The Research Of Cytotoxicity On The N48 NdFeB Magnets Coated With Titanium Nitride

ObjectiveAS a new orthodontic force, magnetic force has the quality of distinctive direction. Magnetic field can promote the rebuild of periodontal tissues and acce-larate tooth moving. But previous magnetic force wasnt large enough in long distance , so there's no fixed magnetic appliance reported. The N48 NdFeB magnets was invented in few years, its magnetic energy product and coercive force are the highest among the magnetic materials until now. Rencently the research results of professor Houzhiming proved that the fine function of the N48 NdFeB magnets can completely meet the demands of fixed appliance in clinic. But the N48 NdFeB magnets is likely to be erosive, it cannot be used in oral for a long time , in order to increase the erosion — risistance of magnets , some scholars plated titanium — nitride on the surface of NdFeB, according to the result of research , the effect of erosion - risistance is fine . As a result , it is the key of use in clinic whether NdFeB coated with titanium nitride has good biocompati-bility.In the experiment, we investigate the cytotoxicity of the N48 NdFeB magnets coated with titanium nitrid. L929 fibroblasts of mice were cultivated with the infusions of the N48 NdFeB magnets coated with titanium nitride. The proliferation of the cells were investigated using a tetrazolium - based colorimetric assay ( MTT assay ) , The rate of apoptosis was detected using flow cytometry ( FCM) AnnexinV - FITC and propidium iodide (PI) double labeling technique, in order to provide a biological basis for the clinical application of N48 NdFeB.Methods1. The experimental materialsSteep samples of Brackets, N48 NdFeB magnet coated with titanium - nitride and bare magnets, the materials were disinfected and sterilized . Then the materials were put into the RPMI -1640 cultivated liquid to cultivate at 37X1 for 72h.2. The experimental methods;2.1 Methods of MTT assay:L929 cells were cultivated in RPMI - 1640 supplemented 10% fetal calf se-ram at 37 Xl in a humidified atmosphere of 5% C02. We chose the logarithms generate term L929 cells. Took the 96 bores culture plates and added the cell suspending liquid of lOOul into every bore . The density of liquid was roughly 5 xl04yfV ml. After 24h, sucked out the liquid, individually added infusions which concentration was 100 % ,50 % ,25% into the bores. Then they were cultivated for 48h. At last, we measured the relative growth rate and the level of toxicity by MTT assay . We chose the SNK to test the results.2. 2 Apoptosis assaywe used the RPMI - 1640 cultivated liquid to prepare the fusions of N48 NdFeB magnet coated with titanium - nitride and bare magnets and collected it every 72h, and preserved it in - 70T!. Then chose the logarithms generate term L929 cells. Took 24 bores culture plates, and added the cell suspending liquids of lml which density was roughly 1 x 10 ^jV ml into each bore. After 24h, sucked out the liquid,added lml fusions which concentration was 100 % , Then they were cultivated for 48 h. Apoptosis was examined using Annexin V - FITC / PI binding assay kit according to the instruction of the manufacturer . Data were analyzed by using analysis of variance.Results1. The toxic levels of N48 NdFeB coated with titanium - nitride wereranked as 0 - 1. The toxic levels of Brackets were ranked as 0 - 1. The toxic levels of bare magnets were ranked as 2. There was no difference between N48 NdFeB coated with titanium - nitride and control group .2. AnnexinV -FITC /PI assay revealed :There was no siginificant differencein the content of apoptostic cell, necrosis cell and normal cell between N48 NdFeB coated with titanium nitride and control group .ConclusionThe N48 NdFeB magnets coated with titanium nitride dont affect the proliferation and apoptosis of cell, they have good biocompatibility. Bare magnets have certain cytotoxicity.