Hydrogels, biocompatible cross-linked polymer networks, could be useful in artificial muscles or cartilage. But they don’t stick well to each other or to living tissues, which limits their use in the body. Shingo Tamesue of Utsunomiya University and colleagues report a solution that resembles sewing fabrics together (Macromolecules 2019, DOI: 10.1021/acs.macromol.9b01084). The team used in situ polymerization reactions to grow polymer threads that weave in and out of hydrogel pieces, binding them together. The researchers first soaked two slices of the polyacrylamide hydrogel in a solution of acrylamide monomers and the radical initiator ammonium peroxodisulfate. They then coated the hydrogels’ surfaces with tetraethylmethylenediamine, which accelerates polymerization of acrylamide to form threads, and quickly pressed the surfaces together. After an hour, they were stuck so tightly that one of the hydrogel slices ripped when the researchers tried to peel them apart. In further tests, the researchers adhered polyacrylamide to another type of hydrogel and to slices of chicken liver. They also used other thread materials formed with nonradical polymerization that may be more biocompatible than ones involving free radicals, Tamesue says.