バイオミネラルの異方的結晶化

Biomineralization. Anisotropic crystallization of biominerals.

　骨を構成するアパタイト結晶は，六方晶系をベースとする極めて異方性の強いイオン結晶であり，骨の力学的性質，さらには化学的・生物学的性質はアパタイトの結晶学的方位に強く依存する。アパタイト配向性は，骨力学機能を支配する重要な骨質指標であり，生体内外の環境因子と骨系細胞との相互作用により制御・構築される。 　本稿では，アパタイト配向性に基づく骨質評価から，細胞周囲環境に応じた細胞形態・配列変化による異方性骨基質の形成過程解明への取り組みについて紹介する。

　Bone tissue exhibits an oriented microstructure comprising apatite crystals and collagen fibers. The mechanical, biological and chemical properties of bone tissue represent the highly anisotropic feature depending on the degree of anisotropy in crystallographic structure of apatite. Preferred orientation of apatite crystals is one of the promising parameters which determine bone quality, because the bone mechanical function is dominated by the degree of apatite crystallographic orientation rather than bone mineral density. The anisotropic microstructure of bone tissue is regulated by the mutual activities of bone cells in response to the various kinds of environmental factors. In this report, we introduce the evaluation of bone quality based on the analysis of preferential orientation of apatite c-axis by using micro-beam XRD method and our recent research about cellular regulation of bone tissue anisotropy, especially focusing on the morphological changes of bone cells regulated by the microenvironment surrounding the cells.