Electrostatic forces on the surface of metals as measured by atomic force microscopy

Electrostatic forces play an important role in modulating the interaction of plasma proteins and blood cellular components with the surface of the vascular endothelium. Based on the concept that electrostatic forces residing on the surface of metal intravascular prostheses, such as the stent, also are critical in influencing blood interactions with those surfaces and the vascular wall, these studies were designed to measure these forces on 4 metals using atomic force microscopy (AFM). AFM measurements performed in a low saline aqueous medium at physiological pH indicate a similar net electronegative surface charge level for gold and 316l stainless steel that is significantly higher than the level measured on an electropolished Nitinol surface. Heat oxidation of the Nitinol surface increased the overall electronegativity and created a more homogeneous surface charge distribution. This study demonstrates that AFM force measurements can be a valuable approach to understanding the electrostatic surface of metallic as well as other biomaterials that may be important in understanding how these surfaces influence vascular healing at intravascular interventional sites.