X-ray-amorphous calcium phosphate (ACP) synthesis in a simple biomineralization medium

Abstract

An inorganic solution similar to the inorganic electrolyte compartment of the DMEM (Dulbecco's modified Eagle's medium) cell culture medium is developed. This biomineralization medium contains 44.05 mM HCO₃⁻, 126.86 mM Na⁺, 93.37 mM Cl⁻, 5.33 mM K⁺, 2.26 mM Ca²⁺, 0.905 mM H₂PO₄⁻, and 0.81 mM Mg²⁺. Its Ca/P molar ratio is set to be identical to that of human blood plasma, i.e., 2.50. The medium is free of any Tris or Hepes but maintains a pH of 7.45 both at 37 and 65 °C. The first novelty of this solution is that it has the unique ability to homogeneously coat X-ray-amorphous calcium phosphate (ACP) on glass slides vertically immersed in it and kept at 37 °C for less than 48 h. The second innovative aspect of this solution is that it has the unprecedented ability to produce monodisperse ACP nanospheres with diameters less than 180 nm when simply heated at 65 °C for 1 h while being stirred. The third novelty of this solution is that it only forms ACP and it does not form apatite in stark contrast to many other synthetic calcification or biomineralization media known. Samples were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, BET surface area, contact angle goniometry, field emission-scanning and transmission electron microscopy analyses.