상온 분사를 이용한 나노구조 수산화아파타이트의 코팅

Abstract

ABSTRACT

Coating of nanostructured hydroxyapatite by room temperature spray

Kim, Sang-Woo Advisor : Prof. Lee, Jong Kook, Ph.D. Dept. of Advanced Materials Engineering, Graduate School of Chosun University.

Calcium phosphates including hydroxyapatite [Ca10(PO4)6(OH)2, HA] have achieved significant fields as bone graft materials in medical and dental fields, because of their mineral components 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. HA obtained from synthetic sources was severely dissolved during exposure to the in vitro and in vivo environments 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 bovine bone which is morphologically and structurally similar to human bone can be used. Bovine bone is stable for a long period in a biological environment. Metallic implant coated by HA is one of the most innovative and most promising materials for biomedical applications, since it has proven to be highly biocompatible between implant and bone tissue. Methods that have been used to apply HA coatings include : plasma spraying, dip coating, pulsed-laser deposition, sputtering, cold spray, room temperature spray. The plasma spray is frequently used for HA coating on metal implants. High temperature process causes thermal decomposition of HA such as dehydroxylation and the adhesion to the substrate may not be sufficient. The room temperature spray is a film fabrication method that utilizes an impact solidification phenomenon of ultrafine particles. The film was performed at room temperature without any heat damage between the substrate and the film. Thus, the room temperature spray coating offers certain advantage because dense coating layer can be formed without cracks. In this study, we tried to obtain the biologically stable coated HA layer on Ti6Al4V substrate using bovine bone derived HA powder as a raw materials and room temperature spray method(or aerosol deposition method) at various incident angles. Starting HA powder for coating was prepared by calcination of bovine bone. Commercial bovine bones were irrigated with a brush in running water and dried at room temperature. Then, the bones were calcined at 800 ˚C for 1 h to completely remove organics and to save from infectious diseases. The bovine bone derived HA powder had a circular structure with uniform shape and weaken agglomeration. To fabricate the HA coated layer, the pressure difference between the powder chamber and deposition chamber was maintained to 1 atm. A gas flow rate was fixed as 5 - 9 l/min, and deposition was continued for 5 min at room temperature. The HA powder of 1.0 – 2.0 µm in size was mixed and vibrated with helium carrier gas to form like an aerosol flow in the powder chamber. The vibration speed for particle dispersion was 600 rpm. The distance between the nozzle and substrate was maintained to 10 mm, and the orifice size of nozzle was 0.3 × 9 mm. The incident angle of the beam was varied from 0° to 60°. Dissolution behavior of bovine bone derived HA coated layer was observed by in vitro experiment. In vitro dissolution experiment using a starting both powders of the bovine bone derived HA and synthetic HA was investigated in pH 7.4 distilled water for 3 - 14 days. Coated HA film on Ti6Al4V had the thickness of 1-2 µm and homogeneous microstructure at incident angles of 60°. Crystallinity of the HA powder was maintained during coating process and new phases by thermal decomposition or phase transformation were not observed. The surface of chemicals derived artificial HA coated layer was partially dissolved in pH 7.4 distilled water for 14 days, however, bovine bone derived HA coated layer was stable during immersion for 14 days. It is believed that biologically derived HA can be a good substance for medical applications, where biological and mechanical stabilities of HA are required.