One-step hydrothermal synthesis with in situ milling of biologically relevant hydroxyapatite

Biologically relevant synthetic hydroxyapatite (HA) has become a much-desired material for use within the medical field with an emphasis on orthopedic applications. However, there are very few sources of sub-micron scale HA powders that are economical. Many current procedures to generate synthetic HA, that is both biological and chemically analogous to naturally occurring HA, tend to involve complicated synthesis procedures that are difficult to simultaneously produce desired stoichiometric ratios and particle diameter. This paper reports the development of a one-step hydrothermal method with in situ ball milling of synthetic HA. That has the potential to be a biological substitute with similar calcium to phosphate stoichiometric ratio and particle diameter of HA found in many natural biologically occulting sources. Parameters affecting particle diameter investigated included varying ball milling media, in situ and ex situ ball milling, and simultaneous agitation. The stoichiometric ratios of the resulting powders indicated that 4-hour hydrothermal reaction time produced materials that are analogous to natural HA, confirmed from spectra acquired via Fourier Transform Infrared spectroscopy (FT-IR). X-ray diffraction and Scanning Electron Microscopy both indicate that the predominant size of primary crystallites is around ~25 nm. Particle size distributions of dried in situ ball-milled HA suggest that primary crystallites exist as aggregates, with aggregate diameters ranging between 1 and 100 μm.