A bulk MgB2 magnet demonstrator for biomedical applications

Bulk superconductors are dense pellets of superconducting material that can be used as compact permanent magnets. Harnessing the ability of these materials to produce considerably higher magnetic fields than conventional ferromagnets will be transformative for a wide range of devices for biomedical and energy applications. These materials have the added safety benefit that the magnetic field can be switched off. However, their enormous potential has yet to be realised in commercial devices for a number of reasons. High temperature superconducting bulk materials, such as YBCO, have the ability to produce very high fields, but they are expensive to produce, cannot be made with large diameter and suffer from relatively poor sample-to-sample reproducibility. Lower temperature superconductors like magnesium diboride (MgB2) are much cheaper and easier to process, but they require expensive and bulky cooling systems. Furthermore, all bulk samples present the additional challenge that they initially need to be magnetised using an external field.
This project involves designing and building a desktop sized magnet to demonstrate that these challenges can be overcome in practical devices by integrating state-of-the-art cryogenics and pulsed magnetisation systems with high performance, low-cost MgB2 superconductor. A bespoke cryostat will be developed by our team at the Rutherford Appleton Laboratory, who are experts in compact and efficient cryocoolers for space applications and coils will be incorporated into the cryostat, enabling the bulk superconductor to be magnetised in situ. The nano-scale structure of the MgB2 material will be optimised for operation at higher temperatures using a novel powder processing strategy, and large, high density samples will be manufactured using the commercial diamond presses at Element Six.
Preliminary experiments will be carried out using the demonstrator magnet, to assess the feasibility of using this technology for magnetically targeted drug delivery, with collaborators at the Institute of Biomedical Engineering in Oxford. More complex shapes of superconductor will be explored, with a view towards developing more sophisticated devices for selected applications such as MRI in future projects.

The UK is recognised world-wide for its strength in superconductivity research, magnet innovation and cryogenics engineering [1]. The MRI/NMR industry, which is dominated by the UK, provides about 90% of the 4Bn Euro global superconductivity market, with over 30,000 MRI scanners installed in hospitals worldwide. These instruments are based on mature low temperature superconducting (LTS) wire technology and operate at 4K. Of increasing importance are a series of emerging technologies that can be best realised using bulk superconducting magnets operating at temperatures over 20K. These applications cut across a range of different sectors including healthcare, electric transport and renewable energy. However, these superconductors are at a much lower technology readiness level, so research investment is required now to develop practical materials and systems in order to accelerate impact and keep the UK at the forefront.
The principal aim of this project is to build a compact and low-cost demonstrator device using MgB2 superconducting bulks capable of producing higher magnetic fields than conventional rare-earth ferromagnets. Our motivation is to revolutionise important therapeutic and diagnostic medical devices by providing easy and cheap access to higher magnetic fields in a clinical and laboratory setting. These applications include magnetic drug targeting (MDT), magnetic cell separation, and compact MRI machines.
MDT has significant potential advantages over non-specific therapies for treating diseases like cancer and arthritis, allowing lower doses and minimising side-effects by concentrating the drug at the target site [2]. It is also a promising method for treating serious neurological disorders such as brain tumours and Alzheimer's disease, by enhancing the transport of drugs across the blood-brain barrier [3]. Other exciting potential applications for this technology include targeted gene therapy [4] and radionuclide therapy [5]. This research is at a fairly early stage, and it is an open question whether magnetic targeting can be used effectively in humans [6]. We will work closely a research group at the Institute of Biomedical Engineering in Oxford to demonstrate that the higher fields achieved using superconducting bulk MgB2 magnets improve the effectiveness of magnetic trapping under conditions relevant to the human body. This will open up opportunities for accessing a greater range of target sites including wider vessels and locations deeper inside the human body.
MRI is an increasingly important medical diagnostic tool, with the NHS reporting a 220% increase in the number of MRI scans over a ten year period, leading to long patient waiting times [7]. Introducing compact, low-cost MRI machines to complement the traditional whole-body scanners is an attractive option for meeting this increasing demand [8]. Current generation MRI machines are very expensive and bulky owing to their reliance on large, low temperature superconducting solenoid magnets. The large volume of liquid helium cryogen needed to cool the magnets is not only inherently dangerous, but concerns over the global supply of helium is leading to price increases and uncertainty. There is a considerable market and appetite for smaller, cheaper units for diagnosing common limb injuries [8], to alleviate pressure on existing whole-body scanners. Replacing permanent magnets with bulk superconductors in compact MRI machines would improve sensitivity, leading to the better image quality desired by doctors and higher patient throughput.

[1]Melhem Z 2011 Materials UK Prelim. Review, Superconducting Materials and Applications: A UK Challenge and an Opportunity [2]Pankhurst 2003 J Phys D 36 R167 [3]Patel 2010 J Pharm Parm Sci 13 536 [4]Hasenpusch 2012 Pharm Res 29 1308 [5]Sofou 2008 Int J Nanomedicine 3 181 [6]Owen 2015 Interface Focus 5 20150001 [7]https://www.england.nhs.uk/statistics/ [8]Trueland 2014, Health Service Journal supplement.