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 pore sizes of 100～600 µm, porosities of 70～80%, and small amounts of metal ions. SEM photograph 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. fg-HAp (3×3×3 mm)/rhBMP-2 were implanted into the subcutaneous tissue in 4-week-old Wistar rats. At 1, 2, 3, 4 and 8 weeks after the implantation, the ceramics were explanted and stained with hematoxylin-eosin and evaluated histopathologically. The ceramics were covered by a thin connective tissue. At 4 weeks, body fluid was well invaded and diffused into the micropores and microcracks of the ceramics and there was new bone formation and marrow in the macropore spaces. The fluid invaded into the HAp was stained with albumin antibody. At 8 weeks, the remaining HAp was retained by bone. Mature bone and fatty marrow were observed. Morphometric analysis showed the HAp volume diminished from 27% at 4 weeks to 25% at 8 weeks. These results indicated that fg-HAp/rhBMP-2 was a bioceramic with characteristics of superior new bone formation, bioabsorption and biocompatibility.
