Antibacterial and Biological Performance of Nanostructured Bioactive Glasses with Silver and Titanium DioxideAbstract
Nanostructured bioactive glasses have attracted increasing attention as multifunctional biomaterials for infection-prone biomedical applications. In this study, pure and doped bioactive glasses incorporating silver (Ag₂O-derived species) and titanium dioxide (TiO₂) were evaluated for their antibacterial performance and in vitro cytocompatibility. Antibacterial activity was assessed against Escherichia coli, Staphylococcus aureus, and methicillin-resistant S. aureus (MRSA). While the undoped bioactive glass showed no antibacterial effect, Ag- and TiO₂-doped formulations significantly reduced bacterial growth in a concentration-dependent manner. Ag-doped glasses exhibited the highest antibacterial efficacy, achieving complete inhibition of E. coli and MRSA at higher concentrations, whereas TiO₂-doped samples showed moderate inhibitory effects. Cytocompatibility was evaluated using an indirect assay with VERO CCL-81 cells, and all formulations maintained cell viability above 80%, including Ag-containing glasses at the highest tested concentrations. These results indicate that the incorporation of Ag and TiO₂ enhances antibacterial performance while preserving acceptable cytocompatibility under the tested conditions. Overall, these findings support the potential application of doped bioactive glasses in infection-prone bone repair scenarios; however, further studies on ion release, long-term stability, and in vivo biocompatibility are required.
Key words
bioactive glass; silver; titanium dioxide; antibacterial activity; MRSA; cytocompatibility
INTRODUCTION
Biomaterials have been widely studied for medical applications, particularly in bone tissue engineering, because they support regeneration and integration with host tissues (Dec et al. 2022, Liu et al. 2025). Among these materials, bioactive glasses stand out for their excellent bioactivity and biocompatibility, facilitating osteointegration by forming a hydroxyapatite layer on their surface (Carvalho 2024, Vallet-Regí 2010). Their composition, primarily based on silica, sodium, calcium, and phosphorus, stimulates cell proliferation and osteogenesis (Al-Harbi et al. 2021).
Despite their advantages, conventional bioactive glasses lack intrinsic antimicrobial properties, which may limit their ability to prevent post-surgical infections and implant-related complications (Nowotnick et al. 2024, Zambon et al. 2021). The increasing prevalence of antibiotic-resistant bacterial strains, such as Staphylococcus aureus (MRSA) and Escherichia coli, poses a significant challenge in clinical settings, leading to implant failure and additional surgical interventions (Mancuso et al. 2021, Masters et al. 2022, Kavanagh et al. 2018). As a result, the functionalization of bioactive glasses with antimicrobial agents has emerged as a promising strategy to combine bioactivity with infection control in a single material platform (Shuaishuai et al. 2023).
Among the antimicrobial strategies explored, silver-based systems are particularly well established. Silver exhibits broad-spectrum antibacterial activity primarily through the controlled release of Ag⁺ ions, which disrupt bacterial membranes, interfere with enzymatic pathways, and induce oxidative stress (Feng et al. 2000, Yin et al. 2020). However, silver incorporation also raises concerns regarding dose-dependent cytotoxicity, highlighting the importance of controlling its concentration, chemical state, and release kinetics within biomaterial matrices, especially for biomedical applications (Qian et al. 2021). In this context, silver-doped bioactive glasses have been reported to provide sustained antimicrobial activity while preserving acceptable cytocompatibility when appropriately engineered (Gibała et al. 2021).
In contrast to silver, titanium-based materials—particularly titanium dioxide (TiO₂)—present a more context-dependent antimicrobial behavior. Unlike Ag, TiO₂ does not exhibit strong intrinsic antibacterial activity under all conditions; its effects are often associated with surface interactions, photocatalytic activity, and the generation of reactive oxygen species, which may depend on environmental factors such as light exposure and surface chemistry (Liu et al. 2025). Therefore, Ag and TiO₂ should not be regarded as equivalent antibacterial agents, but rather as distinct functional dopants that may contribute differently to antimicrobial performance when incorporated into bioactive glass matrices.
