## 3 Results and Discussion
As illustrated in Figure 7i, the PR3/48h specimen displays a well-developed porous microstructure, which is composed of an assembly of plate-like crystals with an approximate diameter of 200 nm, similar to the interconnected porous structures reported in sintered WH granules, which have been shown to facilitate fluid transport and nutrient exchange essential for bone regeneration [13]. It is worth noting that the granule size range of approximately 200-450 um is particularly suitable for use as bone graft substitutes. Previous studies have demonstrated that hydroxyapatite-based granules within the 212-300 um size range promote superior bone formation in vivo compared to larger granules, which tend to limit osteogenesis [28]. An examination of the textural characteristics of samples PR1/24h, PR2/24h, PR3/24h, PR1/48h, PR2/48h, and PR3/48h, as determined by N\({}_{2}\) adsorption-desorption measurements, reveals significant differences in surface area and porosity characteristics (see Table 2). Among the 24 h samples, PR1/24h, consisting of a biphasic mixture of Mg-WH and CDHA, exhibits the highest BET surface area (S\({}_{\text{BET}}\), 35 m\({}^{2}\)/g), external surface area (S\({}_{\text{ext}}\)) of 30 m\({}^{2}\)/g, and total pore volume (V\({}_{\text{p}}\), 0.13 cm\({}^{3}\)/g), indicating a highly porous structure with significant external surface exposure. In contrast, PR2/24h, composed mainly of Mg-WH and a significant amount of DCPA, shows a lower S\({}_{\text{BET}}\) (4 m\({}^{2}\)/g), \({S}_{\text{ext}}\) (3 m\({}^{2}\)/g), and V\({}_{\text{p}}\) (0.010 cm\({}^{3}\)/g), reflecting a denser microstructure. PR3/24h, containing Mg-WH with a smaller amount of DCPA, exhibits intermediate properties, with a relatively high S\({}_{\text{BET}}\) (30 m\({}^{2}\)/g), S\({}_{\text{ext}}\) (27 m\({}^{2}\)/g), and moderate V\({}_{\text{p}}\) (0.069 cm\({}^{3}\)/g). Overall, PR1/24h demonstrates the greatest combination of surface area and pore volume among the 24 h samples, suggesting superior surface accessibility and porosity. For the 48 h samples, PR3/48h exhibits a substantially higher BET surface area (38 m\({}^{2}\)/g) and total pore volume (0.077 cm\({}^{3}\)/g) compared to PR1/48h (9 m\({}^{2}\)/g, 0.025 cm\({}^{3}\)/g) and PR2/48h (11 m\({}^{2}\)/g, 0.027 cm\({}^{3}\)/g). All these samples composed solely of the Mg-WH phase but were derived from three chemically distinct precursor granules and reaction solution chemistries. Specifically, the R3 granules incorporated MgHPO\({}_{4}\)3H\({}_{2}\)O directly into the precursor, providing an intrinsic magnesium source. Unlike the syntheses of PR1 and PR2, the PR3 samples did not require the addition of external magnesium acetate solution. The in situ availability of magnesium likely facilitated a more homogeneous and controlled precipitation process, leading to the formation of finer particles, smaller crystallites (see Table 1) and consequently a larger surface area of PR3/48h sample. The higher surface area of PR3/48h is expected to substantially enhance its bioactivity, as materials with greater surface areas provide expanded sites for ion exchange, faster dissolution kinetics, and increased protein adsorption which all are known as critical factors for bone regeneration [29]. Conversely, the lower surface areas of PR1/48h and PR2/48h suggest denser, less permeable structures with reduced surface exposure, which may limit their bioactivity and hinder effective tissue integration [30]. Micropore analysis further supports these differences. The external surface areas (S\({}_{\text{ext}}\)) of PR1/48h, PR2/48h, and PR3/48h were 7 m\({}^{2}\)/g, 8 m\({}^{2}\)/g, and 35 m\({}^{2}\)/g, respectively,