Heparin conjugation on poly(l-lactide) fibrous scaffolds fabricated by electrospinning was accomplished by surface functionalization with amine (-NH2) groups using a sequential treatment with Ar-NH3 and H-2 plasmas. The density of the incorporated -NH2 groups was determined by combining a chemical derivatization method with X-ray photoelectron spectroscopy. The time of Ar-NH3 plasma treatment significantly affected the N/C, -NH2/N, and -NH2/C fractions, whereas the plasma power, Ar-NH3 gas composition, and time of H-2 plasma treatment only influenced the -NH2/N and -NH2/C fractions. Scaffold surface functionalization by -NH2 groups significantly increased the amount of covalently bonded heparin compared to a hydrolysis method. The function of immobilized heparin was confirmed by the decrease of platelet attachment during the exposure of the scaffolds to blood from Sprague-Dawley rats. In vitro experiments with bovine aorta endothelial cells demonstrated that heparin conjugation enhanced cell infiltration through the fibrous scaffolds, regardless of the amount of covalently immobilized heparin. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 1408-1414, 2014.