In addition to their biological effects, the incorporation of Ag and TiO₂ into bioactive glasses can significantly influence their physicochemical properties. Silver nanoparticles are known to induce localized surface plasmon resonance (LSPR) phenomena, which can modify the optical response of the material, while TiO₂ incorporation may affect electronic transitions and light-scattering behavior (Nowotnick et al. 2024). In this context, the term “structural” refers to surface topography and morphological features of the amorphous glass matrix, rather than to long-range crystalline order, which is absent in bioactive glasses. Surface morphology, particle distribution, and nanostructured domains may play a role in modulating both antibacterial performance and biological interactions at the material–cell interface.
Compared with other antibacterial nanomaterials, such as mesoporous silica nanoparticles (MSNs), doped bioactive glasses offer the advantage of combining antimicrobial functionality with intrinsic bioactivity and osteoconductivity. While MSNs and related systems can provide efficient drug loading and controlled release, they often lack the inherent ability to bond to bone tissue, which is a defining characteristic of bioactive glasses (Guo et al. 2020, Li et al. 2023, Wang et al. 2022). Thus, bioactive glass-based systems represent a distinct and complementary class of antibacterial biomaterials, particularly suited for bone-related applications.
In this study, the term “nanostructured” refers to nanoscale surface heterogeneity and topographical features of the glass matrix, rather than particle size. Based on these considerations, the present study aims to evaluate the antibacterial activity and in vitro cytocompatibility of pure and nanostructured bioactive glasses doped with silver (Ag₂O-derived Ag species) and titanium dioxide (TiO₂). Antibacterial efficacy was assessed against Escherichia coli, Staphylococcus aureus, and methicillin-resistant S. aureus (MRSA), while cytocompatibility was evaluated using an indirect assay with mammalian cells. By comparing undoped and doped formulations, this work seeks to clarify how distinct antimicrobial dopants influence the biological performance of bioactive glasses and to support their potential application in infection-prone biomedical scenarios.
Ethics statement
The VERO CCL-81 cell line used in the cytotoxicity assays is an established cell line obtained from the American Type Culture Collection (ATCC). The antibacterial assays included reference bacterial strains and a clinical methicillin-resistant Staphylococcus aureus (MRSA) isolate. All procedures involving the clinical isolate were conducted in accordance with applicable ethical standards and were approved by the Research Ethics Committee of the Federal University of Triângulo Mineiro (UFTM), under protocols No. 852 and 1475.
MATERIALS AND METHODS
Synthesis and Characterization
The nanostructured bioactive glasses were synthesized using a conventional melt-quenching method. Analytical-grade precursors of silicon dioxide (SiO₂), sodium carbonate (Na₂CO₃, as Na₂O source), calcium carbonate (CaCO₃, as CaO source), and phosphorus pentoxide (P₂O₅) were used to obtain a silicate-based glass system (SNCP).
The precursor materials were weighed within compositional ranges typical of bioactive glasses (SiO₂: 30–60 wt%, Na₂O: 10–40 wt%, CaO: 10–40 wt%, and P₂O₅: 1–10 wt%) and homogenized prior to thermal processing. The mixtures were subjected to high-temperature melting within a controlled thermal range (1000–2000°C), ensuring complete decomposition of carbonate precursors and formation of a homogeneous molten phase, followed by rapid cooling to obtain amorphous glass materials.
Doped formulations were prepared by incorporating silver oxide (Ag₂O, 0.25–1.5 wt%) and titanium dioxide (TiO₂, 10–20 wt%) into the base composition prior to melting. These dopants were incorporated as oxide-derived species within the glass matrix, consistent with commonly reported compositions and processing conditions for bioactive silicate glasses.
Specific processing parameters are within the scope of a patented technology (INPI: BR 10 2023 000062 2); however, the general synthesis approach described here ensures reproducibility of the material system and its physicochemical characteristics.
Optical absorption spectra were obtained at room temperature using a UV–Vis–NIR spectrophotometer (Shimadzu UV-3600, Japan) with a spectral resolution of 1 nm. Spectra were collected over the ultraviolet–visible range (200–800 nm) to evaluate intrinsic glass absorption and dopant-related optical features.
