Measuring interfacial strength of ultra-soft materials with needle-induced cavitation

Needle-induced cavitation (NIC) has been used to characterize the mechanical properties of ultra-soft biological tissues. Previous studies conducted NIC on brain tissue and computed the energy to separate, or fracture, interfaces between regions from the measured NIC critical pressure. These tests revealed the intrinsic correlation between the critical pressure and the interfacial properties. While NIC demonstrated its potential for measuring interfacial properties, independent measurements have not been made to validate the measurements. In this work, we use model interfaces to validate the use of NIC to quantify the interfacial energy of buried interfaces. By inserting a needle into the interface and inducing pressurized separation, we obtained the critical pressure dependence on the needle size and a known residual stress. At the extrapolated residual stress-free state, we obtained the interfacial energy (G_c) by considering energy dissipated in the separation initiation at the critical pressure point, yielding a G_c value that matches an independent measurement.