A technique is described to study simultaneously the adsorption and desorption of colloidal particles on collector surfaces in a parallel plate flow chamber. Using a phase contrast microscope equipped with an ultra long working distance objective, the deposition process can be observed in situ. Analysis of successively stored images yields the time of arrival and departure of each colloidal particle, thus enabling determination of the adsorption and desorption rates, as well as of the total number of particles deposited. In addition the method allows analysis of the spatial arrangement of deposited particles, while distinguishing between upstream and downstream deposition of particles, yielding pair distribution functions, going from -180 ° to + 180 °. In this paper the technique has been applied to study the deposition of 736-nm diameter monodisperse polystyrene latex particles from a potassium nitrate solution ( 1 and 60 raM) to glass, using varying flow rates (0.034 to 0.456 cm 3. s-l). Initial deposition rates J0 were derived from the total number of adhering particles n (t) as well as from the experimentally measured time dependence of the deposition rate j(t). The results showed clear tendencies with ionic strength and flow rate. The desorption ratesjdes(t) were small and the desorption rate coefficients/3 were dependent on the residence times of the adhering particles. The blocked areas, derived from the deposition kinetics, ranged from 8 to 675 times the geometrical cross section of a particle, depending on the experimental conditions.
In this article we studied the adsorption of serum albumin to substrata with a broad range of wettabilities from solutions with protein concentrations between 0.03 and 3.00 mg.mL-1 in a parallel-plate flow cell. Wall shear rates were varied between 20 and 2000 s-1. The amount of albumin adsorbed in a stationary state was always highest on PTFE, the most hydrophobic material employed and decreased with increasing wettability of the substrata. Increasing stationary amounts of adsorbed albumin were observed with increasing wall shear rates at the lowest protein concentration. Inverse observations were made at the highest protein concentration. Transmission electron micrographs of replicas from the albumin-coated substrata showed that proteins were mostly adsorbed in islandlike structures on the hydrophobic substrata. The tendency to form islandlike structures was shear rate- and concentration-dependent and disappeared gradually going to more hydrophilic substrata. On glass, the most hydrophilic material employed, a homogeneous, well distributed, fine knotted, reticulated structure was found. In conclusion, this study demonstrates that both the amount of adsorbed albumin as well as the surface structure of the adsorbed proteins are regulated by the substratum wettability. This observation may well account for the fact that substratum properties can be transferred by an adsorbed protein film to the interface with adhering cells or microorganisms.
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