A drug delivery system based on poly-L-lysine grafted mesoporous silica nanoparticles for quercetin release

This work focuses on the preparation of a pH-sensitive antimicrobial drug delivery system based on Mesoporous silica nanoparticles (MSN), functionalized with aminopropyl-triethoxysilane (MSN-NH2), triethylenetetramine (MSN-TETA) and poly-L-lysine (MSN-NH2-PLL, MSN-TETA-PLL), and loaded with the flavonoid quercetin. The systems were fully characterized by means of several techniques. Besides the role of the different functionalization of MSNs, this work aimed to optimize both loading and release processes of quercetin, using two different ethanol-water mixtures as solvent, namely EtOH:H2O mixtures at the ratios 80:20 and 50:50. Whereas loading was higher using the 80:20 solvent mixture, a more efficient release was ascertained using the solvent mixture 50:50 as demonstrated by the release kinetics, and also by the amount of the released drug. It was suggested that in the presence of less ethanol, quercetin solubility decreases, and a physical adsorption of quercetin at the functional groups of MSNs can be favoured with respect to a random distribution over many surface sites with which only weak interactions can occur. This means that in the presence of high amount of ethanol, used very often when dealing with poorly water-soluble drugs, the impregnation process becomes dominant, loading increases significantly, but subsequently burst release of high amounts of drug occurs. In this work, using the specific case of quercetin, we found a more sustained release as the result of a predominant adsorption mechanism due to the careful choice of the solvent mixture composition during the loading step. Moreover, the new drug delivery system allowed for a significant improvement in quercetin stability and the optimal release concentration attainment.