A Multiscale Approach to Blast Neurotrauma Modeling: Part I – Development of Novel Test Devices for in vivo and in vitro Blast Injury Models

Abstract

The loading conditions used in some current in vivo and in vitro blast-induced neurotrauma models may not be representative of real-world blast conditions. To address these limitations, we developed a compressed-gas driven shock tube with different driven lengths that can generate Friedlander-type blasts. The shock tube can generate overpressures up to 650 kPa with durations between 0.3 and 1.1 ms using compressed helium driver gas, and peak overpressures up to 450 kPa with durations between 0.6 and 3 ms using compressed nitrogen. This device is used for short-duration blast overpressure loading for small animal in vivo injury models, and contrasts the more frequently used long duration/high impulse blast overpressures in the literature. We also developed a new apparatus that is used with the shock tube to recreate the in vivo intracranial overpressure response for loading in vitro culture preparations. The receiver device surrounds the culture with materials of similar impedance to facilitate the propagation of a single overpressure pulse through the tissue. This method prevents pressure waves reflecting off the tissue that can cause unrealistic deformation and injury. The receiver performance was characterized using the longest helium-driven shock tube, and produced in-fluid overpressures up to 1500 kPa at the location where a culture would be placed. This response was well correlated with the overpressure conditions from the shock tube (R2 = 0.97). Finite element models of the shock tube and receiver were developed and validated to better elucidate the mechanics of this methodology. A demonstration exposing a culture to the loading conditions created by this system suggest tissue strains less than 5% for all pressure levels simulated, which was well below functional deficit thresholds for strain rates less than 50 s−1. This novel system is not limited to a specific type of culture model and can be modified to reproduce more complex pressure pulses.

Multiscale Modelling of Blast-Induced TBI Mechanobiology - From Body to Neuron to Molecule

“…Other teams have added various refinements including the improved resolution of the neck, subarachnoid CSF, bridging veins and other anatomical feature [9][10][44][45][46] . In the last few years, FEM head/brain biomechanics models have been adapted for modelling the blast TBI by incorporating head/face anatomical details and by coupling them to the blast physics CFD solvers 7,39,[47][48][49] . In comparison to the blunt brain biomechanics model, the blast injury model has a loading force that is much faster and is spatially and temporally 'distributed' over the entire head during the shock wave propagation around the head.…”

“…A better understanding of blast wave TBI can be achieved with complementary experimentalcomputational modelling approach. However, computational modelling of neurotrauma poses significant challenges as it involves several physical and biomedical disciplines as well as a range of spatial and temporal scales [6][7] . Most computational models of blast TBI confine their focus to modelling macroscopic biomechanics of the brain, often ignoring the presence of the elastic skull, flexibility of the neck and head movements, effects of vascular and cerebral fluids and responses of the rest of the body [8][9][10][11][12] .…”

On the formation of Friedlander waves in a compressed-gas-driven shock tube

“…(e.g. [1][2][3][4][5][6][7][8][9][10]). Lab-scale tests using shock tubes are convenient surrogates for field blast tests as they provide better precision and variable control, increased safety and reduced cost [8].…”

“…However, estimates of the location of the onset of the blast wave are mostly empirical. In Refs [4,8], Bass and co-workers recognize the uncertainty on the location where the Friedlander wave forms and adopt the 'rule of thumb' for shock design that the driven length to diameter ratio should be greater than 10 to ensure that the wave is planar. In Ref.…”

“…CFD simulations have shown that the Riemann shock wave structure eventually leads to the formation of a wave pressure profile which looks like a Friedlander blast wave. The accuracy of CFD numerical tools has been validated by comparing the time evolution of the pressure at specific location in the tube with experimental pressure sensor data [4]. CFD has also been instrumental in describing the flow conditions as the wave approaches and goes past the open end of the tube [7,16].…”