Submicron spheres of amorphous calcium phosphate forming in a stirred SBF solution at 55 °C

• Simple heating of a stirred Lac–SBF solution at 55 to 70 °C forms nanospheres of ACP.
• Lac–SBF with a small amount of gelatin forms monodisperse ACP spheres at 55 °C.
• Monodisperse ACP spheres with diameters < 250 nm can be formed at 55 °C in 15 min.
• ACP spheres can be used as gene, drug, vaccine and active molecule delivery agents.

X-ray-amorphous calcium phosphate (ACP) spheres were synthesized in a simulated/synthetic body fluid (SBF) solution heated to 55 to 70 °C under constant stirring at 850 rpm. The specific SBF solution (Lac–SBF) was buffered by using Na-l-lactate and lactic acid, and did not contain any Tris or Hepes. The Lac–SBF solution of this study flawlessly matched the concentrations of the inorganic electrolyte ions of the human blood plasma. The monodisperse ACP spheres synthesized at 55 °C were 245 nm in diameter when the Lac–SBF solution contained 67 mg/L gelatin. Samples were characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy and inductively-coupled atomic emission spectroscopy.