Detecting Bond Breakage and Fracture in Tough Hydrogels Using Mechanoluminescence

Synthetic hydrogels are soft materials composed of 3-D polymer networks swollen with water. They are promising synthetic analogues of tissues but their excessive brittleness remains an important limitation. Though there have been advances in the design of tough hydrogels, it is not yet possible to quantitatively predict toughness from molecular design. A promising strategy towards this endeavor is based on the incorporation of mechanoluminescent probes in these materials. Upon force-induced bond breakage, emission of visible light allows for spatio-temporal mapping of molecular bond scission during failure.

We have incorporated a mechanoluminescent probe based on bis(adamantyl)-1,2-dioxetane into a model double-network hydrogel composed of stiff PAMPS and soft PAAm. Due to the low quantum yield of the emitter ketone resulting from force-induced ring-opening, we explored a range of FRET agents to detect bond scission during deformation. This information serves not only to establish a relation between polymer network structure and fracture energy, but also to develop multi-scale physical models of fracture in soft materials.