Carriers for hydrophobic drug molecules: lipid-coated hollow mesoporous silica particles, and the influence of shape and size on encapsulation efficiency.

Abstract

Hydrophobic drugs, while designed to interact with specific receptors or enzymes located in lipid-rich cell membranes, often face challenges of limited bioavailability and insufficient circulation time due to their insolubility in aqueous environments. One plausible pathway to increase their blood circulation time is to load these drugs into biocompatible and hydrophilic carriers to enhance their uptake. In this study, mesoporous silica (mSiO2) nanocarriers of various morphologies (including cubes, capsules, and spheres) were synthesized. These nanocarriers were then surface-functionalized with alkyl chain hydrocarbons, specifically octadecyl-trimethoxysilane, (OCH3)3Si(CH2)17CH3, to render them hydrophobic. The resulting nanocarriers (((OCH3)3Si(CH2)17CH3)@mSiO2) showed up to 80% uptake for hydrophobic drugs. However, a significant drawback was observed as most of the drugs were prone to uncontrollable release within 6 h. This challenge of premature drug release was successfully mitigated by effectively sealing the drug-loaded nanocarriers with a pH-sensitive lipid overlayer. The lipid-coated nanocarriers prolonged drug containment and sustained release up to 72 h, compared to 6 h for uncoated nanocarriers, thereby facilitating longer blood circulation times. Moreover, the shape and size of nanocarriers were found to influence both drug entrapment capacity and release behavior with cubic forms exhibiting superior loading capacity due to higher surface area and porosity. Additionally, it was observed that the molecular weight and chemical structure of the drug molecules played a crucial role in determining their uptake and release profiles. Furthermore, the influence of different morphologies of nanocarriers on cell uptake and cytotoxicity in immune cells was elucidated. These findings underscore the importance of nanocarrier morphology and drug properties to enhance loading capacities and controlled release profiles, for designing drug delivery systems tailored for hydrophobic drugs.