Sílica mesoporosa de origem sustentável: desenvolvimento, caracterização e potencial aplicação para o encapsulamento de antioxidantes

Abstract

Mesoporous silica nanoparticles (MSNs) stand out due to their high surface area, organized pores, and biocompatibility, enabling the encapsulation of compounds such as curcumin, a natural antioxidant widely investigated for the prevention and treatment of various diseases. In this study, SBA-15–type MSNs were synthesized from sodium silicate extracted from rice husks (RH) for curcumin loading. The synthesis was performed by the hydrothermal method, followed by calcination at 400 °C for 4 h. Subsequently, curcumin was encapsulated into the MSNs (MSNs-Cur) in an acetone:ethanol medium, achieving a loading efficiency of 99%. The FTIR spectrum obtained for the MSNs revealed bands between 1000–1300 cm⁻¹ and at 960 cm⁻¹, characteristic of Si–O–Si bonds and silanol groups (Si–OH), respectively, while the MSNs-Cur spectrum also exhibited bands at 1628–1600 cm⁻¹, attributed to the C=O and C=C stretching of the aromatic ring and the enolic/keto chain of curcumin. X-ray diffraction (XRD) patterns showed an intense peak at 2θ = 1.07° for the MSNs, which shifted to 1.13° in the MSNs-Cur, indicating that curcumin is found in the pores. For the MSNs, the interplanar spacing was 8.25 nm, the lattice parameter was 9.52 nm, and the wall thickness was 7.51 nm. Adsorption isotherms of de N2(g) revealed a specific surface area (SBET) of 431.4 m²/g for the MSNs, with pore volume and average pore diameter of 0.4334 cm³/g and 2.01 nm, respectively, whereas the MSNs-Cur exhibited an SBET of 2.28 m²/g and an average pore volume of 0.0074 cm³/g, confirming the effective encapsulation of the antioxidant. Zeta potential measurements of the MSNs showed highly stable particles with a surface charge of –30 mV, while MSNs-Cur presented ζ = –11 mV due to the presence of curcumin on the surface. In vitro release assays were carried out with MSNs-Cur in simulated gastric fluid (SGF, pH 1.2) and intestinal fluid (SIF, pH 7.4). The system exhibited pH-responsive behavior, releasing ~60% of the antioxidant after 48 h in a sustained manner in SGF. The antioxidant activity (AA) of the MSNs-Cur system was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, showing continuous and gradual AA, thus being more effective than pure curcumin. Toxicological tests using Allium cepa L. demonstrated that the MSNs-Cur system did not impair cell division, presenting a mitotic index between 83.4 ± 1.0 and 93.0 ± 1.5, indicating the absence of cytotoxic effects. Therefore, the MSNs synthesized from RH proved to be viable nanoplatforms for the storage and controlled release of the antioxidant curcumin.