Characterizing Mechanical Changes in Hydrogels Induced by Drying and Rehydration Processes

• Simran Montagne, Material Science, University of Delaware

• April Kloxin, Chemical and Biomolecular Engineering, University of Delaware

Hydrogels, which are hydrophilic polymer networks capable of absorbing significant amounts of water, are attractive material platforms for three-dimensional (3D) cell culture owing to the tunability of their mechanical properties, biochemical compositions, and viscoelastic properties. Unlike traditional two-dimensional systems or animal models, hydrogels can be engineered to allow for precise spatio-temporal control over the cellular environment. This project primarily uses two hydrogel systems: a strain-promoted azide-alkyne cycloaddition (SPAAC) click chemistry hydrogel with tunable photochemistry for degradation and stiffening of the gel, and a PEGdiPDA hydrogel formed through photoinitiated chain-growth polymerization using LAP as the photoinitiator. 

Dried hydrogels have been explored for more efficient storage and transport, but the effect of drying on their mechanical properties remains unclear. In this study, PEGdiPDA hydrogels were vacuum dried, a common processing procedure, and later rehydrated. This work focused on characterizing the mechanical effects of drying and rehydration on hydrogels and assessing how mechanical modulus, or stiffness, varies across the gel. Atomic force microscopy (AFM) and shear rheometry were used to measure the mechanical moduli of hydrogels. Rheometry provided bulk measurements of properties, while AFM captured localized surface stiffness and probed injured and stiffened areas of the SPAAC gels. These methods aimed to improve understanding of how processing history and photoresponsive components influences the mechanical properties of hydrogels.