Materials Science

Stronger Nanocomposites

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Science  06 Jan 2006:
Vol. 311, Issue 5757, pp. 16
DOI: 10.1126/science.311.5757.16b

The use of hydroxyapatite (HAP) in load-bearing orthopedic implants has been limited by its sintering behavior and mechanical properties. Reinforcing agents have been added to make composites, but only HAP-polymer blends have achieved clinical application. For metal and ceramic reinforcing agents, high particle loadings are required, but this reduces the bioactivity. Furthermore, at high loadings of metallic particles, thermal mismatch is an issue, whereas for ceramics, high loading requires high sintering temperatures that degrade HAP.

Using a previously developed nanocrystalline HAP, Ahn et al. employed a colloidal technique to add small amounts of zirconia to HAP. Optimal Vickers hardness was obtained for loadings as small as 1.5 weight %, which increased the bending strength by about 30%. Adding the Zr during the precipitation of the HAP achieved an intimate mixing, and the Zr acted as seed nuclei for HAP crystallization. A further benefit was that the composites could be fully sintered under relatively mild conditions, preserving the nanocrystalline grain size of the HAP particles, which have higher bioactivity than coarser-grained ones. — MSL

J. Am. Ceram. Soc. 88, 3374 (2005).

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