Tailoring the architecture and composition of titanium for bio-engineering applications
Creators: name: Norrito, Mattia
Publisher: name: Loughborough University
Year: 2021
Subjects: subject: 91399 Mechanical Engineering not elsewhere classified
subject: FOS: Mechanical engineering
subject: FOS: Mechanical engineering

description: Considering factors such as the ageing population, growing demand for mobility at later stages in life, and co-morbidities such as obesity, the incidence of joint replacements will rise considerably in the next decades. However, the enormous mechanical mismatch between orthopaedical titanium implants and bone tissue has a critical impact on the integration of the device in the living tissues, leading to abnormal bone resorption and implant loosening. Because the life-in-service of titanium implants is typically limited to 25 years, secondary surgical revisions are a common occurrence and have a low rate of success compared to the primary surgeries, increasing the rate of mortality among the patients and placing an immense financial burden on the national healthcare system.In this dissertation two different approaches were used to improve the mechanical and osteointegrative properties of titanium implants aiming to increase their life-in-service. These approaches involved the control of the pore size, porosity and alloy composition respectively. The biological properties of these replacements were tested using a murine osteoblast cell line MC3T3-E1 established from mouse calvaria.Addressing the first approach, porous titanium scaffolds were manufactured via powder metallurgy and space holder technique in two different porosities (55% and 70% vol.) to replicate the microstructure of cortical and trabecular bone respectively. Thus, the impact of pore sizes ranging from 45 to 500 μm, were found to influence the biological response of MC3T3-E1 pre-osteoblast cell line in different ways depending on the size of the pore.The results suggest that 70% of porosity scaffolds benefit the osteoblasts differentiation in single pore size scaffolds. Moreover, an increase in transcription of gene marker osteocalcin was detected in pores ranging from 300 to 500 μm. Among the 55% porosity scaffolds, pore size ranging from 106 to 212 μm exhibited good osteogenic performances. Therefore, these two pore size ranges were identified as the most performant. In particular, extensive osteogenic properties were displayed when pores ranging from 300-500 and 106-212 μm were combined in multimodal porous scaffolds.<br>Our results demonstrate that, even though pore size and porosity are dependent on each other, they must be considered as separate structural parameters, as the combination of these two variables influences the general outcome of the implant performances.To deal with the second approach, three innovative titanium alloys were designed using Nb and Sn as alloying elements. Tin (Sn) is a cost-effective and promising alloying element which is often combined with Niobium (Nb) to produce alloys with mechanical properties closer to bone. However, little attention has been paid to the effect of Sn and the combination of Sn and Nb on osteoblastic behaviour.The results showed that the binary Sn and ternary Sn-Nb alloys supported cell differentiation and metabolism, demonstrating the suitability of Sn as an element to enhance the performance of titanium implants.The outcome from this research intends to provide guidelines to increase the life-in-service and successful implantation of orthopaedic load-bearing replacements and minimise the need for revision surgeries, yielding overall benefits to the patient’s quality of life, the healthcare system, and to society.