Localized Tissue Surrogate Deformation due to Controlled Single Bubble Cavitation

Abstract

Cavitation-induced shock wave, as might occur in the head during exposure to blast waves, was investigated as a possible damage mechanism for soft brain tissues. A novel experimental technique was developed to visualize and control single bubble cavitation and its collapse, and the influence of this process on a nearby tissue surrogate was investigated. The experiment utilized a Hopkinson pressure bar system which transmits a simulated blast pressure wave (with over-pressure and under-pressure components) to a fluid-filled test chamber implanted with a seed gas bubble. Growth and collapse of this bubble was recorded during passage of the blast wave with a high speed camera. To investigate the potential for cavitation damage to a tissue surrogate, local changes in strain were measured in hydrogel slices placed in various configurations next to the bubble. The strain measurements were made using digital image correlation (DIC) technique by monitoring the motion of material points on the tissue surrogate. In one configuration, bubble contact dynamics resulted in compression contact (>60 μs) followed by inertially-driven tension (>140 μs). In another configuration, the influence of local shock waves emanating from collapsed bubbles was captured. Large compressive strains (0.25 to 0.5) that were highly localized (0.18 mm 2 ) were measured over a short time period (<24 μs) after bubble collapse. High bubble collapse pressures 29 to 125 times that of peak blast overpressure are predicted to be the source of these large strains. Consistent with theoretical predictions, these cavitation-based strains are far larger than the strains imposed by passage of the simulated blast wave alone. Finally, the value of this experimental platform to investigate the single bubble cavitation-induced damage in a biological tissue is illustrated with an example test on rat brain slices.

Cavitation onset caused by acceleration

“…3), consistent with the theoretical prediction, establishing that the alternative cavitation number Ca is a reasonable criterion for the onset of acceleration-induced cavitation. The alternative cavitation number can potentially be used as a criterion for brain injury caused by impact-induced cavitation (5,6), prediction of water hammer (4), and potentially applied to the development of safety devices (e.g., helmet design). (3,24).…”

Polymeric Hopkinson Bar-Confinement Chamber Apparatus to Evaluate Fluid Cavitation

“…The causes of mTBI are currently unknown, and there is no consensus in the literature of injury mechanisms resulting in mTBI as a result of blast, which further emphasizes the need for additional research in the topic. Theories of possible injury mechanisms caused by overpressure exposure include soft-tissue damage from shearing [4][5][6][7], distortion of cellular structures and cell death in the brain [5,[8][9][10][11][12][13][14], and intracranial fluid cavitation [5,[15][16][17][18][19].…”

Microcavitation: the key to modeling blast traumatic brain injury?

“…These results, along with several other experiments on human brain surrogates of ranging realism demonstrating the existence of cavitation at pressures around -1 atmospheres (or roughly -100 kPa), are pointing to suggestive evidence that microcavitation might indeed be a possible injury mechanism of not just blast but also possibly blunt head trauma [ 13 , 20 , 22 , 23 ]. Works by several groups have shown that pressures near the estimated cavitation threshold of -1 atmosphere can be generated in head impacts sustained from sports-related or vehicular incidents, even in the absence of an explosive pressure wave [ 24 , 25 ].…”

“…Because of the highly localized and short-lived nature of cavitation, documentation of the phenomenon itself has been challenging and efforts are still underway to prove its existence in the human brain during blast exposures. However, increasing mounting evidence, in particular in the last few years, has provided us with a better understanding that inertial microcavitation in the brain might indeed be a real possibility [ 13 , 20–23 ]. For example, Goeller et al.…”