DESIGN AND FINITE ELEMENT ANALYSIS OF BIODEGRADABLE ORTHOPAEDIC SCREWS WITH BULK AND GYROID MATRIX CORE

Abstract

This thesis research aims to design a standard HB 6.5 biodegradable orthopaedic screw and modify its mechanical behaviour by integrating a triply periodic cellular gyroid core. The methodology involves modelling a gyroid lattice with 0.5mm channels and integrating it into the core of the screw. The concept being explored is to investigate the reduction in screw stiffness within a measurable ratio, which could alleviate stress shielding and promote biological integration of growing bone into the exposed gyroid core. A finite element analysis methodology was used to assess and compare the mechanical performance of a gyroid-core HB 6.5 cancellous orthopaedic screw with an identical bulk-core screw. The chosen material for the screw is biodegradable magnesium alloy (WE43), known for its biocompatibility and favourable in vivo characteristics. The decision to use gyroid lattice as the core structure stems from a publication by researchers at the University of Debrecen, which demonstrated that triply minimal surfaces can enhance osteointegration properties. A prototype was developed using a 3D resin-based printer, allowing for further experiments and visualisation for future researchers.