Professor Sahar Al-Malaika from the Chemical Engineering & Applied Chemistry Group is one of the leading figures in the research of oxidation, stabilisation and modification of polymers and polymer additives. The work of Professor Al-Malaika and her group has been a turning point in the understanding of the chemistry of vitamin E in polymers. Professor Al-Malaika
’s significant scientific contributions to the chemistry of vitamin E in polymers over the last 25 years has been instrumental in the subsequent commercialisation of the vitamin (sold as ‘Irganox E201®’) as a safe antioxidant for human-contact polymer applications. Sahar’s work has also been a significant driver for its exploration and use by other researchers in prosthetic surgery to prolonging the lifetime of hip and knee implants, and reducing demand for corrective surgery. Professor Al-Malaika is currently working with a major US-based world manufacturer of vitamin E-containing hip and knee implants. Sahar is investigating the mechanism and fate of the vitamin that is retrieved from patient’s orthopaedic implants as well as newly manufactured implants.
According to the UK National Joint Registry (UK NJR), more than 150,000 total joint hip and knee replacement procedures were carried out last year in the UK. While total joint replacement (TJR) is highly effective in providing pain relief and restoring function and mobility to most patients, approximately 8% of all joint replacements fail and require a second procedure, called revision, to remove the old implants and replace them with new components (Source UK NJR).
The most common indication for revision surgery aseptic loosening of the joint replacements is aseptic loosening (loosening in the absence of infection) (Source: UK NJR). This may occur due to a number of reasons, but most commonly occurs because friction between the metal and polyethylene bearing components generates tiny wear particles. The body's immune response to these particles also attacks nearby bone, which gradually wears away so that the joint no longer securely fixed to bone. Increased wear and failure due to oxidation of the polyethylene bearing is also a common cause of failure, particularly in knee joint replacements.
Revision joint replacement is generally more complicated than primary joint replacement surgery, requiring removal of the old artificial joint and sometimes areas of surrounding bone and tissue. Revision operations are typically associated with more complicated/costlier implants, extended surgery time, greater blood loss and risk of infection and additional in-patient hospital stay. As a result, a revision procedure may cost 2-3 times that of a primary procedure. All of these factors place a significant burden on the patient, surgeon and overall health service.
There have been numerous attempts over the past decade to improve the longevity of orthopaedic joints so that they may survive for the lifetime of the patient. One of the most promising approaches has been to increase the wear resistance of polyethylene by crosslinking it and by incorporating Vitamin E in it to protect it from oxidation, in the same way as Vitamin E protects the linings of our cells. This approach seeks to address the key issues limiting the longevity and durability of polyethylene joint replacements: polyethylene wear, wear particle mediated aseptic loosening and oxidation. These Vitamin E stabilised materials offer the real promise of lifetime function, thereby ensuring improved quality of life of patients and reducing the impact on society of lost productivity and the increased burden on the health service of revision surgery. For more information visit the Polymer Processing and Performance (PPP) Research Group webpages.