Vroman effect

The adsorption experiments were carried out by quantifying each of proteins adsorbed on the material from mono-component protein solutions, from four-component protein solutions, and from plasma and diluted plasma. Adsorption profiles of protein were largely different, depending on the aforementioned experimental conditions. For instance, the behavior of any particular protein from diluted plasma varied in response to the extent of plasma dilution. Cooper s results are illustrated in Fig. 3, on fibrinogen adsorption onto five polymer surfaces. It is seen that the adsorption profiles are different one another, being influenced by the different nature of the polymer surfaces. The surface concentrations of adsorbed protein are mostly time-dependent, and maxima in the adsorption profiles were observed. This is interpreted in terms of replacement of adsorbed fibrinogen molecules by other proteins later in time (Vroman effect). Corresponding profiles were also presented for FN and VN. 

In contrast, on the surface of the amino-containing polymeric materials, protonated amino groups introduced in a small proportion under physiological conditions, destroy their surrounding hydrogen bonds to produce, here and there, gaps in the network [127, 128]. Thus, the network structures are considered to become more or less unstable. As a consequence, the residence time of protein molecules trapped by these defective networks will be shorter than in the case of polyHEMA or cellulose. On the surface of these amino-containing materials, reversible protein adsorption and desorption, and also replacement (Vroman effect) - or even protein rejection - will become possible. 

J.A.H. van Laarhoven, M.A.B. Kruft, and H. Vromans, Effect of supersaturation and crystallization phenomena on the release properties of a controlled release device based on eva copolymer, J. Controlled Release, 82(2-3) 309-317, August 2002. 

Recently Horbettl02) and Brash and ten Hove 103) have quantitatively demonstrated the Vroman effect in a series of experiments studying competitive adsorption of fibrinogen, albumin, IgG, and hemoglobin from diluted plasma. 

Slack SM, Horbett TA (1995) The Vroman effect - a critical review. Proteins Interf Ii 602 112-128... 

Krishnan A, Siedlecki CA, Vogler EA (2004) Mixology of protein solutions and the Vroman effect. Langmuir 20(12) 5071-5078... 

Elwing, H. Askendal, A. Lundstrom, I., Competition between adsorbed fibrinogen and high-molecular weight kiniogen on solid surfaces incubated in human plasma (the Vroman effect) influence of solid surface wettability, J. Biomed. Mat. Res. 1987, 21, 1023-1028... 

Predictive models for competitive adsorption accounting for displacement (Vroman) effects. 

A concerted effort is presently needed to study the mechanisms influencing adsorption behavior in protein mixtures. Does adsorption from mixtures behave as the sum of independent adsorption events determined by specific affinity constants charactertistic of each species Can such a simple explanation suffice to explain the peak in adsorption isotherms seen for fibrinogen from plasma ("the Vroman effect") and also from binary mixtures (56,57) If the differences in adsorption behavior of mixtures compared to single adsorbates are better understood than at present, a greater degree of control of the adsorption process to achieve a desired end (e.g., selection of a desired protein) may be possible. For example, if the Vroman effect is a general feature of all protein mixtures, then clearly there is an optimum concentration for adsorption to achieve the greatest selectivity. 

Fibrinogen adsorption from plasma was found to be maximal at intermediate plasma concentrations, and was considerably lower from 70-100% plasma or from 0.01% plasma than from 0.1 or 1% plasma, an observation called the Vroman effect. 

Slack and T. Horbett, unpublished observations). These latter observations support the generalized mixed surfactant mechanism as an explanation of the Vroman effect. 

As we and others continue this line of investigation it is becoming evident that the whole area of competitiveness of protein adsorption in the blood context, which at the moment seems hopelessly mired and anecdotal, may eventually reveal a rational, orderly nature. Vroman has postulated (50) that a rapid sequence of adsorption and displacement events occurs by which, over time, more abundant proteins are displaced by less abundant. The time frame of these events is such that albumin is adsorbed and replaced in a fraction of a second, thus accounting for the fact that it is not often observed on the surface after plasma contact. Clearly the time frame may be expected to vary with the surface so that in some cases the sequence will be relatively fast and in others relatively slow. Thus the apparent absence of a Vroman Effect for hydrophilic polyurethanes may reflect a very rapid sequence, such that a fibrinogen peak would be observed only at very short times or at low plasma concentrations (less than 0.05%). 

The appearance of the Vroman effect and related phenomena can be inhibited by the roughness and the porosity of a surface or due to the formation of hybrid aggregates with macromolecules and oxide NP (Figure 6.41). All these structural features of the interfaces cause reduction of accessibility of pre-adsorbed macromolecules for co-adsorbate molecules as well as for solvent molecules. The confinement effects in restricted space of pores or surface roughness (valleys, Figure 6.34) diminish the mobility of the adsorbed molecules. Therefore, the possibility of the displacement of these molecules by other molecules (even of a larger size) decreases. 

Thus, the surface properties enhancing the adsorption of the first protein can cause diminution of its fraction displaced by the larger second protein subsequently adsorbed. The real-time dynamics of the Vroman effect for HSA and Fg subsequently adsorbed on various (metal, oxide, nonmetal) surfaces monitored by the QCM technique demonstrates the influence of the nature and nano-relief of the surfaces onto the competitive adsorption of proteins. Obtained results suggest that the dynamics of the competitive adsorption of any polymers, biomacromolecules, cells, and microorganisms in aqueous media may be studied in real timescale using the QCM method in parallel with observation by the QELS method. 

Choi, S., Yang, Y, and Chae, J. 2008. Surface plasmon resonance protein sensor using Vroman effect. Biosens. Bioelectron. 24 893-899. 

FIGURE 15.21 Adsorption of fibrinogen from diluted blood plasma on glass, displayed (a) as a function of time for varying dilutions, and (b) as a function of dilution at various time intervals. (Data taken from Vroman, L. and Adams, A.L., J. Colloid Interface Sci., Ill, 391, 1986.) The transient adsorption of fibrinogen from blood plasma is known as the Vroman effect . 

Physisorbed proteins are not stably bound and can be displaced by other proteins. This especially occurs in complex media such as plasma, where fibrinogen physisorption may occur within seconds, following by displacement of more slowly diffusible but stickier proteins (this is sometimes called the Vroman effect). When the surface is transferred to a different medium after protein coating, the type and amount of physisorbed proteins will change until reaching equilibrium with the proteins in solution above the surface. The time scale for desorption can extend over several hours, thus physisorption can be useful to control the initial attachment of cells at the time of seeding. Over a period of several days of culture, however, virtually all cells will have secreted significant quantities of their own extracellular matrix onto the substrate, and the initial surface properties of the material often become irrelevant. 

Protein adsorption from protein mixtures can be complex. For example, when plasma proteins from whole blood bind to biomaterials, albumin often binds initially and is later displaced by fibrinogen. Fibrinogen can then be displaced by other blood proteins (5). This is the Vroman Effect. Although the Vroman Effect was discovered for blood proteins, it may take place in other situations in which multiple components can bind. 

The in vivo effects of protein adsorption onto solid surfaces are hard to follow, because of the Vroman effect (Bamford et al., 1992). The Vroman effect is the phenomenon whereby, when solid surfaces are exposed to mixtures of bbod plasma proteins, such surfaces adsorb different proteins sequentially, so that with time, first one, then another, and then a third protein, etc., finds itself predominantly adsorbed... 

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