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Failure analysis and design optimisation of the magnetic expansion controlled growing spinal rod medical implant (Advert Reference:RDF22-R/EE/MCE/FARHAD)


   Faculty of Engineering and Environment

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  Dr Farnoosh Farhad, Prof Tom Joyce, Dr Martin Birkett  No more applications being accepted  Competition Funded PhD Project (UK Students Only)

About the Project

Medical implants have improved the quality of life for millions of human beings. However, the failure of the implants can be disastrous to the patients. This emphasises the need in the study of failed implants and development in the products that expands their lifecycle. Magnetically controlled growing rods are the medical implants that are increasingly used in the treatment of early-onset scoliosis (i.e. curvature of the spine >10°) in children. The MAGnetic Expansion Control (MAGEC) system is one such implant that has been licenced for use in Europe since 2009. It has the advantage of being lengthened using an external remote control and therefore significantly reduces the number of surgeries and consequently improves the experience of the patient compared with conventional growing rods, which require surgery every 6-9 months. However, mechanical failure with MAGEC system have been reported. Failure is likely due to multiple factors including over-loading, fatigue, and corrosion. However, the relative importance of each of these factors, and therefore how to mitigate them remains a critical and limiting knowledge gap. This project aims to optimise the design of rods in two phases, phase one is an evaluation of the failure mechanism and phase two is the assessment and ultimate improvement of the design of the rod. The specific objectives of this study are:

  • To analyse the explanted MAGEC rods by means of microscopy techniques and evaluate common failure mechanisms
  • To assess the failure mode of MAGEC rods by performing finite element stress analysis
  • To optimise the MAGEC rods
  • To experimentally examine the life cycle of newly designed rods using a new bespoke corrosion-fatigue test replicating body fluid

Several MAGEC rod implants have been explanted and are available from Newcastle University [6-10]. Specialist support will also be provided by an industrial collaborator, ExplantLab, https://www.explantlab.com/ with expertise in the analysis of a range of medical implants. Scanning Electron Microscopy (SEM) of the failed drive pins will be undertaken to understand their failure mechanisms. The stress analysis of the rods and drive pins using numerical simulation (by ABAQUS/ANSYS software) will provide valuable new insights into the failure mode [2-3]. Based upon the identification of the failure mechanism(s) and analysed life span of the explanted rods, a new optimised design will be proposed. To physically test the optimised version, a bespoke corrosion fatigue vessel that previously was developed in [1,4-5] will be modified for this application and the life cycle of the implant will be examined in a replicated body environment in the laboratory.

The Principal Supervisor for this project is Dr Farnoosh Farhad.

Eligibility and How to Apply:

Please note eligibility requirement:

  • Academic excellence of the proposed student i.e. 2:1 (or equivalent GPA from non-UK universities [preference for 1st class honours]); or a Masters (preference for Merit or above); or APEL evidence of substantial practitioner achievement.
  • Appropriate IELTS score, if required.
  • Applicants cannot apply for this funding if currently engaged in Doctoral study at Northumbria or elsewhere or if they have previously been awarded a PhD.

For further details of how to apply, entry requirements and the application form, see

https://www.northumbria.ac.uk/research/postgraduate-research-degrees/how-to-apply/

Please note: Applications that do not include a research proposal of approximately 1,000 words (not a copy of the advert), or that do not include the advert reference (e.g. RDF22-R/…) will not be considered.

Deadline for applications: 20 June 2022

Start Date: 1 October 2022

Northumbria University takes pride in, and values, the quality and diversity of our staff and students. We welcome applications from all members of the community.

Funding Notes:

Each studentship supports a full stipend, paid for three years at RCUK rates (for 2022/23 full-time study this is £16,602 per year) and full tuition fees. Only UK candidates may apply.

Studentships are available for applicants who wish to study on a part-time basis over 5 years (0.6 FTE, stipend £9,961 per year and full tuition fees) in combination with work or personal responsibilities.

Please note: to be classed as a Home student, candidates must meet the following criteria:

• Be a UK National (meeting residency requirements), or

• have settled status, or

• have pre-settled status (meeting residency requirements), or

• have indefinite leave to remain or enter.


References

1. Farhad, F., Smyth‐Boyle, D. and Zhang, X., 2021. Fatigue of X65 steel in the sour corrosive environment—A novel experimentation and analysis method for predicting fatigue crack initiation life from corrosion pits. Fatigue & Fracture of Engineering Materials & Structures, 44(5), pp.1195-1208.
2. Hashim, M., Farhad, F., Smyth‐Boyle, D., Akid, R., Zhang, X. and Withers, P.J., 2019. Behavior of 316L stainless steel containing corrosion pits under cyclic loading. Materials and Corrosion, 70(11), pp.2009-2019.
3. Farhad, F., Zhang, X. and Smyth-Boyle, D., 2019. Fatigue behaviour of corrosion pits in X65 steel pipelines. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 233(5), pp.1771-1782.
4. Farhad, F., 2019. Influence of sour environment on crack initiation at corrosion pits under cyclic loading (Doctoral dissertation, Coventry University).
5. Farhad, F., Smyth‐Boyle, D., Zhang, X., Wallis, I. and Panggabean, D., 2018. Laboratory apparatus for in‐situ corrosion fatigue testing and characterisation of fatigue cracks using X‐ray micro‐computed tomography. Fatigue & Fracture of Engineering Materials & Structures, 41(12), pp.2629-2637.
6. Joyce, T.J., Smith, S.L., Rushton, P.R., Bowey, A.J. and Gibson, M.J., 2018. Analysis of explanted magnetically controlled growing rods from seven UK spinal centers. Spine, 43(1), pp.E16-E22.
7. Joyce, T.J., Smith, S.L., Kandemir, G., Rushton, P.R., Fender, D., Bowey, A.J. and Gibson, M.J., 2020. The nuvasive MAGEC rod urgent field safety notice concerning locking pin fracture: how does data from an independent explant center compare?. Spine, 45(13), pp.872-876.
8. Rushton, P.R., Smith, S.L., Forbes, L., Bowey, A.J., Gibson, M.J. and Joyce, T.J., 2019. Force testing of explanted magnetically controlled growing rods. Spine, 44(4), pp.233-239.
9. Rushton, P.R., Smith, S.L., Fender, D., Bowey, A.J., Gibson, M.J. and Joyce, T.J., 2021. Metallosis is commonly associated with magnetically controlled growing rods; results from an independent multicentre explant database. European Spine Journal, pp.1-7.
10. Rushton, P.R., Smith, S.L., Kandemir, G., Forbes, L., Fender, D., Bowey, A.J., Gibson, M.J. and Joyce, T.J., 2020. Spinal lengthening with magnetically controlled growing rods: data from the largest series of explanted devices. Spine, 45(3), pp.170-176.

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