Surfaces capable of covalently immobilizing a dense layer of bioactive protein may be used to stimulate desired cellular responses at the surface of an implant. Pulse biased plasma polymerization onto metallic substrates is studied with the aim of producing surfaces suitable for such biomimetic in vivo implants. Plasma polymers were formed that are graded from stainless steel to a pure plasma polymer to provide the exceptionally strong adhesion necessary for in vivo applications, such as in cardiovascular stents. We show that the use of pulsed bias during deposition enhances the density of free radicals and improves the covalent protein binding capacity of the surface, indicating that the free radicals are responsible for the direct covalent attachment of protein observed after incubation in protein-containing buffer solution. The radical density and degree of covalent binding was found to increase with the magnitude of the pulsing voltage. Aging in air reduced the radical density in the plasma polymer surfaces for all deposition conditions examined but substantially more radicals remained for the surfaces deposited with pulsed bias. Annealing in vacuum recovered the density of the radicals in the polymers subjected to pulsed bias while those prepared without pulsed bias showed a reduction in radical density upon annealing. The degree of covalent attachment increased linearly with the thickness of the polymer layer and showed a saturation at a thickness at which the total number of free radicals was equal to the number required to bind a full monolayer of the protein.