Mesoporous Silica Materials Loaded with Gallic Acid with Antimicrobial Potential

Abstract

This paper aimed to develop two types of support materials with a mesoporous structure of mobile crystalline matter (known in the literature as MCM, namely MCM-41 and MCM-48) and to load them with gallic acid. Soft templating methodology was chosen for the preparation of the mesoporous structures—the cylindrical micelles with certain structural characteristics being formed due to the hydrophilic and hydrophobic intermolecular forces which occur between the molecules of the surfactants (cetyltrimethylammonium bromide—CTAB) when a minimal micellar ionic concentration is reached. These mesoporous supports were loaded with gallic acid using three different types of MCM—gallic acid ratios (1:0.41; 1:0.82 and 1:1.21)—and their characterizations by FTIR, SEM, XRD, BET and drug release were performed. It is worth mentioning that the loading was carried out using a vacuum-assisted methodology: the mesoporous materials are firstly kept under vacuum at ~0.1 barr for 30 min followed by the addition of the polyphenol solutions. The concentration of the solutions was adapted such that the final volume covered the wet mesoporous support and—in this case—upon reaching normal atmospheric pressure, the solution was pushed inside the pores, and thus the polyphenols were mainly loaded inside the pores. Based on the SBET data, it can be seen that the specific surface area decreased considerably with the increasing ratio of gallic acid; the specific surface area decreased 3.07 and 4.25 times for MCM-41 and MCM-48, respectively. The sample with the highest polyphenol content was further evaluated from a biological point of view, alone or in association with amoxicillin administration. As expected, the MCM-41 and MCM-48 were not protective against infections—but, due to the loading of the gallic acid, a potentiated inhibition was recorded for the tested gram-negative bacterial strains. Moreover, it is important to mention that these systems can be efficient solutions for the recovery of the gut microbiota after exposure to antibiotics, for instance.

Antioxidant-Loaded Mesoporous Silica—An Evaluation of the Physicochemical Properties

“…It might be assumed that a too high a ratio between GA molecule and pore size might reduce the %Ads. Similar findings were reported for the adsorption of drug molecules—higher drug loading was observed for MCM-41 despite its lower pore size in comparison to SBA-15 [ 56 , 66 ]. Moreover, the impact of different morphologies of MCM-41 (spherical particles) and SBA-15 (rod-like particles) on GA adsorption should also be taken under consideration and requires further studies.…”

“…All GA-loaded SBA-15 samples (both parent and functionalized) exhibited the characteristic compact, elongated, rodlike morphology of the particles [ 55 ]. In the case of the SBA-15-GA and SBA-SH-GA samples, a relatively higher occurrence of precipitated GA plates covered by silica was observed, compared to SBA-NH2-GA [ 56 ].…”

A Comparative Loading and Release Study of Vancomycin from a Green Mesoporous Silica

“…This condensation process, accompanied by elimination of water molecules, is responsible for the formation of silica and densification of the structure. The amount of H 2 O and density of silanol groups were calculated as indicated in [ 16 ] and are summarized in Table 3 . The calculated concentration of silanol groups is quite high, better than the reported values from [ 16 ], and similar to those for raw MCM-41 reported in [ 58 ].…”

“…Finally, the third method, namely vacuum-assisted loading, consisted of the solubilization of 90 mg of vancomycin in 2 mL of water. The method is presented in more detail in our previous work [ 16 ]. Once the vacuum was removed, the drug solution that reached the pores is adsorbed deeper into the pores.…”

“…By virtue of its well-known biocompatibility and lower costs, compared to MOFs, mesoporous silica is somehow preferred by pharmaceutical industry. Several types of MSMs have been synthesized by modifying the starting precursors and the reaction parameters, leading to a wide variety of materials in terms of pore size and/or geometry, with MCM-41 [ 15 , 16 ] and SBA-15 [ 17 , 18 ] being perhaps the most extensively researched for biological applications. Other well-known mesostructured silicas include MCM-48 with a cubic pore arrangement, MCM-50 with a lamellar layout, or COK-12 with a 2D hexagonal arrangement [ 19 ].…”