text: Metallic bonding refers to the specific bonding between positive metal ions and surrounding valence electron clouds. This intermolecular force is relatively strong, and gives rise to the repeated crystalline orientation of atoms, also referred to as its lattice system. There are several types of common lattice formations, and each has its own unique packing density and atomic closeness. The negatively charged electron clouds of the metal ions will sterically hinder the adhesion of negatively charged protein regions due to charge repulsion, thus limiting the available binding sites of a protein to a metal surface.
  The lattice formation can lead to connection with exposed potential metal-ion-dependent adhesion sites (MIDAS)  which are binding sites for collagen and other proteins. The surface of the metal has different properties than the bulk since the normal crystalline repeating subunits is terminated at the surface. This leaves the surface atoms without a neighboring atom on one side, which inherently alters the electron distribution. This phenomenon also explains why the surface atoms have a higher energy than the bulk, often simply referred to as surface energy. This state of higher energy is unfavorable, and the surface atoms will try to reduce it by binding to available reactive molecules.   This is often accomplished by protein adsorption, where the surface atoms are reduced to a more advantageous energy state.
  The internal environment of the body is often modeled to be an aqueous environment at 37 °C at pH 7.3 with plenty of dissolved oxygen, electrolytes, proteins, and cells.  When exposed to oxygen for an extended period of time, many metals may become oxidized and increase their surface oxidation state by losing electrons.  This new cationic state leaves the surface with a net positive charge, and a higher affinity for negatively charged protein side groups. Within the vast diversity of metals and metal alloys, many are susceptible to corrosion when implanted in the body. Elements that are more electronegative are corroded faster when exposed to an electrolyte-rich aqueous environment such as the human body. Both oxidation and corrosion will lower the free energy, thus affecting protein adsorption as seen in Eq. 1.