Silica glass and silylated silica glass have been used extensively as model surfaces for studying the interactions of biological systems with specific chemical functions. In this work, the adsorption of plasminogen to silylated silica glass materials has been investigated with the objective of providing data for the development of a profibrinolytic or clot lysing surface for blood-contacting applications. The adsorption of plasminogen from Tris buffer to silica glass, lysine modified silica glass, and its sulfonated silica glass precursor has been investigated. The isotherms (25-degrees-C) suggest high affinity, Langmuir type adsorption. Adsorption capacities are in the order sulfonated silica > lysinized silica > unmodified silica. Estimates of the apparent affinity constants based on the Langmuir equation indicate that the affinity of plasminogen is greater for the lysinized surface than for either the silica glass or sulfonated silica glass. Experiments on the adsorption of plasminogen to the sulfonated and lysinized silica glass in the presence of epsilon-amino caproic acid (EACA), known to interfere with plasminogen binding to lysine, were also carried out. Adsorption plateau values for the sulfonated surface with and without EACA in the buffer were the same. For the lysinized surface, adsorption was reduced in the presence of EACA. Desorption experiments against Tris buffer showed that for the lysinized and sulfonated surfaces, 70-80% of the protein was irreversibly bound, with slightly higher reversibility on the lysinized surface. It is concluded that the mechanisms of adsorption of plasminogen to the lysinized surface and sulfonated surface are different, and that the lysine binding sites of plasminogen may be utilized in its interactions with the lysinized surface. (C) 1994 Academic Press, Inc.