Bone: A study of machining-induced damage and the role of interstitial fluid

Robles Linares Alvelais, Jose Alberto (2022) Bone: A study of machining-induced damage and the role of interstitial fluid. PhD thesis, University of Nottingham.

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Bone cutting is a common process in orthopaedics, dentistry and neurosurgery. However, it comprises a challenging set of tasks when it comes to machining analysis and damage assessment due to its complex hierarchical and porous microstructure. Additionally, given its biological nature, bone is not only an engineering material, but also a tissue that holds living cells and interstitial fluid within.

During machining, temperature rise is inevitable, and if the temperature surpasses a certain threshold, it will cause cellular death (i.e. necrosis). Histological analysis has been the gold standard technique for assessing bone quality, as it enables a straightforward necrosis measurement. However, being mostly used in the medical field and having a biological nature aimed at cellular observation, this technique does not capture mechanical damage, which is essential for a full material assessment, especially considering that many times following bone machining, an implant might be put in close contact with the machined surface.

To understand and minimise the machining-induced tissue damage, many studies and models have been proposed regarding both conventional and non-conventional machining processes. However, most of these studies have been conducted in a laboratory scenario principally consisting of machining bone in a dry state or with external coolant supply. While all of these are valuable, they have typically neglected the in-vivo conditions of bone by not considering the interstitial fluid that is contained within the porosities of the bone’s microstructure. However, it is believed that this internal irrigation condition of in-vivo bone will locally affect other properties that impact the cutting process, such as the friction coefficient or the shear strength.

This research aims to understand the machining-induced damage in cortical bone not only from a biological point of view, but also from a micromechanical perspective, by employing micromechanical testing (i.e. micropillar compression) post-machining to assess thermomechanical damage. The machining techniques selected for damage assessment are conventional (i.e. drilling, fly cutting) and non-conventional (i.e. laser machining).

This research also presents a novel laboratory machining setup that allows to mimic the in-vivo conditions of cortical bone during a cutting process. The setup permits to fix the sample for machining while also enabling to pump fluid through the vascular porosities of the bone, thereby producing a more realistic method for bone cutting in a laboratory scenario.

This study shows that in conventional machining, micromechanical damage beneath the machined surface could be more significant than necrotic damage, even showing that a ductile-to-brittle failure mode transition can take place at the microscale in regions both inside and outside the necrotic zone. Also, the effect of internal irrigation during bone cutting, as enabled by the novel machining setup, produces a drastic difference in chip formation, cutting forces, surface morphology and thermal damage, as opposed to traditional dry cutting experiments. The results from this work are expected to contribute and promote in-depth research of bone machining towards improved tooling and tooling systems that could improve surgical procedures by minimising damage inducement and benefiting patient recovery.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Axinte, Dragos
Liao, Zhirong
Gameros, Andres
Keywords: cortical bone; bone cutting; bone machining; necrosis; surface damage; histology; micromechanics; micropillar compression; bone failure mechanism; interstitial fluid; chip formation; internal irrigation
Subjects: R Medicine > RD Surgery
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID: 69451
Depositing User: Robles Linares Alvelais, Jose
Date Deposited: 05 Feb 2024 14:00
Last Modified: 05 Feb 2024 14:00

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