One aspect of the invention relates to a hydrogel comprising a non-natural polymer comprising a plurality of pendant nucleophilic groups and a crosslinker comprising at least two pendant electrophilic groups. Another aspect of the invention relates to a hydrogel comprising a non-natural polymer comprising a plurality of pendant electrophilic groups and a crosslinker comprising at least two pendant nucleophilic groups. Yet another aspect of the invention relates to a method for reducing lung volume in a patient comprising the step of administering a hydrogel composition as described herein. Further, hydrogels of the invention may be used to achieve pleurodesis, seal brochopleural fistulas, seal an air leak in a lung, achieve hemostasis, tissue sealing (e.g., blood vessels, internal organs), or any combination thereof. In certain embodiments, the compositions and methods described herein are intended for use in the treatment of patients with emphysema.