Most people are aware of the fact that many of the largest medical device manufacturers in the world now have production and research facilities in Ireland.

They design a wide range of products for use in medicine, particularly for use in non-invasive surgery. Many of these devices are made from metals and alloys, whose stability in body fluid environments (blood, gastric juice) is of critical importance to the health of patients.

The need to ensure minimal corrosion/degradation has been the major determining factor in the selection of materials for use in these complex environments. Stainless steels have been used successfully as implants for many years. They owe their stability to the thin oxide layer on the surface which acts as a barrier between the material and the host solution. They have become particularly important in the construction of stents for use in the treatment of cardiovascular disease (blockage of arteries in particular). A stent is designed to serve as a temporary or permanent scaffold to maintain or increase the diameter of a vessel. Since blood contains around 0.9% sodium chloride, and because chloride ions can attack and destroy the oxide film on steels, attention must be focused on the design of corrosion test procedures for these devices. Any surface pretreatments which can improve the stability of the oxide can also be of considerable benefit. Research in these areas is currently being undertaken in the Chemistry Department of NUI, Galway.

For use in peripheral regions of the body (e.g. oesophageal stents), steels are not suitable because a blow to the neck may damage the stent causing a blockage. For use in these applications a very innovative "shape memory" material called Nitinol is used. Containing 50% Nickel and 50% Titanium, the alloy was discovered at the US Naval Ordnance Laboratory. After being subjected to suitable heat treatments, devices made from this material will return to their original shape after deformation. Flexible spectacle frames (as seen in TV ads) are made from this alloy. The heat treatments used to give these shape memory properties often result in the formation of less protective oxides on the stents, rendering them susceptible to corrosion.

Improving the corrosion resistance and hence the long-term stability of such stents forms the basis of another research effort underway in the Department. The next generation of implants will, it is hoped, have coatings which make them more biocompatible and acceptable in the body. These coatings will also be used to anchor drugs which will be released at the point of deployment. Work in this area is due to start shortly in the Department.