Preparation And Biotribological Properties Of Carboxylic Carbon Nanotube Coating On Medical Titanium Alloy

Biotribology is an important part of tribology,which mainly studies the tribological problems related to biology.The biological friction of medical materials may directly affect the clinical treatment effect and life of patients after operation,especially the implanted objects such as artificial joints.As one of the common artificial joint materials,medical titanium alloy has good biocompatibility,especially Ti-6Al-4V.However,in the process of long-term use,titanium alloy may cause inflammation of surrounding tissue and aseptic loosening of prosthesis due to its high coefficient of friction(COF)and poor wear resistance,further shortening the life of implants.Due to its excellent tribological properties and biocompatibility,multi-walled carbon nanotubes(MWNT)have good application prospects in tribology and biomedical fields.In this paper,MWNT were carboxylated to enhance surface activity,and carboxylic multi-walled carbon nanotubes(CMWNT)were prepared as the surface coating material of medical titanium alloy.In order to improve the tribological properties of Ti-6Al-4V and extend its life as artificial joint material,biotribological characteristics were studied.This study can provide experimental basis for broadening the application of CMWNT in the field of medical materials.The main research contents and conclusions are as follows:(1)SEM results showed that MWNT and CMWNT were tubular structures with nanometer diameter.The surface of CMWNT was smooth and the diameter of CMWNT was slightly smaller.FT-IR results showed that carboxyl groups were found on the surface of CMWNT compared with MWNT,indicating that MWNTs were successfully carboxylated.The dispersion experiments showed that CMWNT could disperse in water stably and evenly,keep long time without settling and have stronger hydrophilicity and better oxidation effect.(2)The CMWNT coating was successfully prepared on the surface of titanium alloy by means of self-assembly method,introducing double transition layers of APS and DA.The concentration of CMWNT suspensions,ultrasonic time and reaction time were discussed.Through friction experiment and wear characterization,the optimum process conditions were determined as 2 g/L,with ultrasonic treatment for 10 h and reaction for 48 h.A-CMWNT samples were prepared on the basis of the optimized conditions.The results of SEM,FT-IR and Raman spectra showed that CMWNT had been successfully prepared on the surface of the samples.Friction test showed that CMWNT coating had obvious friction reducing effect under dry friction.In addition,under the condition of dry friction and SBF lubrication,CMWNT coating had excellent wear resistance.This was related to the self-lubricating performance of CMWNT.Under dry friction,the higher the frequency and the smaller the load,the smaller the COF of the coating.In SBF lubrication,the higher the frequency,the smaller the COF.The wear rate increased with the increase of speed.In the certain load and frequency range,the coating had excellent wear resistance.(3)CMWNT coating was successfully prepared on titanium alloy by electrochemical deposition.The concentration of CMWNT dispersion,current density and deposition time were discussed.Through friction experiment and wear characterization,the optimum process conditions were determined as 1 g/L,1 m A/cm~2 and deposition for 30 min.The E-CMWNT samples were prepared based on the optimized process conditions.The results of SEM and FT-IR showed that CMWNT had been successfully prepared on the sample surface.The porosity of CMWNT coating prepared by electrochemical method was large.CMWNT coating had a certain anti-friction effect under dry friction,but no anti-friction effect under SBF lubrication.The anti-wear effect of CMWNT coating under SBF lubrication was excellent,but it was not obvious under dry friction.Under dry friction and SBF lubrication,the higher the frequency,the smaller the COF,and the higher the wear rate.Under dry friction,the smaller the load,the larger the COF.At 10 N and 5 Hz,the CMWNT coating broke,but it still had wear resistance.(4)Under dry friction,the coating prepared by self-assembly method can effectively reduce the COF by 40%and the wear rate by 30%,while the electrochemical method did not significantly reduce the COF.Under SBF lubrication,both of them increased the COF and decrease the wear rates by90%?93%.The adhesive strength of the coating prepared by the two methods were almost the same(?24 N),and the thickness of the coating prepared by the self-assembly method was relatively larger,which might be caused by the strong adhesion of DA transition layer.The coating prepared by self-assembly method still had a certain bearing capacity after coating cracked.This might be related to the introduction of double transition layers in the self-assembly process,which enhanced the performance of the coating through physical adhesion and chemical reaction.Adhesive wear and abrasive wear were the main wear mechanisms in the friction process.CMWNT had rolling friction between the friction pairs,which effectively reduced adhesive wear and abrasive wear,protecting the substrate and reducing the wear rate.The water molecules in SBF solution formed the lubricating layer between friction surfaces,and the rolling friction with CMWNT greatly improved the biotribological properties of the coating in coordination.