Experimental and theoretical investigation of drug loading to silica alcogels

The loading of a model drug, paracetamol (PC), via diffusion from an ethanol solution to the pores of the silica alcogel was studied. Partial differential equation representing the mass transfer within the cylindrical silica alcogel phase was developed and solved using the finite difference method. The model enabled the prediction of the time needed for maximum amount of loading and also the distribution of the drug inside the matrix at specific time points. It was observed that the concentration in the regions closer to the surface increased rapidly contrary to concentration in the regions close to the center which increased more slowly. The uptake of paracetamol was also measured gravimetrically and these experimental data were found to be in good agreement with the model predictions without any adjustable parameters. The effects of the tortuosity of the aerogels were also investigated by simulations. It was found that the duration for the maximum amount of loading increased with increasing tortuosity values. Moreover, silica alcogels that were loaded with paracetamol were dried with supercritical CO2 which resulted in paracetamol loaded monolithic silica aerogels. Characterization of these paracetamol loaded silica aerogels showed that paracetamol had diffused through the center of the aerogel and it had a crystal structure. (C) 2015 Elsevier B.V. All rights reserved.