 (instantaneous elastic response), τ 0 (relaxation time), and α (fractional order). Further, the compressive rate statistically influenced τ 0 and α.

Deformation of an airfoil-shaped brain surrogate under shock wave loading

“…Figure 20 represents the superposition of elastic modulus versus strain rate from the literature, for soft materials and brain tissue. 1:70 PDMS shows an agreement of elastic modulus at low strain rates, when compared with the brain tissue in unconfined compression experiments (Zhang et al, 2019;McCarty et al, 2019). However, the elastic modulus for 1:70 PDMS exposed to a shock wave is lower than brain tissue.…”

“…side view of a brain's hemisphere). The pig brain was chosen since this animal is often used in experiments investigating brain injury (Begonia et al, 2010;Prabhu et al, 2011;Rashid et al, 2012c;Zhang et al, 2011;McCarty et al, 2019;Zhang et al, 2019). This is because pig brains have anatomic similarity of both the vascular system and the gyri and sulci (folds and depressions), when compared with humans (Säljö et al, 2008).…”

“…To resemble one hemisphere of the pig brain, only the NACA 2414's upper top half was used (Figure 1b). During experiments by McCarty et al (2019), to examine the viscoelastic response of shock wave exposed brain tissue, the pig brain's bottom was fixed on a block to prevent translation by the shock wave. To simulate the shape of the pig brain's fixed bottom, the horizontal line (y = 0) was applied on the modified NACA 2414 airfoil's geometry (Figure 1c).…”

Early Deformation of Deep Brain Stimulation Electrodes Following Surgical Implantation: Intracranial, Brain, and Electrode Mechanics

“…The brain is classically considered as a viscoelastic medium, in which regional differences exist, such as gray versus white matter, cortex versus thalamus or hippocampus, and anisotropy of white matter fiber orientation in the corona radiata and the corpus callosum (Hrapko et al, 2008;Jin et al, 2013;Moran et al, 2014;Finan et al, 2017;McCarty et al, 2019). As we have seen, clinically, it also seems to make sense to subdivide the brain into different mechanical regions or layers.…”

Cerebrospinal Fluid Cavitation as a Mechanism of Blast-Induced Traumatic Brain Injury: A Review of Current Debates, Methods, and Findings

“…There have been over 383,000 traumatic brain injuries (TBIs) reported by military service members since 2000, with blast-induced traumatic brain injury (bTBI) being the most common injury (1). The bTBI occurs when a blast wave, created by detonating improvised explosive devices (IEDs), propagates through the head of an individual (2)(3)(4). Exposure to the blast wave can cause life-threatening injuries and fatalities, with the outcome depending on factors such as how close the individual is to the source and the overpressure (i.e., shock wave) amplitude created (3).…”