*2.5. Inorganic Matrices*

Inorganic porous materials, such as various silica- or aluminosilicate-based materials/composites, clays, calcium carbonate, calcium phosphate, layered double hydroxides (LDHs), etc., have become good candidates for the delivery of a range of drugs, providing some advantages in formulation and engineering. They have suitable architecture, large surface area, and stability in biological fluids; thus, they are used for high loading capacity, controllable release, and improved targeting [119–121].

Comparison of four different capped SiO2 mesoporous particles (MSPs) (i.e., hollow silica shells, MCM-41, SBA-15 and UVM-7) showed that they were able to hinder the delivery of FA at low pH (to stomach) and deliver large amounts of the vitamin at neutral pH (to intestine); nevertheless, the usage of supports with large pore entrance ensured an initial fast release, while the mesoporous material MCM-41 demonstrated a sustained release over the time [122]. The amine-capped MSPs also hindered the release of FA in gastric fluids (pH 2) and progressively delivered it in the presence of a simulated intestinal juice (pH 7.5) [123]. Similarly, the in vitro digestion procedure showed that mesoporous silica support loaded with FA and functionalized with amines inhibited the release of FA in acidic solution at pH 2 (stomach) and enabled its controlled release in neutral pH (intestine), thereby modulating the bioaccessibility [124]. Ruiz-Rico et al. [125] investigated controlled FA delivery and stability in fruit juices to reduce potential for over-fortification risks by using dated MSPs and observed that the encapsulation of FA into MSPs resulted in considerably improved vitamin stability and contributed to controlled release after consumption by modifying FA bioaccessibility.

RES encapsulated in mesoporous silica (MCM-48) NPs with the particle size of 90 nm did not alter its bioactivity and, at lower concentration, i.e., 5 μg/mL, exhibited higher anti-inflammatory activity compared to RES suspension or its solution [126]. Similar findings concerning the enhancement of the biological activity of RES by colloidal mesoporous silica NPs were reported also by Summerlin et al. [127]. Singh et al. [128] reviewed causes and consequences of micronutrient deficiencies and the bioavailability of nutrients, vitamins, minerals, and silica for food and outlined that the release of nutrients from silica in simulated intestinal fluid is better than in simulated gastric fluid.

Simple powders and tablets of inorganic–organic nanostructured hybrids prepared by intercalating FA in the MgAl-LDH and ZnAl-LDH exhibited enhanced FA release compared to crystalline FA, suggesting that such hybrids could be used to enhance the active ingredient dissolution at low pH values in effective nutraceutical products [129].

The analysis and speciation of selenium in nutritional supplements based on next-generation Se ingredients, i.e., Se forms with lower toxicity, higher bioavailability, and controlled release, such as selenium NPs (SeNPs) and selenized polysaccharides, was presented by Constantinescu-Aruxandei et al. [130].
