By Brian Owens
Many products, like leather gloves or sandals, spend a lot of time in close contact with our skin – and some, like surgical implants, are even underneath it. While these products undergo testing to ensure they are safe to use, they can still produce dangerous chemical by-products as they age and weather. Yolanda Hedberg, Canada Research Chair in corrosion science at Western University in London, is using the beamlines at the Canadian Light Source to study how these products break down, to determine what the risks might be, and how to protect against them.
About 90 per cent of leather products are made with chrome-tanned leather, because the process is faster and cheaper than traditional vegetable tanning. In general, this leather is safe to use, because the chromium used in the process is not bioavailable. But as the leather ages and weathers, especially if it gets wet and is heated or left in the sun to dry, some of that chromium can be converted to chromium-6. “That version is very mobile, and can diffuse through skin like water,” says Hedberg.
To simulate this process, Hedberg puts a variety of leathers in weathering chambers then uses the BioXAS Spectroscopy beamlines at CLS to identify the degradation products that are produced. She says that most of the chemical reactions take place on the surface of the leather, so only a small amount of the toxic chromium-6 is formed. But over the long term that small amount can really add up.
Hedberg says the greatest risk comes from chrome-tanned products that frequently get wet and come in contact with alkaline materials like cement that can accelerate the formation of chromium-6 – like cheap leather work gloves, for example. While this is a bigger problem for people who already have a chromium allergy, prolonged exposure to the metal can also lead to the development of allergies. “What matters is how much exposure there is over your lifetime,” she says. “It’s the accumulative dose that matters.”
In the case of medical devices like hip or knee implants, or dental braces, they are mainly made out of alloys that contain metals like nickel, cobalt, and chromium, usually in a form that can’t oxidize into harmful forms. But with time and wear, these devices can begin to degrade both chemically and physically, creating potentially harmful by-products.
Worn out implants can also cause lesions in the bone and damage the surrounding tissue if the get loose, says Matthew Teeter, director of the implant retrieval lab at Western. And metal implants can undergo metallosis, releasing tiny particles into the bloodstream that can cause an immune reaction. The biggest risk comes from cobalt, says Teeter, because if it builds up in the heart it can cause cell death and heart attacks, and a build-up in the brain can cause degenerative symptoms similar or Parkinson’s disease.
To find ways to avoid this, Teeter often collaborates with Hedberg, providing her with corroded implants that have been removed from patients to study. The in-depth study of how the implants corrode that Hedberg provides can help Teeter study new questions about how that corrosion is linked to patient factors – such as whether someone with diabetes might be at greater risk of an adverse outcome, and how dangerous reactions can be avoided. “If we can understand which materials and designs cause problems, we can design better ones,” he says.