A poly-electrolyte composition for forming a water insoluble copolymer suitable as a hydrogel, wherein the copolymer is formed by means of free radical polymerization of at least a first and a second hydrophilic monomer, wherein the first monomer is selected from vinylic sulphonic acids, vinylic phosphonic acids or a water soluble salt thereof, and wherein the second monomer is a vinylic monomer with an electron-withdrawing spacer between the double bond and an acidic group, at least one compound selected from the group consisting of monomers comprising an acidic group either in the free acid form or in the form of a water soluble salt, and of which the logarithm of the acid dissociation constant (pKa) in the free acid form has a value smaller than 3.5.
