The Behaviour of Fibrinogen at Artificial Surfaces

Abstract

The adsorption of fibrinogen from human plasma onto various surfaces was investigated under differing conditions of plasma composition. Previous studies by Vroman have indicated that fibrinogen is only transiently adsorbed from normal human blood plasma, possibly due to displacement by high molecular weight kininogen (HMWK). It is possible that this "Vroman Effect" is a manifestation of the activation of the intrinsic clotting pathway responsible, in part, for thrombus formation on artificial surfaces. The effect was studied using dilutions of human plasma from 0.01% to 20.0% of normal concentration trace-labelled with a small amount of ¹²⁵I labelled fibrinogen. Adsorption of fibrinogen to various materials, including glass and several potentially useful biomaterials was measured. Fibrinogen is initially adsorbed apparently under diffusion limitation and later displaced at a rate which depends on the type of material being tested. There does not appear to be a direct relationship between material properties (contact angle, biocompatibility) and the "Vroman Effect". Studies comparing the effect for a series of clotting factor deficient plasmas seem to indicate that plasminogen and HWNK are the main displacing agents on glass. Factors XI and XII, prekallikrein and other components do not appear to be involved. An attempt to mathematically model the effect was hampered by the lack of adequate models to describe even one-component protein adsorption. An isotherm equation was developed based on a theoretical model of protein exchange and spreading on the surface. The resulting parameter estimates based on data for different surfaces were well conditioned and may provide a good in vitro basis for comparing materials. It is hoped that the theoretical model will also be compatible with dynamic adsorption and ultimately a multicomponent system such as plasma (and the Vroman Effect). This work may lead to a better understanding of blood-material interactions and may provide the basis for a simple in vitro test for the characterization of potential biomaterials.