Process Design to Prevent Prosthetic Infections

Most prosthetics used to replace joint function in the body have a very low chance of infection (<2%). When prosthetics must be inserted following trauma or where individualised implants must be made for patients, the chances of infection are significantly increased and can be as high as 50%. Treatment requires removal of the prosthetic and the implantation of another material that releases high-levels of antibiotics to the site of infection and causes a major risk to the health of the patients. The excessive use of antibiotics is one of the factors that has provoked a rise in the frequency of bacteria that are resistant to antibiotics. Consequently, there is a significant need to develop processes and designs for implants that have enhanced resistance to bacterial contamination. In this project, we will use a combination of 3D printing and silver coating to refine current methods of processing and produce surfaces that are resistant to bacterial infection. We will work with clinicians and industrial partners to develop technologies that can be used with lots of different kinds prosthetics, however, our first target is to reduce infections following the implantation of a metallic plate in the skull.

Many different clinical conditions require that a surgeon makes a hole in the skull of a patient to allow for treatment. This allows the surgeon to relieve pressure, caused by swelling following head injury, or to work on the underlying brain tissue. Although most orthopaedic implants come in a range of sizes that can be made to fit patients, metallic implants that are used in the skull (and the defect), do not fit without further structural refinement. At the moment, these implants are made in hospitals by bending a titanium (or other metal sheet) over a 3D printed model of the defect and then polishing and dipping the surface in acid before sterilisation at more than 100oC. Although this kills the majority of contaminating bacteria, the incidence of infection following the implantation of these plates is much higher than with other metallic implants made outside the clinic (12-50% compared with 2%). If an infection occurs, the plate must be removed from the patient's skull, the site cleaned, and then another plate can be fixed in place. This process is dangerous for the patients since it increases risk due to anaesthesia, further infection and requires that the individual spends a period of time without a plate in place, meaning that the brain remains relatively unprotected.

We aim to use technology that has been developed in a previous EPSRC project (NIDMET) to reduce the incidence of infection following the fitting of a cranial plate. We will refine an existing additive layer manufacturing process so that we are able to produce something quickly, accurately, to a high quality and surface modified with silver such that it is resistant to microbial contamination and therefore unlikely to cause infection. If we are able to reduce the incidence of infection even down to that associated with orthopaedic implants, we will improve the life of a considerable number of patients reducing costs, in terms of days of hospitalisation and cost of treatment.

We will use additive layer manufacturing methodologies to address another major problem that is associated with cranial plates: artefacts that are created by the plate material in a type of MRI scanner that mean that the implant or implant site cannot be evaluated using this important imaging method. We will address incompatibility of the material with gradient field MR imaging using a process that is called topological optimisation. This is an operation that is undertaken by a computer to modify the structure of something so that it is possible to minimise the amount of material that is required for a particular structure. Minimising material, particularly around the edge of the implant, will reduce the imaging problems associated with cranial implants.

Patients: This research will ultimately be of the most benefit to patients. The implications of a prosthetic related infection are clear, with pain, threat to life and temporary (or even permanent) loss of function being major associated risks. The costs of treating these infections and associated loss of working days are both significant and are a burden to the UK NHS and thereby also the taxpayer, meaning that this work would be of potentially significant benefit to both.

Clinicians: The findings of this project would also be of significant importance to the clinicians that are involved in fitting prosthetics that are associated with a higher than normal likelihood of failure. These infections would rarely be associated with poor surgical technique, yet they could be taken to reflect the practice of the fitting clinician, potentially causing severe reputational damage.

The medical technology sector: The work would be of great benefit to two small medical technology companies in the UK (Accentus Medical and Cavendish) and would help them to move their technologies more rapidly into the clinic, potentially (through partnership with the Birmingham Health Partner Hospitals and the military) into widespread use. This would subsequently be of benefit to the economy through job creation and the UK government through increased tax collection.

Educational beneficiaries: Such a multidisciplinary collaboration, particularly with an emphasis on technical development, clearly has great potential from the point of view of training and education. Implant design and regenerative medicine capture the imagination of the general public and are excellent out-reach tools to inspire future generations of researchers into the STEM subjects. We have also found significant educational value in opening many of our design problems to final year engineers (in an appropriate non-confidential manner) who enjoy tackling real-world problems. Clinical Research fellows have also found it very engaging to be involved in Professor Grover's basic science research projects. Overall, we believe that projects like PREVENTION are a fantastic opportunity to create a community of engaged learners who, more often than not, come together to create very innovative solutions to medical issues.