## 4 Discussion
[83] on the effect of cerium on bioactivity, cerium addition slows down the development of the HA layer primarily because it produces insoluble crystalline CePO\({}_{4}\) and increases chemical durability. Additionally, this impact is connected with the sample's ceria content (concentration): at a ceria level of up to 5.3 mol%, HA production was delayed by up to 28 days, but at a ceria content of up to 1 mol%, HA formation was apparent after 7-14 days [33; 84]. Hence, the bioactivity of cerium-doped MBG at higher concentrations requires additional days to develop HA whereas the HA formation of Ag-doped MBG was highest. [PERSON] et al. [53] conducted research by using the XRD peak intensities of the highest peak that has the highest HA (2 = 32.07 and 29.23\({}^{\circ}\)); we compared the XRD peak intensity of the results and found that the bioactivities of the specimens could be categorized as un-doped, Ag-doped, Ce-doped, and Ag-Ce co-doped MBG from 5.75 Ag-doped \(>\) 2.87 Ag/2.87 Ce co-doped \(>\) 2.87 Ag-doped \(>\) 2.87 Ce-doped \(>\) un-doped \(>\) 5.75 Ce-doped (mol%) MBG. This result demonstrates that Ag dopants will increase Ag-doped MBG's bioactivity, speeding up HA growth rates (Figure 8). The other confirmation study of bioactivity was FTIR and SEM morphology. Figure 10 shows the FTIR spectra of un-doped, doped, and co-doped MBGs. The expansion of infrared absorption bands of Si-O-Si stretching vibration is increasingly evident with an increase in the silver content and low content of Ce-doped MBG in glass systems. Ag- and Ce-doped MBGs have XRD patterns that show the presence of hydroxyapatite, metallic silver, and cerium phosphate, which suggests that these materials disrupt the connection of the Si-O-Si glass network. As a result, the FTIR results validated that all MBGs were bioactive in vitro, except 5.75 mol% Ce-doped MBG after 7 days of soaking in SBF, supporting the XRD and SEM (observed the HA morphology, see Figure 9) findings. We will now look at why Ag increases MBG bioactivity. One of the crucial factors in developing novel glass composition designs is, therefore, taking the chemical structure of the glass into account, as doing so would alter the glass's bioactivity. The SiO\({}_{4}\) tetrahedral network forms the basis of the SiO\({}_{2}\)-CaO-P\({}_{2}\)O\({}_{5}\) composition, and the O ions link the individual tetrahedral units to create a three-dimensional structure. The degree of connection in the 3D structure is known to be modified by Ca to create non-bridging oxygen (NBO) groups. These NBO groups are necessary for the exchange with H\({}^{+}\) or H\({}_{3}\)O from the surrounding SBF solution to generate a high dissolution rate, which leads to a high HA production (the first stage in the process of HA creation is the dissolution of biogas surface) [85]. [PERSON] et al. [86] and [PERSON] et al. [87] conducted investigations where they first synthesized BG and then coated Ag at the BG surface to create Ag-containing MBG. The majority of Ag is present at the BG surface and does not interact with the BG structure to reduce the quantity of NBO groups [88]. The Ag ions produced from the Ag particles at the BG surface act as the nucleus of HA [87], which subsequently accelerates the HA production to offer greater bioactivity when the Ag-containing MBG (Figure 5b,c,f) is submerged in SBF. The majority of the Ag particles were present at the surface of the Ag-containing MBG powders used in this investigation, in which the dissolution rate of the Ag solubility rate is higher thus accelerating the ion exchange and speeding up the HA formation. For the other study, [PERSON] et al. [89] employed sol-gel to make the Ag-containing BG particles, and most of the Ag ions were integrated into the glass structure, which allowed them to study the retardation of bioactivity. The Ag-O bonds are therefore anticipated to be more covalent than the Ca-O ones [89].