Adhesion of platelets and neutrophilic granulocytes on glass and FEP teflon during exposure to shear stress in a parallel plate flow chamber system

Abstract

Biocompatibility of biomaterials is an increasingly important aspect of modern medicine. As many materials come into contact with blood, their capacity to activate platelets (PTL) or polymorphonuclear neutrophilic granulocytes (PMN) is relevant for their functioning. In order to obtain more insight into the various steps underlying activation processes, the interaction of platelets and PMN with biomaterials was studied with a newly developed dynamic analysing system, based on a parallel plate flow chamber. The aim of this study was to determine the adhesion and activation of PTL and PMN on glass and FEP-teflon, two materials with different wettabilities, during exposure to shear stress in a flow chamber, using image analysis and biochemical analytical methods. We assessed the reliability of the flow chamber model to stimulate in vivo conditions more closely than hitherto described static models. Platelets and PMN were isolated from freshly obtained human peripheral blood. Both PMN and platelets were observed at 37°C in a flow chamber system exposed to glass and FEP-teflon samples under different conditions of shear stress. A shear stress of 0.28 Pa was chosen, resembling the physiological venous situation and a shear stress of 1.3 Pa was used in order to simulate arterial flow conditions. The number of adherent cells and their two-dimensional area were analysed using an image analysis system. Platelet release of thromboxane A 2 was measured to estimate their state of activation. At the end of both experiments, adherent PMN and platelets were studied by electron microscopy. Non-activated PMN showed a biphasic adhesion kinetic with maximum peaks after 4 and 30 min of venous shear stress under exposure to both glass and FEP-teflon. Activated PMN showed a linear increase of adherent cells up to values of about 1100 cells mm −2 on glass and up to values of about 700 cells mm 2 on FEP. Arterial conditions decreased the number of adherent activated PMN. The adhesion of PTL on glass showed a linear increase, reaching a plateau after 40 min. The maximum thromboxane A 2 release was observed after 20 min. Scanning electron microscopy gave significant ultrastructural differences depending on the biomaterial and shear stress conditions. The dynamic model used in this study on activation of blood cells in contact with biomaterials should prove to be a useful method to give more insight into the individual steps involved in activation processes.