The study of UMHWPE nanowear particle generation in TJR prosthesis using atomic force microscopy

Currently there is a strong shift in the field of materials from continuum macro scale to discrete asperity-to-asperity nanoscale contact, which may provide new insight to the basic problem of cause of submicron wear debris eventually leading to total failure of UHMWPE surface of TJR prosthesis. During sliding between the two contacting surfaces of TJR prosthesis or any other tribosystem, multiple asperity contact occurs at the solid-solid interface. The dependence of material response upon load is a result of complex interface phenomena at each one of these nanocontacts.; The influence of mechanical loading on the UHMWPE surfaces could be amplified when the inhomogeneity of the polymer is taken into account. UHMWPE is inhomogeneous because of fabrication processes and parameters. In addition, the inherent composite-like nature (crystalline and amorphous nanoregions) of the polymer could cause variability in mechanical properties of the respective nanoregions, leading to variability in mechanical response upon multiaxial loading (normal and shear loading) at the nanocontact. This variable mechanical response causes a differential in shear resistance of the material leading to variability in frictional response at the nanocontact of TJR prosthesis. This study illustrates that “a differential frictional force at the nanotribological contact will cause a stress concentration within the polymeric material eventually leading to submicron wear debris generation.” In order to assess the source of UHMWPE submicron or nanoscale wear debris generation and illustrate the above stated hypothesis, the following topics were studied: (1) Frictional changes at the nanotribological contact between UHMWPE and its counterpart to understand the mechanism leading to gross plastic deformation subsequently to abrasive wear. (2) A sample preparation technique that would minimize or not alter the nanostructure of the material thus maintaining the structural and mechanical integrity of the UHMWPE. (3) The nanomechanical properties of the crystalline and amorphous regions within the semicrystalline composite like structure of UHMWPE. (4) The nanofrictional coefficients of the nanoregions of UHMWPE in order to help understand the initiating cause of submicron wear debris particle in TJR prosthesis.; The deformation, controlled wear process, nanomechanical and nanofrictional response of the nanostructure of UHMWPE were studied at the nanocontact of TJR prosthesis using atomic force microscopy (AFM).