Analysis of modes of drug loading in silica aerogels from supercritical CO2 solutions

Drug loading in silica aerogels from solutions of the drug in supercritical carbon dioxide (scCO(2)) occurs in two modes: adsorption of the drug during contact time with the aerogels followed by its precipitation during depressurization. The present work quantifies the relative proportions of drug loading by these modes. Experiments have been conducted with benzoic acid (BA) as a model drug with its saturation in scCO(2) varying from 20% to 90% at 200 bar, 328 K and for a contact time of 5-10 h, followed by fast and slow pressure release. Experiments revealed that additional loading by precipitation on the outer surface of aerogels is comparable to and faster than that by adsorption. A mathematical model validates this additional loading. The model predicts supersaturation of BA, its nucleation and growth, for slow, fast, or isothermal pressure release. (C) 2019 Elsevier B.V. All rights reserved.