Microscopic titanium particles weaken the bonding of hip, knee, and other joint replacements, according to research published online in Proceedings of the National Academy of Sciences by researchers at the University of California, San Diego (UCSD) School of Medicine and the Jacobs School of Engineering. The team demonstrated that titanium implants are safe in large blocks, but at the microscopic level, wear and tear can generate micrometer-sized particles.
"As replacement joints are becoming increasingly common in aging populations, our results explain how such devices fail and suggest that improvements should be made in artificial joint design," said the studys senior author K.L. Paul Sung, Ph.D., UCSD professor of orthopedic surgery and adjunct professor of cellular bioengineering.
The team measured how titanium particles affected the bonding strength of pins implanted in rat thighs. The pins were shown to come out more easily when the titanium particles were present, with the smallest and largest particles causing the greatest weakening. The researchers demonstrated how different-sized titanium particles affected bone-building cells called osteoblasts and bone-destroying cells called osteoclasts. Microscopic studies revealed osteoblasts did not form proper adhesions, with small- and medium-sized titanium particles concentrated inside cells. Increased production of the protein RANKL by osteoblasts recruited and activated osteoclasts at the insertion sites, further weakening the bone. Larger titanium particles also activated metalloproteinases, which chop up the extracellular matrix that holds cells together.
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