Described herein are methods to occlude structures and malformations with radiopaque hydrogel filaments with delayed controlled rates of expansion permitting the repositioning of the device once inside the structure or malformation. Further described is a method for forming a device for implantation in an animal comprising a difunctional, low molecular weight ethylenically unsaturated shapeable macromer an ethylenically unsaturated monomer and a radiopaque element, wherein said device contains no support members.
