Modulation of folic acid bioaccessibility by encapsulation in pH-responsive gated mesoporous silica particles

Abstract

A study on the controlled release of folic acid (FA) from pH-responsive gated mesoporous silica particles (MSP) is reported. The MCM-41 support was synthesized using tetraethyl orthosilicate (TEOS) as hydrolytic inorganic precursor and the surfactant hexadecyltrimethylammonium bromide (CTAB) as porogen species. Calcination of the mesostructured phase resulted in the starting solid. This solid was loaded with FA to obtain the initial support S0. Moreover, this FA-loaded material was further functionalized with 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (N3) in order to obtain the gated polyamine-functionalised material S1. Solids S0 and S1 were characterized using standard solid state procedures. It was found that the functionalization process and the inclusion of FA on the pores did not modify the mesoporous structure of the starting material. FA delivery studies in water with solids S0 and S1 were carried out in water at pH 2 and 7.5. S0 was not able to completely inhibit FA delivery at acidic pH yet a rapid FA release at neutral pH was observed in few minutes. In contrast, S1 was tightly capped at pH 2 and displayed a sustained delivery of FA when the pH was switched to 7.5. In the second part of the study, FA loading and functionalization of S1-like supports was optimized. In particular, solids loaded with FA in phosphate buffered saline (PBS) and capped with N3 in acetate buffer at pH 2 exhibited a delivery capacity up to 95μg FA/mg solid. Finally, FA release from the selected optimized supports was studied following an in vitro digestion procedure. The results showed that amine-capped MSP were not only able to hinder the release of the vitamin in gastric fluids (pH 2), but were also capable of deliver progressively the FA in presence of a simulated intestinal juice (pH 7.5) offering a suitable mechanism to control the bioaccessibility of the vitamin.