Dynamic Rugae Strain Localizations and Instabilities in Soft Viscoelastic Materials During Inertial Microcavitation

Abstract

To constitutively characterize soft material large deformation properties at high loading rates (10³–10⁸ s⁻¹), we recently developed an experimental technique called Inertial Microcavitation Rheometry (IMR). Here, inertial cavitation bubbles are generated through a spatially focused pulsed laser, e.g., hydrogels, tissues, and various polymeric specimens. By recording the spatiotemporally resolved bubble dynamics via high-speed videography, a combined experimental and theoretical investigation of single bubble cavitation in soft viscoelastic materials has been conducted, where we observe evidence of strain localization and surface instabilities near the bubble wall during bubble expansion and collapse. We provide direct experimental observation of how strain localization can lead to various types of surface instabilities within a gel-like soft material giving rise to kink, wrinkle, and crease patterns. These types of dynamic rugae patterns and associated strain concentrations might be of significant interest in medical and engineering applications that utilize or encounter microcavitation, e.g., during ultrasound or laser surgeries, or traumatic brain injuries.