Perforation of thin-membrane-covered soft matter induced by cavitation-initiated extreme mechanics

Abstract

Traumatic events can initiate cavitation within the cerebrospinal fluid surrounding the human brain. While the brain is soft [Young's modulus E∼O(1) kPa], a thin membrane named cranial pia mater [E∼O(1) MPa] separates the cerebral cortex from the liquid. Here, we reveal the effect of this composite boundary on the damage potential of cavitation through well-controlled experiments. Therefore, a soft hydrogel is covered by a thin biomembrane and is exposed to cavitation bubbles created at various distances with a pulsed laser. High-speed imaging reveals a perforation of the membrane and penetration of a liquid jet deep into the composite structure from a single event, and its strong dependence on the stand-off distance of the bubble to the boundary. When the stand-off distance is around 0.65, needlelike liquid jets in excess of 1000 m/s can be formed that pass through the bubble without atomization. The later visible shock-wave emission is related to the phenomenon of shock-wave self-focusing.