Motif‐programmed artificial proteins with mineralization‐related activity were covalently immobilized onto the surface of a hydrogel, poly(2‐hydroxyethyl methacrylate) (PHEMA). We investigated the influence of assaying conditions upon the ability of three selected proteins (PS64, PS382 and PS458) to modulate calcification in vitro. A long‐term assay measuring the real amount of calcium phosphate phase in the protein‐modified PHEMA showed that all proteins enhanced the uptake of calcium by the hydrogel. For PS382 and PS458, this is a behaviour opposite to that displayed when the same proteins were tested in a free state by a rapid solution assay. Such difference may be attributed to a restricted mobility of the proteins due to immobilization.
