Effect of Nitric Acid on the Synthesis and Biological Activity of Silica–Quercetin Hybrid Materials via the Sol-Gel Route

Abstract

The sol-gel technique stands out as a valuable method for synthesizing biomaterials and encapsulating bioactive molecules, offering potential for controlled drug release and tissue regeneration in biomedical contexts. This study focused on synthesizing silica (Si)-based hybrid biomaterials containing 5% quercetin (Q5) using two different approaches: one involving nitric acid as a catalyst (SiQ5-HNO3) and the other being acid-free (SiQ5). Structural characterization using Fourier transform infrared (FTIR) and UV-vis spectroscopy revealed oxidation processes compromising the structural integrity of quercetin in both systems. However, it was observed that these oxidation processes led to the formation of oxidized derivatives of quercetin with distinct structures. Additionally, the bioactivity and release kinetics of quercetin from the silica matrices were evaluated, showing that both systems were capable of forming hydroxyapatite, indicating excellent bioactivity. Furthermore, SiQ5 exhibited a higher percentage release of the encapsulated drug at pH 7.4, representing the physiological environment, compared to SiQ5-HNO3, with a drastic reduction in drug release observed at pH 5.0 (cancer environment). Antibacterial efficacy assessment using the Kirby–Bauer test highlighted the greater antibacterial activity of the SiQ5-HNO3 system against all tested strains. Overall, this research aims to advance the development of more effective biomaterials for various biomedical applications, particularly in tissue engineering and infection control.