## 3 Results
### Morphology and Composition  
The surface structures and inner structures of spray dried 58S, 68S, and 76S BG powders were examined to obtain the particle morphologies, and the corresponding results are shown below. Initially, Figure 2 shows the surface structure information of all spray dried powders with insets of particles at higher magnification. It can be seen from Figure 2a that the 58S BG powder exhibits the spherical  
Figure 1: X-ray diffraction (XRD) patterns of spray dried 58S, 68S and 76S bioactive glass (BG) powders.  
shape which is the typical spray dried shape [23]. Meanwhile, it can also be seen that the surfaces of the particle are rough instead of smooth. This is due to the shell formation and buckling phenomenon happened during the particle formation stage [28]. In addition, 68S and 76S BG powders as shown in Figure 2b,c reveal the same morphology but more severe rough surfaces.  
Next, owing to the particle formation mechanism of the spray drying method, inhomogeneous morphologies have been discussed in previous studies [23; 24; 25; 26; 27; 28; 29]. Therefore, for obtaining particle morphology, the inner structure is required to verify with the surface structure for the correct particle morphology; for example, both hollow particles and solid particles exhibit the same surface structures [30]. Commonly, transmission electron microscopy (TEM) was used to collect information on the inner structure. However, based on the SEM images shown in Figure 2, particle sizes of all spray dried BG powders range around 2-20 \(\upmu\)m. Due to the huge particle sizes of BG powders, the particles might not be electron transparent in the TEM. Therefore, inner structures of all BG powders were examined using FIB-prepared cross section particles instead of TEM. Figure 3 shows the SEM images of FIB-prepared cross section particles with insets of their inner structures. With examination of more than 20 particles among each BG powder, the results show that all spray dried BG powders exhibit either solid (Figure 3a-c) or porous (Figure 3d-f) inner structures.  
Figure 3: SEM images of focused ion beam (FIB)-prepared cross section particles showing solid and porous structure of (**a,d**) 58S; (**b,e**) 68S; and (**c,f**) 76S BG powders with insets of their inner structure captured at higher magnification.  
Figure 2: Scanning electron microscopy (SEM) images of spray dried (**a**) 58S; (**b**) 68S; and (**c**) 76S BG powders with insets of their surfaces captured at higher magnification.  
Elemental analysis of all BG powders was carried out using EDS as shown in Figure 4. It can be seen from the graphs that all spectra have peaks at 0.52, 1.76, 2.05 and 3.69 KeV which correspond to O-K\(\alpha\), Si-K\(\alpha\), P-K\(\alpha\), and Ca-K\(\alpha\) edges, respectively. In addition, an increasing trend of Si-K\(\alpha\) edge can be observed from 58S, 68S to 76S, as well as a decreasing trend of Ca-K\(\alpha\) edge. Moreover, Table 1 shows the atomic compositions derived from the EDS spectra. The result shows that all BG powders exhibit around 10 mol\(\%\) of P with Si ratio of 52, 64 and 74 mol\(\%\) for 58S, 68S and 76S BG powders, respectively. Indicating the successful synthesis of BG powders based on their given composition.