Different cellular and humoral responses to blood -contacting surfaces have been shown for SAMs with varying functional groups. Strong platelet ad hesion and degranulation as well as a high plasmatic coagulation initiatio n on surfaces with both anionic and hydrophobic properties obviously lead to syne rgistic effects resulting in a significantly stronger coagulation activation. Obviously neith er platelet adhesion / activation nor contact activation on anionic moieties singularly leads to strong thrombus formation if no other enhancing factor is present.