Results
Synthesis of CSL-gel and characterization of chitosan core-shell
To obtain the sustained release of lentinan and calcium ions, we developed a novel and multiple-functional hydrogel by cross-linking the mixed solution of sodium alginate and lentinan with calcium ions to form a hydrogel precursor (SL-gel). A chitosan shell was built on the surface of SL-gel to form a lentinan-loaded hydrogel with a core-shell structure (CSL-gel) (Figure 1a ), which is expected to provide the stable and sustained release of lentinan (LNT) and calcium ions (Figure 1b ). To assess the formation of chitosan shell on the surface of CSL-gel, scanning electron microscopy (SEM) and Zeta potential were employed. SEM images of SL-gel and CSL-gel were illustrated inFigure 1c . SEMs showed that the surface of the SL-gel with large pores was loose, but a dense chitosan shell covering the SL-gel was observed on the surface of CSL-gel (Figure 1c ). Moreover, the elemental analysis showed that elemental nitrogen was detected on the surface of the CSL-hydrogel (Table 2 ), indicating that chitosan was added on the surface of CSL-gel. To avoid the influence of LNT on the FTIR and zeta analysis, we performed the Fourier transform infrared spectrometry (FTIR) and zeta analysis using the hydrogel without LNT to characterize the chitosan shell. Figure 1dshowed a shared peak located at approximately 3340 cm−1 was observed in the FTIR spectrum of the S-gel and CS-gel. However, the CS-gel features a fully developed peak on 3340 cm-1, which is attributed to the overlap associated with the peaks of the −OH stretching vibration of SA and the −NH stretching vibration of the chitosan in comparison to the S-hydrogel. Besides, the CS-gel exhibited a peak at approximately 2927 cm-1, which was formed by the C−H stretching vibration of chitosan, suggesting that the reaction of adding chitosan to the S-gel was successful. Sodium alginate is composed of carbon, hydrogen, and oxygen, and the surface is negatively charged. The zeta potential analysis showed that the surface of CS-gel has a positive charge, but the S-gel with a negative charge (Figure 1e ). Taken together, our findings strongly indicate that a chitosan shell is added to the SL-gel, which has the potential to stabilize the structure of CSL-gel and provide the sustained release of LNT and calcium ions.