Disclosed are synthetic polypeptides modeled after NspI nucleoporin which are useful for forming hydrogels characterized by selective permeability. The polypeptides and hydrogels formed from them include phenylalanine-glycine (FG) repeats, which are believed to participate in the selectivity of the nuclear pore complex. Also disclosed are filtering devices, drug delivery devices, and methods of separating or selectively filtering macromolecules using the hydrogels.