Preparation And Biomedical Properties Of Diamond Like Carbon Film

The artificial materials of high abrasion,greatly reduces their service life due to the low lubricating surface.Aiming at this drawback,the diamond like carbon（DLC）thin films with high hardness and ultra-low friction coefficient were deposited on the surface of artificial joints,which can effectively improve their wear resistance.The filtered cathodic vacuum arc deposition and microwave plasma chemical vapor deposition（MPCVD）were respectively used to deposit DLC films.The sp²/sp³ ratios and grain size were adjusted by the deposition parameters.This dissertation studied the influence of films surface morphology,microstructure and chemical composition on their biomedical properties.Firstly,a nano-DLC film was deposited by MPCVD with the precursors of CH₄and N₂.The flow rate of CH₄ was adjusted to obtain the high quality of the nano-DLC film.The SEM results demonstrate that DLC film’s typical surface morphology is cauliflower like structure,and the coverage of DLC film increases with the increase of CH₄ flow rate.The AFM observations indicate that the grain size and surface roughness of DLC films decrease with the increase of CH₄ flow rate,and the minimum grain size and surface roughness is 165.2 nm and 16.7 nm,respectively.The XPS results identify the DLC films are mainly composed of sp²-C and sp³-C with the typical DLC structure,and the sp²/sp³ ratio in the DLC film decreases with the increase of CH₄ flow rate.The contact angle experiments indicate the increase of CH₄ leads to the increasing hydrophobicity,and the maximum value is 83.3°.The biomedical properties of C₂₀samples,which are deposited at 20 sccm CH₄,were investigated by SBF immersion,blood and cell compatibility tests.The SEM,EDS,XRD and XPS results demonstrate that the films exhibit good ability of inducing bone formation.The sample surface is completely covered with a dense and thick hydroxyapatite coating.The hemolysis test presents that the hemolysis of C₂₀ sample is 3.63%,which corresponds to good blood compatibility.Cytotoxicity tests indicate that the toxicity of C₂₀ samples is evaluated at grade 0,fulfilling the clinical requirements of biomedical materials.Secondly,the DLC films were deposited by filtered cathodic vacuum arc with graphite target.The proportion of sp² and sp³ bond were regulated by the N₂ flow rate in the reaction chamber.The SEM results show the morphology of the DLC films transforms from smooth surface to cauliflower like surface with the flow rate of N₂increases during 0²0 sccm.The results of AFM indicate that the grain size and surface roughness of DLC films increase with the increase of N₂ flow rate The Raman and XPS results indicate the sp²/sp³ ratio of the DLC films increases with the increase of N₂ flow rate.The contact angle experiments show the all the DLC films are hydrophilic,and the increment of the sp²/sp³ ratio hardly affects the hydrophilicity of the surface（the range of the contact angle is 77.57°⁷1.71°）.The ability of inducing bone formation of the films was tested by simulated body fluid（SBF）immersion.The results of SEM and EDS show all the films are covered with dense,thick coatings consisted of Ca-P matters after 28 days of immersion.The XRD and XPS results demonstrate the as-deposited coating of Ca-P matters is mainly composed of hydroxyapatite.The sample with sp²/sp³=1.74 is found to have the best ability of inducing hydroxyapatite formation at the early stage of immersion（3¹4 days）.The results of friction test prove that the lubrication of substrate is significantly improved by coating the DLC films,either at the dry friction condition or at the simulated body fluid condition.With the decrease of sp³bond,the friction coefficient of DLC film slightly increases to the maximum value of0.386,which fulfills the requirements of friction performance of artificial joint materials.The results of hemolysis test show the hemolysis of all the DLC films are 0.57%¹.42%,which are less than 5%of the clinical medical requirements.Cytotoxicity tests indicate the cytotoxicity level of all the as-deposited DLC film is 0.The results evidence the DLC films have no harm to the cells.The relationship between the surface morphology,microstructure,chemical composition and biomedical properties of DLC thin films was systematically studied through different preparation processes.Thin films with good ability of inducing bone formation and biocompatibility have been fabricated for the enhancing artificial joints surface performances,showing a promising potential for future clinical application.