Artificial Joints Make Strides with 3D Printing

Metal parts are made by laser sintering, and plastic prototypes are made by inkjet or FDM processes. Plastic production parts could be next.

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“Additive manufacturing is a big strategy for us,” says Ryan Loftus, engineering manager for Exactech, Inc., Gainesville, Fla., a producer of artificial hip, knee, and shoulder joints. His firm, with sales of $250 million annually, is reportedly the fifth largest joint orthopedics supplier, but Loftus claims it is the first to use additive manufacturing (AM, aka 3D printing) in production of metal large-joint components, such as titanium hip cups. “AM is perfect for us because of our low-volume/high-mix product line. For example, each Exactech knee set contains nine sizes, and many parts are designed to accomodate a specific patient’s anatomy. He also notes that AM can make smooth, “organic” surfaces that can improve a product’s aesthetics and functionality over products typically produced by traditional machining.

Exactech has three AM machines (from EOS and Arcam) for laser sintering of metal powders. It also has two machines (Objet and MakerBot) for printing plastic prototypes of instruments and implants, as well as “soft jaws” to hold printed parts for machining (formerly machined out of aluminum). Its Objet 3D printer, supplied by Stratasys, Eden Prairie, Minn., uses inkjet-style deposition of UV-curable acrylate polymers. It “runs every day and overnight,” according to Loftus. He says this “workhorse” machine can make parts accurate to 0.003-0.005 in. for only a few dollars.

More recently, Exactech installed a MakerBot printer, which uses the FDM process of extruding thermoplastic filaments. MakerBot Industries, Brooklyn, N.Y., is a subsidiary of Stratasys. Though a less exact system, it produces parts for less than $1, Loftus says. His firm uses it to make PLA prototypes of surgical devices, which are machined from Radel polyphenylsulfone (PPSU) from Solvay Specialty Polymers, Alpharetta, Ga. Loftus sees a “large opportunity” to reduce costs by 3D printing the actual surgical instruments, but it is not clear that a printable material is available that can withstand multiple autoclave sterilization cycles. And not just the material, but actual printed parts, would have to be subjected to extensive sterilization and other testing before they could be approved for production.

Loftus is chairman of the Advanced Manufacturing Council of the Gainesville Chamber of Commerce. Also involved in the Council are the Wertheim College of Engineering at the Univ. of Florida-Herbert, Santa Fe Community College (Santa Fe, N.M.), and Alachua County (Fla.) Public Schools.

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