A co-polymer with hydrophobic and hydrophilic segments was allowed to adsorb from aqueous solution onto glass previously made hydrophobic by derivatization with octadecyl dimethylchlorosilane. The polymer is thought to adsorb via its hydrophobic segments, leaving the hydrophilic segments free to extend into the water. After allowing cells to settle on the treated surface, the shear stress at the chamber wall required to remove red blood cells, Dictyostelium discoideum amoebae and Escherichia coli was determined in a calibrated laminar flow chamber. On octadecyl glass a shear stress of 2–3 Nm-2 evicts 50% of adherent red cells and E. coli. No D. discoideum amoebae could be removed at 5Nm-2. In striking contrast, the lowest experimentally obtainable shear stress of 0.03 Nm-2 removes 97.0-99.5% of cells of all three types from the polymer-treated surface, even after a cell residence time of 1 h without flow in the absence of free polymer. The minimum shear stress of 0.03Nm-2 corresponds to only approximately equal to 20 times the force of gravity on a red cell. The mechanism of action of the polymer and the implications of the results are discussed.

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