*2.2. FDM Printing*

The applied 3D printer was Creality Ender 3 (Creality 3D Technology Co., Shenzhen, China), with an MK-10 hot-end with a 0.4-mm-diameter nozzle. The heated print platform was customized with 3M blue tape. The temperature during the printing was checked by FLIR with CAT S61 (Caterpillar, Deerfield, IL, USA) The frames were layered on each other with pre-selected points where the temperature was indicated. The visual investigations of the printlets were executed using a Keyence VHX-7000 digital microscope (Keyence International, Mechelen, Belgium).

#### *2.3. Preparation of Riboflavin Containing Liquid Fill*

In every instance, 20 mg/g concentration of riboflavin-PEG 300 (polyoxyethylene glycol) dispersions were created manually in 10-g-sized batches. The samples were prepared before filling at room temperature with light-protection. The dispersion was applied into the vehicle using a 5 mL syringe (Chirana T. Injecta, Stará Turá, Slovakia) applied with a 23-gauge syringe needle. The filling was monitored by the comparison of the mass of the empty and the filled prototypes. In the instance of carriers without orifice, the filling process should be executed during the printing. The filament extrusion was stopped at 80% of the progress, and the dispersion was filled with the 5 mL syringe. After the application, the printing was continued, and the container was closed.
