Bioactivity of Biphasic Calcium Phosphate Granules, the Control of a Needle-Like Apatite Layer Formation for Further Medical Device Developments

Abstract

Biphasic calcium phosphate (BCP) bioceramics (hydroxyapatite/tricalcium phosphate, or HA/TCP) for tissue engineering and drug delivery systems is a unique know-how. A mechanical mixture of HA and TCP does not lead to such bioactive ceramics. The wet elaboration conditions of calcium-deficient apatite (CDA) or CDHA, followed by sintering, converts it into TCP and HA. The dissolution precipitation of nano-sized needle-like crystals at the surface of BCP occurs on time at body temperature. Combining several technics of characterization [scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX), Brunauer-Emmett-Teller method (BET), chemical analysis, x-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR)], we demonstrated an evolution on time of the HA/β-TCP. The current paper describes the crystallographic evolution of initial β-TCP rhombohedral crystallographic structure to microsized needle-like layer corresponding to apatitic TCP form. This phenomenon leads to an increase of the HA/TCP ratio, since hexagonal apatitic TCP is similar to hexagonal HA. However, the Ca/P ratio (reflecting the chemical composition HA/TCP) remains unchanged. Thus, the high reactivity of BCP involves dynamic evolution from rhombohedral to hexagonal structure, but not a chemical change. The dynamic process is reversible by calcination. These events are absolutely necessary for smart scaffolds in bone regeneration and orthobiology.