&nbsp; &nbsp; &nbsp;Acceleration-induced cavitation can be a source of damage in brain injuries. Recently, Lang et al. (Phys. Fluids, 2021) built an&nbsp;artificial head model containing cerebrospinal fluid (CSF) and demonstrated that cavitation can actually occur inside a&nbsp;deformable head system; emphasizing the importance of understanding the dynamics of acceleration-induced cavitation of&nbsp;fluids surrounding the brain. However, there are a limited number of experimental studies on this relatively new topic.&nbsp;&nbsp; &nbsp; &nbsp;In this work, we describe the concept of an experimental setup we have developed for investigating acceleration-induced cavitation. We compare our setup with the existed methods (e.g., Kang et al., Rev. Sci. Instrum., 2017) and discuss the advantages and limitations. We then report our experimental results in terms of the criteria for cavitation onset, and cavitation bubble dynamics for CSF gathered from pigs and sheep, water, and Xanthan Gum/water solutions. We also discuss limitations and possible extensions of the work for future development.&nbsp; &nbsp; &nbsp;Our experimental setup consists of a solid metal sphere that falls from a height (H) to a stage that is connected to a fluid-filled container and accelerometer. Our measurement system records both acceleration data and high-speed images of the impact, which can result in bubble formation consisting of one or more bubbles when the acceleration is large enough. The magnitude of the acceleration is adjusted by changing the height (H). The fluids used are distilled water and CSF collected from the sheep and pig. CSF was kept frozen while being shipped and stored. We gently defrost the sample and warm it up to 37±2 ºC, which is close to body temperature. We also use the aqueous solutions of xanthan gum as the analog of the general body fluids. It is considered Non-Newtonian and its zero-shear viscosity is higher than that of water.&nbsp; &nbsp; &nbsp;In terms of the criteria for cavitation onset, we introduce the mathematical criterion called Cavitation number&nbsp;Ca&nbsp;to evaluate our results. We adopt a sigmoid function to fit the data, which has been used for describing the probability of cavitation caused by acoustic or pressure waves (e.g., Maxwell et al., J. Acoust. Soc. Am., 2011), as a function of Cavitation number&nbsp;Ca. The sigmoid function could describe the cavitation probability of water, where the overall trend was consistent with our previous report (Pan et al., PNAS, 2017). We also report the cavitation onset for CSF samples, though the supply was limited.&nbsp; &nbsp; &nbsp;Regarding the cavitation dynamics, we focus on forming a single cavitation bubble, to simplify the analysis. The lifetime&nbsp;Tlife&nbsp;of cavitation increased as the maximum cavitation radius&nbsp;Rmax&nbsp;increased and there was no significant difference for each fluid type. We compare our data with the Rayleigh model, which predicts the proportional relationship between&nbsp;Tlife&nbsp;and&nbsp;Rmax&nbsp;and found that our data tend to have longer lifetimes than expected from the model. One reason for this is likely the close proximity of the walls, whereas Rayleigh’s model assumes an infinite field. A closer look at the high-speed images reveals that the bubble does not oscillate spherically and often forms a liquid jet when collapsing. The jet direction is qualitatively understood by considering the existence of the container walls (e.g., Brujan et al., J. Fluid Mech., 2018), confirming this hypothesis. In addition, some exceptions including cases where multiple bubbles form suggest that not only the container walls but also the pressure field inside the liquid (e.g., the pressure gradient along with the liquid column depth as well as that from the bubble-bubble interaction) affect the bubble dynamics. The direction of the impact (or the applied acceleration) could also play an important role in the cavitation-induced damage mechanism.&nbsp; &nbsp; &nbsp;These results may deepen the current understanding of cavitation dynamics and cavitation-induced damage and help safety designers when developing helmets etc.

Acceleration-Induced Cavitation of Cerebrospinal Fluid

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

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