Combined heparin and polyethylene oxide surface modification for improved blood compatibility

The main objective of this work was to develop a new method for the modification of polymer surfaces with the aim of improving the biocompatibility of the materials, and to gain an improved understanding of surface-blood interactions.; Low density polyethylene was chosen as a substrate for the studies. Polyethylene substrates were first aminated by plasma polymerization of allylamine using a microwave frequency plasma reactor. PEO grafting and heparin immobilization were then achieved using PEO-diisocyanate (M.W. 3400) as a coupling reagent. The grafted PEO and heparin were expected to endow the surface with nonspecific protein-repelling and anticoagulant properties, respectively. PEO was also used as a flexible spacer to enhance the activity of the surface immobilized heparin. Surfaces containing heparin but no PEO were also prepared by reacting aminated surfaces first with methylene diphenyl diisocyanate (MDI) and then with heparin.; Chemical functions in the allylamine plasma polymer were studied using Fourier Transform Infrared (FTIR) spectroscopy. It was observed that the plasma polymerized allylamine had a complex structure containing amine, imine, amide and nitrile functions. The proportion of reactive functional groups present on the allylamine modified surface was quantified by trifluoroacetic anhydride (TFAA) derivatization followed by XPS analysis. The thickness and deposition rate of the plasma polymer were investigated by ellipsometry and XPS using gold-coated silicon as a model substrate. XPS data showed that the deposition of allylamine plasma polymer was essentially constant with time and independent of the substrate.; The surface properties of the PEO- and heparin-modified surfaces were characterized and compared to the unmodified PE surface using water contact angles, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The changes generally follow the trends expected for the various surface modifications, suggesting that the polyethylene surface had been successfully modified by plasma polymerization and the subsequent chemical reactions. The surface densities of total heparin and active heparin were measured by a toluidine blue colorimetric assay and a chromogenic anti-factor Xa assay respectively. The data indicated that the surface immobilized heparin was bioactive and the use of PEO as a spacer was effective in improving the bioactivity of immobilized heparin.; Protein adsorption studies were performed on the surfaces using 125I-radiolabeled proteins (fibrinogen and antithrombin), total protein assay, and immunoblotting. It was observed that fibrinogen adsorption was generally reduced on PEO-grafted surfaces and somewhat increased on surfaces with immobilized heparin. Fibrinogen adsorption was enhanced on the amine-containing surface. Surfaces with immobilized heparin showed enhanced adsorption of antithrombin from buffer and plasma compared to controls.; Total protein assays indicated that the quantities of protein adsorbed to the various surfaces exposed to normal human plasma were largely dependent on the type of surface and were approximately in the range of monolayer adsorption. Immunoblotting data indicated that protein deposition from plasma was complex and many of the plasma proteins were present in the SDS eluates from the surfaces studied. Albumin, fibrinogen, IgG, apolipoprotein A1 and transferrin were the major components of the proteins deposited on all the surfaces. Other detected proteins include factor XII, prekallikrein, HMWK, AT, C3, vitronectin, beta-2-miacroglobulin, haptoglobin, factor B, facto H, and factor I. Protein adsorption was reduced on the PEO-grafted surfaces and slightly increased in the presence of heparin. The amine-containing surface generally adsorbed more proteins than the other surfaces. These results demonstrate that PEO grafting is efficient in reducing nonspecific protein adsorption while immobilized heparin may have weak interactions with pl...