## 3 Results
### Characterization and Evaluation of ALG-PIC Fibers  
To confirm the PIC layer on the ALG-PICs fibers, fluorescein-conjugated chondro sulfate C sodium salt (FL-CS) was blended with CS for PIC formation and the obtained fibers were evaluated using fluorescence microscopy [49]. Figure S2A showed fluorescence microscopic images of ALG-PIC fibers with each concentration of CHI solution. When 0.1 wt% CHI solution was used, the fluorescence was weak, indicating that PIC was barely coated. In the case of high concentrations of CHI solutions, each fiber showed strong fluorescence. This tendency was consistent with the results for the diameter (Figure S1): it indicated that the diameter of the PIC layer increased with increasing concentration of CHI solution. Furthermore, the ALG-PIC fibers with 0.3 and 0.5 wt% of CHI solution were darker in the center and the edge of the fibers showed strong fluorescence. This indicated that the light for the excitation path through the PIC layer at the edge of the fiber was longer than that at the center of the fiber, as shown in Figure S2B. Accordingly, a thicker layer of PIC was coated on the ALG-Ca fibers when a higher concentration of CHI solution was used. Figure 4 shows the FT-IR spectra of ALG-Ca fibers, ALG-PIC-1.0 wt% fibers, and PIC fibers. The PIC fibers were prepared by wet spinning with several modifications [42; 43]. Peaks at 1607 cm\({}^{-1}\) and 1433 cm\({}^{-1}\) originating from COO\({}^{-}\) in ALG appeared in the spectrum of ALG-Ca fibers. On the other hand, ALG-PIC-1.0 wt% fiber showed peaks originating from functional groups in CS: two peaks at 1632 cm\({}^{-1}\) and 1411 cm\({}^{-1}\) (COO\({}^{-}\)), at 1219 cm\({}^{-1}\) (SO\({}_{3}\)\({}^{-}\)), and a peak at 1540 cm\({}^{-1}\) originating from NH\({}_{3}\)\({}^{+}\) in CHI. These peaks also appeared in the FT-IR spectrum of the PIC fiber, and both of them supported electrostatic interactions between CS and CHI [27; 28]. This is because the penetration depth of the IR by attenuated total reflection (ATR) is a few micrometers at IR wavelengths, which is much smaller than the PIC layer of the ALG-PIC fiber. Therefore, only the surface PIC layer was detected, and the same spectrum as the PIC fiber was obtained for the ALG-PIC fibers. SEM observation and EDS measurements of each fiber were also performed to evaluate their microscopic morphologies and elemental compositions (Figure 5). In the EDS mapping, Ca element (red) and S element (green) were used to observe ALG-Ca fibers and PIC layers, respectively. The SEM image of a cross-section of the ALG-Ca fiber showed smooth and dense structures without cracks and pores. Further, the presence of Ca in the whole region of the ALG-Ca fiber was confirmed by EDS mapping. In the case of ALG-PIC-0.1 wt% fiber, the fiber was distorted due to the tension created by the winding fibers in the PIC coating process. EDS mapping showed that Ca elements were detected not only in the core region of the cross-section but also on the outer surface of the fibers, indicating that PICs were slightly coated on the ALG-Ca fiber. On the contrary, EDS mappings of ALG-PIC-0.3 wt%, ALG-PIC-0.5 wt%, and ALG-PIC-1.0 wt% showed that PIC layers were fully coated on the ALG-Ca fiber. These results were consistent with the observation by fluorescence microscopy (Figure S2). Thus, the diameter of fibers increases with the coatings of PICs, and the thickness of the PIC coating layer can be adjusted by changing the concentration of CHI solution. Unfortunately, accurate measurement of the thickness of the PIC layers was hardly achieved because of the inhomogeneous morphology of the core and shell regions of the fibers in the EDS mappings. Figure 4: FT-IR spectra of ALG-PICs-1.0 wt% fiber, PIC fiber, and ALG-Ca fiber. ((**Top**): 4000–400 cm\({}^{-1}\), (**bottom**): 1800–600 cm\({}^{-1}\)). To evaluate the mechanical properties of the fibers, tensile tests of ALG-Ca fibers, PIC fibers, and each ALG-PIC fiber were conducted (Figure 6).