WEAR REDUCTION IN UHMWPE ORTHOPEDIC COMPONENTS

ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE (UHMWPE) IS PRESENTLY THE PLASTIC MATERIAL MOST COMMONLY USED IN ORTHOPEDIC PROSTHESES. WEAR OF THIS MATERIAL IN LOAD-BEARING COMPONENTS (E.G., KNEE AND HIP REPLACEMENTS) ISA SERIOUS PROBLEM THAT LIMITS THE LIFETIME OF THE PROSTHETIC DEVICES. SPIRE CORPORATION WILL STUDY THE USE OF ION IMPLANTATION TO IMPROVE THE WEAR PERFORMANCE OF UHMWPE. HIGH-ENERGY IONS OF HELIUM, TITANIUM, AND FLUORINE WILL BE IMPLANTED INTO UHMWPE SAMPLES. PRELIMINARY EXPERIMENTS ON UHMWPE SAMPLES CLEARLY INDICATE THAT THE ION IMPLANTATION PROCESS INCREASES THE DENSITY AND MICROHARDNESS OF THE SURFACE, AT THE SAME TIME REDUCING THE COEFFICIENT OF FRICTION. INCREASED SURFACE DENSITY AND HARDNESS COUPLED WITH A LOWER FRICTION SHOULD SUCCESSFULLY REDUCE THE WEAR OF UHMWPE. PHASE I WORK WILL CONCENTRATE ON OBTAINING THE OPTIMUM ION BEAM PARAMETERS FOR TREATMENT OF UHMWPE. THE CHOICE OF ION SPECIES, ENERGY, CURRENT DENSITY, AND DOSE OF IONS WILL BE EXPLORED TO OBTAIN THE MAXIMUM HARDNESS AND MINIMUM COEFFICIENT OF FRICTION. SOME PIN-ON-DISK EXPERIMENTS WILL BE PERFORMED TO COMPARE THE ION IMPLANTATION RESULTS WITH CONTROL SAMPLES. HOWEVER, DUE TO LARGE VARIATION IN WEAR DATA, MICROHARDNESS AND COEFFICIENT OF FRICTION WILL PRIMARILY BE USED TO OBTAIN THE OPTIMUM PROCESS PARAMETERS.