ETH: Metallic glass for bone surgery

Development opportunity

Materials researchers at ETH Zurich have developed a metallic glass alloy that could herald a new generation of biodegradable bone implants.

Currently, when bones break, surgeons need screws and metal plates, usually made of stainless steel or titanium to fix them in place. Once the bones have healed, the metal parts have to be removed from the body via further surgery.

In recent years much research has focused on producing implants from bioabsorbable metals that stabilise the bones only for as long as they need to heal. The metal dissolves in the body over time, rendering removal surgery unnecessary. Implants made of magnesium-based alloys are proving particularly promising. Magnesium is mechanically stable and degrades completely by releasing ions that are tolerated by the body.

But all magnesium alloys have one major drawback: when they dissolve they produce hydrogen, which can be harmful to the body. Around the magnesium implants gas bubbles develop which hinder bone growth and can cause infection.

Materials researchers working with Jörg Löffler, Professor of Metal Physics and Technology at ETH Zurich, have now eliminated these side effects. They have succeeded in producing a magnesium-zinc-calcium alloy in the form of a metallic glass, which is biocompatible and degrades in a significantly more favourable way.

Metallic glasses are produced by rapid cooling of the molten material, with the speed of cooling preventing the atoms from adopting the crystal structure found in traditional metals. As a result, metallic glasses have an amorphous structure like that of window glass. This makes it possible to add much more zinc to the molten magnesium than is possible with conventional alloys.

The glassy alloy developed by the ETH researchers Bruno Zberg, Peter Uggo-witzer and Jörg Löffler contains up to 35 per cent zinc and 5 per cent calcium atoms, with the rest made up of magnesium. The major advantage of a high percentage of zinc is that it changes the corrosion behaviour of the magnesium fundamentally. In fact, clinical tests with small platelets of the new magnesium-zinc-calcium alloy showed no hydrogen evolution. Thus this new alloy, in the form of a metallic glass, has considerable potential as a non-harmful bone implant material.