## 3 Results
### Characterization and Evaluation of ALG-PIC Fibers
In a comparison of ALG-Ca fibers and PIC fibers, the ALG-Ca fibers exhibited low strength and were easily stretched, but the PIC fiber was high in strength and difficult to stretch. On the other hand, it was clearly demonstrated that the ALG-PIC fibers exhibited higher strength than the ALG-Ca fibers. Further, the strength of the ALG-PIC fibers increased with an increasing number of PIC coatings, whereas the strain of the ALG-PIC fibers decreased. This is because the ratio of PICs to the fiber was increased, and therefore the strength of the fibers was improved. In a comparison of the ALG-PIC-1.0 wt% fiber and the PIC fiber, the ALG-PIC-1.0 wt% fiber showed larger test force, whereas the PIC fiber showed higher strength. ALG-PIC-1.0 wt% contained ALG-Ca core, which had lower mechanical strength and higher elongation properties than PIC. This is because the diameter of ALG-PIC-1.0 wt% was larger than that of the PIC fiber, and the average strength per cross-sectional area decreased due to the lower strength of ALG-Ca. From the above, although the strength of ALG-Ca fiber was low, the strength was improved by coating with PIC. Accordingly, PIC coatings on ALG-PIC fibers were useful in improving the mechanical properties of the fibers. To clarify the stability of each fiber in an aqueous solution, the weight loss of each fiber after immersion in phosphate buffer saline (PBS, pH 7.4) was evaluated (Figure 7). The ALG-Ca fibers dissolved and lost their shape after immersion in PBS for 1 day. This  
Figure 5: (**A**–**E**) SEM images and (**F**–**J**) EDS mapping of ALG-Ca fibers and ALG-PIC fibers. (Red: Ca, green: S, scale bar: 100 \(\upmu\)m). Figure 6: Results of tensile tests of ALG-Ca fibers, ALG-PIC fibers, and PIC fibers. is because the interaction between ALG and Ca\({}^{2+}\) was relaxed by water, and Ca\({}^{2+}\) was replaced with monovalent ions such as Na\({}^{+}\) and K\({}^{+}\) in PBS, resulting in the solubilization of ALG-Ca fibers [53]. In the case of the ALG-PIC-0.1 wt%, about 7% of the weight remained after immersion for 1 day. After immersion for 3 days, the fiber lost its shape and dissolved in PBS. When a 0.1 wt% CHI solution was used, a small amount of PIC was present on the fiber surface and thus remained longer than ALG-Ca fiber due to the greater stability of PIC in PBS than ALG-Ca, but the effect of the PIC was minimal. When 0.3, 0.5, and 1.0 wt% ALG-PIC fibers were used, the weight loss was low after 1-day of immersion, indicating that the amount of PIC coating on the fibers was large, and ALG was immobilized by electrostatic interaction and hydrogen bonding with CHI of PICs (Figure 8). The weight loss gradually increased with increasing immersion time, and ALG-PIC-1.0% had the lowest weight loss in the fabricated fibers, indicating that the fiber had the highest amount of PIC coating. ALG-PIC-0.3 wt% and -0.5 wt% showed smaller remaining weights for 5 days to 7 days compared to ALG-PIC-1.0 wt%. The final residual weight was 27.5% with the ALG-PIC-0.3 wt% fiber, 30.1% with the ALG-PIC-0.5 wt% fiber, and 39.8% with the ALG-PIC-1.0 wt% fiber, respectively. This is because ALG-Ca was less stable than the PICs and showed a larger weight loss. Thus, PIC coatings improve the stability of ALG-Ca fibers, and this approach is promising for improving the mechanical stability of other types of fibers. Figure 8: Schematic illustration of interactions between ALG-Ca and CS/CHI PICs layer. Figure 7: Time course of weight loss of ALG-Ca fibers, ALG-Ca/PIC fibers immersed in PBS.