Neurosurgeons have longed for a lumbar cage that is light enough to limit the load on a patient's spine but also fuses well with surrounding lumbar vertebrae.
Conventional lumbar cages are made of titanium or polyether ether ketone, known as PEEK, which can put a heavy load on the spine. Although some implants have porous material added to their surfaces to help with fusion, bone doesn't grow through PEEK or solid titanium.
Rather than look for a new material, engineers at Stryker Corp. decided to fundamentally change how the device is manufactured. The Kalamazoo, Mich.-based devicemaker concluded that 3-D-printing could yield a significantly more porous titanium lumbar cage. The product could be lighter and better imitate the porous nature of bone, encouraging spinal fusion.
Physicians have increasingly looked to 3-D printing for unique implants and surgical models, and some manufacturers are now using the method to mass produce medical devices and even drugs that are more precise, customizable and biocompatible than conventionally produced products.
3-D printing generally refers to the process of depositing material, one layer at a time, based on instructions from a digital file. Though physicians and biomedical engineers have been tinkering with the technology in growing numbers over the past decade, 3-D printers and the science of additive manufacturing have also become sophisticated enough that drugmakers and devicemakers have started to take notice.
Although the technology can be expensive for complex manufacturing, proponents in the healthcare industry insist that costs will come down over time, and that the benefits in many cases already justify those costs. In many cases, 3-D printing provides physicians with a remarkably cheap way to fashion a device that fits or models the precise size and shape of a particular patient's anatomy.
Stryker's Ireland-based additive manufacturing experts determined that instead of carving a device out of a block of titanium, they could 3-D print it using a laser beam that melts a powder of titanium alloy particles, building the lumbar cage from the base up, layer by layer.
“It's fitted just like a glove,” said Dr. Juan Jimenez, a neurosurgeon who implants the cages in patients at Riverside Healthcare in Kankakee, Ill. “The cells will intrinsically travel ... if you interface (the spine) with a structure that will mimic (it) and a product that will adhere, you've got something great.”
It's the spine division's first 3-D printed product, though the devicemaker has used 3-D printing in other divisions, including knees and craniomaxillofacial products (involving the jaws, face and skull). Stryker's 3-D printers build 700 to 800 layers into the spinal implant, creating a “cookie sheet” of multiple implants in each batch. Including post-processing, it takes roughly two days to create a batch of implants, of which Stryker offers 64 sizes.
“From an engineering standpoint, this technique became popular just because of your design freedoms,” said John Mayor, vice president of marketing for Stryker Spine.
Although Stryker's titanium process is expensive, it wastes less raw material. The excess powder can be re-used for the next batch. It also commands a premium in the marketplace and is boosting the company's profits. Mayor declined to disclose prices, but he said they will inevitably come down as the device becomes more popular, and Stryker uses the manufacturing process in more applications.
When basic plastics are used to make models or patient-specific devices, 3-D printers are often significantly faster and cheaper than conventional manufacturing methods—sometimes allowing production for as little as 10% of the cost of conventional molds, said Michael Gaisford, director of medical industry marketing for Stratasys, an Eden Prairie, Minn.-based manufacturer of 3-D printers. For some products, such as patient-specific models created for surgical planning, there's no comparable cost. They simply weren't possible before.