Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session E4: MB Blast Injury |
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Chair: James Leighs, Cranfield University Room: Vashon |
Monday, July 8, 2013 3:30PM - 4:00PM |
E4.00001: Integrated Experimental Platforms to Study Blast Injuries: a Bottom-Up Approach Invited Speaker: Chiara Bo Developing a cellular and molecular understanding of the nature of traumatic and post-traumatic effects of blast events on live biological samples is critical for improving clinical outcomes$^{\mathrm{1}}$. To investigate the consequences of pressure waves upon cellular structures and the underlying physiological and biochemical changes, we are using an integrated approach to study the material and biological properties of cells, tissues and organs when subjected to extreme conditions. In particular we have developed a confined Split Hopkinson Pressure Bar (SHPB) system, which allows us to subject cells in suspension or in a monolayer to compression waves of the order of few MPa and duration of hundreds of microseconds$^{2}$. The chamber design also enables recovery of the biological samples for cellular and molecular analysis. Specifically, cell survivability, viability, proliferation and morphological changes are investigated post compression for different cell populations. The SHPB platform, coupled with Quasi-Static experiments, is also used to determine stress-strain curves of soft biological tissues under compression at low, medium and high strain rates. Samples are also examined using histological techniques to study macro- and microscopical changes induced by compression waves. Finally, a shock tube has been developed to replicate primary blast damage on organs (i.e. mice lungs) and cell monolayers by generating single or multiple air blast of the order of kPa and few milliseconds duration. This platform allows us to visualize post-traumatic morphological changes at the cellular level as a function of the stimulus pressure and duration as well as biomarker signatures of blast injuries. Adapting and integrating a variety of approaches with different experimental platforms allows us to sample a vast pressure-time space in terms of biological and structural damage that mimic blast injuries and also to determine which physical parameters (peak pressure, stimulus duration, impulse) are contributing to the injury process. Moreover, understanding biological damage following blast events is crucial to developing novel clinical approaches to detect and treat traumatic injury pathologies.\\[4pt] [1] Phil. Trans. R. Soc. B 27 366 (1562),160-170 (2011)\\[0pt] [2] Eur. Phys. J. Appl. Phys. 55, 31201 (2011). [Preview Abstract] |
Monday, July 8, 2013 4:00PM - 4:30PM |
E4.00002: Microjet Penetrator - medical use of laser induced shock waves and bubbles Invited Speaker: Jack J. Yoh The laser-driven microjet penetrator system accelerates liquids drug and delivers them without a needle, which is shown to overcome the weaknesses of existing piston-driven jet injectors. The system consists of two back-to-back chambers separated by a rubber membrane, one containing ``driving'' water behind another of the liquid drug to be delivered. The laser pulse is sent once, and a bubble forms in the water chamber, which puts elastic strain on the membrane, causing the drug to be forcefully ejected from a miniature nozzle in a narrow jet of 150 micron in diameter. The impacting jet pressure is higher than the skin tensile strength and thus causes the jet to penetrate into the targeted depth underneath the skin. Multiple pulses of the laser increase the desired dosage. The experiments are performed with commercially available Nd:YAG and Er:YAG lasers for clinical applications in laser dermatology and dentistry. The difference in bubble behavior within the water chamber comes from pulse duration and wavelength. For Nd:YAG laser, the pulse duration is very short relative to the bubble lifetime making the bubble behavior close to that of a cavitation bubble (inertial), while in Er:YAG case the high absorption in water and the longer pulse duration change the initial behavior of the bubble making it close to a vapor bubble (thermal). The contraction and subsequent rebound for both cases were seen typical of cavitation bubble. The laser-induced microjet penetrators generate velocities which are sufficient for delivery of drug into a guinea-pig skin for both laser beams of different pulse duration and wavelength. We estimate the typical velocity within 30-80 m/s range and the breakup length to be larger than 1 mm, thus making it a contamination-free medical procedure. Hydrodynamic theory confirms the nozzle exit jet velocity obtained by the microjet system. A significant increase in the delivered dose of drugs is achieved with multiple pulses of a 2.9$\mu\mbox{m}$ Er:YAG laser at 250$\mu\mbox{s}$ pulse duration. At this wavelength, the beam is best absorbable by water. Further, to increase the bubble size, a sapphire based fiber tip is entered into a water chamber as a beam is gathered at the bottom of this fiber tip's conical end, which is polished at an angle graduated from 30$^{\circ}$ over the full core diameter. The power density at the exit of the conical fiber tip is increased in comparison with the direct radiation at water. The water superheats and thus a larger bubble forms right at the tip. The bubble is typically an elongated (stretched) shape in case of a direct laser irradiation in water, but when light is irradiated through a conical fiber tip, the resulting bubble is an enlarged spherical bubble which is several times larger in its volume when compared to the direct beam radiation in water. In this talk, a review of our recent research effort in achieving high-throughput injection of drug via the microjet penetrator is given with its potential medical applications. [Preview Abstract] |