Particle morphology and surface topography were analyzed using atomic force microscopy (AFM) with a Shimadzu SPM-9700 microscope. Imaging was performed in dynamic and phase modes using cantilevers from NT-MDT (Russia). Two-dimensional (2D) and three-dimensional (3D) images were processed using Gwyddion software to assess surface morphology, roughness, and nanoscale surface heterogeneity.
Surface profile analyses were conducted at selected regions to evaluate height variations and topographical features of the amorphous glass particles.
Cytotoxicity analysis
The cytotoxicity of the materials was assessed using resazurin (7-Hydroxy-3H-phenoxazin-3-one 10-oxide) (Sigma Aldrich Corp., St. Louis, MO, USA), which detects cellular metabolic activity as an indicator of cell viability (Rezende et al. 2019). An indirect cytotoxicity approach was employed in order to evaluate the biological response to soluble species released from the bioactive glasses, while avoiding direct physical contact between glass particles and cells.
The experiments were conducted in triplicate using VERO CCL-81 cells (American Type Culture Collection, ATCC, USA) seeded at a density of 2 × 10⁵ cells per well in 96-well plates and cultivated in RPMI medium supplemented with 10% fetal bovine serum (FBS) and gentamicin (40 µg/mL; Ariston, Brazil). Cells were maintained in an incubator at 37°C under a humidified atmosphere containing 5% CO₂ for 4 h to allow cell adhesion.
After this period, extracts of pure and doped bioactive glasses were applied to the cells at an initial concentration of 1000 µg/mL, followed by serial dilutions at a 1:2 ratio, resulting in final concentrations of 1000, 500, 250, 125, 62.5, and 31.25 µg/mL for each formulation. Throughout this study, concentrations are expressed in mass per volume (µg/mL) to ensure clarity and consistency. Untreated cells were used as the cell viability control, while cells treated with 1% paraformaldehyde (Sigma-Aldrich Corp., St. Louis, MO, USA) were used as the cytotoxicity control.
The cells were then incubated for 24 h at 37°C with 5% CO₂. After the incubation period, 5 µL of resazurin solution (2.5 mg/mL) was added to each well. Following an additional 3 h of incubation at 37°C, absorbance was measured at wavelengths of 550 nm and 590 nm using a Biotek Eon microplate reader (PerkinElmer, Germany).
Bacterial strains
Frozen stocks (−80°C) of Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 29213), and a clinical methicillin-resistant Staphylococcus aureus (MRSA) isolate were maintained in brain heart infusion (BHI) broth (Acumedia–Neogen, USA) supplemented with 20% (v/v) glycerol to ensure long-term preservation of bacterial viability and genetic stability.
For bacterial reactivation, aliquots (30 µL) of each frozen stock were aseptically transferred to 3 mL of sterile, freshly prepared BHI medium (Sigma-Aldrich, USA) and incubated at 37ºC under constant orbital shaking (180 rpm) for 24 h, allowing cultures to reach the late exponential or early stationary growth phase.
Following incubation, bacterial suspensions were standardized to 0.5 McFarland turbidity, corresponding to approximately 1 × 10⁸ colony-forming units per milliliter (CFU/mL). Standardization was performed using optical density measurements at 470 nm, ensuring uniform bacterial concentrations prior to antibacterial testing. This standardization step was essential to guarantee reproducibility and comparability across all experimental conditions.
Antibacterial activity
The antibacterial activity of the bioactive glasses was evaluated using the broth microdilution method, adapted from Perini et al. (2024). This method was selected to quantitatively assess bacterial growth inhibition in the presence of particulate bioactive glass suspensions.
Overnight cultures of E. coli, S. aureus, and MRSA were standardized to an initial concentration of 1 × 10² CFU/mL in BHI broth. Subsequently, 100 µL of each standardized bacterial suspension was transferred to sterile 96-well polystyrene microplates containing 100 µL of BHI broth (growth control) or 100 µL of particulate suspensions of pure bioactive glass (SNCP) and doped nanostructured bioactive glasses (SNCP:0.5Ag; SNCP:1.25Ag; SNCP:10TiO₂; SNCP:20TiO₂).
