A hydrogel precursor formulation which is in the form of an unreacted powder. The formulation comprises an activating enzyme, preferably thrombin, a cross-linking enzyme, preferably a transglutaminase, and more preferably factor XIII transglutaminase. The cross-linking enzyme is activatable by the activating enzyme in water with or without a buffer, and at least one structural compound A. The structural compound is crosslinkable by a selective reaction mediated by the crosslinking enzyme to form a hydrogel, wherein the cross-linking enzyme is activated.