Metallic Glass Could Help Set Broken Bones

An alloy based on metallic glass could be the forerunner of a new generation of biodegradable bone implants.

Researchers at ETH Zurich (Switzerland) have succeeded in producing an innovative magnesium-zinc-calcium (MgZnCa) alloy in the form of a metallic glass which is both biocompatible and shows significantly more favorable degradation behavior than currently used bio-absorbable metals, which are based on magnesium alloys. These magnesium alloys have one major drawback: when they dissolve, they produce hydrogen (H2) gas bubbles, which hinder bone growth and thus the healing process, and potentially cause infection. The new MgZnCa glass alloy, on the other hand, contains up to 35% zinc and 5% calcium atoms, with the rest made up of magnesium, resulting in no hydrogen evolution. This was achieved by rapid cooling of the molten material, preventing the atoms from adopting the crystal structure found in traditional metals, allowing the addition of more zinc to the molten magnesium than is possible with conventional alloys. The major advantage of a high percentage of zinc is that it changes the corrosion behavior of the magnesium fundamentally. The study was published ahead of print on September 27, 2009, in the online edition of Nature Materials.

"Above a particular Zinc-alloying threshold (approximately 28%), a Zinc and Oxygen-rich passivating layer forms on the alloy surface,” explained lead author Jörg Löffler, Ph.D., a professor of metal physics and technology at ETH. "Thus, the glassy Magnesium-Zinc-Calcium alloys show great potential for deployment in a new generation of biodegradable implants.”

Bioabsorbable metallic implants are used to stabilize 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, since Magnesium is mechanically stable and degrades completely by releasing ions, which are tolerated by the body.

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