## 3 Results and Discussion
### EDS Analysis--Elements Mapping  
The EDS mapping of the surfaces and cross-sections of L-FDM-printed cylinders (Figure 15) illustrated the distribution of the elements introduced with the L-FDM technique in the polymer matrix. The surfaces of the cylinder walls of the samples printed from polymers and copolymers such as ABS, ASA, PLA, and PET-G were characterized by a uniform distribution of the elements in the matrix (Figure 15A-C,E). On the other hand, in the cross-section of the printing layer (see also Figure S1 in the Supplementary Materials), a higher content of lead was visible on its outer edge and at the contact point of the individual layers. The distribution of iron and rubidium in the EDS images of unfilled fiber samples was more homogeneous (Figure 15H,L,J). The large clusters visible in the EDS images of the PLA WOOD prints with silver nitrate and ferric chloride were probably the result of increased absorption of the modifier solution by the porous filler, which consisted of wood fibers and dust. When comparing the EDS images of the L-FDM prints with lead acetate dissolved in methanol (saturated solution), differences in the lead dispersion could be observed. Based on this, it could be concluded that, with the printing parameters used, the material from which the filament was made had either a better or worse ability to mix with the modifier used. This dependence was visibly better on the EDS images of the cylinder cross-sections (Figure 15A and Supplementary Figure S1A-C). As could be seen, the ASA polymer showed the lowest ability to penetrate the polymer matrix, while ABS and PLA WOOD showed the highest concentration of lead on the outer edges and at the interface of the individual layers. PET-G exhibited the most homogeneous lead dispersion in the polymer matrix using the L-FDM technique with lead acetate dissolved in methanol. The color intensity on the EDS maps was higher for the PLA WOOD polymer. This effect occurred due to better wetting of the filament surface (rough structure of the filament surface) and its greater absorbency caused by the presence of wood fibers and dust. The EDS analysis provided evidence of elements in the polymer matrix of the L-FDM prints. This finding confirmed the possibility of using this technique as a tool for introducing various chemical substances into the polymer matrix.  
Figure 13: Optical microscope images with 300\(\times\) magnifications of color L-FDM-printed parts. The images (**A–C,G–I,M–O**) depict the surface of the printed cylinder’s wall, while images (**D–F–J–L,P–R**) show its adequate cross-section. (**A,D**) WOODFILL reference sample marked ref. 5, (**B,C,E,F**)—WOODFILL dyed with rhodamine B marked 5.1 and 5.2, (**G–R**) PLA (**J.M**) samples dyed with (**H,K**) navy blue fabric dye marked 2.4, (**L,L**) transparent blue turquoise dye by Ag-Bet marked 2.5, (**M–R**) rhodamine B dissolved in different solvents, (**M,P**) sample marked 2.10, (**N,Q**) 2.11, and (**O,R**) 2.7.  
Figure 14: Optical microscope images of color L-FDM-printed parts. Images (**C**,**F**) made with a magnification 500\(\times\), the rest with 300\(\times\). The images (**A**,**D**,**G**–**I**,**M**–**O**) depict the surface of the printed cylinder’s wall, while images (**B**,**C**,**E**,**F**,**J**–**L**,**P**–**R**) show its cross-section. (**A**–**C**) The reference PLA sample; (**D**–**F**) silver nitrate in the PLA matrix sample marked 7.1; (**G**–**L**) PET-G samples dyed with silver nitrate; (**G**,**J**) the reference PET-G sample marked ref. 3; (**H**,**K**) the sample marked 8.4; (**I**,**L**) the sample marked 8.3; (**M**,**R**) PLA WOOD modified with (**M**,**P**) reference unmodified sample marked ref. 6, (**N**,**Q**) iron (III) chloride marked 6.5, and (**O**,**R**) silver nitrate sample marked 6.4.