Cavitation is the sudden, unstable expansion of a void or bubble within a liquid or solid subjected to a negative hydrostatic stress. Cavitation rheology is a field emerging from the development of a suite of materials characterization, damage quantification, and therapeutic techniques that exploit the physical principles of cavitation. Cavitation rheology is inherently complex and broad in scope with wide-ranging applications in the biology, chemistry, materials, and mechanics communities. This perspective aims to drive collaboration among these communities and guide discussion by defining a common core of highpriority goals while highlighting emerging opportunities in the field of cavitation rheology. A brief overview of the mechanics and dynamics of cavitation in soft matter is presented. This overview is followed by a discussion of the overarching goals of cavitation rheology and an overview of common experimental techniques. The larger unmet needs and challenges of cavitation in soft matter are then presented alongside specific opportunities for researchers from different disciplines to contribute to the field. soft solids | traumatic brain injury | TBI | rheology | bubble Cavitation is the sudden, unstable expansion of a void or bubble within a liquid or solid subjected to a negative hydrostatic stress. While predominantly studied in fluids, cavitation is also an origin of damage in soft materials, including biological tissues. Examples of cavitation in fluids and soft solids are shown in Fig. 1 A-C. As one key example, strong evidence suggests that cavitation occurs in the brain during sudden impacts, leading to traumatic brain injury (TBI) (3). Research on this life-impacting injury and its relation to cavitation has accelerated in recent years (4-8). A broader and deeper understanding of cavitation within soft matter is necessary to navigate the complex paths that lead to damage in the brain and other soft materials. Cavitation in fluids has been studied extensively since Rayleigh's (9) formulation in 1917, which predicted that the maximum pressure in a cavitating liquid is proportional to the far-field pressure and inversely proportional to the cavity size. As surface energy

Advances in polymer chemistry over the last decade have enabled the synthesis of molecularly precise polymer networks that exhibit homogeneous structure. These precise polymer gels create the opportunity to establish true multiscale, molecular to macroscopic, relationships that define their elastic and failure properties. In this work, a theory of network fracture that accounts for loop defects is developed by drawing on recent advances in network elasticity. This loop-modified Lake–Thomas theory is tested against both molecular dynamics (MD) simulations and experimental fracture measurements on model gels, and good agreement between theory, which does not use an enhancement factor, and measurement is observed. Insight into the local and global contributions to energy dissipated during network failure and their relation to the bond dissociation energy is also provided. These findings enable a priori estimates of fracture energy in swollen gels where chain scission becomes an important failure mechanism.

Phase-separated networks made from different macromonomers with disparate properties provide a platform where the molecular weight between cross-links (M c ) can be varied leading to tunable mechanical and conductive properties. To form networks with bimodal M c 's, two volume fraction series, A and B, were synthesized from telechelic polystyrene (PS) and poly(ethylene oxide) (PEO) of varying molecular weights (MW), using thiol− norbornene chemistry to tune M c . Series A consisted of 4K PEO and 12K PS, and series B consisted of 12K PEO and 5K PS. Phase separation in the network was confirmed by DSC where two distinct glass transition temperatures were observed and by SAXS where broad, weakly ordered scattering was observed. The networks were further characterized to probe how bimodal M c affects the mechanical and conductive properties of phase-separated networks. The two series demonstrated that the asymmetric MW studied herein had little effect on mechanical and lithium conductive properties while changes in these properties were primarily influenced by the volume fraction of PEO.

Characterizing the high-strain-rate and high-strain mechanics of soft materials is critical to understanding the complex behavior of polymers and various dynamic injury mechanisms, including traumatic brain injury. However, their dynamic...

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