Monday, July 8, 2013 4:30PM - 4:45PM |
E4.00003: Traumatic eye injuries as a result of blunt impact Chiara Clemente, Luca Esposito, Nicola Bonora, Jerome Limido, Jean-Luc Lacome, Tommaso Rossi The detachment or tearing of the retina in the human eye as a result of a collision is a phenomenon that occurs very often. This research is aimed at identifying and understanding the actual dynamic physical mechanisms responsible for traumatic eye injuries accompanying blunt impact, with particular attention to the damage processes that take place at the retina. To this purpose, a numerical and experimental investigation of the dynamic response of the eye during an impact event was performed. Numerical simulation of both tests was performed with IMPETUS-FEA, a general non-linear finite element software which offers NURBS finite element technology for the simulation of large deformation and fracture in materials. Computational results were compared with the experimental results on fresh enucleated porcine eyes impacted with airsoft pellets. The eyes were placed in a container filled with 10 percent ballistic gelatin simulating the fatty tissue surrounding the eye. A miniature pressure transducer was inserted into the eye bulb through the optic nerve in order to measure the pressure of the eye during blunt-projectile impacts. Each test was recorded using a high speed video camera. The ocular injuries observed in the impacted eyes were assessed by an ophthalmologist in order to evaluate the correlation between the pressure measures and the risk of retinal damage. [Preview Abstract] |
Monday, July 8, 2013 4:45PM - 5:00PM |
E4.00004: Prediction of Shock-Induced Cavitation in Water Aaron Brundage Fluid-structure interaction problems that require estimating the response of thin structures within fluids to shock loading has wide applicability. For example, these problems may include underwater explosions and the dynamic response of ships and submarines; and biological applications such as Traumatic Brain Injury (TBI) and wound ballistics. In all of these applications the process of cavitation, where small cavities with dissolved gases or vapor are formed as the local pressure drops below the vapor pressure due to shock hydrodynamics, can cause significant damage to the surrounding thin structures or membranes if these bubbles collapse, generating additional shock loading. Hence, a two-phase equation of state (EOS) with three distinct regions of compression, expansion, and tension was developed to model shock-induced cavitation. This EOS was evaluated by comparing data from pressure and temperature shock Hugoniot measurements for water up to 400 kbar, and data from ultrasonic pressure measurements in tension to -0.3 kbar, to simulated responses from CTH, an Eulerian, finite volume shock code. The new EOS model showed significant improvement over pre-existing CTH models such as the SESAME EOS for capturing cavitation. [Preview Abstract] |
Monday, July 8, 2013 5:00PM - 5:15PM |
E4.00005: On the interaction between blast wave and reticulated foams James Wilgeroth, William Proud, Thuy-Tien Ngoc Nguyen Injuries to the tympanic membrane (ear drum) and inner ear are particularly common in individuals subjected to blast overpressure, such as military personnel engaged in conflict. Consequently, there is a demand for improved auditory protection systems, which are capable of both preventing this type of injury while providing maximum situational awareness to the user. In this study, a number of reticulated (open cell) foams have been subjected to dynamic compression using shock tube apparatus. Specific effects of porosity; relative density, which is determined by the ratio of cellular material to solid material from which the foam is made; sample thickness; incident pressure; and shock pulses of varying timescale upon the evolution of peak overpressure behind foam samples have been investigated. In addition, the use of Schlieren imaging techniques has allowed for detailed examination of gaseous flow at the rear surface of shocked foam samples. [Preview Abstract] |
Monday, July 8, 2013 5:15PM - 5:30PM |
E4.00006: Shockless compression (loading rate of 5 x 10$^{5}$/s) of ballistic gel to 1 GPa Yoshimasa Toyoda, Yogendra Gupta Ballistic gel has been commonly used as a soft tissue simulant in ballistic experiments for decades. However, experimental results needed to develop material models at stresses and loading rates comparable to ballistic loading are lacking. To examine the dynamic response of ballistic gel at the desired stresses and loading-rates, shockless uniaxial-strain compression experiments were conducted on 10 and 20 weight percent ballistic gel to 1 GPa peak stress. Plate-impact experiments were conducted using the following target configurations: fused silica/gel/PMMA optical window. The anomalous compression of fused silica resulted in a near-linear, shockless compression (5 x 10$^{5}$/s). Velocity histories at the front and the rear ballistic gel interfaces were simultaneously recorded using laser interferometry (VISAR). From the velocity histories, the loading paths (in the pressure-volume plane) for each gel concentration were determined. The 20 wt.{\%} ballistic gel resulted in the steeper loading path, demonstrating that the dynamic compression response of 20 wt.{\%} gel is stiffer than the 10 wt.{\%} gel. The wave profiles and the quantitative results will be discussed. Dr. D. P. Dandekar (ARL) is thanked for his help and insightful discussions. Work supported by ARL and DOE/NNSA. [Preview Abstract] |
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