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Protein adsorption on polymeric biomaterials: II. Adsorption kinetics

Abstract The adsorption kinetics of seven human proteins on four polymer surfaces were studied under a wide range of solution concentrations. The proteins were albumin (HSA), transferrin (TF), a2-macroglobulin (a2-), three immunoglobulin G monoclonal antibodies (IgG), and fibrinogen (FGN). The polymers were a polyurethaneurea (PEUU), plasticized polyvinyl chloride (PVC), silicone rubber (SR), and polyethylene (PE). The susceptibility of these proteins toward denaturation was estimated by determining the amount of ethanol required to precipitate the proteins from aqueous solution. The results showed that, in general, the intrinsic adsorption rates and the amount adsorbed increased in the order TF, a2-M, HSA, IgGs, and FGN. With the exception of HSA, this is the same order in which the tendency toward precipitation by ethanol increased. At dilute solution concentrations, the measured adsorption rates of HSA, FGN, and one IgG were diffusion-controlled at short adsorption times on SR and PE. In non-diffusion-controlled adsorption, the adsorption rates from dilute solutions were faster on the more hydrophobic SR and PE surfaces, although FGN was an exception to this trend. At higher solution concentrations, multilayer protein adsorption was observed for some protein-surface combinations. Multilayer adsorption was more extensive when the protein or surface involved was HSA, SR, or PEUU.

The influence of preadsorbed canine von Willebrand factor, fibronectin and fibrinogen on ex vivo artificial surface-induced thrombosis

We have examined the effects of preadsorption of several canine plasma proteins on surface-induced thrombogenesis in a canine ex vivo model. Our technique allowed determination of initial deposition and subsequent embolization of 51Cr-labeled platelets and 125I-fibrinogen onto and from polymeric arterio-venous shunts in non-anticoagulated canines. Segments of the tubing were removed at various time points between 2 and 120 minutes of blood contact for examination of the morphology of the thrombus by scanning electron microscopy. Thrombus deposition was measured on uncoated plasticized poly(vinyl chloride) (PVC) and PVC precoated with canine von Willebrand factor (vWF), fibronectin, partially purified fibrinogen (fibrinogen which contained vWF and fibronectin as impurities), or purified fibrinogen (fibrinogen which had been further purified to remove fibronectin and vWF). Preadsorption of all proteins studied enhanced the thrombogenic response relative to that of the uncoated surface. Precoating with vWF or partially purified fibrinogen resulted in the deposition of the greatest number of thrombi, and embolization was slower than on shunts precoated with canine fibronectin or purified fibrinogen. The deposition-embolization profiles for the fibronectin and purified fibrinogen-coated surfaces were similar. The amount and time sequence of initial adhesion and spreading of platelets was related to the extent and time sequence of peak thrombus formation. The partially purified fibrinogen-coated and vWF-coated surfaces had more adhered and spread platelets at the earliest time points and a greater number of larger thrombi at the peak deposition times. The slowest rate of platelet adhesion and spreading was seen on the purified fibrinogen-coated surface. White blood cells were present very early on surfaces precoated with vWF and partially purified fibrinogen, and were present prior to embolization on all surfaces. Major conclusions from this work indicate that, although fibrinogen and fibronectin promote thrombogenesis when adsorbed to a surface, vWF is even more active in promoting platelet deposition and in anchoring thrombi to the surface of biomaterials. Thus, differences in vWF adsorption to biomaterials may be a determinant of surface-induced thrombogenesis.