322 Adsorption of baboon fibrinogen and the adhesion of platelets to a thin film polymer deposited by radio-frequency glow discharge of allylamine J.A. Chinn, B.D. Ratner and T.A. Horbett Department of Chemical Engineering and Center for Bioengineering, BF-10 University of Washington, Seattle, WA 98195, USA Platelet adhesion under static and flow conditions from a washed platelet suspension containing albumin to a polymer deposited by radio-frequency glow discharge of allylamine vapour on a poly(ethylene terephthalate) substrate was measured. Electron spectroscopy for chemical analysis was used to characterize the surface. Fibrinogen adsorption from a series of dilute plasma solutions to radio-frequency glow discharge/allylamine, measured using ‘*? radiolabelled baboon fibrinogen, increased with decreasing plasma dilution to a level much higher than that previously observed on polyurethanes. Elutability by sodium dodecyl sulphate of fibrinogen adsorbed from dilute plasma also increased with increasing plasma concentration, but fibrinogen preadsorbed from plasma became non-elutable when surfaces were stored in buffer for 5 d before contact with sodium dodecyl sulphate. Platelet adhesion to substrates which had been pre-adsorbed with dilute plasma was measured using baboon platelets radiolabelled with “‘In. Adhesion greatly decreased as the plasma concentration used for preadsorption increased, suggesting that non-specific platelet binding to the bare surface occurs when protein coverage is incomplete. Non-specific platelet binding was inhibited to varying degrees by preadsorption of different proteins to the surface. Platelet adhesion to surfaces preadsorbed with dilute (1.0%) baboon and human plasmas lacking fibrinogen (i.e. serum, heat- defibrinogenated plasma and congenitally afibrinogenemic plasma) was diminished compared with normal plasma. Addition of exogenous fibrinogen to the deficient plasma partially restored platelet adhesion to normal levels. Adhesion to surfaces preadsorbed with human plasma deficient in von Willebrand factor was comparable to that observed with normal plasma. The plasma preadsorption studies with fibrinogen deficient media suggested that adsorbed fibrinogen is necessary for platelet adhesion to the radio-frequency glow discharge/allylamine substrate at high protein coverage. However, since adhesion was greatly reduced when the plasma preadsorbed substrate was stored in buffer before platelet contact, the conformation of adsorbed fibrinogen is also important in mediating platelet adhesion to radio-frequency glow discharge. Keywords: P/ate/et, fibrinogen, plasma, allylamine Received 16 July 1990, revised 26 February 1991; accepted 1 March 1991 The adsorption of plasma proteins to foreign materials upon contact with blood is implicated in the blood and tissue compatibility of biomaterials’-4. After initial exposure of a polymer to blood, a protein layer which can mediate subsequent cellular reactions rapidly adheres to the polymer surface . 5-8 While adsorbed fibrinogen has been implicated in mediating the adhesion of blood platelets to numerous polymersg-*3, adsorbed von Willebrand factor may dictate adhesion to subendothelial tissues’4-‘6. In the absence of adsorbed proteins, few Correspondence to Dr B.D. Ratner. polymers are as reactive as subendothelial tissues or collagen-coated substrates”. Investigations of fibrinogen adsorption from plasma and dilute plasma to a variety of polymer surfaces showed fibrinogen adsorption to be greater from inter- mediate dilutions of plasma than from either undiluted or very dilute plasma, and greater at short than at long adsorption times”* lg. The subsequent adhesion of platelets to plasma preadsorbed polyetherurethanes has also been shown to be maximal at intermediate dilutions of plasma13. However, these substrates tend to adsorb relatively little fibrinogen from plasma, compared with 0 1992 Butterworth-Heinemann Ltd 0142-9612/92/050322-11 Biomaterials 1992, Vol. 13 No. 5