Formation Of Graphite-like Carbon Layer Between The Friction Interface Of Cu Doped Film In Bovine Serum Albumin Solution

This protein molecules can transform into a graphite-like carbon layer–via shear force between the tribo-pairs and interactions between the metal ions and the protein–with the potential to reduce the wear resistance of Mo M implants.What needs to be pointed out is that,for the more commonly used CoCrMoo alloy MOM bearings,the transformation process of the protein layer into the carbonaceous layer will occur over a long time in the body.The metal ions and debris released from the metal tribo pairs would cause complications such as,allergy,pain,pseudotumor.In order to reduce the releasing of metal ions and debris of Mo M joint,we designed and prepared one kind of copper doped diamond-like carbon(Cu-DLC)film and copper doped titanium nitride(Cu-TiN)film by plasma technology.When the Cu doped film modified Mo M joint servicing in human body,the Cu ions can be released from the films by the friction between the artificial joint tribo-pairs.Graphite-like carbon layer can be formed by the synergism of the catalytic abilities of Cu and the shear force between the tribo-pairs.This layer can lubricate and heal the wear of the Cu doped film.Diamond-like carbon(DLC)film has been considered as a potential material in the modification of artificial joints.The electron cyclotron resonance-chemical vapor deposition(ECR-CVD),as one method to prepare DLC film,presents many advantages such as high ionization and high deposition rate.However,The applications of this method is limited by the non-uniform deposition rate and non-uniform film properties.The self-sustained discharge induced by high bias potential(U_s)can improve the ionization of the gas and the uniformity of ECR plasma,the effects of U_s on the structure and mechanical uniformity of the DLC films deposited by ECR-CVD were investigated in this work.The results show that,When the biasing is-200 V,the plasma exhibits a longitudinal decrease in its ion density when the distance between the substrate and plasma source(D_ecr-s)increasing.As a result,the mechanical properties of the films are nonuniform.When a biasing potential of-800 V applied to the substrate noticeably improves the mechanical properties and uniformity of the films.On the one hand,the energy of the ions can be raised obviously by the high biasing.On the other hand,the ionization and uniformity of the plasma can be improved by a high biasing.As a result,the structure uniformity of the DLC films deposited at-800 V is better than that of the films prepared at-200 V.The self-sustained discharge will promote the application of ECR-CVD in Mo M joint surface modification field.The friction interface behaviour of Cu and CoCrMoo in bovine serum albumin(BSA)solution has been investigated in this work.The ball-on-disc mode was used to investigate the formation of a graphite-like carbon layer in the contact regions of different tribo-pairs(CoCrMoo/Al₂O₃ and Cu/Al₂O₃)in a BSA solution.The results show that the release of Cu ions upon friction between tribo-pair can promote the adsorption of BSA onto the wear track to form a“protein-layer”.This“protein-layer”can transform into a graphite-like carbon layer under friction conditions of the Cu/Al₂O₃ tribo-pair,and this graphite-like carbon layer can in turn lubricate the Cu/Al₂O₃ tribo-pair against further wear and ion release.Under the same conditions,however,this graphite-like carbon layer cannot be obtained in the CoCrMoo/Al₂O₃tribo-pair.This reveals that Cu ions are more efficient catalysts for the formation of the graphitic carbon on the contact regions of the tribo-pair compared to the metal ions released from the CoCrMoo.Because all of the characterization methods we used in this work,cannot distingrish the carbon in DLC films and the carbon in“graphite-like carbon layer”,which transformed from the protein layer.So,it is indeed hard for us to investigate the formation of graphite-like carbon layer on the surface of Cu doped DLC films.On the base of previous research,we Cu doped TiN films(TiCuN film)using magnetron sputtering method,which can be used to modify the surface of metal artificial joints and ceramic artificial joints.When the TiCuN film modified CoCrMoo alloy wear used to carry out friction experiments in BSA solution,the Cu ions can be released from the films under the friction between the tribo-pairs,and bond with the BSA in fluid to promote the formation of protein-layer on the surface of the friction interface.And then this kind of protein-layer would transform to be graphite-like carbon layer by the synergism of the catalytic abilities of Cu and the shear force between the tribo-pairs.The Vienna Ab-initio Simulation Package(VASP)was applied to simulate the adsorption energy of the aspartic acid composed BSA and the molecular fragments,shch as C,CH,CH₂ and OCH₂ et al,on the surface of Cu and TiN,the results show that the adsorption of molecules on the surface of Cu is more stable than that of the molecules on the surface of TiN.The Covalent bond can form at the interface of aspartic acid and the surface of the Cu,and the aspartic acid would break into three carbonaceous fragments under the shear force.These carbonaceous fragments would provide the carbon source to form the graphite-like carbon layer on the surface of the tribo-pairs.This kind of film which can promote the formation of graphite-like carbon layer on the surface of the tribo-pairs has been considered as a potential material in the modification of metal and ceramic artificial joints...