Experimental studies on hydroxyapatite powder-carboxymethyl chitin composite: injectable material for bone augmentation.

We developed a hydroxyapatite (HA) powder-carboxymethyl chitin composite (HA-CMC composite) that can be injected with a 14G needle by adding distilled water. We prepared Materials I (HA = 57.0 wt%) and II (HA = 40.2 wt%) and examined their biocompatibility and osteoconductivity. With a 2-mm skin stab, the material was injected on the calvarial bone of rats. The periosteum was denuded blindly in half of the cases and preserved in the other half of the cases. Simultaneously, the material was injected subdermally into the abdominal skin to examine diachronic volume alteration of the material. Our results indicated that the new materials had biocompatibility as high as that achieved with previously developed HA materials. The difference in HA concentration did not influence the osteoconductivity, but the periosteum and the soft tissue on the cranium seemed to be an obstacle to bone ingrowth. On the other hand, the volume alteration was significantly smaller in Material I than in Material II. This composite may be especially useful in facial bone augmentation because it can be injected with only a small skin stab. When used for that purpose, the periosteum of the host bone should be denuded to facilitate bone ingrowth, and Material I will be preferable to Material II in terms of the maintenance of the initial volume.