The bioactive glass suspensions were prepared at an initial concentration of 1000 µg/mL and subsequently serially diluted at a 1:2 ratio, yielding final concentrations ranging from 1000 to 0.48 µg/mL. All concentrations are expressed in mass per volume (µg/mL) to ensure consistency and avoid ambiguity regarding the physical state of the materials.
Microplates were incubated at 37°C for 18 h under static conditions. After incubation, bacterial growth was assessed by measuring the absorbance at 475 nm using a microplate reader. Absorbance values were used as an indirect indicator of bacterial proliferation, and results were expressed as percentage viability relative to untreated control cultures.
All assays were performed in triplicate and repeated in three independent experiments, ensuring reproducibility and statistical robustness.
Ethics statement. The VERO CCL-81 cell line used in the cytotoxicity assays is an established cell line obtained from the American Type Culture Collection (ATCC). The bacterial assays included reference strains and a clinical methicillin-resistant Staphylococcus aureus (MRSA) isolate. All procedures involving the clinical isolate were conducted in accordance with applicable ethical standards and were approved by the Research Ethics Committee of the Federal University of Triângulo Mineiro (UFTM), under protocols No 852 and 1475.
Statistical analysis
Statistical analyses were performed using GraphPad Prism software (version 8.0). Data were initially evaluated for normality using the Shapiro–Wilk test and for homogeneity of variances using the F test. Comparisons between groups were conducted using two-way analysis of variance (ANOVA), followed by Tukey’s post hoc test for multiple comparisons.
Results are expressed as mean ± standard deviation, and all experiments were performed in triplicate and repeated in at least three independent assays, as specified in the corresponding experimental sections. Differences were considered statistically significant when p < 0.05.
RESULTS
Optical absorption spectra of the bioactive glasses were analyzed to investigate their optical behavior and the influence of dopant incorporation on the electronic structure of the glass matrix. A strong absorption band centered at approximately 240 nm was observed for all samples and is attributed to the intrinsic electronic transitions of the silicate-based bioactive glass network.
An additional absorption feature in the visible region, centered near 450 nm, was observed exclusively in Ag-containing samples, indicating the presence of silver-derived species within the bioactive glass. This band is attributed to the localized surface plasmon resonance (LSPR) associated with silver-related nanostructures dispersed in the amorphous glass matrix, confirming the successful incorporation of Ag₂O-derived silver species. The intensity of this absorption band increased with increasing silver content, suggesting a concentration-dependent plasmonic contribution.
In contrast, TiO₂-doped bioactive glass samples exhibited a broad absorption feature in a similar spectral region; however, this behavior is not associated with plasmonic effects, as titanium dioxide does not exhibit LSPR under visible light. Instead, this absorption is attributed to charge-transfer transitions, defect-related states, and light scattering phenomena induced by TiO₂ domains interacting with the glass network. Higher TiO₂ concentrations (10–20 wt%) resulted in more pronounced spectral modifications, indicating strong electronic and structural interactions between TiO₂ species and the amorphous bioglass matrix.
A gradual shift in the absorption edge was observed upon incorporation of Ag and TiO₂ species, suggesting modifications in the optical band gap of the materials. Such changes are commonly associated with the introduction of localized electronic states, defect levels, and increased structural disorder within the glass network. These effects alter the optical response of the bioactive glasses; however, no direct extrapolation to optoelectronic or photocatalytic applications is made in this study, and the observed optical changes are discussed primarily in the context of material characterization and dopant–matrix interactions (Fig. 1).
Optical absorption spectra of bioactive glass samples with varying silver (Ag) and titanium dioxide (TiO₂) contents. The absorption band at ©40 nm corresponds to intrinsic electronic transitions of the silicate glass matrix, while the feature near 50 nm is associated with localized surface plasmon resonance (LSPR) in Ag-containing samples and electronic transitions influenced by TiO₂ incorporation. Variations in dopant concentration lead to changes in absorption intensity and edge position, indicating modifications in the optical properties of the glass matrix.
