Nanomechanical Properties of UHMWPE irradiated with N ions

P.M.FRONTINI; L.A. FASCE; J. CURA; M.F. DEL GROSSO; V. C. CHAPPA; G. GARCÍA BERMÚDEZ

Milwaukee, Wisconsin, USA

Conferencia; Society of Plastics Engineers Annual Technical Conference; 2008

Society of Plastics Engineers

Inadequate mechanical surface properties limit theservice life of ultra-high molecular weight polyethylene(UHMWPE) hip and knee joint components. It is wellknown that in vivo wear resistance of UHMWPE can beimproved by crosslinking, but concomitantly its fatiguestrength is reduced. M. del Grosso et al. have shown thatirradiation with 33MeV N ion beam at fluences rangingfrom 5x1010 to 1x1014 ions/cm2 induces strong chemicalmodifications in the outer layers of the polymer [1]. Thusit appears that, by means of this irradiation technique, itmay be possible to generate suitable surface modificationswithout affecting the desirable bulk properties ofUHMWPE. The motivation of this work was to examinenanoscale mechanical properties of the outer layer regionof N beam irradiated UHMWPE using depth-sensingindentation. Reduced elastic modulus and universalhardness were determined applying trapezoidal loadingfunctions with a Berkovich tip by means of the Oliver-Pharr approach. The apparent friction coefficient wasevaluated from nanoscratch tests carried out with a 20 μmconospherical tip. The irradiated samples exhibited betterperformance than unirradiated ones, ie. higher elasticmodulus and hardness, and lower friction coefficient,suggesting a better wear resistance. The magnitude ofthese properties was shown to be dependent on fluenceunder the irradiation conditions used. UHMWPEirradiated with 1x1012 ions/cm2 exhibited a four-foldincrease of hardness and elastic modulus and at one pointfive-fold decrease of friction coefficient.