Abstract
Micro/nanosizing effect of materials onto biological organism was investigated by both in vitro biochemical cell functional test and in vivo animal implantation test. Dependence of reaction of cells and tissue, and that of bone formation of apatite on particle size were studied. The increase of specific surface area causes the enhancement of chemical reactivity and therefore toxicity in many cases. This is the most usually and easily recognizable and strongest effect in most cases. However there is the other effect which becomes prominent especially for biocompatible materials such as Ti and TiO2. Stimulus was increased with the decrease of particle size and pronounced below 3 μm by inducing phagocytosis to cells and inflammation to tissue. For the size below 50nm, particles invade into the internal body through the respiratory or digestive system and diffuse inside body. For bone, synthetic hydroxyapatite exhibits excellent osteoconductivity but it is not substituted with natural bone and remains permanently in the body. When the composite with collagen and nanoapatite synthesized in the biomimetic aspects is implanted, resorption of nanocomposite through phagocytosis by osteoclasts and new bone formation by osteoblasts occurred simultaneously after inflammation. Nanocomposite leads to the bone substitutional properties, which resembles the remodeling process in natural bone. Thus nanosizing induces the intrinsic functions of biological organism and results in the conversion of functions such as from biocompatibility to stimulus and from osteoconductivity but non-bone substitutional to bone substitutional properties through biological process.
