The present invention provides both crosslinked polymer compositions capable of forming hydrogel upon exposure to an aqueous environment and thiosulfonate hydrogel-forming components. The thiosulfonate hydrogel-forming components of the invention are preferably multi-arm thiosulfonate polymer derivatives that form a crosslinked polymer composition when exposed to a base without requiring the presence of a second cross-linking reagent, redox catalyst, or radiation. Methods for forming hydrogel compositions, as well as methods for using the hydrogel, are also provided.