A total hip replacement involves replacing both the natural socket of the hip joint (the acetabulum) and the rounded head of the thigh-bone (the femur) with artificial parts. These parts replicate the natural motion of the hip joint. However, the load-bearing surfaces used in conventional hip replacements bear no resemblance to their natural counterparts in terms of composition, structure and properties, and can be prone to failure.

A failing hip replacement causes increasing discomfort, pain and loss of mobility for the patient. Revision surgery costs nearly three times as much as the original surgery, and is associated with longer hospital stays and recovery times, as well as a higher rate of complications, associated health problems and even death. Moreover, patients never regain the quality of function they had after the first procedure.

In 2015, over 89,000 total hip replacements were performed in England, Wales and Northern Ireland, a rise of 12% in two years. 10% of these were revisions, and this is increasing. Problems with loosening or wear of the bearings accounted for 70% of these operations.

The most common type of artificial joint uses metal on polyethylene bearings (MoP). But polyethylene is susceptible to wear and the resulting debris can cause bone loss (osteolysis) and loosening of the components. Alternative pairings (metal on metal, ceramic on ceramic and ceramic on polyethylene) have their own shortcomings: ceramics, although durable, are prone to fracture, and metal on metal shows wear, producing metal particles and ions that can pose a health risk to patients.

But thanks to funding from the EBI, a materials scientist and engineer, a chemist, and a clinician in trauma and orthopaedics have brought their combined skills and expertise to bear on the problem.

The EBI Research for Health Challenge Scheme encourages health practitioners and University of Bristol researchers to work together to develop innovative thinking around clinical problems. Dr Michael Whitehouse, Clinical Lecturer in Trauma and Orthopaedics at the School of Clinical Sciences, challenged researchers to come up with an alternative bearing surface for total hip replacements that would reduce failure and produce longer lasting implants.

The challenge was answered by Professor Bo Su at the School of Oral and Dental Sciences, who has more than 25 years’ research experience in materials processing, including ceramics and composites used in bone fractures and hip resurfacing. Working with Dr Wuge Briscoe at the School of Chemistry, a specialist in surface forces, he proposed developing a new type of composite material for the bearings surface that closely mimics the structural and mechanical properties of natural bone and cartilage. The idea was that this would combine the toughness of bone with a cartilage-like surface and lubrication, and so address the problems of conventional implants.

The work was in two stages and included the following:

• Fabricating ‘biomimetic’ titanium and composite scaffolds with bone-like structure and mechanical properties.

• Synthesising cartilage-mimicking polymers (e.g. DN hydrogel) as a replacement material for articular cartilage.

• Integrating DN hydrogel with titanium scaffolds to generate biomimetic implants for cartilage repair and joint replacement.

The results of this research show great promise for creating more realistic implants. The team now intends to apply for funding from Arthritis Research UK or the Engineering and Physical Sciences Research Council to take the work forward. Data from the project has also helped facilitate a UK-China collaboration and inform a pan-European collaborative grant application.  Three papers are published in materials journals on the findings.

Professor Su said, ‘Our research explores a novel solution to a longstanding problem in orthopaedics and EBI funding has been invaluable in gathering data to progress this further. If we can use this to create more realistic implants, it could transform clinical practice, not just for the many thousands of patients in the UK needing hip operations, but also for other joint replacements such as the knee and shoulder.’

Dr Michael Whitehouse said: ‘The potential benefits of this work are huge. Joint replacement are very common procedures and they are very good at relieving the pain and suffering associated with arthritis for patients and the numbers done each year in the UK and around the world continue to rise. Despite the success of the initial operation, the most common reasons for patients to need complex and expensive revision surgery are related to the wear and failure of the baring surfaces. The current bearing options we have are very different to the native joint and this is one of the main reasons why they wear out more quickly than native joints and fail. The development of artificial joints that can mimic the native joint would be a huge step forward to increasing the time that artificial joints last and hence improving the quality of life for patients, reducing the costs of treatment in the lifetime of the patient and reducing the risks that patients are exposed to.‘