AbstractThe objective of this study was to investigate the bioactivity and protein‐resistant properties of dual functioning surfaces modified with PEG for protein resistance and corn trypsin inhibitor (CTI) for anticoagulant effect. Surfaces on gold substrate were prepared with varying ratios of free PEG to CTI‐conjugated PEG. Two methods designated, respectively, “sequential” and “direct” were used. For sequential surfaces, PEG was first immobilized on gold and the surfaces were incubated with CTI at varying concentration. For direct surfaces, a PEG–CTI conjugate was synthesized and gold surfaces were modified using solutions of the conjugate of varying concentration. The CTI density on these surfaces was measured using radiolabeled CTI. Water contact angles were measured and the thickness of PEG–CTI layers was determined by ellipsometry. Fibrinogen adsorption from buffer and human plasma, and adsorption from binary solutions of fibrinogen and α‐lactalbumin were investigated using radiolabeling methods. Bioactivity of the surfaces was evaluated via their effects on FXIIa inhibition and plasma clotting time. It was found that as the ratio of CTI‐conjugated PEG to free PEG increased, bioactivity increased but protein resistance was relatively constant. It is concluded that on these surfaces conjugation of PEG to CTI does not greatly compromise the protein resistance of the PEG but results in improved interactions between the CTI and the “target” protein FXIIa. At the same CTI density, sequential surfaces were more effective in terms of inhibiting FXIIa and prolonging clotting time. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2012.