PSI - Issue 82

Tsanka Dikova et al. / Procedia Structural Integrity 82 (2026) 58–64 Dikova et al. / Structural Integrity Procedia 00 (2026) 000–000

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and elongated along the Z-axis. The bone pores samples (Fig. 3d,e,f) have more dense structure, keeping the pores elongation along the Z-axis. The top and bottom surfaces are observed by SEM and the images of the top surfaces are given in Fig. 4. Undoubtedly, the SEM images show much more clearly the differences between the porous structures in the two groups. The pores of the samples with original sizes in Group 1 are larger than that in Group 2 (Fig. 4a,d). Increasing the samples magnification up to 40 % leads to considerable enlargement of pores in Group 1 compared to Group 2 (Fig. 4c,f).

The porosity of bone samples is higher than that of the bone pores sample (Fig. 5). It is about 49 % in the samples with original sizes of Group 1 and about 10% in Group 2. Increasing the sample sizes with 20 % leads to increase of porosity in the two groups: up to 60 % in bone samples and 15 % in the bone pores samples. The 40 % magnification causes only slight increase of the porosity with 4 % in the first group and 1.5 % in the second. Fig. 4. SEM images of top surface of: (a), (b) and (c) Group 1 - bone samples; (c), (d) and (f) Group 2 - bone pores samples enlarged with different rate: (a), (d) 0%; (b), (e) 20%; (c), (f) 40 %.

Investigation of pore width by SEM and CBCT showed no clear difference in the dimensions of samples in Group 1, however for Group 2, the SEM values were about two times lower than that of CBCT (Fig. 6). The not so clear CBCT images of the denser bone pores samples (Fig. 3d f) are the most likely reason. The SEM study have shown that average width of pores in the bone samples with original sizes is 0.527 mm, while that of bone pores samples is twice lower – 0.293 mm (Fig. 6). The 20 % increase in sizes leads to increase of the pore width in the samples of the two groups up to 0.786 mm in Group 1 and 0.371 mm in Group 2. The 40 % magnification does not cause noticeable increase of the average pores width in both groups. The interval of the pores width in the samples of Group 1 is higher compared to Group 2. The pores width in the first group varies between 212-962 μm in the specimens of original sizes,

Fig. 5. Porosity of 3D printed samples (Group 1 – bone samples, Group 2 – bone pores samples.

223-1463 μm in 20 % magnification and 256-2056 μm in 40 % magnification (Fig. 7a,b,c). The corresponding values for the samples in Group 2 are lower: 122-522 μm, 97-797 μm and 124-1124 μm respectively (Fig. 7d,e,f). For the description of the geometry of empty spaces through the scaffold, three parameters are used – porosity, minimum/maximum pore size and general structure of the pores (Law et al. (2024). The porosity is percentage of the empty spaces through the scaffold, relative to the solid substance and for the bone tissue ideally it should be between 75% and 85% (Luo et al. (2021). Minimum and maximum pore size provide space for the development of newly