Osteoblast reaction at the interface between surface-active materials and bone in vivo: a study using in situ hybridization.

Osteoblast activation after implantation of two kinds of surface-active material in bone was investigated chronologically using in situ hybridization with digoxygenin-labeled procollagen alpha 1(I) complementary RNA probe. The bioactive materials used were hydroxyapatite (HA) and apatite- and wollastonite-containing glass-ceramic (A-W GC). A hole was drilled bilaterally in the distal epiphysis of rabbit femurs with subsequent implantation of HA or A-W GC cylinders in a press-fit manner. Specimens were collected at 3, 7, 14, and 28 days after operation and decalcified. Then the undecalcified implant cores were pushed out of the hole without causing damage to the bony side of the interface. In situ hybridization documented no qualitative differences in the expression of procollagen alpha 1(I) RNA between HA and A-W GC. Few osteoblasts at the bone-material interface showed a specific signal at day 3, whereas many osteoblasts were positive around the materials at days 7 and 14, indicative of active new bone formation. The positive osteoblasts seemed to originate from preexisting trabeculae and lined the trabeculae, newly formed bone, and material surface. At day 28, many osteoblasts lining material-surrounding bone were negative, whereas those in remodeling canals were positive, suggesting that the bone was in the remodeling stage after bone formation. These findings were comparable to those with beta-tricalcium phosphate in a previous study, thus suggesting osteoconductive bone formation on HA and A-W GC.