Surface properties of carbonated and non-carbonated hydroxyapatites obtained after bone calcination at different temperatures

•Surface properties of carbonated and non-carbonated hydroxyapatite were assessed.•Specific retention volumes were over five times higher for the carbonated mineral.•Specific interactions with Lewis acidic probes were higher for the carbonated sample.•Carbonate can be newly formed at a outer surface of non-carbonated hydroxyapatite.•The carbonated mineral should have a better compatibility for organic matrices.

The hydroxyapatite surface characterization may be important regarding its reactivity in the synthesis of composites and in the context of the multiple interactions with the biological environment, after in vivo implantation, including protein adhesion and cell attachment on the mineral surface. In this work, the surface properties of a bone-derived hydroxyapatite with ca. 3.5 wt% of carbonate content (named as carbonated) and a hydroxyapatite obtained by calcination of the carbonated one at 1000 °C (non-carbonated) were assessed by inverse gas chromatography (IGC) and X-ray photoelectron spectroscopy (XPS). The specific retention volumes of a wide range of probes measured by IGC were more than five times higher for the carbonated hydroxyapatite. The dispersive component of the surface energy was similar for both materials (45–47 mJ m−2, at 37 °C) as well as the values of the specific interactions with weak Lewis basic probes. The magnitude of the specific interactions with typical Lewis acidic probes was slightly higher for the carbonated mineral. Although it was not detected by FTIR spectroscopy, XPS analysis evidenced the presence of carbonate at the surface of the hydroxyapatite sample treated at 1000 °C. The detected carbonate was rapidly formed at a thin outer surface layer probably due to the sample contact with atmospheric carbon dioxide.The most outstanding differences observed in the probes retention volumes clearly suggest that the carbonated hydroxyapatite should have more compatibility with organic matrices, as polymers and proteins. The greater adsorption capacity of this mineral is in good agreement with its porous microstructure and higher specific surface area.

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