Formation Process of Hydroxyapatite Granules in Agarose Hydrogel by Electrophoresis

Biomimetic mineralization is useful in obtaining organic-inorganic composite and inorganic materials with controlled sizes and morphologies. The formation of hydroxyapatite (HA) granules with porous structures can be achieved by using electrophoresis processes inside an agarose gel in which the compulsory migration of calcium and phosphate ions are driven by an electric field, causing precipitation of the granules. In the present study, we examined the formation process of HA granules through electrophoresis and the subsequent aging process. Spherical particles of amorphous calcium phosphate (ACP) precipitated, increasing their size with increased running time during electrophoresis; then the ACP granules gradually transformed to the HA granules during the aging process in ultrapure water. When the ACP granules were large, one HA granule was formed from one ACP granule. One HA granule was formed from multiple ACP granules for small-sized ACP granules. The size of ACP granules depends on the gel concentration and pH in the electrophoresis. The dominant transformation process from ACP to HA was the dissolution-precipitation process.