More than 746,000 Americans have knees or hips replaced every year. But the joints, made of metal and polymer, aren't a permanent solution because everyday wear and tear grinds off tiny bits that cause inflammation. That isn't all: the inflamed areas cause cells near the implants to actually eat away at the bone itself.
Coating the joints with a nanometer-thick layer of diamond could change that, not only lengthening the useful life of a replacement (which is currently about a decade or so) but also reducing the inflammation.
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The inflammation comes from cells in the body called macrophages. These cells eat the metal that gets worn off artificial joints and releases chemicals that cause pain, swelling and bone damage.
A study at the University of Alabamaat Birmingham, led by Vinoy Thomas, has shown that at least in the lab, the macrophages that absorb metal debris will do the same for the tiny bits of diamond, but with less inflammation.
The key seems to be the concentration, rather than the particle size. The cells were exposed to nanodiamonds of varying sizes and concentrations. At less than 50 micrograms per milliliter of solution — the typical debris in a joint — the particles weren't toxic. The macrophages thrived even in the presence of the largest pieces, which were 500 nanometers across. When the concentrations topped 200 micrograms per milliliter, the cells' vitality was reduced.
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The experiment was done with macrophages in a dish, so it is unclear what would happen inside the body. The next step is looking at where nanodiamond particles would accumulate, experiments with mice showed they tend to gather in the liver, spleen and lungs with no ill effects. But mice are not humans and they weren't given joint replacements.
Still, if this works joint replacements will be a lot less frequent, and the new joints a lot less painful.
Image: University of Alabama at Birmingham
