PROTECTIVE EFFECT OF ORDERED MESOPOROUS SILICA AS CARRIER FOR PROTEINS

Ordered mesoporous silica has great potential as nanocarriers for most protein-based biomedical applications, which is primarily attributed to its tunable structural and textural properties and remarkable structural stability under physiological conditions. However, achieving the optimal parameters to ensure both the structural integrity and functional protection of proteins during the encapsulation process remains a challenge.
In this work, three model proteins were individually incorporated into SBA-15 particles with hexagonal symmetry (space group p6mm) to obtain the biocomposites, using the wet impregnation method at two different silica-to-protein ratios (10:1 and 5:1, w/w).
The SBA-15 particles were characterized using Scanning Electron Microscopy (SEM), Small Angle X-Ray Scattering (SAXS), and Nitrogen Adsorption Isotherms (NAI) measures. The synthesis yielded particles with a substantial surface area of 781.5 m²/g and a pore volume of 1.5 cm³/g. Additionally, the particles exhibited low dispersity in the mesopores size, with a mean diameter of 9.3 nm. SAXS was employed to assess the native oligomeric state of each protein and determined the gyration radius for each protein of ~ 1.8 nm for the all-α protein, 3.2 nm for the all-β protein, and 2.5 nm for the low-regular structured protein, suggesting a population that can enter the mesopores. SAXS analyses on the biocomposite revealed that protein adsorption also occurred on the external surface, likely associated with the presence of higher oligomeric states. However, when compared to pure silica, the surface area of the biocomposites decreased by approximately 54% on average. In contrast, in the presence of ions from the buffer solution in the control sample (buffer + SBA-15), the reduction was milder, averaging 28%. This finding indicates that the incorporation process also involved the mesopores, contributing to the reduction in surface area. Circular Dichroism (CD) analyses revealed the preservation of the native secondary structure for each protein, after redispersion in aqueous solutions under different pH conditions (pH 7.0 and 2.2) and temperatures (25°C and 37°C). Additionally, fluorescence analysis in the biocomposites revealed that tryptophan environment is less exposed to solvent interactions at the pH 7.0 buffer solution, evidencing the protective role of the mesoporous ordered silica.

This work was supported by grants # 158984/2022 6 from CNPq Brazil and # 2019/19567 7 and # 2017/17844-8 from São Paulo Research Foundation (FAPESP) Brazil