Computational nodal displacement analysis of acetabulum fossa for injection molded cemented polyethylene acetabular liner

Abstract

The acetabular liner (AL) is one of the key components that determine the functionality and durability of the total hip joint replacement (THR) device. The performance of Ultra high molecular weight polyethylene (UHMWPE)-based AL depends critically on the manufacturing route and its properties, which are evaluated pre-clinically using a host of experimental and computational analyses. The conventional manufacturing of an AL involves multiple stages, including extrusion/compression molding followed by machining, which is time/cost intensive and leads to material loss. In such a scenario, injection molding is a promising alternative, yet its feasbility remains unexplored for the manufacturing of AL for THA applications. Against this backdrop, the two-fold objectives of this work are to report our recent efforts to establish the efficacy of the injection molding of new generation UHMWPE biomaterial; HU (60 wt% HDPE- 40 wt% UHMWPE blend) for manufacturing AL prototype and to present the key biomechanical response analysis of this prototype, in silico. A range of manufacturing relevant material properties, as well as customized mold design to manufacture HU-based AL with external design features, are discussed. Such guidelines are particularly relevant to mold polymeric parts with a higher thickness (>8 mm). As part of the pre-clinical validation of AL with new design features, a less explored in silico approach to assess biomechanical micro-strain in the acetabulum fossa is presented, and the results are analysed in accordance with the mechanostat theory. The outcomes revealed that for a 100 kg subject weight, average micro-strain in the remodelling region was 1132, while it was determined as 723 for a 55 kg subject weight. Such results highlight the influence of subject weight on micro-strain generation and distribution in the acetabulum fossa. The von Mises stress in AL also increased with subject weight from 17 MPa in a subject weight of 55 kg to 28 MPa in a subject weight of 100 kg. Taken together, this work demonstrates the feasibility and competence of this new generation biomaterial in terms of implant manufacturing via injection molding with a clinically desired biomechanical response.