## 3 Results  
### Setting of CAp Granules  
CAp granules with a long axis length of 300-400 um were used (Figure 2a). The CAp granules were set in a cylindrical mold. The SG 0.33 partially collapsed at the top and bottom of the cylinder (Figure 2b). However, in SG 0.43, SG 0.54, SG 0.67, and SG 0.82, the granules were completely set into cylinders without collapsing (Figure 2c-f). SEM images showed that the CAp granules had smooth surfaces (Figure 2g), whereas the SG 0.33 surface was coarse (Figure 2h), indicating that CSD precipitated on the CAp granule surface. As the CSH/CAp ratio increased, the density of the precipitates among the granules increased (Figure 2i-l). A high-magnification image of CAp granules showed that the granules were composed of spherical aggregates with a diameter of 1.06 um (Figure 2m). In SG 0.33, SG 0.43, SG 0.54, SG 0.67, and SG 0.82, rod-shaped crystals formed among the CAp granules (Figure 2n-r). Thus, SG 0.33, SG 0.43, SG 0.54, SG 0.67, and SG 0.82 have structures of interconnected granules with rod-shaped crystals, a characteristic of CSD. The crystal lengths of CSD increased from 6.58 to 6.79 um as the CSH/CAp ratio increased from 0.33 to 0.82: the crystal lengths at CSH/CAp ratios of 0.33, 0.43, 0.54, 0.67, 0.82 were 6.58, 6.66, 6.74, 6.79, and 6.79 um, respectively. The diffractions of CSH, CSD, and CAp were detected in the XRD patterns of SG 0.33, SG 0.43, SG 0.54, SG 0.67, and SG 0.82 (Figure 3). The presence of CSD diffraction indicated the transformation of CSH into CSD. Additionally, the CAp/CSD peak intensity ratio decreased with an increasing CSH/CAp ratio under the setting conditions, with ratios of 0.96, 0.83, 0.74, 0.63, and 0.55 in SG 0.33, SG 0.43, SG 0.54, SG 0.67, and SG 0.82, respectively. The initial setting time decreased from 30.3 \(\pm\) 1.68 to 15.5 \(\pm\) 1.34 min as the CSH/CAp ratio increased from 0.33 to 0.82 (Figure 4). Significant differences in setting time were observed between SG 0.33 and all other groups, including SG 0.43, SG 0.54, SG 0.67, and SG 0.82. Additionally, SG 0.43 and SG 0.54 showed significant differences in relation to SG 0.67 and SG 0.82. Figure 2: Images of the set CAp granules fabricated at different CSH/CAp ratios (**a**–**f**) and SEM images of the surfaces at low magnification (**g**-**l**) and high magnification (**m**–**r**). The black box in images (**g**–**l**) highlights regions of interest analyzed for surface morphology. SEM: scanning electron microscopy; CSH: calcium sulfate hemihydrate; CAp: carbonate apatite; CSD: calcium sulfate dihydrate. Cross-sectional \(\upmu\)-CT images showed that the packing density of granules increased as the CSH/CAp ratio increased (Figure 5a-e). The intergranular spaces in SG 0.33, SG 0.43, SG 0.54, SG 0.67, and SG 0.82 were measured at 109 \(\pm\) 38.2, 100 \(\pm\) 36.2, 98.6 \(\pm\) 26.8, 96.7 \(\pm\) 22.4, and 77.3 \(\pm\) 27.7 \(\upmu\)m, respectively, indicating a decrease in intergranular space with increasing CSH content (Figure 5a-e). This reduction in the intergranular space with increasing CSH/CAp ratio indicates that a higher CSH content promotes efficient packing of the granules. Despite this compaction, SG (0.33), SG (0.43), SG (0.54), SG (0.67), and SG 0.82 maintained intergranular spaces to allow for cell penetration. Figure 4: Initial setting time of the set CAp granules at different CSH/CAp ratios (\(n\) = 8, * \(p\) \(<\) 0.05). CSH: calcium sulfate hemihydrate; Cap: carbonate apatite. Figure 3: XRD patterns of the set CAp granules at different CSH/CAp ratios (**c–g**). XRD patterns of standard CSD (**a**), CAp granules (**b**), and CSH (**h**) are provided as references. XRD: X-ray diffraction; CSD: calcium sulfate dihydrate; Cap: carbonate apatite; CSH: calcium sulfate hemihydrate. Dye penetration tests revealed that all sets of granules were stained with dye in SG 0.43, SG 0.54, SG 0.67, and SG 0.82 (Figure 6).