Fiber Structure in Calcium Alginate Hydrogel

Abstract: Calcium alginate hydrogels are thought to have an egg-box structure in which the G-block of an alginate block copolymer consisting of β-d-mannuronic acid (M-block) and α-l-guluronic acid (G-block) is cross-linked by Ca2+ cations. The egg-box model has been verified in many studies. In this study, we showed that calcium alginate hydrogels were composed of fibers by slicing samples of calcium alginate hydrogels, staining them with calcein (C30H26N2O13) solution, and observing them under a fluorescence microscope. Fibers were extracted from the calcium alginate hydrogels when they were immersed in calcein solution for a long time. The fibers were several micrometers thick and had a bamboo-like structure consisting of nodes and cavities. We also used calcium alginate bead samples to observe the fibers. Fluorescence microscopy and scanning electron microscopy of the beads revealed that the calcium alginate hydrogel contained both ribbon-like and bamboo-like fibers. Observation of the bamboo-like fibers in the sliced samples and ribbon-like fibers in the beads showed that these fibers branched and merged to form a complex entangled network. This network of fibers allowed the calcium alginate hydrogel to hold large amounts of water. Although the fibers are larger than the egg-box structure, we believe that understanding the characteristics of the fibers containing calcium alginate will lead to an understanding of the molecular structure of calcium alginate.