All Cracked Up: How Solvents Stress Out Hydrogels

Poly(ethylene glycol)-based hydrogels are widely used in biomedical and soft robotic systems such as drug delivery and tissue engineering due to their ability to absorb solvents while maintaining their structural integrity and then revert back to their size. Here, we study drying, the dynamic process which occurs when solvent evaporates from a fully swollen gel. The drying process induces internal stress gradients that can lead to cracking, peeling, or fracturing, which limits practical applications for these materials.

Here, we investigate drying-induced fracturing and peeling of PEG-based hydrogels, focusing on how solvent volatility, crosslinking density, and gel thickness influences these behaviors. We find that cracking and peeling behavior does not vary significantly across changes in gel thickness or crosslinker density, but it does depend on the volatility of the solvent. More volatile solvents lead to faster drying, as well as a greater extent of material fracturing.

By quantifying the behaviors of drying-induced fractures, our research provides insights into these mechanics and offers strategies to design more durable PEG-based hydrogels. These insights also advance our understanding of solvent-gel interactions in various drying conditions and can be used to help inform the design of systems that rely on structural integrity and minimal instabilities.