Session C2: BG-1: Biological Materials

Blast Loading Experiments of Developed Surrogate Models for TBI Scenarios

This study aims to characterize the interaction of explosive blast waves through simulated anatomical systems. We have developed physical models and a systematic approach for testing traumatic brain injury (TBI) mechanisms and occurrences. A simplified series of models consisting of spherical PMMA shells followed by SLA prototyped skulls housing synthetic gelatins as brain simulants have been utilized. A series of experiments was conducted with the simple geometries to compare the sensitivity of the system response to mechanical properties of the simulants under high strain-rate explosive blasts. Small explosive charges were directed at the models to produce a realistic blast wave in a scaled laboratory setting. Blast profiles were measured and analyzed to compare system response severity. High-speed shadowgraph imaging captured blast wave interaction with the head model while particle tracking captured internal response for displacement and strain correlation. The results suggest amplification of shock waves inside the head due to impedance mismatches. Results from the strain correlations added to the theory of internal shearing between tissues.   

Shock Compression of Seeds in Impacts at 1 -- 5 km s$^{-1}$

Panspermia (``seeds everywhere'') is an old idea, suggesting that life can naturally migrate through space. The survival of microbial life under the shock compression involved with transfer of a body through space between planets has been much studied; e.g. Burchell et al., \textit{Origin of Life and Evol. of the Biosphere}, \textbf{33}, 53 -- 74, 2003 showed that micro-organisms could survive in high speed ejecta from a hypervelocity impact (the favoured launch mechanism to spray life into space from its home planet) and Burchell et al., \textit{Icarus} \textbf{154}, 545-547 2001; \textit{MNRAS} \textbf{352}, 1273 -- 1278, 2004 showed that micro-organisms carried on projectiles in hypervelocity impacts can successfully transfer to a target (with survival rates that fall with a power law for GPa shock pressures). Here we address survival of more complex biological materials under shock compression, namely seeds. We report on experiments firing seeds at speeds of 1 -- 5 km s$^{-1}$ into water targets ($\sim $0.5 to 5 GPa for short durations). The method is described in a preliminary report (Jerling et al., \textit{Int. J. Astrobiology} \textbf{7}, 217 -- 222, 2008). In new data presented here we are finding intact capture of seeds at 1 km s$^{-1}$, but above this speed increasing fragmentation occurs. Tests are underway to try to germinate the seeds captured at 1 km s$^{-1}$ and the results will be described.   

Drug Delivery and Cell Transfection Using Shock Waves Produced by Nanothermites

Shock waves have non-destructive life science applications in cell transfection and drug delivery. Based on molecular dynamics simulations, the shockwave causes transient compression of the cell membrane, which causes the hydrophobic interior of the lipid bilayer to become thinner. This allows diffusion of water molecules across the membrane. Recently, the nanothermite composition consisting of CuO nanorods and Al nanoparticles was shown to propagate at velocities in the same range as metallic azides and fulminates; however, the CuO/Al mixture produces lower pressure levels. An \textit{in vitro} testing system was developed to deliver shock waves produced by nanothermites into cell suspensions and/or tissues. The plasmid encoded for production of green-fluorescent protein was delivered into cells including, among other types, chicken cardiomyocytes, cell lines (T47-D and Ins-1), and Arabidopsis plant cells. It was found that the nanothermite pressure impulses induced transfection resulting in production of green fluorescent protein in 99{\%} of the cardiomyocytes. Additionally, transfected cell survival was evaluated, and the pressure impulses did not produce any elevated levels of cell death compared with control cell suspensions.   

Iodine Oxide Thermite Reactions: Physical and Biological Effects

We investigated the potential for some thermite-like material reactions to kill bacteria spores. Iodine oxides and silver oxides react vigorously with metals like aluminum, tantalum, and neodymium. These reactions theoretically produce temperatures as high as 8000K, leading to vaporization of the reactants, producing very hot iodine and/or silver gases. We performed a series of computations and experiments to characterize these reactions under both quasi-static and ballistic impact conditions. Criteria for impact reaction were established. Measurements of temperature and pressure changes and chemical evolution will be reported. Basic combustion characterizations of these reactions, such as thermal equilibrium analysis and reaction propagation rates as well as ignition sensitivity, will be discussed. Additionally, testing protocols were developed to characterize the biocidal effects of these reactive materials on \textit{B. subtilis} spores. The evidence from these tests indicates that these reactions produce heat, pressure, and highly biocidal gases.   

Shock compression and recovery of microorganism-loaded broths and an emulsion

The microorganisms \textit{Escherichia coli, Enterococcus feacalis} and \textit{Zygosaccharomyces bailii} and an oil-based emulsion, have been subjected to shock compression using the flyer-plate technique to initial pressures of 0.8 GPa (in the suspension). In each experiment, a stainless steel capsule was used to contain the broths and allow for recovery without contamination. Where cavitation was suppressed by virtue of simultaneous shock and quasi-static compression, no kill was observed. By introducing an air gap behind the suspension, limited kill was measured in the yeast. Results also suggest that emulsification occurs in oil-based emulsions that are subjected to shock.