Preparation, chemistry and physical properties of bone-derived hydroxyapatite particles having a negative zeta potential

Animal bone-derived calcium hydroxyapatite (HA) particles were produced and characterized. Adult bovine femoral bone was boiled, washed, cleaned and heated in air at 700 °C for 2 h. The resulting macro-porous solid was ground, crushed and sieved into particles <50 μm. SEM showed the particles were agglomerations of crystals ∼50–500 nm across. XRD showed highly crystalline HA with nominal MgO and no detectable CaO. FTIR spectroscopy yielded typical HA absorptions, plus absorptions at 1457 and 1412 cm−1 (MgCO3 or CaCO3) and 874 cm−1 (CaHPO4). Main elements by EDXRF were Ca and P (molar ratio 1.93 vs. theoretical ratio 1.67). Minor amounts of Si, Mg and Na were detected, plus traces of K, Sr, Zn, Ba, V, Al, Mn, Pb, Cu and Fe. EDX detected Ca, P, Na and Mg. BET gas adsorption surface area was ∼2.23 m2 g−1 and theoretical particle size ∼857 nm. Laser DLS indicated ∼40% of particles were ∼952 nm in diameter, plus ∼50% were ∼760 nm – in close agreement with BET calculations. By laser Doppler electrophoresis (LDE) the zeta potential of the bone-derived HA particles suspended in 0.154 M NaCl was negative for pH 6–11 and −9.25 ± 0.9 mV at pH 7.4. Negative zeta potential is reported to favor attachment and proliferation of bone cells. HA particles produced synthetically are reported to have positive zeta potentials. The source of the negative potential was not determined but may stem from factors peculiar to producing HA particles from bone. The results suggest further investigation for biomedical use.