An Optoacoustic System for Fast and Nondestructive Hydrogel Bulk Mechanical Property Characterization

Physicochemical characteristics of hydrogels have been extensively studied with the aim of employing these materials for various biomedical purposes. The elasticity of hydrogels is recognized to significantly influence their interaction with cells and tissues, and this property can be quantified through compression/tension testing equipment. Nevertheless, this measurement technique requires the hydrogel to exhibit substantial elasticity and dimensions, and it is destructive, rendering the hydrogel test samples nonreusable. Here we report an acoustic-pulse-imaging-based method for hydrogel mechanical property measurement, which includes an optical system that measures the velocity of acoustic pulses as they propagate through a hydrogel specimen, which is later converted to a longitudinal storage modulus. Results obtained using the proposed system demonstrate its capability of conducting nondestructive longitudinal storage modulus measurements of hydrogels, which correlated well with their Young’s modulus for chemically cross-linked hydrogels with relatively dense network structures. Furthermore, the proposed approach effectively monitored the time-dependent alterations in elasticity that manifest during the gelation process of chemically cross-linked networks, exhibiting the system’s potential in tracking temporal changes in hydrogel elasticity.