The HO• is the most abundant radical which can further react and create alkyne radicals. Subsequently, these alkyne radicals can form crosslinks with adjacent alkyne groups resulting in the observed hydrogel contraction. Propagation can occur via an attack on the radical C1 carbon or to the cationic C2 carbon of adjacent alkyne moieties forming new C-C bonds. Another possible secondary crosslink mechanism is by an attack of a radical C1 carbon on carbon C3, C4 or C5. Additionally, phosphate buffer is found to act as a radical scavenger, which might explain the lower degree of hydrogel contraction we have observed in our g-irradiation experiments (Figure and). The reactivity of the residual alkyne groups suggested that it should be possible to glue or fuse hydrogel objects using g-irradiation (Figure ). We designed an experiment in which two hydrogel cubes where placed on top of each other inside a closed glass vial. Prior to initial gelation, a pipet tip was placed in the liquid dextran solution to provide for an easy grip handle used for lifting the hydrogels and assessing the g-irradiation induced fusion. One set of hydrogel gel cubes was then placed in a 60 Co source for 24 hours and one set was kept aside as a control experiment. We found that the hydrogel cubes in the control experiment did not fuse together. When lifting the top hydrogel, the bottom hydrogel immediately detached indicating that capillary forces do not play any significant role (Figure and 3C). In contrast, the g-irradiated set of hydrogels had fused together and could be lifted with the top hydrogel cube holding the weight of the bottom hydrogel cube (Figure and).