Zirconium shaping in vitro dissolution of Na-K-Ca-Si-O bioactive glass-ceramics

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The incorporation of bioactive glass-ceramics into biomedical applications requires careful control over their dissolution behavior and ion release to maintain a balance between bioactivity and structural stability. This study explores the effect of ZrO 2 addition (0 - 10 mol%) on the structure, dissolution behavior, mineralization capacity, and antibacterial potential of Na-K-Ca-Si-O-based glass-ceramics synthesized via the melt-quenching method. Structural characterization revealed that zirconium incorporation promoted the formation of crystalline phases such as CaZrO 3 , resulting in an increase in crystallinity from 54% in the undoped sample to ~70% after doping. It also altered the silicate network structure, as evidenced by a higher proportion of Q 3 units in Zr-containing glass-ceramics. In vitro dissolution tests conducted in phosphate-buffered saline (PBS) and deionized water (DI) showed that addition of 2.5 mol% ZrO 2 visibly reduced the dissolution rate, with mass loss decreasing from over 10% to nearly 0% after 1 day of immersion. However, higher zirconium contents did not yield further improvement and, in some cases, increased mass loss up to 15% when 10 mol% ZrO 2 was added. Ion release from the glass-ceramics caused a sharp increase in solution pH, reaching values up to 12 during the first day of immersion. All compositions retained their ability to form hydroxyapatite-like calcium phosphate layers upon PBS immersion, as confirmed by Ca/P ratios between 1.6 – 2.0 after long term immersion. In addition, antibacterial assays demonstrated that the dissolution products of Zr-doped glasses exhibited inhibitory effects against both Escherichia coli (EC K-12) and methicillin-resistant Staphylococcus aureus (MRSA), with enhanced activity observed for supernatants in PBS. These effects are attributed to ion-mediated mechanisms and the influence of medium composition on solubility and ionic interactions. • ZrO 2 -doped Na-K-Ca-Si-O glass-ceramics were synthesized via a one-step melt-quenching process. • ZrO 2 promoted crystallization of CaZrO 3 phase and enhanced silicate network polymerization. • ZrO 2 -doped samples showed decreasing crystallinity upon long-term PBS immersion. • All samples formed hydroxyapatite after prolonged PBS immersion. • Antibacterial activity was observed in DI and PBS supernatants, highlighting the role of dissolved ions. • PBS-derived supernatants were more effective against MRSA than DI.

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