## 3 Results
### Utilization of ALG-PIC Fibers as a DDS Carrier  
The ALG-PIC fibers exhibited swellability and stability in an aqueous solution, and thus they can be applied as a DDS carrier. Previously, we have reported that polysaccharide composite films made of PICs of CS and CHI exhibit drug loading and sustained-release properties [30]. We thought that PIC-coated fibers could also exhibit sustained drug release ability. Here, the PIC layer is expected to suppress the burst release of the drug to control its permeation rate. In this experiment, FITC-BSA was used as a model drug and loaded onto the ALG-Ca core fiber to evaluate the release behavior. FITC-BSA-loaded ALG-Ca fibers and the corresponding PIC-coated fibers were fabricated. The FITC-BSA was obtained by the reaction of BSA and FITC, and the fluorescence spectrum showed that about 1.8 moles of FITC were conjugated per mole of BSA. A mixed solution of FITC-BSA and ALG was injected into an CaCl\({}_{2}\) bath to obtain FITC-BSA-loaded ALG-Ca fibers. The obtained fibers possessed 96.0 \(\upmu\)g/m (7.3 \(\upmu\)g/mg) of FITC-BSA. The fibers were colored pale yellow and showed fluorescence with irradiation of UV light (Figure 9A). Afterward, the PIC layer was coated on the fibers in the same manner as aforementioned using CHI solutions of various concentrations to obtain FITC-BSA-loaded ALG-PIC fibers. The appearance of the fibers (Figure 9B) was similar to that of the ALG-PIC fibers. Under a UV light, the color of the FITC-BSA-loaded ALG-PIC fibers looked slightly different from that of the FITC-BSA-loaded ALG-Ca fibers. This was probably due to the effect of scattering originating from the surface roughness. The release behavior of FITC-BSA of FITC-BSA-loaded fibers in PBS was investigated. For the case of the FITC-BSA-loaded ALG-Ca fiber, the release ratio reached 36% in 4 h and then remained constant (Figure 10A). This is because FITC-BSA might interact with ALG by intermolecular interactions such as hydrogen bonding and electrostatic interactions. FITC-BSA-loaded ALG-PIC fibers prepared using 0.1 wt% CHI showed FITC-BSA release with almost the same behavior, indicating that the PIC layer is too thin to suppress the FITC-BSA release. In the case of using higher concentrations of CHI solution, the release ratios of FITC-BSA decreased. The release ratio of FITC-BSA-loaded ALG-PIC fibers prepared using 0.3, 0.5, and 1.0 wt% of CHI showed 31%, 22%, and 12% in 1 day, respectively. Further, focusing on the initial burst release rate, ALG-Ca was the fastest at 0.91 \(\upmu\)g/min. Notably, FITC-BSA-loaded ALG-PIC fibers with 0.1 wt% CHI were much slower at 0.36 \(\upmu\)g/min than ALG-Ca fiber. This indicated that the initial burst release was greatly suppressed by a thin PIC layer on ALG-Ca fiber (Figure 10B). As the cause of these results, the surface charge of ALG-PIC was considered. It was reported that surface charge of the drug carriers can affect the interaction with drugs and their loading/releasing properties, through electrostatic [54] and/or electro-induced [55] mechanisms. The zeta potential of PICs consisting of chondro sulfate C (CS) and CHI in PBS (pH 7.4) was \(-9\) mV [56], indicating  
Figure 9: Photographs of (**A**) FITC-BSA-loaded ALG-Ca fiber and (**B**) FITC-BSA-loaded ALG-PIC fiber under visible light (**tops**) and with UV irradiation (**bottoms**). (Grid: 0.5 \(\times\) 0.5 cm\({}^{2}\)). that the PIC layers were slightly negatively charged in PBS. On the other hand, the pI of BSA and its derivatives is 5.0-5.5, suggesting that BSA is also negatively charged in PBS at pH 7.4. Accordingly, it was indicated that electrostatic repulsions between FITC-BSA and the PIC layers occurred when FITC-BSA that was released from the ALG-Ca core crossed the PIC layers to be released to PBS. In the case of fibers prepared using 0.3 wt% CHI or more, the initial burst velocity was about 0.10 \(\upmu\)g/min. These results were consistent with the tendency of PIC thickness, with thicker PICs suppressing the initial burst.