the invention provides fabricated tough hydrogels , hydrogel - containing compositions , and methods of making the same . the invention also provides methods of implanting or administering the tough hydrogels , or the hydrogel - containing compositions to treat a subject in need . methods of cross - linking pre - solidified or pre - gelled hydrogel particles and making crosslinked tough hydrogels , and crosslinked tough hydrogel - containing compositions also are disclosed herein .