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

Electrostatic forces play an important role in modulating the interaction o f plasma proteins and blood cellular components with the surface of the vas cular endothelium. Based on the concept that electrostatic forces residing on the surface of metal intravascular prostheses, such as the stent, also a re critical in influencing blood interactions with those surfaces and the v ascular wall, these studies were designed to measure these forces on 4 meta ls using atomic force microscopy (AFM). AFM measurements performed in a low saline aqueous medium at physiological pH indicate a similar net electrone gative surface charge level for gold and 316l stainless steel that is signi ficantly higher than the level measured on an electropolished Nitinol surfa ce. Heat oxidation of the Nitinol surface increased the overall electronega tivity and created a more homogeneous surface charge distribution. This stu dy demonstrates that AFM force measurements can be a valuable approach to u nderstanding the electrostatic surface of metallic as well as other biomate rials that may be important in understanding how these surfaces influence v ascular healing at intravascular interventional sites.