3. Metals as Biomaterials

Metals are generally hard, opaque, shiny, malleable, ductile, and conductive materials. Organization of the atoms in solid metals is generally close-packed surrounded by others, having crystal structures as body-centered cubic (bcc), face-centered cubic (fcc), or hexagonal close-packed (hcp). Outer shell electrons are delocalized and free to move and form a kind of cloud around atoms. Meanwhile atoms stay together due to the electrostatic interactions created among each other. This kind of bond is named as metallic bond. Since the outer shell electrons are not strongly bonded to the total structure, metals can easily loose them in chemical reactions and form cations. Electrostatic interactions among cations and anions form salts which are soluble in aqueous media. Metals can form alloys by mixing them with other metallic elements at the molecular level. The main purpose of forming alloys is to enhance some properties of the metal such as make it less brittle, harder, and more resistant to corrosion or have a more desirable color and luster. Metals have several properties that are specific to them, including malleability, which allows the shaping of metal into implants, and ductility, which refers to the ability to draw out metal in the shape of wire and is an important property in allowing the manufacture of intramedullary rods, screws, and long stems.