Unveiling the Critical Role of Pressure in Supercritical CO ₂ -Assisted Drug Impregnation into SBA-15 Mesoporous Silica

Mesoporous silica is increasingly recognized as an efficient drug delivery vehicle, thanks to its extensive surface area, adaptable pore structure, and ability to stabilize poorly soluble drugs. Employing supercritical fluid deposition (SCFD) with CO2 presents an environmentally friendly method for drug incorporation. Nonetheless, the effect of impregnation pressure on loading efficiency remains underexplored. This study investigated the impregnation of ibuprofen and ketoprofen into SBA-15 mesoporous silica at 333 K using a batch-type SCFD process with supercritical CO2 pressures ranging from 8 MPa to 20 MPa. Drug loading was assessed through thermogravimetric analysis, while nitrogen adsorption tests revealed alterations in pore structure. Both drugs exhibited a non-linear pressure dependence, achieving peak loading at 15 MPa. The increase in loading up to this point was linked to improved drug solubility in supercritical CO2, whereas the decline at 20 MPa was attributed to intensified competitive adsorption of CO2 molecules on the silica surface. Structural analysis indicated that ibuprofen penetrated deeply into the mesopores, resulting in relatively uniform filling and moderate pore contraction, whereas ketoprofen primarily accumulated near pore openings, leading to significant pore blockage despite lower overall uptake. These findings provide clear evidence that impregnation pressure is a crucial, adjustable factor influencing SCFD performance, with drug solubility and surface interactions playing vital roles in loading behavior. The results offer practical insights for designing pressure-controlled mesoporous silica carriers for efficient drug delivery systems.