Shear Thickening Behavior in Injectable Tetra-PEG Hydrogels Cross-Linked via Dynamic Thia-Michael Addition Bonds

Injectable poly(ethylene glycol)-based hydrogels were reversibly crosslinked through thia-conjugate addition bonds and demonstrated to shear thicken at low shear rates. In this system, crosslinking bond exchange kinetics and polymer concentration were leveraged to tune hydrogel plateau moduli (about 60 - 650 Pa) and relaxation times (2 - 8 seconds). These properties affected the shear thickening behavior of the hydrogels, including the onset of shear thickening (at a Weissenberg number of 0.2) and the degree of shear thickening (up to 4.5 fold) that was achieved before a flow instability occurred. Despite the shear thickening behavior of the hydrogels at low shear rates, the hydrogels were injectable, with injection forces that increased with a higher polymer concentration and slower bond exchange kinetics. Altogether, these results demonstrate shear thickening in reversibly crosslinked, injectable tetra-PEG hydrogels and show design parameters by which the shear thickening behavior and injection force can be tuned.