生体模倣傾斜機能アパタイトの生体内吸収特性

抄録

Hydroxyapatite (HAp) has been used as a biomaterial for hard tissues, because of its excellent biocompatibility and osteoconduction. However, the non-absorbable HAp remains as a foreign body in a living body and may trigger inflammation. The aim of this study was to develop biomimetic ceramics from bovine bone and to estimate the absorbable property in vivo histomorphometrically.
Spongy and cortical bones in bovine femur were used as starting materials and calcined at 500～800℃ to obtain b-HAp. The spongy b-HAp was partially dissolved in HNO₃ solution, and the cortical b-HAp was completely dissolved in the other HNO₃ solution. After the two solutions were mixed, HAp (r-HAp) crystals were precipitated on the macropores and micropores of spongy b-HAp at pH 10.5 and 25℃. The modified spongy b-HAp was filtrated and dried to fabricate the functionally graded HAp (fg-HAp) ceramics. The fg-HAp ceramics were characterized by the pore sizes of 100～600μm, porosities of 70～80%, and small amounts of metal ions. SEM photographs of the fg-HAp showed spherical moss-like grains of about 1.0μm in size, which consisted of about 10-nm r-HAp microcrystals. Micro-XRD analyses indicated that the crystallinity of fg-HAp single phase was better from the surface layer to bulk region in the ceramics.
The fg-HAp (3×3×3mm) ceramics were implanted into the subcutaneous tissue in 4-weeks old Wistar rats. At 1, 2, 3, 4 and 8 weeks after the implantation, the ceramics were explanted and stained with hematoxylin and eosin and evaluated histopathologically.
The ceramics were covered by a thin connective tissue. At 4 weeks, body fluid had well invaded and diffused into the micropores and microcracks of the ceramics and fibroblasts populated in the macropore spaces. The fluid that had invaded into the HAp was stained with albumin antibody. At 8 weeks, the HAp was degraded from not only the surface layer of the ceramics but also the bulk region, and many giant cells appeared on the surface and inside of the ceramics. Morphometric analysis showed the HAp volume diminished from 40% at 4 weeks to 32% at 8 weeks.
These results indicated that the newly developed biomimetic fg-HAp bioceramic had superior bioabsorption and biocompatibility characteristics.