Fracture and fatigue properties of acrylic bone cement - The effects of mixing method, sterilization treatment, and molecular weight

The purpose of this study was to characterize the relative and combined eff ects of sterilization, molecular weight, and mixing method on the fracture and fatigue performance of acrylic bone cement. Palacos(R) R brand bone cem ent powder was sterilized using ethylene oxide gas (EtO) or gamma irradiati on. Nonsterile material was used as a control. Molecular weights of the bon e-cement powders and cured cements were measured using gel permeation chrom atography. Hand and vacuum mixing were employed to mold single edge-notched bend specimens for fracture toughness testing. Molded dog-bone specimens w ere used for fatigue tests. Electron microscopy was used to study fracture mechanisms. Analysis of variance and Student t-tests were used to compare f racture and fatigue performance between sterilization and mixing groups. Ou r results indicate that vacuum mixing improved significantly the fracture a nd fatigue resistance (P <.05, P <.07) over hand mixing in radiation-steril ized and EtO-sterilized groups. In vacuum-mixed cement, the degradation in molecular weight resulting from gamma irradiation decreased fracture resist ance significantly when compared with EtO sterilization and control (P <.05 ). A corresponding decrease in fatigue resistance was observed in the cemen t that was degraded severely by a radiation dose of 10 MRad (P <.05). In co ntrast, EtO sterilization did not result in a significantly different fract ure resistance when compared with unsterilized controls for vacuum-mixed ce ment (P >.1). For hand-mixed cement, fracture and fatigue resistance appear ed to be independent of sterilization method. This independence is believed to be the result of higher porosity that compromised the mechanical proper ties and obscures any effect of sterilization. Our results indicate that a combination of nonionizing sterilization and vacuum mixing resulted in the best mechanical performance and is most likely to contribute to enhanced lo ngevity in vivo.