Dynamics of confined cavitation bubbles, a possible link with mild traumatic brain injuries.

Traumatic Brain Injury (TBI) is a major healthcare problem, increasingly occurring in sports like rugby, boxing or football. The occurrence of TBI is dependent on the head acceleration and the duration of the shock, as expressed by the empirical Wayne State Tolerance Curve (WSTC). One of the possible causes of TBI is the formation of cavitation bubbles in the cerebro-spinal fluid (CSF). To investigate the link between TBI and cavitation bubbles, we built a model experiment to induce cavitation bubbles through an impact. A tank is entirely filled with water (representing the CSF) and hermetically closed with a flexible membrane (mimicking the CSF circulation between the head and the spinal cord). The tank is impacted on a damper, and the formation and dynamics of cavitation bubbles is observed and studied. After showing that the damaging capacities of such bubbles are in good agreement with the WSTC, we seeked to study the influence of the brain: the CSF does not fill the whole cranial cavity, but is confined between the skull and the brain on a thickness of approximately 1mm. We introduced a confined area in the head-like water tank that allows us to compare the dynamics of confined and unconfined bubbles for the same shock. Modeling those confined cavitation bubbles induced by a shock allows us to compute their damaging capacities and conclude on the dangerousness of shocks received by athletes.