IN-VITRO LEUKOCYTE ADHESION TO MODIFIED POLYURETHANE SURFACES .3. EFFECT OF FLOW, FLUID MEDIUM, AND PLATELETS ON PMN ADHESION

The operation of filters used to remove leukocytes from red cell conce ntrates may depend on the adhesion and mechanical trapping of leukocyt es. If adhesion is a major component of filtration then filter materia ls which augment leukocyte adhesion will be useful. In previous leukoc yte adhesion studies, done without flow, poly(ethyleneimene) (PEI) mod ified polyurethane (PU) films were shown to have greater adhesion when compared with unmodified PU. Since filtration is done under flow cond itions, it was decided to study PMN adhesion at a number of flow rates using an established parallel plate flow cell. The influence of dival ent cations, plasma and platelets were investigated in the presence of red cells, 40% Hematocrit. The number of adherent PMNs to the PEI mod ified films was always substantially higher than that for the unmodifi ed ones when the shear rate was set at 30 s-1. When using Tyrode's sol ution containing albumin, with or without divalent cations, a maximum in PMN adhesion was found between the shear rates of 10 and 100 s-1. W ith Tyrode's solution containing albumin and with 10% (v/v) plasma in saline, the addition of platelets increased PMN adhesion when divalent cations were absent. Adhesion levels with 10% (v/v) plasma in saline were reduced when compared to Tyrode's solution containing albumin wit hout divalent cations. These results support the use of filtration con ditions where the concentration of plasma is reduced and the concentra tion of divalent cations is increased. Detailed evaluation of filter f unction with flow rate is also recommended. A cell adhesion promoting polymer coating, such as PEI, may be useful in improving filter effici ency.