Surface Modification Of High Molecular Weight Polyethylene And Its Wear-Resistance

Ultra-high molecular weight polyethylene (UHMWPE) paired with a metal or ceramic are the most common combination of materials used in artificial joint replacement. However, the polymeric nature of UHMWPE makes it susceptible to wearing, releasing micro particles into the joint capsule, causing chronic inflammation and osteolysis which leads to aseptic loosening and eventual failure of the implant. Therefore, many efforts are being carried out to reduce the wear rate of UHMWPE by physical or chemical methodes. In this paper, UHMWPE was modified by plasma pretreating and DLC coating. Plasma was generated by microwave electron cyclotron resonance (ECR), and the DLC films was prepared with the method of microwave electron cyclotron resonance plasma chemical vapor deposition (ECR-PECVD).Firstly, the effect of plasma treating on the UHMWPE, which includes the component and structure, surface morphology, surface energy and surface mechanical property of UHMWPE were investigated. Then, these effects on the tribological property of UHMWPE were further analysed. Secondly, the effect of the process parameters of ECR-PECVD on the structure of DLC based on an orthogonal experimental design and analysis method were studied. Lastly DLC were deposited on UHMWPE, and its structure, mechanical proptery and tribologycial proptery were characterized. The main resulsts of this paper are as follows:(1) Treated by plasma, oxygen containing groups and trans vinylene groups were introduced into the UHMWPE, and the surface crosslinking degree and crystallinlity degree of UHMWPE also increased. The polar groups increased the surface engergy of UHMWPE. And the increased crosslinking degree or crystallinlity degree can improve the surface mechnical propery of UHMWPE, including hardess and anti-plastic deformation. Specially treated by oxygen or nitrogy plasma, UHMWPE has best comprehensive mechanical properties (proper hardness and toughness).(2) The roughness of UHMWPE has been increased after it was treated by oxygen, hydrogen or argon plasma, but the deference of roughness was not clear among different plasmas. However, the roughness of UHMWPE has been little decreased after it was treated by nitrogen plasma. (3) The tribology propery of UHMWPE can be changed by plasma treating. The friction coefficient of UHMWPE increased, but the volume wear rate decreased after plasma treating. The sample treated by nitrogen or oxygen has the lowest wear rate. The main factor of improvement in wear resistance should attribute to the improved mechanical properties and increased surface engery of UHMWPE when it was modified by plasma.(4) When the DLC films were prepared by ECR-PECVD, the importance of each process parameter on the sp3/sp2 bonding ratio of DLC is in the following order:microwave power > C2H2/Ar gas flow ratio > substrate bias voltage > deposition pressure. The sp3/sp2 decreased with the rise of microwave power or deposition pressure, and that increased with the rise of Ar fraction in C2H2/Ar mix gas or substrate bias voltage.The importance of each parameter on the hydrogen content in DLC films is in the following order:substrate bias voltage > C2H2/Ar gas flow ratio > deposition pressure > microwave power. The hydrogen content in DLC films decreased with the rise of substrate bias voltage, and it increased with the rise of microwave power, operating pressure and Ar fraction in C2H2/Ar gas mixture.(5) Typical DLC films were deposited on UHMWPE successfully. The hardness, wear-resistance and anti-scratch of UHMWPE can be significantly improved by the DLC films coating.(6) With the introduction of thin metal transition films, the deposition rate, hardness and sp3/sp2 bonding ratio of DLC deposited on UHMWPE can be increased, And the wear-resistance of UHMWPE can be further improved.