For years the main source of bone for replacement purposes was cadavers (dead bodies). In fact, the Red Cross maintains a "bone bank" for just this purpose. Recently, physicians have experimented with using metals for bone replacement. Two alloys (mixtures of two or more metals)—titanium and cobalt chromium—have been frequently tested. Because any foreign substance in the body is subject to rejection, scientists are constantly trying to find more acceptable materials.
Specifically, scientists are looking for substances that more closely resemble real bone. Hydroxyapatite is a mineral that makes up about 65 percent of living bone. Attempts to bake natural hydroxyapatite powder into a hard bone substitute have often failed. The high processing temperature needed for baking causes the hydrogen-oxygen mixture to boil off, leaving researchers with a weak ceramic (a material like pottery or tile). Strengthening the ceramic with silica (a hard, glassy mineral) and other elements usually causes a high body rejection rate.
A chemist at the University of Texas named Richard J. Lagow developed a way the synthesize hydroxyapatite. His process created a strong and porous (full of small pores, or holes, through which material may pass) form similar to tooth enamel. When this material is introduced into the body, its porous nature allows blood vessels and cells to enter. The absoption process gradually breaks down the implant and creates pores into which natural bone can grow. In the late 1980s testing began of Lagow's discovery for dental and orthopedic use.