Development of a novel pH-responsive anti-caries nanocomposite hydrogel

To develop a pH-responsive nanocomposite hydrogel (NCH) with antibacterial and inhibiting demineralisation properties for anti-caries applications.

The NCH was formulated from methacrylated hyaluronic acid, methacrylated silk fibroin, and chitosan, and incorporated nano-hydroxyapatite, nano-silver, and nano-zinc oxide. Its morphology, optical properties, functional groups, crystalline phases, and chemical states were characterised by scanning electron microscopy, ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Cytotoxicity towards human gingival fibroblasts (HGF-1) and stem cells from human exfoliated deciduous teeth (SHED) was assessed by half-maximal inhibitory concentration (IC₅₀). pH-dependent release of calcium, silver, and zinc ions was measured by inductively coupled plasma mass spectrometry. Antibacterial activity against Streptococcus mutans was evaluated using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Biofilm morphology and bacterial damage were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of NCH on dentine demineralisation was assessed by micro-computed tomography after pH cycling, using water as the control.

Characterisation confirmed successful synthesis of the NCH. The IC₅₀ values were 1440±121 ppm for HGF-1 and 1069±78 ppm for SHED. Calcium, silver, and zinc ion release over 180 min was significantly greater at pH 4.5 than at pH 7.5 (p < 0.001). The MIC was 211±31 ppm and MBC was 500±71 ppm. SEM showed reduced bacterial colonisation. TEM showed membrane disruption after NCH treatment. Compared with the control, NCH-treated dentine showed a shallower lesion depth (35±6 μm vs 111±19 μm; p < 0.001) and lower mineral loss (0.17± 0.14 gHA/cm³ vs 0.73±0.09 gHA/cm³; p < 0.001).

This biocompatible NCH showed pH-triggered ion release, antibacterial activity against Streptococcus mutans, and mineral-protective effects against dentine demineralisation, indicating promise as an anti-caries biomaterial.

A pH-responsive NCH that preferentially releases antibacterial and mineralising ions under acidic conditions may support the development of more targeted and non-invasive strategies for caries management.