title: Nanoindentation properties of compression-moulded ultra-high molecular weight polyethylene.
abstract: This paper investigates the elastic modulus and hardness of untreated and treated compression-moulded ultra-high molecular weight polyethylene (UHMWPE) tibial inserts of a total knee replacement (TKR) prosthesis. Investigations were carried out at a nanoscale using a Nanoindenter at penetration depths of 100,250 and 500 nm. The nanomechanical properties of surface and subsurface layers of the compression-moulded tibial inserts were studied using the untreated UHMWPE. The nanomechanical properties of intermediate and core layers of the compression-moulded tibial insert were studied using the cryoultrasectioned and etched UHMWPE treated samples. The cryoultrasectioning temperature (-150 degrees C) of the samples was below the glass transition temperature, Tg (-122 +/- 2 degrees C ), of UHMWPE. The measurement of the mechanical response of crystalline regions within the nanostructure of UHMWPE was accomplished by removing the amorphous regions using a time-varying permanganic-etching technique. The percentage crystallinity of UHMWPE was measured using differential scanning calorimetry (DSC) and the Tg of UHMWPE was determined by dynamic mechanical analysis (DMA). Atomic force microscopy (AFM) was used to assess the effect of surface preparation on the samples average surface roughness, Ra. In this study, it was demonstrated that the untreated UHMWPE samples had a significantly lower (p < 0.0001) elastic modulus and hardness relative to treated UHMWPE cryoultrasectioned and etched samples at all penetration depths. No significant difference (p > 0.05) in elastic modulus and hardness between the cryoultrasectioned and etched samples was observed. These results suggest that the surface nanomechanical response of an UHMWPE insert in a total joint replacement (TJR) prosthesis is significantly lower compared with the bulk of the material. Additionally, it was concluded that the nanomechanical response of material with higher percentage crystallinity (67 per cent) was predominantly determined by the crystalline regions within the semi-crystalline UHMWPE nanostructure.
authors.affiliation: Department of Preventative and Restorative Dental Sciences, University of California San Francisco, San Francisco, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: Ho
authors.forename: L
authors.initials: L
authors.lastname: Riester
authors.forename: M
authors.initials: M
authors.lastname: Drews
authors.forename: T
authors.initials: T
authors.lastname: Boland
authors.forename: M
authors.initials: M
authors.lastname: LaBerge
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D019245:Compressive Strength; D004548:Elasticity; D019544:Equipment Failure Analysis / Q000379:methods*; D006244:Hardness; D006245:Hardness Tests / Q000379:methods*; D006358:Hot Temperature; D007720:Knee Prosthesis; D008420:Manufactured Materials; D008422:Materials Testing / Q000379:methods*; D036103:Nanotechnology / Q000379:methods*; D011095:Polyethylenes / Q000737:chemistry*; D011312:Pressure; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D001672:Biocompatible Materials; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene