Although only being able to produce short hydrogel fibers, production of hydrogel fiber by polymerizing the hydrogel network inside a tubular mold and push out the fiber forcefully can also be achieved. But the friction will increase with the increasing length, and only short hydrogel fibers are feasible.
A case would be the production of poly(acrylamide-co-poly(ethylene glycol) diacrylate) fiber reported by yun et al. The pregel solution was a mixture of AAM,  [https://www.sigmaaldrich.com/catalog/product/aldrich/455008?lang=en&region=US poly(ethylene glycol) diacrylate] (PEGDA, crosslinker), and [https://www.sigmaaldrich.com/catalog/product/aldrich/405655?lang=en&region=US&cm_sp=Insite-_-caSrpResults_srpRecs_srpModel_2-hydroxy-2-methylpropiophenone-_-srpRecs3-1 2-hydroxy-2-methylpropiophenone] (photoinitiator). The mixture was injected into a tubular mold and extracted through hydrostatic force afterwards.