## 4 Discussion  
The aerogel fibers were fabricated using a semi-pilot scale wet spinning line and utilizing sCO\({}_{2}\) drying unit. sCO\({}_{2}\) processes are gaining more attention in the biomedical field since they are being used as a mild temperature processing method to produce porous materials, such as aerogels, besides being used as a sterilization technique for biomedical products [10]. The significant difference in the type of polysaccharide used for fabricating the aerogels, especially in the structure and length of chains, might have an impact on the morphological properties of fibers because the properties of the cellulose products rely on the biomacromolecule assembly and its degree of polymerization [49; 50]. Two fabricated CA microfibers (\(\phi\approx 270\) um) from low and high molecular weight cellulose exhibited different physical and textural properties in the structural, morphological, thermal, and biological assessment. The FTIR results proved that the dissolution of the initial biomacromolecule in salt melt hydrate altered the crystalline structure of the material from cellulose I to cellulose II, but no presence of salt leftover was observed. The NCS groups (N bonded) can appear around 2060-2100 cm\({}^{-1}\), and SCN groups (S bonded) can appear above 2100 cm\({}^{-1}\). As there is no clear peak in the mentioned range of FTIR patterns (Figure 2), it implies that NCS groups are not present in the structure of the fiber after washing steps [51]. Furthermore, XRD showed that the regenerated CA fibers were in the amorphous state and mainly in the form of cellulose II, and F\({}_{\text{c}}\) had higher crystallinity than F\({}_{\text{s}}\) as it was originated from high crystalline initial cellulose (C\({}_{\text{c}}\)). From XRD and FTIR measurements, it can be concluded that the dissolution and the spinning of cellulose in Ca(SCN)\({}_{2}\) molten salt hydrate did not change the cellulose chemical structure during the dissolution and regeneration but weakened or broke the inter- and intracellular hydrogen bonding and inevitably deranged the final CA fiber crystalline arrangement [27; 43]. The thermogravimetric measurements disclosed that the CA fibers were slightly less thermally stable than their original cellulose powder due to the decrease of initial degradation temperature. This lower thermal stability was based on several elements such as the conversion of cellulose I to cellulose II, degradation of cellulose chains known for cellulose during dissolution in inorganic salts, and higher specific surface area of the CA fibers compared to the powders, which made the internal surface of fibers more prone to thermal degradation [27; 38; 52]. To reveal structural and textural properties of the CA fibers SEM, \(\mu\)-CT, and BET/BJH results needed to be integrated as different compartment length scales from nanometer to micrometer existed in the fiber matrix [53]. The SEM and \(\mu\)-CT outcomes showed that CA fibers consist of randomly ordered nanofibrils with interconnected pore structure. The BET calculated average nanofibril diameters were 13.5 and 31 nm for F\({}_{\text{s}}\) and F\({}_{\text{c}}\), respectively, which were close to the diameter range of the results obtained via SEM image analysis (\(\sim\)20-38 nm). The larger diameter of F\({}_{\text{c}}\)'s fibrils might trigger some small pores to get closer and agglomerate, leading to lower pore volume [34]. The SEM analysis showed that the average pore width quantities in both samples (\(\sim\)3-4 nm) were lower than the obtained results in BJH desorption method (\(\sim\)17-20 nm), but both methods proved that F\({}_{\text{s}}\) had a higher pore size diameter than F\({}_{\text{c}}\). The low percentage of closed pores in both fibers achieved by \(\mu\)-CT (\(<\)0.01%) was in line with the SEM and N\({}_{2}\) adsorption-desorption results. Alongside sCO\({}_{2}\) drying processes, the regeneration solvent is also essential in achieving a low amount of closed pores.