Synthesis and characterization of needlelike apatitic nanocomposite with controlled aspect ratios

Calcium-deficient apatitic (cd-HA) crystals with core-shell nanostructure with needlelike shape, 5–10 nm in diameter and 20–80 nm in length, were prepared via an in situ formation in the presence of polyacrylic acid (PAA) under aqueous solution of different pH values, ranging from 9 to 11. Nanostructure of the resulting crystals showing a core-shell configuration with a thin layer of PAA shell of about 1 nm thickness was investigated. Aspect ratio (AR) of the needlelike composite was found to depend on the concentration of the PAA and solution pH. At lower solution pH, crystal growth was inhibited, i.e., leading to a decreased AR, with increase of PAA concentration, while an increased AR was detected at higher solution pH, suggesting a preferential growth of the cd-HA nanocrystals. Mechanism of such preferential growth was tentatively proposed and is suggested to correct PAA adsorption along the long axis of the needlelike nanoparticles.