Background

Alumina is a highly inert material and resistant to most corrosive environments, including the highly dynamic environment that is the human body. Under physiological conditions, it is also extremely unreactive and is classed as nearly inert, eliciting little if any response from surrounding tissues and remaining essentially unchanged after many tears of service.

However, the body does recognise it as a foreign material and does attempt to isolate it by forming a layer of non adherent fibrous tissue around the implant where possible.
Key Properties

Properties making alumina suited to biomaterial applications include:

· High degree of chemical inertness under physiological conditions

· Excellent wear resistance

· Ability to be polished to a high surface finish

· Excellent hardness
Applications
Articulating surfaces in joint replacements

Due to its ability to be polished to a high surface finish and its excellent wear resistance, alumina is often used for wear surfaces in joint replacement prostheses. Such applications include femoral heads for hip replacements and wear plates in knee replacements. In hip replacements, the alumina femoral head would be used in conjunction with a metallic femoral stem and an acetabular cup made from ultra high molecular weight polyethylene (UHMWPE) for the opposing articulating surface.

Wear rates for alumina on UHMWPE have been reported to be as much as 20 times less than that for metal on UHMWPE, making this combination far superior and producing less tribological debris. This debris could lead to complications in surrounding tissues, so keeping it to a minimum is advantageous.
Bone Spacers

Porous alumina may also be used to replace large sections of bone that have been removed for reasons such as cancer. These may take the shape of rings that are concentric around a metallic pin, inserted up the centre of the remaining bone itself. The porous nature of these implants will allow new bone to grow into the pores, effectively using the alumina as a scaffold for new bone formation.
Dental Applications

Alumina has been used in dental applications. Specifically, it has been used for tooth replacements. In many of these cases single crystal alumina or sapphire is used. However, this is declining in popularity, being replaced by other materials such as dental porcelains.