Mechanical properties and anisotropy in hydroxyapatite single crystals

The mechanical behavior of single crystalline hydroxyapatite is examined through instrumented nano- and microindentation experiments on prism and basal planes. The results indicate that the c-axis orientation is stiff and hard, and significant anisotropy in properties was found. Nanoscale plasticity is observed in the form of pile-up along the nanoindentation edges and manifests as discrete displacement bursts in the load vs. depth of penetration curves. Toughness also shows significant anisotropy and is lower compared with the values reported for the polycrystalline hydroxyapatite.