Formation and biological affinity evaluation of crystallographically aligned hydroxyapatite

Hydroxyapatite (HAp) is a type of calcium phosphate widely applied in the biomedical field. HAp is a main inorganic component of hard tissues of vertebrates and is a bioactive ceramic which shows a high biological affinity. The crystal of HAp exhibits an anisotropic nature depending on its crystal planes which is stemmed from its anisotropic crystal structure belonging to the hexagonal system. For instance, anions and acidic proteins are mainly adsorbed onto the a-plane of HAp crystals while cations and basic proteins are adsorbed onto the c-plane. Anisotropic nature like so can be utilized by controlling the alignment of crystals consisting the material. Alignment control of HAp crystals in a particular direction is an effective way to improve the properties like absorbability, bioactivity and biological affinity on the surface of biomedical materials. On the other hand, the recent development of superconducting technology has enabled us to control the crystal alignment of not only magnetic substances but also nonmagnetic substances with magnetic anisotropy like HAp by imposing a high magnetic field. In this study, we formed crystallographically aligned HAp bulks by using a high magnetic field and evaluated the degree of the crystal alignment. In addition, we evaluated the biological affinity on the surface of the samples.