Characterization of transient platelet contacts on a polyvinyl alcohol hydrogel by video microscopy

Acridine orange labelled, washed human platelets were counted and tracked o n polyvinyl alcohol (PVA), heparin-PVA and polyethylene (PE)-coated coversl ips with a view to understand why transient contact on the PVA hydrogels le ad to elevated platelet activation and consumption relative to polyethylene . Over the 4 min of initial contact that was studied, platelet adhesion was higher on PE than on PVA or heparin-PVA at both 40 and 200 s(-1), as expec ted, regardless of whether the surfaces were pre-treated with albumin or fi brinogen. Not all platelets appearing to make contact with the surface, act ually attached. For example, less than 2% of the platelets contacting album in pre-treated PVA (at 40 s(-1)) remained adherent at the end of the initia l 60 s observation time, while the corresponding number for PE was greater than 9%. A greater fraction of the platelets remained adherent at the highe r shear rate or with fibrinogen pre-treatment, but the difference between P VA and PE remained similar: for example, with fibrinogen pretreatment at 20 0 s(-1), similar to 25% of the platelet contacts resulted in adhesion on PV A while 66% did so on PE. While net platelet adhesion was less for the hydr ogels, than for PE, the total number of contacts (adherents + non-adherents ) were more comparable and unexpectedly higher for albumin pre-treatment th an for fibrinogen. Net platelet adhesion is but one component of the total platelet interaction with a material surface. Fluorescent video microscopy has been shown to be a useful, albeit not unequivocal, method for assessing the platelets that make contact with but do not adhere to a surface. (C) 1 999 Elsevier Science Ltd. All rights reserved.