Atomic force microscopy (AFM) analyses were performed to investigate the surface morphology and topographical features of the nanostructured bioactive glasses. AFM contrast images revealed two distinct tonal variations across the glass surface, indicating heterogeneity in surface composition and topography rather than crystalline order, consistent with the amorphous nature of bioactive glasses (Fig. 2a).
Atomic Force Microscopy (AFM) analysis of nanostructured bioactive glass. a) AFM contrast image showing variations in surface composition and topography. b) Topographic mapping of glass particle morphology. c) Three-dimensional AFM reconstruction illustrating surface morphology and thickness variations.
The AFM topographic mapping (Fig. 2b) provided detailed visualization of individual bioactive glass particles, with measurements indicating an average lateral dimension of approximately 2 µm in width and 3.5 µm in length. It should be emphasized that these features correspond to glass particles rather than crystalline domains. Three-dimensional AFM reconstruction (Fig. 2c) further characterized the surface morphology, revealing thickness variations ranging from approximately −0.03 µm to 0.47 µm, indicative of surface roughness and nanoscale heterogeneity.
Additional AFM analyses were conducted at three distinct surface regions to further evaluate topographical variations. Height profile analyses demonstrated localized variations in surface thickness, particularly near particle boundaries and surface irregularities (Fig. 3a). The corresponding histogram (Fig. 3b) illustrates the distribution of height values, providing quantitative insight into the surface roughness and nanostructured features of the bioactive glass.
AFM surface analysis of nanostructured bioactive glass. a) AFM image with three selected regions for surface profiling. b) Corresponding height profiles showing topographical variations across different regions, indicating surface heterogeneity of the amorphous glass.
Figure 3 presents a detailed AFM surface analysis of the nanostructured bioactive glass. In Figure 3a, three regions of interest were selected for surface profiling, as indicated by white lines. Figure 3b shows the corresponding height profiles, revealing pronounced topographical transitions in Profiles 1 and 2, consistent with localized surface heterogeneities, while Profile 3 exhibits a more uniform surface region.
These AFM results demonstrate that the incorporation of Ag and TiO₂ species leads to heterogeneous surface topography and increased nanoscale roughness, which may influence interfacial interactions with biological environments. Importantly, the observed features are associated with surface morphology variations rather than nanoparticle accumulation at crystal edges, as the bioactive glass system is amorphous in nature.
Cytotoxicity analysis
Cell viability was assessed after exposure to increasing concentrations of pure and doped bioactive glass extracts using an indirect resazurin-based assay. Figure 4 illustrates that cells exposed to extracts of the undoped bioactive glass (SNCP) maintained high viability across all tested concentrations, indicating negligible cytotoxic effects associated with the base glass composition.
Cytocompatibility of bioactive glass extracts on VERO CCL-81 cells evaluated by resazurin assay after 24 h of exposure. Cell viability is expressed as a percentage relative to untreated controls.
Similarly, TiO₂-doped bioactive glasses (SNCP:10TiO₂ and SNCP:20TiO₂) did not induce significant reductions in cell viability, with values remaining comparable to the untreated control across the evaluated concentration range. These results suggest that the incorporation of TiO₂ at the tested levels does not adversely affect cellular metabolic activity under indirect exposure conditions.
In contrast, silver-doped bioactive glasses (SNCP:0.5Ag and SNCP:1.25Ag) exhibited a modest, concentration-dependent decrease in cell viability, which became more evident at the highest tested concentration (1000 µg/mL). Despite this reduction, cell viability remained above 80% for all Ag-containing formulations, a threshold commonly used as an indicator of acceptable cytocompatibility in in vitro screening assays.
Taken together, these findings indicate that, under indirect exposure conditions, Ag-doped bioactive glasses maintain a favorable balance between antibacterial effectiveness (Fig. 5) and cellular tolerance. However, these results are limited to in vitro metabolic activity assessments and do not substitute for comprehensive biocompatibility evaluations, such as ion release analysis or in vivo testing, which are required for future translational applications.
Antibacterial activity of bioactive glass formulations against a) Escherichia coli, b) Staphylococcus aureus, and c) methicillin-resistant Staphylococcus aureus (MRSA). Bacterial viability is expressed as a percentage relative to untreated controls after 18 h of incubation.
