Nanomechanical Properties of UHMWPE Irradiated with N Ions

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

Milwaukee, Wisconsin USA.

Conferencia; Society of Plastics Engineers Annual Technical Conference ANTEC 2008; 2008

Society of Plastics Engineers

Inadequate mechanical surface properties limit the service life of ultra-high molecular weight polyethylene (UHMWPE) hip and knee joint components. It is well known that in vivo wear resistance of UHMWPE can be improved by crosslinking, but concomitantly its fatigue strength is reduced. M. del Grosso et al. have shown that irradiation with 33MeV N ion beam at fluences ranging from 5x1010 to 1x1014 ions/cm2 induces strong chemical modifications in the outer layers of the polymer [1]. Thus it appears that, by means of this irradiation technique, it may be possible to generate suitable surface modifications without affecting the desirable bulk properties of UHMWPE. The motivation of this work was to examine nanoscale mechanical properties of the outer layer region of N beam irradiated UHMWPE using depth-sensing indentation. Reduced elastic modulus and universal hardness were determined applying trapezoidal loading functions with a Berkovich tip by means of the Oliver- Pharr approach. The apparent friction coefficient was evaluated from nanoscratch tests carried out with a 20 µm conospherical tip. The irradiated samples exhibited better performance than unirradiated ones, ie. higher elastic modulus and hardness, and lower friction coefficient, suggesting a better wear resistance. The magnitude of these properties was shown to be dependent on fluence under the irradiation conditions used. UHMWPE irradiated with 1x1012 ions/cm2 exhibited a four-fold increase of hardness and elastic modulus and at one point five-fold decrease of friction coefficient.10 to 1x1014 ions/cm2 induces strong chemical modifications in the outer layers of the polymer [1]. Thus it appears that, by means of this irradiation technique, it may be possible to generate suitable surface modifications without affecting the desirable bulk properties of UHMWPE. The motivation of this work was to examine nanoscale mechanical properties of the outer layer region of N beam irradiated UHMWPE using depth-sensing indentation. Reduced elastic modulus and universal hardness were determined applying trapezoidal loading functions with a Berkovich tip by means of the Oliver- Pharr approach. The apparent friction coefficient was evaluated from nanoscratch tests carried out with a 20 µm conospherical tip. The irradiated samples exhibited better performance than unirradiated ones, ie. higher elastic modulus and hardness, and lower friction coefficient, suggesting a better wear resistance. The magnitude of these properties was shown to be dependent on fluence under the irradiation conditions used. UHMWPE irradiated with 1x1012 ions/cm2 exhibited a four-fold increase of hardness and elastic modulus and at one point five-fold decrease of friction coefficient.