Added-value porous materials for controlled thymol release obtained by supercritical CO2 impregnation process

This study explores utilization of biodegradable and biocompatible polymers for controlled release of natural bioactive substance. For that purpose, poly(ε-caprolactone) (PCL) beads, cellulose acetate (CA) film, and poly lactic-co-glycolic acid (PLGA) flakes were impregnated with thymol by employing environmentally friendly process of supercritical carbon dioxide (scCO2) impregnation. At selected pressure and temperature, prolongation of operating time increased thymol loading. Pure scCO2 did not affect CA film with average pore diameter of approximately 3 µm, while it enabled change of PCL beads and PLGA flakes into foams with average pore diameter approximately 175 µm and 87 µm, respectively. Additionally to scCO2, thymol acted as a plasticizer increasing pore size of polymers up to three times. Kinetic of thymol release from selected samples was tested using phosphate buffer saline at 37°C and successfully described with Korsmeyer–Peppas, zero-order, first-order, and Higuchi models. The suggested method of PCL, CA, and PLGA supercritical impregnation led to development of porous, solvent free, added-value materials that release thymol in a controlled manner from 5 h to several days.