Multiprotein Adsorption Lab Report

A Comprehensive Model of Multiprotein Adsorption on Surfaces

Adsorption

It occurs when a solution containing dissolved proteins comes into contact with a solid surface

The mechanism suggested here for protein adsorption is an extension of the classic reaction-diffusion mechanism which is followed by a wide variety of physical phenomena. The vroman effect arises when this basic mechanism is coupled with the presence of multiple proteins, each diffusing at different rates to the surface and engaging in competitive adsorption here.

All proteins have uniform concentration everywhere before the surface comes into contact with blood or any other multiprotein solution. Experiments show that upon contact with surface proteins are adsorbed as a monolayer.

The rate at which reversibly adsorbed protein changes to irreversibly adsorbed protein depends on rate constant of irreversible adsorption, and on the concentration of reversibly adsorbed protein.

The driving force for increasing the surface affinity are: hydrophobicity of a surface (directly proportional, dominating factor), Electrostatic forces, Van der Waal forces, and Steric repulsion (in case surface is coated with a polymer such as polyethlylene oxide)

This study deals with uncoated surfaces in which first three kind of forces are active. The hydrophobic and van der Waal forces act in similar fashion, although hydrophobic forces are much larger.

Hence, adsorption is primarily caused by hydrophobic and van der Waal forces, with some electrostatic contribution.

Desorption occurs because the proteins in the solution modify the electrochemical environment or the adsorbed protein to overcome its hydrophobic attraction of the surface. It supports the fact that desorption does not occur in a protein free

Every time a protein is displaced by another, a fraction of the first protein will remain on the surface. The magnitude of this fraction will depend on how long the protein remained on the surface before displacement, that is, on the time of two successive protein peaks. Larger differences in diffusivity and smaller differences in surface affinity will increase the tie between peaks, and consequently the magnitude of non-elutable protein on the surface and final composition of the adsorbed layer.

Finally, the flow of solution will increase the diffusion or transport rates of the all proteins to the surface. This in effect decrease the differences in diffusion rates and will cause all the protein peaks to occur earlier and cause a crowding of these peaks. Higher fluid flow rates will increase the crowding, although this does not qualitatively change the adsorption process.

Mathematical Model

Consider a multiprotein solution in contact with a surface below it at the point z=0, where z is the vertical distance in the solution measured from the surface. In the absence of convection, assuming that there are no horizontal concentration variations, the domain equation for species mass conservation is

(∂x_i)/∂t=D_i (∂^2 x_i)/(∂z^2 ) x = mole