To evaluate the osteoinductive activity and the biocompatibility of BMP-agarose composite, three kinds of experimental samples (BMP pellet samples, agarose samples, and BMP-agarose composite samples) were implanted into the hindquarter muscle pouch of ddy conventional mice.
The mice were killed 21 days after implantation, and the hind limbs were examined by roentgenographic and histologic methods. The osteoinductive activity of the samples was confirmed by computer assisted analysis of soft X-ray photographs to determine the volume of induced new bone.
BMP pellet samples induced stable heterotopic new bone formation.
Three weight-percent agarose samples induced no bone formation. Histologically, the implant was surrounded by a thin fibrous layer, but did not cause inflammatory cell aggregation. Therefore, agarose has excellent biocompatibility and is very stable in living tissue.
BMP-agarose composite samples induced stable heterotopic new bone formation. Histologically the induced bone region was surrounded by a thin fibrous tissue layer and consisted of bone-like calcified tissue with osteocyte-like cells, cartilaginous cells, and bone marrow. However, the bone induced by BMP-agarose composite samples seemed to be less mature than that induced by BMP pellet samples. This suggested that the initial effects of BMP remained because of slow release from the composite, and that the BMP continuously formed bone, which contained less mature tissue during the initial period of bone formation.
A comparison of the volume of induced bone showed a trend toward an increase in bone with higher concentrations of agarose in the composite. The BMP-agarose composite, made with 2 and 3 weight-percent agarose solution, induced significantly greater bone formation than did BMP pellet samples.
These results show that BMP-agarose composite has the advantage of acting as an osteoinductive implant material in vivo.
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