Production of polycaprolactone foams incorporating Hibiscus sabdariffa extract

Hibiscus sabdariffa is a plant characterized by a high content of antioxidant molecules; its aqueous extract (karkadé) offers considerable potential benefits during the healing process. Since most antioxidant molecules are sensitive to thermo-oxidative degradation during extraction and encapsulation processes, this study proposes a novel application to preserve karkadé inhibition power, by entrapping it in poly-ε-caprolactone (PCL) foams. Karkadé was obtained using Rapid Solid-Liquid Dynamic Extraction, processed at 20 °C and below 10 bar. The concentration of karkadé solid residue was 195.0 ± 4.6 g/L, while the reduction of the antioxidant inhibition power was 26.0 ± 1.4 % after 450 min of extraction, much greater than native karkadé extracted using other techniques (>60 %). Entrapment of karkadé occurred during the preparation of 3 mg/mL PCL in an acetone solution, which solidified upon solvent evaporation at 20 °C, obtaining a disk. Then, the disk was foamed using CO2 as physical blowing agent at optimized parameters (45 °C, 100 bar, and sorption for 60 min). Foam density of 180 kg/m3, cell number density of 4.1E06 cell/cm3, and an average pore dimension of 56 ± 28 µm were obtained, with karkadé entrapment efficiency up to 97 %. This study focused on manipulating PCL foam cells density and diameter, to influence release time of karkadé extract into an aqueous receiving medium. Different cells diameters and number density were achieved by varying sorption time of CO2 in PCL, set at 30, 60, and 90 min, respectively. Sorption time of 60 min was demonstrated to be sufficient for creating a uniform porous structure, while a 30 min sorption time resulted in a delayed release rate. Foams were soaked in cell culture medium, which was then put in contact with human keratinocytes, thus demonstrating their biocompatibility up to 9 days.