In vitro and in vivo antimicrobial properties of silver-containing hydroxyapatite prepared via ultrasonic spray pyrolysis route

• Ag-HAp powders were synthesized by an ultrasonic spray pyrolysis technique.
• Ag-HAp powders with low crystallinity induced the release of Ag+ ions.
• Ag+ ion was released from Ag-HAp powders over the course of 30 days.
• Ag-HAp discs greatly affected antimicrobial activity in vitro and in vivo.
• Optimal Ag content (5 mol%) did not affect osteoblastic cell proliferation.

Hydroxyapatite (HAp), with its high biocompatibility and osteoconductivity, readily absorbs proteins, amino acids and other substances, which in turn favor the adsorption and colonization of bacteria. To prevent bacterial growth and biofilm formation on HAp discs, silver-containing (1–20 mol%) HAp (Ag-HAp) powders were synthesized using an ultrasonic spray pyrolysis (USSP) technique. The X-ray diffraction (XRD) peaks were very broad, indicating low crystallinity, and this induced the release of Ag+ ions from Ag-HAp powders. In addition, a gradual increase in Ca2 + ion release was observed. These results suggest that dissolution of Ca2 + ion in Ag-HAp triggered the release of Ag+ ions.The antimicrobial efficacy of Ag-HAp disc was tested against Staphylococcus aureus. Samples with Ag contents of more than 5 mol% were found to be highly effective against bacterial colonization and biofilm formation in vitro. In vivo antibacterial tests using bioluminescent strains also showed reductions in the viability of bacteria with Ag-HAp (5 mol%) discs. Biocompatibility tests using a modified Transwell® insert method showed that Ag-HAp (5 mol%) discs have negative effects on osteoblast proliferation. These results indicate that Ag-HAp (5 mol%) has effective antibacterial activity and good biocompatibility both in vitro and in vivo together with good biocompatibility, thus confirming its utility as a bactericidal material.