Hydroxyapatite (HAp) is the main mineral component of bone and is used as a raw material for artificial bones and teeth, and as an adsorbent in liquid chromatography, among its other uses. As a result of its anisotropic crystal structure, HAp shows adsorption behavior that depends on the crystal plane. However, the differences between the a-plane and the c-plane of the HAp crystal in terms of their bioactivity, cellpropagation behavior, etc., have not yet been fully clarified. In this study, we fabricated highly crystallographically aligned samples of HAp by using a 10-T magnetic field, and we studied the effects of the specific crystal plane of HAp on its bioactivity by immersing the samples in a simulated body fluid.HAp is precipitated on both a-plane-and c-plane-aligned HAp sample surfaces. The rate of precipitation on a HAp sample immersed in the simulated body fluid depended on the crystal plane, especially during the first 24 h of immersion. Because the rate of precipitation on the c-plane is faster than on the a-plane, HAp is precipitated preferentially on the c-plane during the early stages of precipitation.
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.
Hydroxyapatite ceramics has been demonstrated to be an appropriate material for biomedical applications owing to its bioactivity and high biocompatibility. It has an anisotropic crystal structure that belongs to the hexagonal system, and two types of crystal planes mainly appear on its crystal, which are a-plane and c-plane. Since these two crystal planes are very different in atomic elements, numbers and arrangements, they exhibit different nature (anisotropy). For this reason, it is said that crystal orientation might be intensifying its bioactivity and biocompatibility. However, the differences in biological features on these two crystal planes are not fully clarified yet. In this study, we have conducted an assessment to reveal anisotropic biological features of hydroxyapatite by using hydroxyapatite ceramics with controlled orientation fabricated by slip casting under a magnetic field. Tanase et al. have recently reported the difference in bioactivity on the two crystal planes by immersing crystal oriented hydroxyapatite ceramics into the simulated body fluid and found that c-plane oriented hydroxyapatite ceramics formed a precipitate layer earlier and thicker on its surface compared to a-plane oriented one. We first carried out Welch's t-test on the difference in the thickness of the precipitate layer, reported previously to reveal the difference in bioactivity. Secondly, we conducted an osteoblast culture experiment on hydroxyapatite ceramics with controlled orientation to reveal the difference in initial cell attachment and cell morphology on the two crystal planes of hydroxyapatite using optical microscope observations. In the former case, the results of the Welch's t-test indicated that the thickness of the precipitate significantly differed on each crystal oriented hydroxyapatite ceramics (P < 0:05). In the latter case, initial cell attachment seemed to be better on the a-plane oriented hydroxyapatite ceramics and also the morphology of the osteoblasts seemed to be rounded on the a-plane oriented hydroxyapatite ceramics compared to the c-plane oriented one.
Formation of crystallographically orientaed hydroxyapatite (HAp) is one of the promising ways to utilize their anisotropic nature of chemical and biological properties. On the other hand, the development of super conducting magnet technology enables to introduce a high magnetic field which can control crystal orientation of non-magnetic materials with magnetic anisotropy. In this study, a high magnetic field and sample rotation are simultaneously imposed on the hydroxyapatite during a slip casting process in order to align its c-plane within a horizontal plane. From X-ray diffraction, it has been found that the HAp crystals in the sample treated with the magnetic field and the sample rotation were oriented to a particular direction in the slip casting process and it was enhanced by the subsequent sintering process, while the c-axis crystal orientation of the sample treated without the magnetic field and with the sample rotation was not observed before and after the sintering.
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