title: A computational investigation of biomimetic and functionally graded lattice structures for orthopaedic applications
Creators: name: Vafaeefar, Mahtab
Publisher: name: University of Galway
Year: 2024
Subjects: subject: orthopaedic applications
subject: lattice structures
subject: Engineering
subject: Biomedical engineering

description: This thesis developed computational lattice-based structures, inspired by trabecular bone microarchitectures, and mechanically evaluated and characterised them. A suite of computational tools that enable the efficient generation of biomimetic lattice-based structures, were developed. The computational tools used alongside a novel computational optimisation framework, enabled the efficient design of functionally graded biomimetic lattice structures for orthopaedic medical implant applications. In the first study, a computational investigation of the performance of three algorithms, as biomimetic models of trabecular bone architecture, was conducted through systematic evaluation of morphometric, topological, and mechanical properties. The studied structures were the gyroid lattice structure, the recently developed spinodoid structure, and a Voronoi-like lattice was introduced as the dual-lattice structure. While all computational models were calibrated to recreate the trabecular tissue volume, it was found that both the gyroid- and spinodoid-based structures showed substantial differences in many other morphometric and topological parameters and, in turn, showed lower effective mechanical properties compared to trabecular bone when their mechanical response was simulated using finite element analysis. The newly developed dual-lattice structures better captured both morphometric parameters and mechanical properties, despite certain differences being evident in their topological configuration compared to trabecular bone. The second study evaluated the mechanical properties and energy absorption characteristics of as biomimetic lattices, through finite element analysis and experimental characterization. Computational models were calibrated to the observed experimental data, from mechanically tested 3D printed samples of low volume fractions of gyroid and dual-lattice structures, and the response of higher volume fractions were simulated. Energy absorption parameters were calculated and analysed. The results of the study showed that the dual-lattice was capable of absorbing more energy at each volume fraction cohort. However, gyroid structures showed to be a better candidate for energy absorption applications, with higher energy absorption efficiency and the onset of densification at higher strains. In third study a new open-source MATALB toolbox “LatticeWorks” was developed, and the underlying theory was described. This toolbox enabled efficient design and generation of functionally graded, non-uniform, and multi-morphology lattice structures, in different configurations, such as cylindrical and spherical boundary shapes and boundary transitions. The LatticeWorks toolbox provided the necessary tools for mapping spatially varying lattices on optimised mechanical or structural properties, besides volume infill using lattice structures. The final study presented a computational optimisation framework of a hip implant through the development of a functionally graded biomimetic lattice structure, whose design was structurally optimised to limit stress shielding. The optimisation technique was inspired by the inverse of the bone remodelling algorithm, promoting an even stress distribution throughout the design region, by reducing the density and consequently the stiffness, in regions where strain energy was higher than the reference level. The result of the optimisation technique was a non-uniform graded density distribution field, that showed lower density on the sides of the implant stem, and higher material density around the medial axis. The performance of the porous implant design was evaluated through implementation of bone remodelling algorithm and comparing the bone response with a fully solid implanted bone. The results of the analysis showed improved bone formation on the bone-implant interface, and enhanced stress transmission to the surrounding bone from the implant.