Probing Local Mechanical Properties in Polymer-Ceramic Hybrid Acetabular Sockets Using Spherical Indentation Stress-Strain Protocols

Mechanical properties exhibited by the materials used in biomedical device components for articulating joints play an important role in determining the implant performance. In the fabrication of complex-shaped parts, the thermomechanical history experienced in different locations of the final part can be substantially dissimilar, which may lead to large differences in the local microstructures and properties. In many instances, it is not feasible to evaluate experimentally the local mechanical properties in the as-manufactured bioimplant prototypes using standardized tests, and use this information in refining the manufacturing cycle to develop implants with improved performance. In order to bridge this critical gap between materials development and manufacturing, we explore here the use of recently developed spherical indentation stress-strain analysis protocols for the mechanical characterization of local properties in the as-manufactured biomedical device prototype. More specifically, this paper presents two main advances: (i) extension of spherical indentation stress-strain analysis protocols needed to extract reliable estimates of elastic modulus and indentation yield strength from polymer matrix composite (PMC) samples and (ii) demonstration of the differences in the properties between samples produced specifically for the standard tension tests and the as-fabricated PMC acetabular socket prototype intended for total hip joint replacement applications. The results of the present study revealed large differences in the mean and variance of the measured moduli and indentation yield strengths in the acetabular socket and the tensile specimen. Based on the extensive micro-computed tomography (micro-CT) analysis, an attempt has been made to rationalize the local property differences on the basis of microstructural attributes.