| The ultra-high molecular weight polyethylene (UHMWPE) is one of the most important artificial joint replacement materials, and it has been researched for many years. However, wear debris produced in this articular surface has been recognized as one of the common causes for the loosening and premature failure of artificial joints. Thus, the improvement of lubrication and wear resistance for this artificial joint material is very important in order to prolong its life span.The aim of the present paper was to mimic the structure and function of brushy lubricants in superficial zone of natural articular cartilage. The modified UHMWPE was prepared by the grafting, and the properties of friction and wear for this material were investigated.1. In this paper, four new compounds of phosphorylcholine derivatives were synthesized. The lubrication and the molecular lubrication mechanism were studied on the pin-on-plate wear tester under water lubrication. The experiment showed that the compound of phosphorylcholine derivative behaves the better lubrication than acrylic acid under water lubrication due to the structure of the zwitterionic group.If the polyacrylic acid (PAA) is grafted onto the UHMWPE by chemical bond, adhesive strength will become stronger so that the PAA is not easy to be removed out of the rubbing surface. At the same time, the thickness of brushes will become thicker and the amount of hydrophilic groups within brushes will be much more. Thus, the lubrication will be advanced by three effects. Furthermore, if the phosphorylcholine is grafted onto the UHMWPE, its biocompatibility will be improved. We carried out the following invesgitates basing on the above discussions.2. Mimicking the structure and the function of brushy lubricants in superficial zone of natural articular cartilage, the modified UHMWPE was prepared. The tribological properties for the modified UHMWPE were studied under the dry and water lubrication.2.1 The UHMWPE powders were grafted by the PAA using the benzoperoxide (BPO) and benzophenone (BP) as the initiators respectively. The effects of conditions on graft yields were discussed particularly. The result showed that the graft yield of 20% was obtained as for the benzoperoxide initiator under the conditions of UHMWPE=5g,100℃, 1h, BPO=0.03g, and [AA]=0.14 g/ml. However, for the BP initiator, the graft yield of 8.9% was obtained under the conditions of UHMWPE=5g,60℃, BP=0.15g,15min, and [AA]=0.16g/mL. The flat of UHMWPE material grafted by PAA was prepared by the hot pressing under the conditions:190℃,30min. The properties for this material of friction and wear were tested on the pin-on-plate wear tester under the dry and water lubrication. The results suggested that the modified material showed the lower friction coefficient and wear rate.2.2 The compound of phosphorylcholine was grafted onto the UHMWPE powders by the esterification and ring opening reaction, and the effect of conditions on the graft yields were discussed in detail. Then, the flat of UHMWPE modified by the phosphorylcholine was prepared by the hot pressing. The pressing temperature was 190℃, and the time was 30 minutes.The tribology characteristics of this modified material were tested on the pin-on-plate wear tester under the dry and water lubrication. The results showed that this material modified by phosphorylcholine behaved the lower friction coefficient and wear rate.On the whole, from the point of view of bionics, mimicking the structure and function of brushy lubricants in superficial zone of natural articular cartilage, the UHMWPE modified by PAA and phosphorylcholine was prepared. This material showed the improvement of lubrication and the lower wear rate.
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