## 3 Results and Discussion
### In Vitro bioactivity Study  
The term bioactivity refers to the ability of an implant to form the calcium phosphate compound hydroxyapatite on its surface when it comes into contact with body fluids or with fluids that simulate those of the body (simulated body fluid, SBF). SBF is an acellular and protein-free solution that has a composition of inorganic species similar to that of blood plasma. In order to accelerate the mineralization time, many modified SBF solutions have been used in the literature [35]. In the present work, twice simulated SBF (2 xSBF) was used by doubling calcium and phosphorous concentrations in comparison with SBF solution [20]. Mineralization of scaffolds with hydroxyapatite improves their structural stability and makes these materials more biocompatible, enhancing osteoblast adhesion and osteointegration [36]. The FTIR spectra of all samples are shown in Figure 5a. The spectrum of Alg/MC/TMC in the spectral range between 525 and 1600 cm\({}^{-1}\) is characterized by two characteristic vibrations of alginate due to the carboxylate group, an antisymmetric stretch at 1596 cm\({}^{-1}\), and a symmetric stretch at 1410 cm\({}^{-1}\)[37]. The spectrum also shows the characteristic cellulose peaks in the range 1000-1200 cm\({}^{-1}\) and the ring stretching peak at 943 cm\({}^{-1}\)[38]. In the case of composite samples, the characteristic peak of the asymmetric stretching of the Si-O-Si group is hardly distinguished due to overlapping with peaks attributed to alginate and methylcellulose. The FTIR spectra of the samples after immersion in 2 xSBF solution together with the spectrum of synthetic HAp are shown in Figure 5b. The peaks observed in the spectrum of synthetic HAp are attributed as follows: The bands at 600 (s), 559 (s), and \(\sim\)1020 (vs) cm\({}^{-1}\) are assigned to the vibrations of the phosphate group. Specifically, the peaks at 600 (s) and 559 (s) are related to the triple-degenerated vibration of the O-P-O bond. The third component should appear at 574 cm\({}^{-1}\) (s, sh). The band at \(\sim\)1020 (vs) cm\({}^{-1}\) is assigned to the stretching vibration of the P-O bond, while the band at 630 cm\({}^{-1}\) is assigned to the hydroxyl libration mode. The peaks at 963 and 1090 cm\({}^{-1}\) are attributed to the non-degenerated, symmetrical stretching vibration and to the antisymmetric stretching modes of the P-O bond in the phosphate group [39]. Through comparison of the FTIR spectra of the scaffolds after their exposure to SBF solution with the reference spectrum of HAp, the presence of HAp is evident from the absorption peaks at 600 and 559 cm\({}^{-1}\). The presence of the above peaks is observed in all samples; however, their intensity is lower in sample Alg/MC/TMC and composite samples containing 5% glasses. The presence of phosphate vibrational modes in the 1000-1100 cm\({}^{-1}\) range is difficult to be distinguished due to overlapping with the peaks of alginates and MC. In addition to FTIR spectroscopy, the X-ray diffraction technique was used to characterize the formation of HAp on the scaffolds after exposure to SBF solution. Figure 5c,d show the XRD graphs of the samples before and after immersion in the solution. The amorphous phase of all samples is observed in Figure 5c. All scaffolds, except for sample Alg100 Si10, after immersion in SBF show the characteristic reflections at 20 at 26\({}^{\circ}\) and 31\({}^{\circ}\) attributed to the (002) and (211) planes of HAp. The standard JCPDS (Joint Committee on Powder Diffraction Standards) card No 9-432 of HAp is also shown for comparison. The samples containing the bioactive glass 70 Si30 Ca show the highest intensity at 20: 26\({}^{\circ}\), indicating that the presence of bioactive glasses affects the in vitro bioactivity. Although the samples were washed, diffraction peaks of NaCl are present in sample Alg/100 Si10. The peaks are attributed to the crystallization of sodium chloride entrapped inside the hydrogel. The peaks assigned to NaCl (Halite) are observed at 20: 27.3\({}^{\circ}\) and 45.4\({}^{\circ}\).