동물 뼈로부터 수산화아파타이트 분말의 제조 및 소결특성

Abstract

As the population of the old generation increases in recent years, the injuries which were causing bone damage frequently occur due to various kinds of accidents and aging. Due to the limited supply of natural bone for grafting, the need for bone substitutes which have the same physicochemical and biological properties as natural bone is ever increasing. Calcium phosphates including hydroxyapatite [Ca_(10)(PO₄)_(6)(OH)₂, HA] have achieved significant fields as a bone graft material in a range of medical and dental fields, because of their mineral component being similar to bone and teeth of the human body. In addition, the HA derived either from synthetic sources or from animal sources can form a strong chemical bond with host bone tissue. In case of HA obtained from synthetic sources which is expected to be stable in body fluid, HA was severely dissolved during exposure to the in vitro and in vivo environment resulting in the presence of loose particles and microstructural degradation. As a result, it will provoke inflammation or third body friction. Therefore, HA with dissolution/degradation resistance should be required. As an alternative method, HA derived from animal bone which is morphologically and structurally similar to human bone can be used. Animal bone is stable for a long period in a biological environment. As the material level, animal bone is composed of organic and inorganic components. It is easy to produce calcium phosphate from animal bone by burning out the organic. Although HA from animal bone has great potential for use as graft materials in clinical application, patients may feel that HA from animal bone for implant can potentially bear fatal diseases, such as human immunodeficiency virus(HIV), or bovine spongiform encephalopathy (BSE). The disease would be solved through calcination and sintering at elevated temperature by removing the organic. In this study, HA derived from animal bones (bone ash, bovine bone and tuna bone) were prepared by calcination to remove organics in bones. Using the obtained powders, HA sinters were prepared by pressureless-sintering and hot-pressing. In addition, dissolution of HA derived from animal bone was investigated in liquid environment. The bones were calcined at above 800 °C for 1 h to completely remove organics. After calcination, compacts were obtained by pressureless-sintering and hot-pressing using the calcined powders. The powders were uniaxially and cold isostatically pressed into pellets. The pellets were sintered at 1200 °C for 1 h in humid atmosphere. In case of hot-pressing, the sinters were prepared by hot-pressing at 1000 °C for 0.5 h under the pressure of 30 MPa in Ar atmosphere. Dissolution of the animal bone derived HA was investigated in pH 7.4 distilled water for 3, 7 and 14 days. Calcined HA from bone ash contained mainly HA and small amount of α-tricalcium phosphate (α-TCP). However, calcined HA from bovine bone and tuna bone were consisted of mainly HA and small amount of magnesium oxide. The densities of compacts prepared by pressureless sintering was about 70-80% with large pores. However, the densities of compacts prepared by hot-pressing had higher sintering density (95%) and smaller in pore size. The microstructure surface of HA from bone ash was partially dissolved in pH 7.4 distilled water compared with HA from bovine bone and tuna bone because of the presence of soluble α-TCP in bone ash derived HA. In addition, more calcium ions were released from bone ash derived HA in compared with bovine bone derived HA and tuna bone derived HA. Hardness of HA from bone ash was decreased with immersion due to the surface dissolution, whereas hardness of HA from bovine bone and tuna bone were constant. It is considered that dissolution resistance of bovine bone and tuna bone derived HA may be attributed to the presence of Mg in HA. Furthermore, the obsence of soluble phase such as α-TCP may also be the reason of dissolution resistance. It is believed that biologically derived HA can be a good substance for medical applications, where biological and mechanical stabilities of HA are required.