Abstract
The micrometer-sized network structure of a calcium-alginate hydrogel, which was synthesized from sodium alginate, calcium sulfate dihydrate, trisodium phosphate 12-hydrate, glycerol, and water, was observed using an optical microscope, cryogenic-scanning electron microscope, and an energy-dispersive X-ray spectrometer. For observation with the optical microscope, the calcium-alginate hydrogel was stained with Calcein, which emits green fluorescence by binding with calcium ions. Calcium ions act as a crosslinking agent in calcium-alginate hydrogels. For observation with the cryogenic-scanning electron microscope and energy-dispersive X-ray spectrometer, the hydrogel was frozen at -130 °C in a state containing water without drying or xerogelation. The optical microscope and cryogenic-scanning electron microscope observations revealed that the calcium-alginate hydrogel had a mixed structure of regions where large-scale gel networks and domains existed, and regions where they did not exist. The scale of each region was several hundred micrometers to several millimeters. In regions of the large-scale network structure, the domains were several tens of micrometers or less in size, and were surrounded by networks that were several hundred nanometers or more thick. Fluorescence emission of Calcein as observed by the optical microscope and elemental analysis with the energy-dispersive X-ray spectrometer indicated that the large-scale network is composed of accumulated calcium-alginate networks. Energy-dispersive X-ray spectroscopy also indicated that calcium alginate exists in the large-scale domains and in regions where no large-scale network structure exists. We considered that calcium-alginate networks of molecular sizes with a well-known egg-box structure exist in the large-scale network structure and regions where no large-scale network structure exists, and that the water constituting the hydrogel is preserved in them.

Keywords
hydrogel, alginate, gel network, domain structure, cryogenic-scanning electron microscopy

Cite this paper
Minoru Aoyagi, Takahiro Ueno, Observation of Calcium-Alginate Gel with Micrometer-sized Network Structure , SCIREA Journal of Materials. Volume 3, Issue 3, June 2018 | PP. 76-89.

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