Microarc Oxidation Technology Applied In Surface Modification Of Pure Titanium

Nowadays, pure titanium has been widely used as an implant material. The favorable biocompatibility of pure titanium is due to a oxide film several nanometers thick quickly formed after it is exploded in nature. The film can prevent inner metal from further oxidation and reduce metallic ions releasing into surrounding tissues. However, the bioactivity of pure titanium is dissatisfying. Pure titanium implants combine with surrounding bones mostly by mechanical bond and they can not form firm chemical bond with bones like other bioactive materials, so the bond strength is not high. Otherwise, the oxide film formed naturally on titanium surface is very thin and some cases have been reported that metallic ions released through oxide film do harm to surrounding tissues. Microarc oxidation (MAO) is a new technology of forming oxide film on valve metal, which makes a breakthrough in the field of anodizing. Using this technology, people can get a thick oxide film on the surface of pure titanium and titanium alloy, which is dense in inner layer and porous in outer layer. Few reports have been found to apply miccroarc oxidation technology in surface modification of pure titanium.The objective of this study is to introduce the microarc oxidation technology into surface modification of pure titanium implant and to form a porous oxide film several micrometers thick on the surface of pure titanium, which is full of elements of calcium and phosphorus and contains the component of hydroxyapatite(HA). The elements of calcium and phosphorus are indispensable to ossification and the component of hydroxyapatite is accepted bioactive, so applying the technology of microarc oxidation, it is hopeful to improve the bioactivity of pure titanium surface. On the other hand, the oxide film forming by microarc oxidation is much thicker than that forming by nature, the former can prevent the release of mental ions more effectively and ensure further biocompatibility of pure titanium. This study consists of two parts. The first part:The pulse direct MAO power source was used to run a microarc oxidation process on the surface of pure titanium discs in the solution of glycerophosphate sodium and calcium acetate as electrolyte. The thicknesse of the microarc oxidion film was measured by eddy current pachometer; the surface morphology was observed by scanning electron microscope (SEM); the element composition was analyzed by energy dispersive spectroscopy (EDAX); the crystalline property was determined by X-ray diffractometry (XRD); the bond strength between oxide film and metal substrate was scaled by electric multifunctional testing machine.The results showed: the average thickness of MAO film on the pure titanium discs is 32.7 micrometers. It is possible to observe from SEM micrographs that the films presented alveolate pores with diameter from several micrometers to a hundred micrometers and some of them wereconnected. The MAO films are full of elements of calcium and phosphorus; in addition, there are hydroxyapatite in the films. The average bond strength between MAO films and metal substrates is 8..29MP.The second part:Study the biocompatibility of modified pure titanium using laboratorial cytology and experimental zoology. L929 cells were cultured on the samples and SEM was used to observe the growth of those cells; evaluate the cytotoxicity of the modified pure titanium by molecular filter test; evaluate the sensitization of the modified pure titanium by maximization test (Magnusson & Kligman) using guinea pig as testing animals.The results showed: 24h after L929 cells were cultured on the pure titanium discs modified by microarc oxidation, the cells grew well with normal shape and smooth appearance, moreover, many cells had been growing into the pores of the MAO films. The cytotoxicity rate of the pure titanium discs modified by MAO is 0, so the pure titanium modified by MAO has no cytotoxicity. The skin sensitization rate of the pure titanium discs modified by MAO is 0, so the pure titanium modified by MAO has no sensitization.