| Medical titanium alloys are widely used as implant materials because of their good mechanical properties and biocompatibility.However,because of their poor wear resistance,the implants may be loosened or caused toxic debris.Some surface treatment techniques have been developed to improve the bioactivity and wear resistance of titanium alloys.In order to improve the bioactivity of titanium alloys,a layer of bioactive hydroxyapatite(HA)coating is usually prepared on the titanium alloy surface.With its good biocompatibility and bioactivity,HA is suitable for the repair and replacement of damaged bone tissue,and has been widely used in the medical field.However,HA still faces the problem that its mechanical properties are not ideal enough and brittle fracture is prone to occur,besides,the bond strength between metal substrate is not high enough.In recent years,in order to solve these problems,researchers have adopted different methods to prepare composite coatings,such as hydroxyapatite and silver and titanium dioxide,to improve their strength.Organic polymers such as collagen,chitosan(CS)and other organic polymers have gradually aroused people's attention.However,the research on HA/CS composite coatings is mainly focused on mechanical properties and biocompatibility.In addition,because of the complexity of human environment,from the serum protein in the body fluid to the ions produced by the material degradation,many factors will interact with the implant materials,so it is necessary to study the influence of the main active substances(water proteins and minerals)in the human body on the tribological properties of artificial joint in addition to the discovery and development of a new type of implant material with excellent performance.This research results will enlighten the development of new artificial bone.In this paper,three coatings,hydroxyapatite/silver(HA/Ag),hydroxyapatite/silver/ chitosan(HA/Ag/CS),hydroxyapatite/silver/polypyrrole(HA/Ag/PPy),and three kinds of coatings on their surface with carbon quantum dots solution respectively,were used as samples.The Tribological test was carried out in the sphere plane contact mode,and the chitosan was investigated.The influence of polymer and carbon quantum dots on the tribological behavior of hydroxyapatite coating and its mechanism are discussed.Then the Tribological test was carried out with hydroxyapatite/silver/chitosan/carbon quantum dots(HA/Ag/CS/CDs)coating as samples in different degrees of mineralization and immersed in different concentrations of calf serum solution.The effect of bone like mineralization layer on the tribological properties of hydroxyapatite composite coating and the tribological performance under different lubrication conditions were studied.The main conclusions are as follows:(1)the Tribological test results show that the HA/Ag/CS coating has the best friction and wear properties,and CS plays an important role in the friction reducing and wear resistance of the coating.The main reason is that chitosan has connected HA and Ag particles,so that the coating is compact and uniform and has good elasticity and toughness,and plastic deformation and plastic flow play a protective role in the substrate.In addition,the addition of carbon quantum dots significantly improved the friction properties of the coating,because CDs added to the surface of the coating played a role in the "nano bearing".(2)the Tribological test results of different mineralized coatings showed that the bone like mineralized layer on the coating aggravated the wear of the coating.The conclusion is that the surface mineralized layer is quickly removed during the friction process and the debris particles produced by the particles entered the coating and acted as the third body abrasive particles between the pair and the grinding pair,which makes the friction coefficient increase,and the wear increases.(3)the test results under different liquid lubrication conditions are different from what we expected: the friction coefficient and wear amount in three liquid lubrication environments are higher than the dry friction condition.The reasons are as follows: the high hardness carbon quantum dots particles are lubricated by the deformation carrying and rolling.This particle flow lubrication makes HA/Ag/CS/CDs coating exhibit excellent tribological performance.Under three liquids,the adsorption of ions in the solution and the flow of liquid make the condition of particle flow lubrication is also available any more,so the friction coefficient increases and the wear increases.Because of the strong corrosiveness and the permeation of water,the PBS buffer has caused severe damaged to the coating.So the degree of wear is very high.The attrition rate of 25% and 100% calf serum solutions are relatively lighter because of the lubrication of the film of serum proteins,but it is worth noting that the lubrication effect does not increase with the increase of serum concentration. |
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