## 4 Discussion  
This study demonstrates that the transformation of CSH to needle-shaped CSD on the surfaces of CAp granules via a dissolution-precipitation reaction sets the CAp granules into an integrated structure by interlocking the CSD crystals. As the CSH/CAp ratio increased from 0.33 to 0.82, the crystal length of the CSD increased, promoting the interlocking of CSD crystals. Therefore, at higher proportions of CSH, the phase transition was accelerated, resulting in a shorter setting time. The shaking test revealed that the weight of the set CAp granules decreased over six days in saline, and the intergranular space and specific surface area increased due to the partial dissolution of CSD [42]. Interestingly, at SG 0.82, the set granules maintained their original shape and structural integrity, whereas SG 0.43, SG 0.54, and SG 0.67 partially collapsed, and SG 0.33 completely collapsed, reflecting the influence of CSD on maintaining scaffold integrity. Elemental analysis for the remaining material shows significant changes in composition. For SG 0.43, SG 0.54, SG 0.67, and SG 0.82, calcium (Ca) remained the dominant element, followed by phosphorus (P), indicating that the calcium phosphate structure (CAp) remained even after partial dissolution of the CSD. Notably, sulfur (S) levels were significantly lower in SG 0.82, which suggests that a higher proportion of CSD  
Figure 10: Elemental composition of the surfaces of set CAp granules as function of different CSH/CAp ratios, after immersed in physiological saline for 6 days. (Ca, calcium; S, sulphur; P, phosphorus; C, carbon; and O, oxygen, \(\#\); complete collapse), (\(n=4,^{*}p<0.05\)). CAp: carbonate apatite; CSH: calcium sulfate hemihydrate. Figure 9: Bulk porosity (**a**) and compressive strength (**b**) of the set CAp granules as a function of CSH/CAp ratios before and after the collapse test for 6 days (\(n=4\), and \(n=8\), \({}^{*}p<0.05\)). CSH: calcium sulfate hemihydrate; CAp: carbonate apatite. dissolved, while the CAp phase remained more intact in SG 0.82 compared to the other ratios. For SG 0.82, the EDX results showed 23.47% Ca, 0.67% S, and 11.76% P, which aligns with the observed minimal dissolution and the retention of set CAp granules. In contrast, at lower CSH/CAp ratios (e.g., SG 0.33), a larger proportion of CSD dissolved, as seen by the absence of sulfur in the EDX analysis. The presence of significant amounts of Ca and P in the remaining material indicates that CAp granules largely persisted in these conditions. These results indicate that SG 0.82 can prevent granule migration during and after implantation. While SG 0.82 initially exhibited partially poor pore interconnectivity due to limited intergranular space before collapse test, the dissolution of CSD over six days in the saline solution caused intergranular spaces to expand. This process improved porosity and the specific surface area, creating a more favorable environment for cell attachment and infiltration. These dynamic changes enhance its potential as a scaffold for bone tissue engineering by balancing the need for initial structural stability with the progressive development of porosity for biological integration. Thus, SG 0.82 is considered a promising material for reconstructing bone defects while preventing granule migration. Conventional bone graft materials such as \(\beta\)-TCP and HAp either dissolve too quickly, leading to early scaffold failure, or degrade too slowly, hindering timely bone remodeling [2,4]. In contrast, CAp granules with a CSH/CAp ratio of 0.82 exhibit dual degradation behavior characterized by fast and moderate dissolution. Due to the rapid dissolution of CSD and the moderate dissolution of CAp, the set CAp granules develop increased intergranular space and specific surface area while maintaining structural integrity. Moreover, the controlled release of Ca\({}^{2+}\) ions has been reported to create a favorable environment for osteogenic cell activity, mineralization, and tissue integration, facilitating bone formation [42, 43, 44].