Anisotropic hydroxyapatite formation inside agarose gels by integration of electrophoretic and alternate soaking...

We report here anisotropic hydroxyapatite (HAp) formation inside an agarose gel using an electrophoretic approach and an alternate soaking process. Effective ion migration is shown to be crucial to integrate hydrogel with biominerals, for example, calcium carbonate and HAp. Calcium and phosphate ions easily migrated into the gel interior from ionic solutions when an electric field was applied to both terminals of the gel. The time to reach complete biomineral formation was only 3 min. In this process, roughly 75-300 microg of HAp was formed in 1 mg of dry gel. Moreover, we carried out alternate soaking using the resulting materials and further HAp formation was observed (750 microg HAp/mg dry gel). HAp was characterized by infrared spectroscopy and X-ray diffraction, and was then assigned. Moreover, the HAp was formed in an anisotropic manner. First, (210) and (211) were preferentially formed by the electrophoretic approach. Alternatively, (002) and (211) were formed after the alternate soaking process. This result indicated that preparative conditions were shown to be crucial to regulate anisotropic crystal growth and to keep it the major component. In summary, it is considered that anisotropic ion diffusion inside the hydrogel would be the dominant factor by electrophoretic and alternate soaking approaches.