Crosslink density increase is typically employed for increasing mechanical properties such as stiffness or yield stress, or to heal damage. Here, we present a novel g-radiation triggered secondary crosslink strategy that enables us to have direct control over the crosslink density and eventually the macroscopic contraction of dextran hydrogels. With this finding we demonstrate that a molecular event, such as secondary crosslinking, can be translated into macroscopic motion (hydrogel contraction). Most strategies for hydrogel contraction in literature rely on physical transitions. A well-known physical strategy for hydrogel contraction is the temperature triggered phase transition of poly(N-isopropylacrylamide) (PNIPAM) based hydrogels. When such hydrogels are heated above 32 ºC, a sharp decrease in material volume is observed which is caused by the polymer switching from a hydrophilic phase to a hydrophobic phase. Alternatively, photoredox responsive hydrogels can undergo macroscopic contraction as a result of polymer chain folding. Blue light, via an excited ruthenium photocatalyst, triggers the folding of polyviologen chains in the hydrogel network resulting in a reduction of the hydrogel volume. Mechanical entanglement can also be used for material contraction using a UV light driven molecular motor to entangle a polymer network. Finally, enzymatic activity is employed to trigger a secondary crosslinker strategy leading to hydrogel contraction accompanied by an increased hydrogel stiffness. Hydrogels find many different applications where they provide a protective environment to a loaded cargo. These loaded hydrogels enable controlled release of the cargo, through either an active or a passive release mechanism. Passive release is typically described by the standard Fickian diffusion model, where the hydrogel structure remains intact. On the contrary, active release can be controlled using external triggers such as (UV) light, temperature, pH, biological molecules or oxidative stress and changes the integrity of the hydrogel network or the hydrogel completely disintegrates. A less common trigger is ionizing radiation. A few examples exist where g-radiation induces scissions in dendrimer structures , generates reactive oxygen species (ROS) which damage the bilayer of liposomes and promote cargo release or the cleavage of doxorubicin from nanoparticle drug carriers. 17 g-radiation is a powerful tool to generate radicals on unsaturated polymer chains, leading to crosslink formation, which is widely applied. Crosslinking by gamma radiation is an efficient technique to form hydrogels as no monomers, initiators or catalysts are used, which are potentially harmful or toxic and are thus problematic when these hydrogels find a biological application. In general, the crosslink density can be controlled by varying the radiation dose, this enables control over the degree of swelling and material properties such as stiffness. When prolonged irradiation is used, the formed material continues to form crosslinks which eventually results in material contraction. This effect was observed by Angelini et al., who reported material contraction when 3% gelatin solutions were exposed to g-irradiation dose higher than 50 kGy. In our research we demonstrate contraction of stable pre-crosslinked hydrogels, where g-irradiation leads to immediate contraction, indicating high sensitivity.