China
Africa
Explore chapters and articles related to this topic
Surface Functionalization Techniques
Published in Jay L. Nadeau, Introduction to Experimental Biophysics, 2017
The Vroman effect refers to a phenomenon where abundant, easily adsorbed proteins adhere to a surface first, and then are displaced by less abundant proteins with stronger binding constants. In blood plasma, the first protein adsorbed is fibrinogen; it is later replaced by other, less abundant proteins. Consider a solution consisting of only two proteins in solution above a sensor surface: fibrinogen and kininogen. The association and dissociation constants of fibrinogen are ka and kd, respectively. The association constant for kininogen is ks when it binds to the bare surface, and kc when it binds to a site containing fibrinogen, and it binds irreversibly. Write differential equations for this system and solve them with the assumption that fibrinogen binding is fast relative to kininogen binding.
Protein, Cellular and Soft Tissue Interactions with Polyurethanes
Published in Nina M. K. Lamba, Kimberly A. Woodhouse, Stuart L. Cooper, Polyurethanes in Biomedical Applications, 2017
Nina M. K. Lamba, Kimberly A. Woodhouse, Stuart L. Cooper
The composition of the adsorbed protein layer deposited from plasma or a multi-component protein solutions is time-dependent with respect to composition.102 The most widely studied compositional change of the protein layer adsorbed from plasma has been termed the “Vroman Effect”. This phenomenon first was reported by Vroman & Adams,102 who found that although fibrinogen was adsorbed from plasma onto glass in the initial course of events, it was later “converted” and could no longer be detected. This “conversion” was actually the displacement of adsorbed fibrinogen by high molecular weight kininogen (HMWK), a low abundance protein with a higher affinity than fibrinogen for the glass surface (Figure 2).103 The majority of studies of the Vroman Effect have been conducted on glass. It is now believed that the Vroman Effect is only part of a sequence of protein deposition and displacement; the proteins adsorb to the surface according to an order that is determined by their relative concentration and transport rates in the blood, and displaced by lower concentration proteins with higher affinity for the particular surface. Albumin, the most abundant protein, adsorbs first and unless the surface has a high affinity for this protein over the other proteins present, albumin will be replaced with IgG, then fibrinogen, and HMWK.104 It is expected that other trace proteins in the blood are also adsorbed and replaced, and the sequence of adsorption and replacement will terminate when a minimum in surface free energy is achieved.105 Investigations into the Vroman Effect on polymer surfaces have involved studies of the maximum in fibrinogen adsorption that is observed on a surface upon plasma dilution, and the surface concentration of fibrinogen against time. Some results are shown in Figures 3 and 4. The observed maximum is material dependent and it should be noted that differences in the concentration at which maximum protein adsorption occurs to a given material have been reported.64 Maximum fibrinogen adsorption onto polyurethane surfaces occurs at a 0.5–1.0% plasma solution;52,74,106 for glass it is 1%, for polyethylene, 0.1%, and for Teflon, 10%.63 Both the observed displacement of fibrinogen from glass by HMWK and the unusual concentration dependence of fibrinogen adsorption from plasma can be explained in terms of mass action effects. The competition between proteins for binding sites on a surface increases as the number of vacant binding sites decreases.107
In Vitro models for thrombogenicity testing of blood-recirculating medical devices
Published in Expert Review of Medical Devices, 2019
Within seconds of blood exposure, biomaterial surfaces rapidly adsorb serum proteins onto their surface. These proteins desorb and are exchanged for higher binding affinity proteins in a process known as the Vroman Effect. Figure 1 illustrates the pro-thrombotic events catalyzed by biomaterial contact and the Vroman pattern: albumin, immunoglobulin G (IgG), fibrinogen, and high molecular weight kininogen (HMWK) [15]. Platelets interacting with these bound proteins adhere to the material and upregulate membrane-bound phosphatidylserine [16]. The downstream pro-thrombotic processes from platelet activation are illustrated in Figure 2. When serum proenzymes such as prothrombin bind at this active site, zymogen-protease conversions produce the active form of the enzyme, thrombin [17–19]. In platelet aggregates, thrombin amplifies the coagulation response. A positive feedback loop is created that increases platelet activation through platelet activation factor (PAF), proteinase-activated receptor (PAR) 1 and 4 on platelet membranes [20]. Platelets also degranulate, releasing cytokines [21] and develop pseudopodia to strengthen adherence to the surface and other platelets [22]. Thromboxane A2 diffuses across the platelet plasma membrane and acts as an activator for other platelets [23]. Under flow conditions, platelets are captured through interaction with von Willebrand factor (vWF). This interaction is mediated through two receptors: GPIb-IX-V and platelet integrin (αIIbβ3). Active thrombin cleaves at least two sites on the fibrinogen molecule making non-covalent interactions between fibrinogen molecules [24,25] producing aggregated insoluble fibrin fibers. The fibers are crosslinked by Factor XIII [26] to form an aggregated structure that can trap platelets, red blood cells, and thrombin by binding at two distinct binding sites [20]. The fibrin-mediated clot is susceptible to fibrinolysis via plasmin, an enzyme protease [24].