Conversion of functions by nanosizing—from osteoconductivity to bone substitutional properties in apatite

Abstract

Synthetic hydroxyapatite, in the usual case, of a macroscopic size, exhibits excellent osteoconductivity. However, it is not substituted with natural bone and remains permanently in the body; therefore it is suitable for using as an implant. It is well known that natural bone is composed of collagen and nanocrystallites of apatite with the size of approximately 50 nm. When the composite with collagen and nanoapatite synthesized in the biomimetic aspects is implanted, phagocytosis and inflammation are induced. Osteoclasts and osteoblasts are then differentiated and activated. The bone resemblant material and its phagocytizable nanometer size provide the conditions that composite is biologically degradable through phagocytosis by osteoclasts, and new bone formation by osteoblasts is simultaneously activated and proceeded. As a result, nanocomposite leads to the bone substitutional properties. Thus the conversion of functions is attained for apatite by nanosizing—from osteoconductivity in macroscopic size to bone substitutional properties in nano/micro scale. This tendency is more enhanced for carbonated hydroxyapatite. The mineralization surrounding collagen fibrils determines the crystallization of apatite for their size and orientations. Nanoparticles cause the reaction of cells/tissue and stimulate the occurrence of inflammation, which works as a stimulus in most cases or pronounces the conversion of functions leading to the bioactive properties for some cases, depending on the situation. Nano structure is essential for these stages to be processed.