A method of concentrating proteins from whole blood comprising exposing whole blood to covalently crosslinked hydrogel to remove water from the blood into the hydrogel to thereby concentrate the proteins in the whole blood. The hydrogel may absorb, for example, 50% or 90% of the water from the blood while excluding proteins with a weight of more than about 15,000 Daltons. In some embodiment, the hydrogels are dry, sterile, and spherical.