Research On Artificial Joint Lubrication And Tribological Test Technology

Joint replacement, is one of the most effective treatments to joint diseases, in which an arthritic or damaged joint is replaced by an artificial joint. Long term clinical results show that wear of artificial joints determines the lifetime of such implants. The biotribological performance of prostheses has significant impact on its reliability and functionality. Therefore, researches on artificial joint lubrication and tribological testing are required, in order to qualify the tribological property of the artificial joints and prolong the product duration.In this thesis, researches cover two main aspects, including lubrication technology investigation and development of tribological test apparatus in related to artificial joints. In artificial joint lubrication, biomimetic synovial fluids were developed; biocompatibility, rheology, electrochemical and tribological property were experimental studied. Moreover, surface texturing was applied in hard-on-hard artificial joint materials, tribo-acoustic performance were carried out for fundamental validation. In the second aspect, tribological test apparatus, such as multi-functional hip joint simulator, multi-directional pin on disk tribometer, were built up for wear tests of artificial products and materials. Furthermore, a tribo-acoustic test system was also established for the initial study on friction induced squeaking phenomenon in hard-on-hard artificial joints. Main research points and conclusions can be reached as below,In the study of biomimetic synovial fluids, by biocompatibility test, the results validated safety and non-toxicity of such fluids towards human body. Wear test were carried out on UHMWPE/CoCrMo artificial joints, results showed that biomimetic synovial fluids had the best lubrication performance among all the fluids in this study. And protein membrane could be observed on the surface of UHMWPE in biomimetic synovial fluids, which provided thin film lubrication towards the wear couples. As a therapeutic composition, alendronic acid sodium had positive impact on the UHMWPE wear debris. For metal-on-metal artificial joint lubrication, the electrochemical property of biomimetic synovial fluids has been investigated. In tribological test of CoCrMo on CoCrMo materials, friction and wear were mainly dominated by the mechanical and electrochemical performance of the biomimetic synovial fluids. By orthogonal analysis, results showed that hyaluronic acid dominated the viscosity of the fluids, thus directly affected the friction between CoCrMo balls. High albumin concentration would reduce friction, while increasing wear rate due to the electrochemical effect. Alendronic acid sodium was found to reduce the biocorrosion of CoCrMo as well as improving lubrication.Surface texturing technology has been introduced and applied on hard-on-hard artificial joints in regard to the friction induced squeaking and wear problems. An elastohydrodynamic (EHL) model was set up for surface texture designing reference. Then, laser surface texturing processes on hard artificial joint materials was studied and optimized. Finally, via a tribo-acoustic system, laser surface textured ceramic materials were tested. Results showed that surface texture helped to reduce the squeaking sound emission as well as the friction, consequently, verified the potential application of this technology in artificial joints.Concerned artificial joint product level, material level tribological tests and tribo-acoustic test, three test equipments, as one multi-functional hip joint simulator, one multi-directional pin on disk tribometer and a tribo-acoustic test system, were designed, built and validated. Moreover, test methods were also proposed and testified. Preliminary test results summarized, (a) the multi-functional hip joint simulator, generated by a hip joint simulator and a general pin on disk module, could support both artificial hip joint wear tests and common material tribological experiments. Motion configurations and wear factors observed in this simulator agreed well with those in clinics, and it offered a reliable test bench for artificial hip joint products. (b) The multi-directional pin on disk test methods provided a better solution for artificial joint material level wear tests. Compared with common pin on disk tests, experimental results in such test apparatus was more accurate referring to clinical issues. (c) Via the tribo-acoustic test system, both tribological and acoustic signal could be measured simultaneously, thus, providing a test platform and a feasible methodology for the fundamental understanding of friction induced squeaking phenomenon in hard-on-hard artificial joints and investigation of other potential solutions toward this problems.