Antibacterial activity
The treatment with undoped bioglass (SNCP) did not exhibit detectable antibacterial activity against any of the tested bacterial strains. In contrast, the incorporation of Ag and TiO₂ species into the bioactive glass matrix resulted in a marked enhancement of antibacterial performance, as evidenced by reduced bacterial growth across all evaluated conditions (Fig. 5).
The undoped SNCP bioactive glass did not exhibit antibacterial activity against the tested bacterial strains (Fig. 5). In contrast, Ag-doped bioactive glasses showed a concentration-dependent antibacterial effect, with the formulation containing 1.25 wt% Ag exhibiting the strongest antibacterial activity. In contrast, Ag-doped bioactive glasses demonstrated superior antibacterial efficacy against E. coli compared to TiO₂-doped formulations. Notably, the SNCP:1.25Ag formulation achieved complete growth inhibition (100%) at a concentration of 250 µg/mL, while SNCP:0.5Ag promoted more than 70% inhibition at 62.5 µg/mL (Fig. 5a). These results indicate a strong, concentration-dependent antibacterial response associated with silver incorporation.
All tested nanostructured bioactive glasses were able to reduce the growth of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) at the highest evaluated concentration (1000 µg/mL). However, only the SNCP:1.25Ag formulation resulted in complete bacterial inhibition against both strains (Fig. 5b and 5c). Furthermore, the antibacterial activity of SNCP:1.25Ag was maintained at lower concentrations, remaining effective down to 62.5 µg/mL, which represents a substantial improvement compared to the undoped SNCP control.
Regarding TiO₂-doped bioactive glasses, antibacterial effects were observed at higher concentrations, with measurable inhibition detected at 250 µg/mL against MRSA and at 500 µg/mL against S. aureus (Fig. 5b and 5c). Although less pronounced than those observed for Ag-doped samples, these results suggest that TiO₂ incorporation contributes to antibacterial activity in a dose-dependent manner.
Overall, the results demonstrate that both Ag and TiO₂ incorporation enhance the antibacterial performance of bioactive glasses; however, Ag-doped formulations exhibit a more pronounced, sustained, and broad-spectrum inhibitory effect across Gram-negative and Gram-positive bacterial strains.
DISCUSSION
The optical absorption spectra of the bioactive glasses were analyzed to investigate their optical behavior and the influence of dopant incorporation on the electronic structure of the glass matrix. A strong absorption band at approximately 240 nm was attributed to the intrinsic electronic transitions of the silicate-based bioglass network, while an additional absorption feature near 450 nm was observed exclusively in Ag-containing samples.
The absorption band in the visible region (~450 nm) is attributed to the localized surface plasmon resonance (LSPR) associated with Ag-related nanostructures dispersed within the amorphous bioglass matrix, confirming the successful incorporation of Ag₂O-derived silver species. This plasmonic behavior arises from the collective oscillation of conduction electrons under incident light, and the progressive increase in band intensity with Ag concentration suggests a concentration-dependent plasmonic contribution, consistent with previous reports on silver-containing glass systems.
In contrast, TiO₂-doped bioactive glass samples exhibited a broad absorption feature in a similar spectral range; however, this behavior is not related to plasmonic effects, as titanium dioxide does not exhibit LSPR in the visible region. Instead, this absorption is likely associated with charge-transfer transitions, defect-related states, and light-scattering phenomena induced by TiO₂ domains interacting with the glass network. Higher TiO₂ concentrations (10–20 wt%) resulted in further spectral modifications, indicating strong electronic and structural interactions between TiO₂ species and the amorphous bioglass matrix. Although incorporation of Ag and TiO₂ species induced shifts in the absorption edge, these changes are discussed here primarily as indicators of dopant–matrix interactions rather than as evidence of applicability in optoelectronic or photocatalytic systems.
Atomic Force Microscopy (AFM) analysis provided further insights into the morphology and topographical features of the nanostructured bioactive glasses. AFM contrast images revealed heterogeneous surface features rather than crystalline domains, consistent with the amorphous nature of bioactive glasses. Topographic mapping confirmed the presence of individual glass particles with average lateral dimensions of approximately 2 µm in width and 3.5 µm in length, while three-dimensional reconstructions revealed thickness variations ranging from approximately −0.03 µm to 0.47 µm, indicative of nanoscale surface roughness.
