TISSUE-RESPONSE TO NANO-HYDROXYAPATITE COLLAGEN COMPOSITE IMPLANTS INMARROW CAVITY/

The tissue response to a nano-hydroxyapatite/collagen composite implan ted in a marrow cavity was investigated by histology and scanning elec tron microscopy. A Knoop microhardness test was performed to compare t he mechanical behavior of the composite and bone. The ultrastructural features of the composite, especially the carbonate-substituted hydrox yapatite with low crystallinity and nanometer size, made it a bone-res embling material. It was bioactive, as well as biodegradable. At the i nterface of the implant and marrow tissue, solution-mediated dissoluti on and giant cell mediated resorption led to the degradation of the co mposite. Interfacial bone formation by osteoblasts was also evident. T he process of implant degradation and bone substitution was reminiscen t of bone remodeling. The composite can be incorporated into bone meta bolism instead of being a permanent implant. For lack of the hierarchi cal organization similar to that of bone, the composite exhibited an i sotropic mechanical behavior. However, the resistance of the composite to localized pressure could reach the lower limit of that of the femu r compacta. (C) 1998 John Wiley & Sons, Inc.