Surface Hydration and Cationic Sites of Nanohydroxyapatites with Amorphous or Crystalline Surfaces: A Comparative Study

Abstract

This paper is an extension of previous work devoted to the characterization of platelet-like hydroxyapatite (HA) nanoparticles constituted by a crystalline core coated by an amorphous surface layer 1-2 nm thick (Bertinetti et al. J. Phys. Chem. C. 2007, 111, 4027-4035). By increasing the preparation temperature, the platelet morphology was retained but HA nanoparticles exhibited a higher degree of crystallinity (evaluated by X-ray diffractometry). High-resolution transmission electron microscopy revealed that, in this case, the crystalline order was extended up to the particles' surfaces, which were of the ( 010), (100), and (001) types. IR spectroscopy was used to investigate the surface hydration of both materials, in terms of adsorbed H 2 O molecules and surface hydroxy groups, as well as the Lewis acidity of surface cations, by removing water and adsorbing CO. For both features, strong similarities between amorphous and crystalline surfaces were found.

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“…A more precise problem [47] stands in line with this way of thinking: "Focusing on nano-HAp morphology, needlelike [48][49][50][51] and platelike [52][53][54] nano-particles can be prepared, while in bone tissue only the second type seems to be present [55][56][57]. For both morphologies the prevailing surface terminations are of the {010} type, which in the case of needlelike nano-HAp are the lateral facets of the hexagonal nano-particles elongated along the crystallographic c-axis, while, for the platelike nano-particles they are the basal facets of nano-particles preferentially grown along both the c-and a-(or b-) axis [53,54,58] breaking the crystal symmetry through a mechanism still matter of investigation [52,58].…”

Surface Treatments and Functional Coatings for Biocompatibility Improvement and Bacterial Adhesion Reduction in Dental Implantology

“…Still, in recent years, several studies [102][103][104][105] revealed that HA nanoparticles can be coated by an amorphous, non-apatitic surface layer surrounding a crystalline hydroxyapatite bulk. However, the possibility of obtaining apatitic particles with crystalline structure extended up to the surface was recently reported [106]. In addition, HA surface feature may be modified by exchanging part of calcium ions with other divalent cations.…”

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“…The highest shift is attributed to a tiny fraction of the most exposed calcium ions, which are those modeled in our studies, so proving a good agreement. On the other hand, the majority of calcium sites contribute to the lowest shift (Bertinetti et al, 2007;Sakhno et al, 2010).…”