Bone formation by cells from femurs cultured among three-dimensionally arranged hydroxyapatite granules

In vitro bone formation by cells derived from adult rabbit femurs was investigated on or in several substrates with small porous hydroxyapatite granules (HAGs). When the bone fragments were cultured in HAG-packed glass tubes, which were inclined (5 degrees -30 degrees ) and rotated 90 degrees per day after one week of culture, thin lamellar tissues were newly formed in narrow spaces among the HAGs. By 11 days of culture, these tissues had been mineralized except for their periphery and had well developed collagen bundles and several monolayer cells. Some cells resided in bone lacuna-like spaces. By contrast, mineralization was negligible in 6-week cultures on two-dimensional glass and polystyrene plates with or without two-dimensionally arranged HAGs on their surfaces and in three-dimensional collagen gels with or without HAGs in spite of active cell proliferation. These results suggest that osteogenesis is accelerated in a specific three-dimensional constitution of extracellular matrix and/or under the effects of mechanical forces for the new tissue and that bioactive HAGs offer favorable three-dimensional spaces for osteogenic tissue formation.