Biomedical Engineering Reference
In-Depth Information
Figure 6.8
Interaction of blood components with a surface: (a) coagulation pathway and (b) fi bri-
nolytic pathway.
steps, and since one enzyme can activate many substrate molecules, the reactions
are quickly amplified to generate significant amounts of thrombin and subsequent
platelet activation, form fibrin, and stop bleeding.
6.4.3.1 Platelet Interaction to Artifi cial Surfaces
Platelets are the smallest (diameter 2-4 mm) anuclear cells present in human blood
and play an important role in the formation of blood clot. The number varies from
150,000 to 300,000/mL blood (~0.3% of blood volume). Platelets serve three pri-
mary functions in blood clot formation:
1.
Adhering to the surface
. Platelets interact with the adsorbed proteins
present on the synthetic surface through the mediation of the von Will-
ebrand factor and platelet membrane glycoproteins. Since platelets interact
predominantly with the bound proteins and not the prosthetic material
itself, the concentration of surface ligands presented by the bound proteins
affect short and long term functionality of the biomaterial.
2.
Releasing and providing molecules required for many of the reactions for
the processes of the coagulation cascade.
After adherence, platelets undergo
morphological changes, from discoid cells to spherical cells with tentacles
or pseodopodia. Granules within the cells release a number of components
including platelet factor 4 (PF4),
β
thromboglobulin (bTG), ADP, Ca
2+
,
and
fibrinogen.
3.
Recruiting, activating other platelets and attaching to them to form aggre-
gates.
Activated platelet-surface phospholipids tend to recruit and stimulate
