**2. Materials and Methods**

Two commercially available biodegradable polymers were used as printing filament: the water-soluble polyvinyl alcohol (PVA) fiber (Orbi-Tech advanced, Leichlingen, Germany) and the water-insoluble polylactic acid (PLA) fiber (bq Easy Go, Madrid, Spain). The PVA filament has a diameter of 1.75 mm and a melting point of 183 ◦C, density: 1.13 g/cm3. According to the manufacturer's specification, the orange PLA fiber had a diameter of 1.75 mm and a density of 1.24 g/cm3 (ASTM D792), while the melting point temperature is between 145 and 160 ◦C. As model API riboflavin (Hungaropharma, Budapest, Hungary) was used. Polyethylene glycol 300 (Sigma Aldrich, St. Louis, MO, USA) was applied as the dispersing agent of the API containing liquid filled into the 3D printed carriers.
