Synthesis and characterisation of large chlorapatite single-crystals with controlled morphology and surface roughness.

This work describes the synthesis of chlorapatite single crystals using the molten salt method with CaCl(2) as a flux. By manipulating the processing conditions (amount of flux, firing time and temperature, and cooling rates) it is possible to manipulate the crystal morphology from microscopic fibres to large crystals (up to few millimetre long and ~100 μm thick). The crystal roughness can be controlled to achieve very flat surfaces by changing the melt composition "in situ" at high temperature. The Young modulus and hardness of the crystals are 110 ± 15 and 6.6 ± 1.5 GPa respectively as measured by nanoindentation. Crystal dissolution in Hanks solution starts around the defects. Several in vitro assays were performed; ClAp crystals with different size and shape are biocompatible. Cell apoptosis was very low at 5, 10, and 15 days (Caspase-3) for all the samples. Proliferation (MTT) showed to be influenced by surface roughness and size of the crystals.