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Cellular and Molecular Bioengineering

Cellular and Molecular Bioengineering - Poster Session E

Poster V11 - The effects of blast-induced traumatic brain injury on brain cellular mechanics

Saturday, October 26, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  TBI is one of the primary reasons of death and disability in the United States. Blast events accounted for nearly 70 % of injuries in wounded service members in both Iraq and Afghanistan and are the main cause of traumatic brain injury (TBI). bTBI may cause a variety of heterogeneous symptoms including concentration problems, blurred vision, irritability, headaches, sleep disorders and depression, post-traumatic stress disorder (PTSD) and chronic traumatic encephalopathy (CTE). Therefore, gaining fundamental understanding of post trauma cellular mechanics in bTBI is crucial in terms of filling the current knowledge gap aiding faster development of novel therapeutic approaches. The adult human brain consists of a diverse cell population of billions of neurons, glial cells such as astrocytes, oligodendrocytes, microglia, pericytes (figure 1). The primary injuries due to bTBI lead to physical destruction of the neurons, axons, and glia followed by secondary injuries. To improve TBI aftermath and dampen the secondary damage, we need an improved understanding of how nanoscale structural, and mechanical properties (Young’s modulus, deformation, adhesion, dissipation) and viscoelastic properties (viscosity, retardation time) of brain cells: neuronal, glial as well as blood brain barrier (BBB) endothelial cells vary due to bTBI. Our goal is to explore that and generate new knowledge on the effects of blast-induced traumatic brain injury (bTBI) on cellular mechanics of brain cells (such as neurons, astrocytes, oligodendrocytes etc.) at nanoscale.

Materials and

Methods:  We used custom fabricated and state-of-the-art oxyacetylene-driven shock tube to expose live cells to blast waves inducing similar effects as bTBI. The shock tube diameter is comprised of a 5-ft driver and 15-ft driven sections, separated by a diaphragm. Rupturing the Mylar diaphragm creates a shock wave. Young’s modulus, viscosity, and retardation time measurements were performed on adult hippocampal progenitor cells (AHPC) pre and post shock wave exposures of two different overpressure magnitudes (14.5 psi, 29 psi), one direction (top to bottom), and 2 ms duration using Peak-Force QNM mode (Figure 2 and Figure 3). AFM force-distance curves at each pixel on live cells (representing the variation of the force acting on the probe vs. tip–sample separating distance) were fit with the Hertz model or Sneddon model (conical indenter) to calculate Young’s modulus values. Nanomechanical and viscoelastic measurements were performed on 20-25 live cells pre and post shock wave exposures using the same PFQNM-LC-CAL-A probe with calibrated spring constant of 0.08 N/m. The purpose of this task is to understand if these shock wave exposures are affecting actin cytoskeletal network and if these changes are permanent or temporary (by maintaining shock wave exposed cells).

Results, Conclusions, and Discussions: We observed strong actin cytoskeleton network in form of striations/ actin stress fibers in AHPC cells in the AFM height and peak force error images before exposure. With shock wave exposures of overpressure magnitude: 14.5 psi, and 29 psi, we observed the disorganization of actin filaments and no striations. Also, we observed slight increase in the average Young’s modulus values for 14.5 psi shock wave exposure and decrease in Young’s modulus values for 29.0 psi shock wave exposure compared to the control or ‘before exposure’ values (Figure 2). So, nanoscale mechanical properties were not that much affected as cells were plated on the bottom of AFM compatible dishes and direction of shock wave exposure was from top to bottom. That’s why the average Young’s modulus was only affected by 29.0 psi shock wave exposure making actin cytoskeleton (main force generating network of cells) weaker, and cells more likely to migrate. Our hypothesis is that when the propagation direction is changed to ‘bottom to top’ (our future work), cellular mechanics and Young’s modulus will be affected even with 14.5 psi shock wave exposure and Young’s modulus values will continue to decrease with increasing shock wave exposure magnitude and duration.

Maintaining a constant distance between the AFM tip and the cell while tracking time-dependent force (stress relaxation) on the cell or delivering a constant compressive force and tracking time-dependent displacement (creep) of the AFM tip are the two main approaches for viscoelastic measurement. We conducted stress relaxation studies (Figure 3) on live AHPC cells using MLCT-D probe (spring constant of 0.03 N/m) pre and post shock wave exposures. The results showed that the average viscosity and retardation time of AHPC cells slightly increased for 14.5 psi (w.r.t ‘before exposure’ scenario) and decreased notably for 29.0 psi shock wave exposure. Our hypothesis is that the viscosity and retardation time of the cells will keep decreasing even more with higher overpressure magnitude. The lower the viscosity, the easier it is for live cells to migrate which matches with our initial hypothesis on nanomechanical properties of live cells post shock wave exposure.

Acknowledgements (Optional):  We would like acknowledge Prof. Sarah Bentil and Prof. Donald Sakaguchi for their help with the usage of shock tube and maintaining AHPC cells respectively.