*2.1. Design*

Autodesk Fusion 360 (Autodesk Inc., San Rafael, CA, USA) was used during the planning phase of the experiment which exported the prepared structure into a stereolithography file. Further settings should be applied during the slicing. This is an algorithmical step in which the slicing program Ultimaker Cura (Ultimaker, Geldermalsen, Holland) divides the designed object into several, well defined horizontal slices. The exported g-code file includes not only the coordinates the extruder is going to follow but all the other printing parameters which can be set, e.g., printing temperature, bed temperature, cooling fan speed, printing resolution, and the infill percentage.

The PVA and PLA-based carriers were designed as a 9.75 mm high by 9.6 mm in diameter. The structure of the wall was built by concentric movements making 1-mm-thick sides to the printed object. Each carrier was designed to have a hollow structure with approximately 0.4 mL reservoir volume. During the examination of the effects of holes, 1-mm-diameter orifices were designed into the cylinder mantle and top (Figure 1), equally divided around the circumference of the prototype. There was a version of carrier without orifices in order to investigate only the release-modifying effect of the wall. Carriers were also made of PVA and PLA containing 2 or more orifices (Figure 2). The distance between the orifices is the circumference of the cover circle divided by the number of holes. The printer process parameters were set as the following: print speed, 20 mm/s; travel speed, 120 mm/s. The layer parameters were set as a 0.16 mm layer height with a 0.2 mm layer thickness. The printing temperature was 200 ◦C, accompanied by a 50 ◦C bed temperature in order to ensure the perfect bonding to the plate. The infill percentage was set to 100%, with maximum cooling fan performance (5000 rpm).

**Figure 1.** Printlet preparation process and digital microscopic images of polyvinyl alcohol (PVA-) and polylactic acid (PLA)-based prototype with one orifice.

**Figure 2.** CAD models and digital microscopic images of PVA and PLA-based prototype with multiple orifices.
