3D-printed lattice structures for next-generation orthopaedic implants: Considerations on design and post-processing for biomechanical performance and osteoconductivity
File(s)
Author(s)
Kechagias, Stylianos
Type
Thesis
Abstract
Additive manufacturing (3D printing) has enabled the fabrication of joint replacement implants which incorporate porous lattice structures to promote bone in-growth for strong biological fixation after surgery. To meet load-bearing requirements and reduce the risk of aseptic loosening, an ideal lattice should combine high fatigue strength, bone-matching stiffness, together with a micro-architecture and surface finish that benefit the formation of mature bone tissue on implant surface.
In this direction, this thesis comprised of four studies aiming to: (a) develop a parametric model for designing lattices with biomimetic mechanical properties and micro-architecture, (b) assess the impact of lattice micro-architecture (topology) on mechanical behaviour across different specimen sizes, (c) tailor lattice design parameters and (d) explore post-processing methods to enhance fatigue strength and drive in vitro bone tissue formation (osteogenesis).
Stochastic lattices with stiffness ranging from 0.1 to 8 GPa were developed by varying nodal connectivity, strut density and thickness. A key finding revealed that increasing connectivity induces a stretch-dominated behaviour, improving fatigue strength by up to 60% compared to bend-dominated low-connectivity lattices. Moreover, the bend or stretch dominated behaviour was found to control the stiffening mechanism of lattices depending on aspect ratio and specimen size.
From a biological perspective, high connectivity emerged as a critical parameter for tissue growth and maturation owing to the high surface area and multiple concavities introduced around the nodes. Additionally, struts with thickness similar to natural trabeculae (200−300 µm) provided a perfect balance of high surface area-to-volume ratio, essential for osteogenesis, and mechanical strength, for load-bearing capacity. Finally, a chemical-electrochemical surface treatment to smoothen lattice surface was found to improve fatigue strength and promote osteogenic differentiation.
Collectively, this work presents a holistic methodology for the development of lattices with high design flexibility, tailored mechanical properties and topological characteristics optimised to offer support mature bone tissue formation.
In this direction, this thesis comprised of four studies aiming to: (a) develop a parametric model for designing lattices with biomimetic mechanical properties and micro-architecture, (b) assess the impact of lattice micro-architecture (topology) on mechanical behaviour across different specimen sizes, (c) tailor lattice design parameters and (d) explore post-processing methods to enhance fatigue strength and drive in vitro bone tissue formation (osteogenesis).
Stochastic lattices with stiffness ranging from 0.1 to 8 GPa were developed by varying nodal connectivity, strut density and thickness. A key finding revealed that increasing connectivity induces a stretch-dominated behaviour, improving fatigue strength by up to 60% compared to bend-dominated low-connectivity lattices. Moreover, the bend or stretch dominated behaviour was found to control the stiffening mechanism of lattices depending on aspect ratio and specimen size.
From a biological perspective, high connectivity emerged as a critical parameter for tissue growth and maturation owing to the high surface area and multiple concavities introduced around the nodes. Additionally, struts with thickness similar to natural trabeculae (200−300 µm) provided a perfect balance of high surface area-to-volume ratio, essential for osteogenesis, and mechanical strength, for load-bearing capacity. Finally, a chemical-electrochemical surface treatment to smoothen lattice surface was found to improve fatigue strength and promote osteogenic differentiation.
Collectively, this work presents a holistic methodology for the development of lattices with high design flexibility, tailored mechanical properties and topological characteristics optimised to offer support mature bone tissue formation.
Version
Open Access
Date Issued
2024-10-03
Date Awarded
01/03/2025
Advisor
Jeffers, Jonathan
Publisher Department
Department of Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)