Development of UHMWPE acetabular cup for improved fixation and wear in total hip replacement

The acetabular cup made of ultra-high molecular weight polyethylene (UHMWPE) is difficult to adhere directly to the host bone in total hip joint replacement. The polymethymethacryate (PMMA) bone cement is introduced as a grouting material. In spite of this, the UHMWPE does not adhere to the PMMA bone cement due to chemical incompatibility, resulting in detachment of the cup from the cement, which may lead the dislocation. Furthermore, it produces wear debris after long-term use, which may contribute to the aseptic loosening of cup.; In this study, first, an adhesive interlayer was devised to enhance the adhesion strength between the PMMA and UHMWPE. The interlayer was sandwiched between PMMA and UHMWPE powder and compression-molded at high pressure (35.3 MPa) and temperature (170°C). The higher interfacial strength in tension, 18.8 +/- 1.8 MPa was obtained by the addition of benzoyl peroxide (BPO) based on the optimal blending ratio of UHMWPE to PMMA/MMA solution in the interlayer.; Second, the effect of gamma-irradiation on UHMWPE was investigated. The irradiation dose varied from 2.5 to 30 Mrad and the environment, additive, and aging on UHMWPE investigated. As irradiation dose increased, gamma-irradiated UHMWPE in vacuum showed a decrease in melting temperature (Tm) and percent crystallinity (C%). Furthermore, swell ratio significantly decreased indicating increased cross-link density although mechanical strength and plastic deformation decreased as the gamma-irradiation dose increased. In addition to gamma-irradiated, accelerated aging treated UHMWPE slightly decreased in Tm and an increase in C% at high doses, and increased the oxidation index. The addition of hydroquinone stabilized against gamma-irradiation and prevented the oxidation after irradiation.; Finally, the ball-on-disk simulator was used to determine the friction coefficient and wear loss of irradiated UHMWPE. As the irradiation dose increased, the friction coefficient deceased, as a result of higher cross-linking. Furthermore, irradiated UHMWPE in vacuum showed lower friction coefficient than irradiated in air. In conclusion, the adhesive interlayer showed a promising means for fixing UHMWPE acetabular cup to bone firmly. In addition, the cross-linked UHMWPE by gamma-irradiation treatment enhanced wear and friction.