Experimentally supported computational method for the optimal design selection of 3D printed fracture healing implant geometries

Lehder, Eric Federico (2023) Experimentally supported computational method for the optimal design selection of 3D printed fracture healing implant geometries. PhD thesis, University of Nottingham.

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The development of AM technologies has brought about very promising opportunities in the field of tissue regeneration, especially due to the design freedom they enable. However, the tools and procedures needed to enable medical designers to make use of these revolutionary technologies still need to be developed. In particular, design tools to make implants with optimal geometries for tissue regeneration and procedures to manufacture and test such implants need to be developed to enable the adoption of these technologies by medical designers and biologists designing implants. This thesis aims to address this need.

In order to best use the design freedom that AM brings; it is necessary to define the optimal geometries for specific applications. A novel tool that enables the design of optimal scaffold geometries and could be easily adopted by medical designers was developed here by proposing an intuitive design selection framework that graphically allows the user to gain an understanding of how design variables affect the chosen response variables. The novel framework is flexible, enabling the incorporation of any number of necessary computational models. Triply periodic minimal surface (TPMS) equations were used to simplify the design variables needed to generate an optimal porous scaffold geometry. The potential of this framework was demonstrated by using it to find the optimal TPMS type and volume fraction for a fracture fixation scaffold.

Experiments were carried out to demonstrate that TCDMDA biocompatible scaffolds of appropriate pore size could be manufactured via projection micro stereolithography. The experiments successfully demonstrate for the first time that TCDMDA scaffolds can be manufactured via PµSLA by using a suitable combination of UV intensity and layer time. It was also demonstrated for the first time that hMSCs adhere to the surface of TCDMDA samples manufactured via PµSLA. To further enhance the cell adhesion, an oxygen plasma treatment was carried out. For the second part of this study it was found that the media could not penetrate the scaffold pores sufficiently, invalidating the results. The presented results highlighting a permeability challenge with TCDMDA scaffolds manufactured via PµSLA are nevertheless expected to contribute to future studies in this area.

Experiments were also carried out to demonstrate the biocompatibility of scaffolds manufactured via stereolithography using Dental LT resin (Formlabs, UK). Successful adhesion of hMSCs to the surface of these scaffolds was shown in Chapter 4. Another novel finding of this thesis was that the Dental LT scaffolds manufactured via SLA were able to successfully enable cell growth, cell differentiation and mineralization in the presence of osteogenic media and BMP-2.

The final part of the thesis focused on expanding the developed design selection framework to include not only a scaffold for fracture healing, but also a matching fracture fixation plate. Fracture fixation plates have been studied for centuries, but there is little research investigating the combination of a fracture fixation plate and a scaffold. The rise of AM has inspired the development of auxetic geometries, which have been applied to fracture fixation plates before and shown to reduce stress shielding. Moreover, stiffness grading has also proved very promising in improving fracture healing. In this thesis these two promising concepts are combined for the first time demonstrating reduced stress shielding compared to a conventional fixation plate geometry. Moreover, the thesis presents a novel computational design selection framework to find optimal scaffold and fracture plate geometries which lead to an improved healing outcome. The framework may be easily adopted by medical designers.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Maskery, Ian
Ashcroft, Ian
Ruiz-Cantu, Laura
Wildman, Ricky
Keywords: Additive manufacturing; Bone regeneration; Fractures; Internal fixation in fractures
Subjects: R Medicine > RD Surgery
T Technology > TS Manufactures
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 72374
Depositing User: Lehder, Eric
Date Deposited: 21 Jul 2023 04:40
Last Modified: 21 Jul 2023 04:40
URI: https://eprints.nottingham.ac.uk/id/eprint/72374

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