Rapid microwave synthesis of needle-liked hydroxyapatite nanoparticles via template directing ball-milled spindle-shaped eggshell particles

Needle-like hydroxyapatite nanoparticles were synthesized by fast microwave irradiation of partially acid etched ball-milled eggshell particles which were guided milled using two sets of stainless steel balls. The milled eggshell samples were irradiated for 7.5, 15 and 30 min while reagent concentration, the temperature (50 degrees C), and argon purge pressure of 60 psi were kept constant using a CEU microwave. The Scanning Electron Micrographs showed that the precursor milled eggshell particles which were prepared using a combination of 12 of 6 mm and 6 of 3 mm balls displayed spindle-shaped morphology whereas eggshells milled with 12 of 3 mm and 6 of 6 mm stainless steel balls did not show distinct morphology. The XRD patterns of the nano-hydroxyapatite prepared using spindled-shaped eggshells as synthetic precursors are in preferential crystalline orientations in the [211] and [300] directions. The XRD patterns and TEM images of partially acid etched spindle-shaped CaCO3 particles and (NH4)(2)HPO4 irradiated for 7.5 min produced a mixture of hydroxyapatite and CaCO3 particles but produced only pure needle-liked hydroxyapatite particles when the microwave irradiation was extended to 30 min. The irradiation of eggshell particles with no clear shape (milled using 12 of 3 mm and 6 of 6 mm stainless steel balls) and (NH4)(2)HPO4 produced agglomerated hydroxyapatite particles with indistinct morphology. The absence of modulating functional groups in the FTIR chromatograms showed that etched spindle-shaped CaCO3 served as templates which directed the growth of the needle-liked hydroxyapatite particles. This material could be a useful biomaterial as there are no concerns due to surfactant contamination.