Structured surfaces platelet adhesion

The majority of hemocompatibility studies are performed under static conditions, but some groups considered the effect of flow on platelet adhesion in dynamic experiments. As one example, randomly structured PMMA surfaces with feature sizes of 40 nm, 80 nm, and 400 nm and heights of 3nm, 13 nm, and 50 nm were investigated under flow conditions [108,109], Experiments with human whole blood showed a preferred adsorption of vWF compared to that of fibrinogen and albumin, which is in conflict with other static studies. It is apparent that different adsorption behaviors of plasma proteins can be observed under different flow conditions. The platelet adhesion was highest on those samples with the most vWF adhesion, namely the larger structures. Experiments were carried out with washed platelets and revealed other results. Platelets preferred the smaller structured surfaces for adhesion, which shows the severe influence of blood cells and plasma proteins on the adhesion behavior of platelets [108]. 

When platelets were mica-activated they exhibited a dramatic changes of cell shape (Fig. 2a). The most striking features of the mica-activated platelets surface morphology were the formation of two different actin-based structures, filopodia and lamellipodia, and the increase in area of platelet surface. Platelets in the initial stages of adhesion to mica produced several long filopodia with width of 180-300 nm and height of 60-90 nm extending over the substrate. As the adhesion process advanced, the filopodia expanded laterally over the... 

Discoid platelets become spherical with numerous short, blunt irregular membrane projections and extend long filopodia after ADP-activation in the suspension. In contrast, platelet adhesion and spreading to mica involve the formation of two different actin-based structures, filopodia and lamellipodia, and the increase of the platelet surface. These results indicate that the SFM which generates image contrast by a way completely different from light and electron microscopy is applicable for a hemostasis analysis. 

In this article it is shown that a completely antithrombogenic surface can be obtained from synthetic polymers without any help of bioactive polymers as heparin and urokinase. Such a surface has a diffuse structure, which essentially differs from that of so-called hydrogels which have a relatively low water content. There is no reason to suspect that the interaction of the polymer surface with plasma proteins initiates a series of complex biochemical events leading to thrombus formation. Rec i% it has been reported that even if proteins deposit on a material to a multilayer, the proteins at the outermost layer of multi-layered protein deposit might remain intact, which would eventually prevent platelet adhesion... 

Figure 10.10 Plain (a) and pillar structured (b) PDMS surfaces after platelet adhesion experiments.

PDMS Protrusions and ridges rf=39.7nm 20 pm length Platelet adhesion Static, in vitro ADP-activated platelets Double-structured surfaces most effective [98]... 

PU Nano tubes Protrusions h 40nm rf=lOOnm Ridges /t = 100nm w = 500nm Platelet adhesion and activation Dynamic, in vitro Human PRP Structured surfaces with higher contact angle few platelets, no shape change [99]... 

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