Surfactant-free synthesis of copper-incorporated bioactive glass nanoparticles for controlled ion release, antibacterial activity, and apatite-forming ability.

Abstract

Objectives: Infection-driven failure remains a major challenge in regenerative endodontics, underscoring the need for advanced biomaterials that can simultaneously promote dentin regeneration and provide sustained antimicrobial activity. This study developed a surfactant- and template-free sol-gel strategy, combined with controlled calcium precursor addition and freeze-drying, to synthesize copper-containing mesoporous bioactive glass nanoparticles (Cu-nBG) with regenerative and antibacterial properties.

Methods: Spherical nBG (60-100 nm) were synthesized using a modified template-free Stöber process, followed by copper incorporation (0.5-1.5% w/v). The effects of calcium precursor addition timing on particle morphology were evaluated. Physicochemical properties and ion release were characterized by HR-SEM, TEM, BET, FTIR, XRD, XPS, and ICP-OES. Apatite-forming ability was assessed by hydroxyapatite formation following immersion in simulated body fluid. Antibacterial activity against Enterococcus faecalis and Streptococcus mutans, and cytocompatibility using NIH/3T3 fibroblasts, were assessed.

Results: Optimized precursor addition yielded predominantly spherical nanoparticles (60-100 nm). Copper incorporation preserved the amorphous structure while reducing specific surface area and pore volume. Cu-nBG exhibited sustained concentration-dependent Cu²⁺ release over 28 days without burst release. All formulations supported hydroxyapatite formation following immersion in SBF from day 7, demonstrating preserved apatite-forming ability. Copper incorporation conferred concentration-dependent antibacterial activity, with 1.5% Cu-nBG showing the most sustained inhibition of E. faecalis and S. mutans. All formulations exhibited cytocompatibility at 1-5 mg·mL^-1.

Significance: The surfactant-free, freeze-drying-assisted sol-gel strategy enables controlled synthesis of Cu-nBG with sustained Cu²⁺ release, apatite-forming ability, antibacterial activity, and cytocompatibility, supporting further investigation as functional additives in future endodontic biomaterials.