Abstract
Human platelets play a vital role in haemostasis, pathological bleeding and thrombosis. The haemostatic mechanism is concerned with the control of bleeding from injured blood vessels, whereby platelets interact with the damaged inner vessel wall to form a clot (thrombus) at the site of injury. This adhesion of platelets and their subsequent aggregation is dependent on the presence of the blood protein von Willebrand Factor (vWF). It is proposed here that the entrapment of vWF on a substrate surface offers the opportunity to assess an individual’s platelet function in a clinical diagnostic context. Spin coating from demixed solutions of polystyrene (PS) and poly(methyl methacrylate) (PMMA) onto glass slides has been shown previously to support platelet adhesion but the mechanism by which this interaction occurs, including the role of vWF, is not fully understood. In this work, we report a study of the interaction of platelets in whole blood with surfaces produced by spin coating from a solution of a weight/weight mixture of a 25% PS and 75% PMMA (25PS/75PMMA) in chloroform in the context of the properties required for their use as a Dynamic Platelet Function Assay (DPFA) substrate. Atomic Force Microscopy (AFM) indicates the presence of topographical features on the polymer demixed surfaces in the sub-micron to nanometer range. X-ray Photoelectron Spectroscopy (XPS) analysis confirms that the uppermost surface chemistry of the coatings is solely that of PMMA. The deliberate addition of various amounts of 50 μm diameter PS microspheres to the 25PS/75PMMA system has been shown to maintain the PMMA chemistry, but to significantly change the surface topography and to subsequently effect the scale of the resultant platelet interactions. By blocking specific platelet binding sites, it has been shown that their interaction with these surfaces is a consequence of the entrapment and build-up of vWF from the same whole blood sample.
Highlights
Platelets play a vital role in haemostasis and thrombosis [1]
Direct observation of the coatings created by spin coating the solution of 25PS/75PMMA onto glass slides shows a distribution of solidified PS particles embedded in poly(methyl methacrylate) (PMMA) with rounded features glass slides shows a distribution of solidified PS particles embedded in PMMA with rounded features and long striations that radiate in various directions
Surfaces produced by spin coating a 25PS/75PMMA demixed solution in chloroform onto glass slides have been shown to have topographical features that are capable of the direct entrapment of autologous von Willebrand Factor in a form that can induce subsequent platelet interactions within the same blood sample
Summary
Haemostasis is concerned with the arrest of bleeding from injured blood vessels, whereby platelets are recruited by blood proteins to form a thrombus (clot) [2]. The normally coiled vWF uncoils on adherence to the collagen that is exposed when the vessel endothelium layer is no longer intact, resulting in the availability of receptors for subsequent platelet interactions [4]. Under these conditions, the platelets initially bind, release and roll off the surface until the vWF has attained its final conformation at which point they adhere permanently thereby commencing the formation of a thrombus. This a critically important part of the natural processes for the control of bleeding, obviously if any part of the process does not behave as required there can be adverse consequences [1]
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