Modifications of Hydroxyapatite by Gallium and Silver Ions-Physicochemical Characterization, Cytotoxicity and Antibacterial Evaluation

Hydroxyapatite (HA) powders enriched with silver or gallium ions or both were synthesized by two different routes: standard precipitation and the solid-state method. The powders were characterized by using several methods: inductively coupled plasma optical emission spectrometry (ICP-OES), powder X-ray diffractometry (PXRD), transmission electron microscopy (TEM), infrared spectroscopy (FT-IR) and solid-state nuclear magnetic resonance spectroscopy (ssNMR). The effects of enrichment of the HAs in Ag⁺ or Ga³⁺ or both on in vitro cytotoxicity and microbiological activity were discussed. PXRD experiments showed that the samples obtained by the wet method consisted of single-phase nanocrystalline HA, while the samples prepared via the solid-state method are microcrystalline with a small amount of calcium oxide. The introduction of higher amounts of silver ions was found to be more effective than enriching HA with small amounts of Ag⁺. Gallium and silver ions were found not to affect the lattice parameters. Ga³⁺ affected the crystallinity of the samples as well as the content of structural hydroxyl groups. Among samples synthesized by the wet method, only one (5Ag-HAw) was cytotoxic, whereas all Ga-containing samples obtained by the dry method showed cytotoxicity. In the preliminary antimicrobial test all the materials containing "foreign" ions showed high antibacterial activity.