Building Better Bones: Additive manufacturing promises to make metal implants obsolete

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Physicians have used metal to repair the human body for over a century, beginning with vanadium steel in the early 1900s.

That corrosion-prone material has since been replaced by a number of high strength, low corrosion alloys – stainless steel and cobalt-chrome are favourites for orthopaedic implants, and titanium screws and bone plates are common. Despite their life-saving attributes, however, metal implants sometimes don’t sit well in humans: allergic reactions, heavy metal poisoning, discomfort and temperature sensitivity are some of the complaints raised against these reconstructive medical products. “Metallic-type implants can be problematic,” says Dr. Ehsan Toyserkani, associate professor of the Multi-Scale Additive Manufacturing Lab at the University of Waterloo. “After ten years or so, they may have to be replaced due to inflammation, calcification, and so forth. Also, machined metal surfaces do not provide an ideal surface to which bone can adhere.”

If Toyserkani and his collaborators have their way, the decades-old use of titanium in the human body will one day go the way of mercury treatments and bloodletting. His lab’s Additive Biofabrication project is designed to use 3D printing in a novel approach to implant building. Known ast (SFF), Toyserkani has shown that it is now possible to print complex, anatomically shaped “scaffolds” from calcium polyphosphate. “This is a biodegradable material with very good mechanical strength. Using a two-step process including our 3D printing technology and a sintering protocol that is a proprietary of our collaborator at the University of Toronto, we are able to fabricate complex-shaped implants with internal channels and porosity similar to bone,” Toyserkani says. In collaboration with Mount Sinai Hospital of the University of Toronto, some types of these implants were then placed in a culture of cartilage cells prior to “in vivo” testing in rabbits and sheep. The results were impressive. “The original calcium polyphosphate scaffold was replaced by natural bone and cartilage after a while.”

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