Orthopaedic implants improve the quality of life of thousands of people every year, reducing pain and increasing mobility and function. In the past implants have been made of metal alloys and polyethylene, but these implants can fail, causing discomfort and, could ultimately mean further surgery. Recently implants have been developed made from irradiated and annealed ultra high molecular weight polyethylene (UHMWPE) that should have better performance. However, the molecular processes that occur during irradiation are not fully understood. Scientists from the University of Limerick have used Diamond’s SAXS beamline I22 to study UHMWPE under tension to understand these processes in detail. Their research has been published in the journal RSC Advances.
For all materials yield is associated with lamellar reorganisation as the sample deforms, thought to be a “slip and glide” process where the folds unravel and reform. The SAXS patterns showed that this reorganisation occurred much faster in the irradiated materials. The team propose that this is facilitated by nucleation sites on the lamellar surfaces caused by radiation damage. Simultaneous SAXS and WAXS analysis of the samples under strain showed that the annealing process restores crystal perfection, improving the performance of the material under strain.
Dr. Maurice Collins from the University of Limerick led the study. He says,
“It must be remembered that this is a single experiment on samples that are known to age, but nevertheless we believe it offers valuable insights into the morphological processes that occurs when UHMWPE is under strain. Studying unirradiated, irradiated and both irradiated and annealed samples in situ allowed us to identify how annealing restores crystal perfection to improve performance. This gives us a much greater understanding of how we can produce stable implant grade UHMWPE.”
Dr. Maurice Collins, University of Limerick
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