Surface profile analyses demonstrated localized variations in surface height, particularly near particle boundaries and surface irregularities, rather than preferential nanoparticle accumulation at “crystal edges”. These topographical heterogeneities are more accurately interpreted as surface morphology variations resulting from dopant incorporation and glass processing, which may influence interfacial interactions with biological environments rather than mechanical stability per se.
The antibacterial activity observed for TiO₂-doped bioactive glasses, although less pronounced than that of Ag-doped formulations, remains relevant. Titanium dioxide is widely reported to exhibit antibacterial effects primarily through the generation of reactive oxygen species (ROS), particularly under photoactivation or in nanostructured forms, which can damage bacterial membranes and intracellular components (Shuaishuai et al. 2023). Consistently, Nowotnick et al. (2024) demonstrated that polymeric systems incorporating TiO₂ nanoparticles exhibit measurable antibacterial activity against several bacterial strains.
The enhanced antibacterial performance of Ag-doped bioactive glasses can be attributed to the well-established antimicrobial mechanisms of silver, including membrane disruption, interaction with thiol-containing proteins, and interference with DNA replication. Previous studies have shown that the dispersion and availability of silver-related species within glass matrices are critical parameters influencing antimicrobial efficacy, rather than nanoparticle size alone (Amini et al. 2012).
The pronounced activity of Ag- and TiO₂-doped bioactive glasses against methicillin-resistant Staphylococcus aureus (MRSA) is particularly significant, given the increasing prevalence of antibiotic-resistant infections. The ability of these materials to inhibit MRSA growth supports their potential as antimicrobial biomaterials, although not as substitutes for conventional antimicrobial therapies (Kavanagh et al. 2018). The observed antibacterial effects are likely the result of combined physicochemical interactions at the material–bacteria interface rather than solely optical or morphological properties.
Cytotoxicity assessments further demonstrated that, under indirect exposure conditions, Ag-doped bioactive glasses (SNCP:0.5Ag and SNCP:1.25Ag) induced only a modest reduction in cell viability, with values remaining above 80% even at the highest tested concentration (1000 µg/mL). Similarly, TiO₂-doped bioactive glasses (SNCP:10TiO₂ and SNCP:20TiO₂) exhibited negligible cytotoxic effects, reinforcing their cytocompatibility under the conditions evaluated. These findings indicate a favorable balance between antibacterial efficacy and cellular tolerance in vitro.
However, it is important to emphasize that the present cytotoxicity results are limited to metabolic activity assessments and do not account for long-term exposure or ion release dynamics. As highlighted in recent studies (Liu et al. 2025), the release of metal ions from doped bioactive glasses may contribute to both antimicrobial effects and cytotoxic responses, particularly at higher concentrations. Further investigations, including ion release studies and in vivo evaluations, are therefore required to fully assess the translational potential of these materials for biomedical applications.
CONCLUSIONS
This study demonstrates that the incorporation of silver- and titanium dioxide–derived species into an amorphous bioactive glass matrix significantly enhances antibacterial performance while preserving acceptable cytocompatibility under indirect exposure conditions. Ag-doped formulations exhibited the most pronounced and sustained antibacterial activity, including against methicillin-resistant Staphylococcus aureus (MRSA), whereas TiO2-doped glasses showed moderate, concentration-dependent effects. Optical and surface analyses confirmed dopant–matrix interactions and heterogeneous surface topography characteristic of doped bioactive glasses, without evidence of crystalline domains or nanoparticle aggregation at specific sites. Overall, these findings indicate that doped bioactive glasses represent promising antimicrobial biomaterials; however, further investigations addressing ion release behavior and in vivo biocompatibility are required to support future biomedical applications.
Acknowledgements
The authors acknowledge the financial and institutional support from FAPEMIG (RED-00224-23 – Rede Mineira de Nanobioplataformas Translacionais), CNPq, CAPES, and FUNEPU.
Data availability
References
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