Titanium As Biomaterial
There exists a great number of metals and alloys, but only a very few are suitable candidates for use as a biomaterial. Why? A living body is a relatively corrosive environment, and therefore a biomaterial must resist corrosion. Some metals, such as nickel, provoke allergic reactions in about 10% of people. Some metals release corrosion products in the body that are harmful, even in minute concentrations.
Of the metals that possess the qualities required for consideration as biomaterials, yet fewer have the mechanical proporties needed to be used as orthopedic aids or implants.
Efforts to use titanium in prostheses date back into the 1930's. Aluminium is a widely used allowing element, as is vanadium. Titanium does have poor shear strenght is is not the best choice for bone screws or plates, but its strength/density ratio is most desirable.
Demand for titanium as a biomaterial is constantly increasing on account of demographic factors such as longer life expectancy, ageing of the population, and popularity of joint-damaging sports. Total hip or knee join replacements now number about 1 milllion interventions annually. Dental implants have entered the mainstream. Pacemaker cases and defibrillators are ferquently made from titanium. Externally, prostheses made from titanium are especially light weight, corrosion-resistant, and warm to the touch.
Medical grade titanium alloys, in particular, have a significantly higher strength/density ratio than medical stainless steels. Osseointegration, where the biomaterial and the tissue join with each other, is possible with titanium, reducing the probability of undesirable bone resorption.