Click here for PDF - Society of Manufacturing Engineers

More documents

Recommendations

Info

Materials component marketplace, expects growth in the medical industry, which currently accounts for 40% of its manufacturing. MacNeal’s entire career has been in FDA-regulated industries; she kindly walked ME Media through a virtual bazaar of medical materials Tracy MacNeal, chief strategy and discussed their strengths officer at ATW Companies. and challenges. Implants: Biocompatibility and Wear Issues Implants, orthopedic and otherwise, are all FDA Class Two and Class Three devices, with stringent requirements, the foremost of which is biocompatibility, MacNeal said. “Of the materials that are favored from a biocompatibility standpoint in metals, titanium would be the number one choice for implants—it’s basically inert in the body. There are also some alloys of stainless steel—people talk about ‘surgical stainless steel’ and those two would be the two big ones.” But as manufacturers in other industries know, titanium has its challenges: “Titanium is difficult to work with because it does catch fire. When you’re machining it, you really have to control your feeds and speeds. Its ratio of hardness to brittleness is not great, and it doesn’t have good wear properties—it abrades. In an articulating joint like a knee or hip, you can’t have metal-on-metal there, it’s much too soft.” Cobalt chrome, another popular medical metal, has been used as a wear surface in orthopedic implants, but, as has been widely reported, it’s under fire right now: “People who have cobalt chrome metal-on-metal interfaces in their orthopedic joints get wear debris resulting in much higher than average levels of chromium ions in their body,” MacNeal noted. 78 ManufacturingEngineeringMedia.com | May 2013
Materials “Those higher levels weren’t planned for and weren’t in the original filing data, so even though they haven’t been linked to any health problems, they’re an unexpected outcome, and the FDA is asking questions. So orthopedics companies are trying to get away from cobalt chrome for such applications. “Instead of a metal-on-metal wear surface, companies typically will have a HDPE—high-density polyethylene wear surface, which simulates cartilage. In an actual hip joint, the bone is covered with cartilage, which when lubricated with synovial fluid is essentially friction-free. Inside the orthopedic joint, a biocompatible metal is coated with HDPE to mimic the cartilage role. But HDPE too can abrade, and in this case, the wear debris—inert polyethylene particles—builds up behind the metal, and as the body attempts to clean up these wear particles it can trigger an autoimmune reaction which causes resorption of bone tissue—a condition called osteolysis. The bone pulls away from the metal joint that had been screwed into it, and the joint can start to become loose. That’s usually why some patients need revision surgery—and why people who are, say, 65 years old may elect to put off having replacement surgery, in order to not need to replace the joint at age 75. “Some hospitals are looking at reclaim and reuse, and considering investing in metal versions ... and reuse instead of disposables.” “So the hunt has been on for a better wear surface. Enter ceramics. Ceramics are super-hard and are great wear surfaces. They don’t abrade so you don’t have the wear debris issues. There have been two issues with ceramics, however. The first is that if the clearance isn’t completely and totally perfect, you end up with ceramic squeaking against 80 ManufacturingEngineeringMedia.com | May 2013
Page 1: Photo courtesy Seco Tools Materials
Page 5 and 6: Materials second in size only to or
Page 7: Materials Photo courtesy ATW Compan

Click here for PDF - Society of Manufacturing Engineers

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?